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Sample records for ca sr substitution

  1. Magnetic characterization of Ca substituted Ba and Sr hexaferrites

    NASA Astrophysics Data System (ADS)

    Asti, G.; Carbucicchio, M.; Deriu, A.; Lucchini, E.; Slokar, G.

    1980-04-01

    A magnetic characterization has been worked out for the solid solution from Ba and Sr hexaferrites (BaFe 1 2O 1 9, SrFe 1 2O 1 9) towards CaO- xFe 2O 3 (2 ⪕ x ⪕5.5). Measurements of Curie temperature, saturation magnetization, magnetic anisotropy, together with Mössbauer characterization indicate that the intrinsic properties of the studied compounds do not change appreciably with increasing Ca content. These results, together with the X-ray data, are consistent with the formation of an undistorted M-type cell with a low content of iron and oxygen vacancies.

  2. Proton Matrix ENDOR Studies on Ca2+-depleted and Sr2+-substituted Manganese Cluster in Photosystem II.

    PubMed

    Nagashima, Hiroki; Nakajima, Yoshiki; Shen, Jian-Ren; Mino, Hiroyuki

    2015-11-20

    Proton matrix ENDOR spectra were measured for Ca(2+)-depleted and Sr(2+)-substituted photosystem II (PSII) membrane samples from spinach and core complexes from Thermosynechococcus vulcanus in the S2 state. The ENDOR spectra obtained were similar for untreated PSII from T. vulcanus and spinach, as well as for Ca(2+)-containing and Sr(2+)-substituted PSII, indicating that the proton arrangements around the manganese cluster in cyanobacterial and higher plant PSII and Ca(2+)-containing and Sr(2+)-substituted PSII are similar in the S2 state, in agreement with the similarity of the crystal structure of both Ca(2+)-containing and Sr(2+)-substituted PSII in the S1 state. Nevertheless, slightly different hyperfine separations were found between Ca(2+)-containing and Sr(2+)-substituted PSII because of modifications of the water protons ligating to the Sr(2+) ion. Importantly, Ca(2+) depletion caused the loss of ENDOR signals with a 1.36-MHz separation because of the loss of the water proton W4 connecting Ca(2+) and YZ directly. With respect to the crystal structure and the functions of Ca(2+) in oxygen evolution, it was concluded that the roles of Ca(2+) and Sr(2+) involve the maintenance of the hydrogen bond network near the Ca(2+) site and electron transfer pathway to the manganese cluster.

  3. Superconductivity in TlSr 2- xCa xYbCu 2O 7 by isovalent cation substitution

    NASA Astrophysics Data System (ADS)

    Ohshima, Eriko; Kikuchi, Masae; Syono, Yasuhiko

    1996-02-01

    TlSr 2YbCu 2O 7 was found to be non-superconducting, in harmony with the formal valence of Cu 2+ and Tl 3+. However, isovalent cation substitution of Ca 2+ for Sr 2+ made TlSr 2- xCa xYbCu 2O 7 superconducting for x ≥ 0.2, although no change would be expected in the formal valence of Cu. These observations strongly suggest that hole carriers are self-doped due to overlap between Tl 6s and Cu 3d x2- y2 bands, which is enhanced by the observed shortening of the Cu bond length in the CuO 2 sheet by Ca substitution for Sr.

  4. Influence of SrO substitution for CaO on the properties of bioactive glass S53P4.

    PubMed

    Massera, Jonathan; Hupa, Leena

    2014-03-01

    Commercial melt-quenched bioactive glasses consist of the oxides of silicon, phosphorus, calcium and sodium. Doping of the glasses with oxides of some other elements is known to affect their capability to support hydroxyapatite formation and thus bone tissue healing but also to modify their high temperature processing parameters. In the present study, the influence of gradual substitution of SrO for CaO on the properties of the bioactive glass S53P4 was studied. Thermal analysis and hot stage microscopy were utilized to measure the thermal properties of the glasses. The in vitro bioactivity and solubility was measured by immersing the glasses in simulated body fluid for 6 h to 1 week. The formation of silica rich and hydroxyapatite layers was assessed from FTIR spectra analysis and SEM images of the glass surface. Increasing substitution of SrO for CaO decreased all characteristic temperatures and led to a slightly stronger glass network. The initial glass dissolution rate increased with SrO content. Hydroxyapatite layer was formed on all glasses but on the SrO containing glasses the layer was thinner and contained also strontium. The results suggest that substituting SrO for CaO in S53P4 glass retards the bioactivity. However, substitution greater than 10 mol% allow for precipitation of a strontium substituted hydroxyapatite layer. PMID:24338267

  5. Penta-substituted benzimidazoles as potent antagonists of the calcium-sensing receptor (CaSR-antagonists).

    PubMed

    Gerspacher, Marc; Altmann, Eva; Beerli, René; Buhl, Thomas; Endres, Ralf; Gamse, Rainer; Kameni-Tcheudji, Jacques; Kneissel, Michaela; Krawinkler, Karl Heinz; Missbach, Martin; Schmidt, Alfred; Seuwen, Klaus; Weiler, Sven; Widler, Leo

    2010-09-01

    A series of novel benzimidazole derivatives has been designed via a scaffold morphing approach based on known calcilytics chemotypes. Subsequent lead optimisation led to the discovery of penta-substituted benzimidazoles that exhibit attractive in vitro and in vivo calcium-sensing receptor (CaSR) inhibitory profiles. In addition, synthesis and structure-activity relationship data are provided.

  6. Electrical conductivity of cobalt-titanium substituted SrCaM hexaferrites

    NASA Astrophysics Data System (ADS)

    Eraky, M. R.

    2012-03-01

    A series of polycrystalline M-type hexagonal ferrites with the composition Sr0.5Ca0.5CoxTixFe12-2xO19 (where x=0.0-0.8) were prepared by the conventional ceramic technique. The electrical conductivity has been measured from 300 to 590 K. The dc conductivity, σdc, exhibited a semiconductor behavior. The negative sign of thermoelectric power coefficient S reveals that all samples are n-type semiconductors. Both σdc and mobility, μd, increases with the substitution of Co2+ and Ti4+ ions, reach maximum at x=0.4 and start decreasing at x>0.4. Many conduction mechanisms were discussed to explain the electric conduction in the system. It was found that the hopping conduction is the predominant conduction mechanism. For samples with compositional parameter x=0.0 and 0.8, the band conduction mechanism shares in electric conduction beside the hopping process.

  7. Substitution of extracellular Ca2+ by Sr2+ prolongs inspiratory burst in pre-Bötzinger complex inspiratory neurons.

    PubMed

    Morgado-Valle, Consuelo; Fernandez-Ruiz, Juan; Lopez-Meraz, Leonor; Beltran-Parrazal, Luis

    2015-02-15

    The pre-Bötzinger complex (preBötC) underlies inspiratory rhythm generation. As a result of network interactions, preBötC neurons burst synchronously to produce rhythmic premotor inspiratory activity. Each inspiratory burst consists of action potentials (APs) on top of a 10- to 20-mV synchronous depolarization lasting 0.3-0.8 s known as inspiratory drive potential. The mechanisms underlying the initiation and termination of the inspiratory burst are unclear, and the role of Ca(2+) is a matter of intense debate. To investigate the role of extracellular Ca(2+) in inspiratory burst initiation and termination, we substituted extracellular Ca(2+) with Sr(2+). We found for the first time an ionic manipulation that significantly interferes with burst termination. In a rhythmically active slice, we current-clamped preBötC neurons (Vm ≅ -60 mV) while recording integrated hypoglossal nerve (∫XIIn) activity as motor output. Substitution of extracellular Ca(2+) with either 1.5 or 2.5 mM Sr(2+) significantly prolonged the duration of inspiratory bursts from 653.4 ± 30.7 ms in control conditions to 981.6 ± 78.5 ms in 1.5 mM Sr(2+) and 2,048.2 ± 448.5 ms in 2.5 mM Sr(2+), with a concomitant increase in decay time and area. Substitution of extracellular Ca(2+) by Sr(2+) is a well-established method to desynchronize neurotransmitter release. Our findings suggest that the increase in inspiratory burst duration is determined by a presynaptic mechanism involving desynchronization of glutamate release within the network.

  8. Ca-for-Sr substitution in the thermoelectric [(Sr,Ca){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] misfit-layered cobalt-oxide system

    SciTech Connect

    Yamauchi, Hisao; Karvonen, Lassi; Egashira, Takayuki; Tanaka, Yoshiaki; Karppinen, Maarit

    2011-01-15

    Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}], were successfully synthesized up to x=0.2 with a sample-encapsulation technique originally developed for the x=0 end phase. While the x=0 sample has a commensurate match between the two layer blocks (i.e. q=0.5), isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q>0.5). At the same time the Seebeck coefficient gets increased, but the increase in resistivity results in suppressing the thermoelectric power factor. The magnetic anomaly in the x=0 sample gets released upon the Ca substitution for the x=0.2 sample to exhibit an almost Curie-Weiss behavior. It is concluded that with increasing x in [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca{sub 1.7}O{sub 2.1}H{sub 2.4}]{sub 0.58}[CoO{sub 2}]. -- Graphical abstract: In the misfit-layered [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] (0.0{<=}x{<=}0.2) system the x=0 phase has a commensurate match between the two layer blocks (i.e. q=0.5), while isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q>0.5). At the same time Seebeck coefficient gets increased. Simultaneous increase in resistivity however outweighs this benefit, and accordingly the thermoelectric power factor is decreased. Display Omitted

  9. Observation of low-temperature magnetic ordering in mixed-phase Sr-Ca-Cu-O superconductors substituted by iron

    NASA Astrophysics Data System (ADS)

    Sklyarova, A.; Shinoda, S.; Nagumo, T.; Chizhik, V. I.; Matveev, V. V.; Suematsu, H.

    2016-08-01

    The series of unsubstituted Sr2CaCu2O6 and iron-substituted Sr2CaCu2‑x Fe x O6 (x=0.1,x=0.05) materials were produced by a high-pressure synthesis route and characterized using X-ray diffraction and SQUID magnetometry. The change of contained phase ratio was found at different substituent concentrations in the samples synthesized under the same conditions: unexpected growth of 0201 and CuO phase with decrease of iron content was observed. Synthesis temperature-dependence of obtained phase fractions was found for the samples with x=0.05. The superconductivity transition was found for all obtained samples and the highest critical temperature was around 103 K. From the SQUID measurements distortions of the magnetic susceptibility curves were found; these were explained by the magnetic ordering arising at low temperatures. This magnetic ordering was associated with the magnetic moment appearing in iron-doped 0201 phase.

  10. Observation of low-temperature magnetic ordering in mixed-phase Sr-Ca-Cu-O superconductors substituted by iron

    NASA Astrophysics Data System (ADS)

    Sklyarova, A.; Shinoda, S.; Nagumo, T.; Chizhik, V. I.; Matveev, V. V.; Suematsu, H.

    2016-08-01

    The series of unsubstituted Sr2CaCu2O6 and iron-substituted Sr2CaCu2-x Fe x O6 (x=0.1,x=0.05) materials were produced by a high-pressure synthesis route and characterized using X-ray diffraction and SQUID magnetometry. The change of contained phase ratio was found at different substituent concentrations in the samples synthesized under the same conditions: unexpected growth of 0201 and CuO phase with decrease of iron content was observed. Synthesis temperature-dependence of obtained phase fractions was found for the samples with x=0.05. The superconductivity transition was found for all obtained samples and the highest critical temperature was around 103 K. From the SQUID measurements distortions of the magnetic susceptibility curves were found; these were explained by the magnetic ordering arising at low temperatures. This magnetic ordering was associated with the magnetic moment appearing in iron-doped 0201 phase.

  11. Microstructure and magnetic properties of Ca-substituted M-type SrLaCo hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Huang, Xin; Liu, Xiansong; Yang, Yujie; Huang, Kai; Niu, Xiaofei; Jin, Dali; Gao, Shang; Ma, Yuqi; Huang, Feng; Lv, Farui; Feng, Shuangjiu

    2015-03-01

    M-type strontium hexaferrites with chemical composition of Sr0.80-xCaxLa0.20Fe11.85Co0.15O19 (x=0-0.15) were prepared by the ceramic process. The samples were sintered at temperatures of 1175, 1185 and 1195 °C for 2 h in air. Effects of the substituted amount x of Ca2+ on the ferrites microstructure and magnetic properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and B-H hysteresis curve measurements. As a result, at x≤0.12, all samples are single phase after the Ca substitution. At x=0.15, another phase of hematite (α-Fe2O3) is present. In addition, the maximum values of the remanence (Br) and maximum energy product ((BH)max) for the magnets have been obtained at x=0.08 for sintering temperature=1185 °C. The maximum value of the intrinsic coercive force (Hcj) for the magnets has been obtained at x=0.12 when the magnets were sintered at 1185 °C.

  12. Ti doping-induced magnetic and morphological transformations in Sr- and Ca-substituted BiFeO3

    NASA Astrophysics Data System (ADS)

    Khomchenko, V. A.; Paixão, J. A.

    2016-04-01

    The investigation focuses on the crystal structure, microstructure, local ferroelectric and magnetic properties of the Bi0.9Sr0.1Fe1-x Ti x O3-δ (x  =  0.05, 0.1, 0.15; δ  =  (0.1  -  x)/2) multiferroics prepared by a solid-state reaction method. All the samples have been found to be isostructural with the pure BiFeO3 (the material crystallizes in a polar rhombohedral structure belonging to the space group R3c). It has been shown that the pattern of changes in the lattice parameters of the Bi0.9Sr0.1Fe1-x Ti x O3-δ samples can be interpreted as consistent with the doping-driven elimination of anion vacancies at x  ⩽  0.1 and the formation of cation vacancies at x  >  0.1. The readjustment of the defect structure associated with the mechanism of charge compensation in the aliovalent-substituted BiFeO3 is accompanied by correlated changes in the morphology, ferroelectric/ferroelastic domain structure and magnetic properties of the materials. In particular, it has been found that the deviation from the ideal (δ  =  0) cation-anion stoichiometry in the Bi0.9Sr0.1Fe1-x Ti x O3-δ system leads to a significant decrease in the average size of crystal grain and ferroelectric domains and gives rise to an antiferromagnetic-weak ferromagnetic transformation. Results of this study have been compared with those obtained for equally substituted samples of the Bi0.9Ca0.1Fe1-x Ti x O3-δ series (Khomchenko and Paixão 2015 J. Phys.: Condens. Matter 27 436002) to demonstrate how the variation in the chemical pressure introduced by the partial replacement of Bi3+ with bigger (Sr2+) and smaller (Ca2+) ions can affect the multiferroic behavior of Ti-doped bismuth ferrites.

  13. Control of the superconducting properties of Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs through isovalent substitution

    SciTech Connect

    Corkett, Alex J.; Free, David G.; Cassidy, Simon J.; Ramos, Silvia; Clarke, Simon J.

    2014-08-15

    The effect of the isovalent substitution of Sr{sup 2+} by Ca{sup 2+} on the structure and superconducting properties of Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs is described in the compositional range 0≤x≤0.5. SQUID magnetometry measurements reveal that after an initial increase in T{sub c}, which is maximised at 29.5 K in Sr{sub 1.95}Ca{sub 0.05}VO{sub 3}FeAs, a rapid suppression of superconductivity is observed with increasing x. XANES spectra of Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs collected on the Fe and V absorption K-edges show that the position of both edges are invariant with composition within the experimental uncertainty. A combination of synchrotron X-ray powder diffraction and neutron powder diffraction techniques is used to rationalise the observed changes in T{sub c} with x, in terms of changes to the structure of the FeAs layer upon partial Ca substitution. These findings demonstrate that superconductivity in the Fe-based superconductors is extremely sensitive to the crystal structure with T{sub c} maximised in samples with regular FeAs{sub 4}-tetrahedra. - Graphical abstract: Superconducting transition temperature is controlled by structural parameters in Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs. - Highlights: • Substitution of Sr by Ca in the superconductor Sr{sub 2}VO{sub 3}FeAs is isovalent. • Relationship between superconducting T{sub c} and structural parameters is demonstrated. • Linear dependence of T{sub c} on structural parameters rather than composition.

  14. AC Dielectric Properties and Positron Annihilation Study on Co and Ti Substitution Effect on Ca-Sr M-Hexaferrites

    NASA Astrophysics Data System (ADS)

    Mahmoud, K. R.; Eraky, M. R.

    2016-06-01

    The dependence of AC conductivity σ AC, dielectric constant έ, and dielectric loss tangent tan δ on frequency and composition have been investigated at room temperature for polycrystalline Ca0.5Sr0.5Co x Ti x Fe12 - 2 x O19 (where 0.0 ≤ x ≤ 0.8) hexaferrites. It was found that the parameters σ AC, ɛ ', and tan δ have maximum values at x = 0.4 of the Co and Ti substitution. The behavior of σ AC, ɛ ', and tan δ with frequency and composition was explained on the basis of the hopping conduction mechanism and the Koops model. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the defects and changes in electron density for hexaferrite samples. The PAL parameters ( τ 1, I 1, τ 2, I 2, and mean lifetime) show that altering the doping percentage of the Co and Ti ions affects the size and concentration of defects. The results reveal that there are some large voids in the studied samples. The obtained results indicate the high sensitivity of the PALS technique to the enhanced structure changes with changing composition of the investigated samples and correlate the results with the measured electrical parameters.

  15. Ab-initio study of the magnetism, structure and spin dependent electronic states of Ti substituted MO (M = Mg, Ca, Sr)

    SciTech Connect

    Jaiganesh, G. Jaya, S. Mathi

    2015-06-24

    The magnetism, structure and spin polarized electronic structure of Ti substituted MO (M = Mg, Ca, Sr) are studied using the ab-initio techniques within the framework of the density functional theory. Appropriately constructed supercell along with the full structural optimization of these cells is used for studying the influence of Ti substitution on the magnetism and electronic structure of these compounds. We find from our calculations that the Ti substituted MO compounds energetically favor magnetically ordered state. The Ti concentration is found to be important in deciding the magnetic order and we have observed antiferromagnetic order for the Ti concentration of 0.25. The Ti substituted MO compounds are thus an interesting class of materials that deserve further studies.

  16. Microstructural and transport properties in substituted Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}-modulated compounds

    SciTech Connect

    Autret-Lambert, C. . E-mail: cecile.autret@univ-tours.fr; Pignon, B.; Gervais, M.; Monot-Laffez, I.; Ruyter, A.; Ammor, L.; Gervais, F.; Bassat, J.M.; Decourt, R.

    2006-06-15

    X-ray powder diffraction and resistivity measurements were performed on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} ceramics substituted by Y and Zn for Ca and Cu sites, respectively. X-ray diffraction patterns show an incommensurate modulated structure along the b-axis. The structural refinements were carried out using the four-dimensional space group Bbmb(0{beta}1)000. From the X-ray peak profiles analysis, an anisotropic line-shape broadening was observed. The use of the ''Williamson and Hall'' method allows distinguishing the origin of broadening as mainly due to microstrains. A large transition from a metallic to semiconductor behaviour is observed on the resistivity curves at x{approx}0.4 for Bi{sub 2}Sr{sub 2}Ca{sub 1-x}Y{sub x}Cu{sub 2}O{sub 8+{delta}} and at x{sup '}{approx}0.36 for Bi{sub 2}Sr{sub 2}Ca{sub 1-x}Y{sub x}Cu{sub 1.94}Zn{sub 0.06}O{sub 8+{delta}}, which can be also correlated to the defects. Oppositely to the metallic behaviour, which satisfies the Mathiessen's rule, the semiconducting one can be modelled by a variable range hopping process.

  17. Effect of cation substitution on structural transition: synthesis, characterization and theoretical studies of NaCa4B3O9, NaCaBO3, NaSrBO3 and Li4CaB2O6.

    PubMed

    Yang, Yun; Su, Xin; Pan, Shilie; Yang, Zhihua

    2015-10-21

    Single crystals of NaCa4B3O9, NaCaBO3, NaSrBO3 and Li4CaB2O6 have been successfully synthesized through conventional high-temperature solid-state reactions. They are structurally characterized by single crystal X-ray diffraction and exhibit three-dimensional crystal structures consisting of isolated planar BO3 as fundamental building blocks. Interestingly, for the centrosymmetric crystal structure of NaCaBO3 (Na3Ca3B3O9), as 2/3 of the Na(+) ions are substituted by Ca(2+) ions, NaCa4B3O9 is obtained and crystallizes in the noncentrosymmetric space group Ama2 (crystal class mm2). A second harmonic generation (SHG) test of the title compound by the Kurtz-Perry method shows that NaCa4B3O9 can be phase matchable with an effective SHG coefficient approximately one-half that of KH2PO4 (KDP). Studies of their optical properties as well as band structure calculations based on density functional theory methods have been also performed. NaCa4B3O9 possesses a moderate birefringence of about 0.05 at 1064 nm. To explain the difference in optical nonlinearity we compared the electronic structures of NaCa4B3O9, KCa4B3O9 and KSr4B3O9 crystals, in particular at the bottom of the conduction band (CB) and the top of the valence band (VB), since they are known to play a primary role in SHG. These electronic structures are responsible for the optical-nonlinearity of NaCa4B3O9, KCa4B3O9 and KSr4B3O9 crystals. PMID:26387438

  18. Crystal structure refinement, dielectric and magnetic properties of Ca/Pb substituted SrFe12O19 hexaferrites

    NASA Astrophysics Data System (ADS)

    Hooda, Ashima; Sanghi, Sujata; Agarwal, Ashish; Dahiya, Reetu

    2015-08-01

    SrFe12O19 (SFO), Sr0.5Ca0.5Fe12O19 (SCFO) and Sr0.5Pb0.5Fe12O19 (SPFO) hexaferrites have been synthesized by a conventional solid state reaction technique. Powder X-ray diffraction and Rietveld refinement confirm the presence of M-type hexagonal phase in prepared samples. However in SCFO, secondary phase was also present with main phase. Analysis of Nyquist's plots of SFO hexaferrite revealed the contribution of many electrically active regions corresponding to bulk mechanism, distribution of grain boundaries and electrode processes also. Both conductivity and electric modulus formalisms have been employed to study the relaxation dynamics of charge carriers. A perfect overlapping of the normalized plots of modulus isotherms on a single 'super curve' for all the studied temperatures reveals a temperature independence of dynamic processes involved in conduction and for relaxation. In SPFO sample coercivity is reduced effectively but accompanied with increase in magnetization, which is requirement for hexaferrites to be used as magnetic recording media.

  19. Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2

    NASA Astrophysics Data System (ADS)

    Chou, T. L.; Mustonen, O.; Tripathi, T. S.; Karppinen, M.

    2016-01-01

    Multilayered compounds typically present exotic functionalities, and some of them have been suggested as potential materials for thermoelectric conversion owing to their unique capability to decouple electronic and heat transport. Here we report new [CoO2] and [Cu2Se2] layered A 2CoO2Cu2Se2 compounds in which Sr at the intervening alkaline-earth A site is partially replaced with Ca or Ba. The parent Sr2CoO2Cu2Se2 phase is a direct gap p-type semiconductor, and density functional theory (DFT) calculations indicate its topmost valence band consists of Cu 3d-Se 4p states. Upon the isovalent cation substitution the lattice modification in the ab plane is constrained by the stiff [CoO2] layer such that the lattice shrinkage/expansion mainly happens along the c axis. Substitution of Sr with the heavier and larger Ba significantly enhances the thermopower but more hole states would be required to optimize the thermoelectric performance. Thermal stability is related to the inter-oxide-selenide-layer interaction, and our thermogravimetric measurement data reveal that the A 2CoO2Cu2Se2 materials could operate in the intermediate temperature region.

  20. Substitution of chromium for univalent copper in superconducting Pb{sub 2}Sr{sub 2}(Ca, Y)Cu{sub 3}O{sub 8-{delta}}

    SciTech Connect

    Seshadri, R.; Maignan, A.; Hervieu, M.

    1996-11-15

    Following considerations of geometry and the similarity between chromate and carbonate groups in terms of size and charge, the authors have investigated the possibility of replacing the two-coordinate Cu{sup I} in superconducting lead cuprates of the general formula Pb{sub 2}Sr{sub 2}(Ca, Y)Cu{sub 3}O{sub 8} by Cr. A high-resolution electron microscopy study coupled with energy dispersive X-ray analysis on small crystals of the title phases suggests that between 10 and 15% of the Cu{sup 1} can be replaced by Cr. While from the present structural study using HRTEM and Rietveld refinement of X-ray powder data the authors are unable to precisely obtain the oxidation state and oxygen coordination of Cr, the authors suggest in analogy with Cr substitution in other similar cuprates that in the title phases Cu{sup I}O{sub 2} rods are partially replaced by tetrahedral CrO{sub 4}{sup 2-} groups. Infrared spectroscopy supports the presence of CrO{sub 4}{sup 2-} groups. The phases Pb{sub 1.75}Sr{sub 2}Ca{sub 0.2}Y{sub 0.8}Cu{sub 3}O{sub 8-{delta}} and Pb{sub 1.75}Sr{sub 2}Ca{sub 0.2}Y{sub 0.8}Cu{sub 2.85}Cr{sub 0.15}O{sub 8-{delta}} are superconducting as-prepared, but the substitution of Cr for Cu{sup I} results in a decrease of the T{sub C} as well as the superconducting volume fraction.

  1. Computational insights on crystal structures of the oxygen-evolving complex of photosystem II with either Ca²⁺ or Ca²⁺ substituted by Sr²⁺

    SciTech Connect

    Vogt, Leslie; Ertem, Mehmed Z.; Pal, Rhitankar; Brudvig, Gary W.; Batista, Victor S.

    2015-01-15

    The oxygen-evolving complex of photosystem II can function with either Ca²⁺ or Sr²⁺ as the heterocation, but the reason for differing turnover rates remains unresolved despite reported X-ray crystal structures for both forms. Using quantum mechanics/molecular mechanics (QM/MM) calculations, we optimize structures with each cation in both the resting state (S₁) and in a series of reduced states (S₀, S₋₁, and S-₂). Through comparison with experimental data, we determine that X-ray crystal structures with either Ca²⁺ or Sr²⁺ are most consistent with the S-₂ state, Mn₄[III,III,III,II] with O4 and O5 protonated. As expected, the QM/MM models show that Ca²⁺/Sr²⁺ substitution results in elongation of the heterocation bonds and displaces terminal waters W3 and W4. The optimized structures also show that hydrogen-bonded W5 is displaced in all S states with Sr²⁺ as the heterocation, suggesting that this water may play a critical role during water oxidation.

  2. Hydrothermal removal of Sr2+ in aqueous solution via formation of Sr-substituted hydroxyapatite.

    PubMed

    Tan, Sheng-Heng; Chen, Xue-Gang; Ye, Ying; Sun, Jie; Dai, Ling-Qing; Ding, Qian

    2010-07-15

    We removed Sr(2+) in simulating wastewater and simultaneously prepared Sr-substituted hydroxyapatite via chemical precipitation and hydrothermal treatment. Both higher initial pH value and higher molar ratio of Sr/(Sr+Ca) contributed to lower residual Sr(2+) concentration and higher removal efficiency. About two thirds of Sr(2+) residual in solution after chemical precipitation were further reduced by hydrothermal treatment. The optimal Sr removal result was 99.66% with an ultimate concentration of 2.0 mg L(-1) when the initial pH was 12 and Sr/(Sr+Ca) was 0.2. Sr-substituted hydroxyapatite phase with hexagonal structure was identified by XRD and EDS results. However, it was found that SrHPO(4) phase was formed in the samples with high Sr composition. The lattice constants became larger with the increase of Sr(2+) and the crystallinity became higher with the increase of pH value. Rod-like particles were observed in SEM images of synthesized Sr-substituted hydroxyapatite samples, with the size of 20-30 nm in width and 70-100 nm in length. With little secondary waste and simple treating procedure, this method is an effective and prospective measure to deal with (90)Sr in nuclear waste and industry wastewater.

  3. Substitution effects of barium and calcium on magnetic properties of AxSr1-x(Fe0.5Ru0.5)O3 double perovskites (x =0.05, A =Ba,Ca)

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Zboril, R.; Tucek, J.; Kosaka, W.; Ohkoshi, S.; Felner, I.

    2007-07-01

    AxSr1-x(Fe0.5Ru0.5)O3 double perovskites (x =0.05 and A =Ba,Ca) were prepared by a sol-gel method and an effect of the cation substitution at the A site of the crystal structure of SrFe0.5Ru0.5O3 on their magnetic properties was monitored by x-ray diffraction (XRD), magnetic measurements, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and temperature-dependent and in-field Fe57 Mössbauer spectroscopy. Both Ca- and Ba-substituted samples reveal the orthorhombic structure similar to the undoped perovskite; however, the cell volume changes with the substituting ion radius. TEM and SEM micrographs manifest agglomerated nanocrystalline samples with particle sizes of about 20-60, 15-50, and 40-70nm for the undoped, Ba-doped, and Ca-doped perovskites, respectively. Generally, the magnetic regime of both substituted and undoped perovskites can be described by a spin-glass behavior caused by a spin frustration. Among other factors, this is manifested by a nonsaturation of the hysteresis loops even at a high field of 50kOe, by a low-temperature divergence of the zero-field-cooled and field-cooled magnetization curves, and by a cusp in the zero-field-cooled magnetization curve. The low-temperature spin-glass state is also supported by the in-field Mössbauer spectra, recorded on these systems. The isomer shift parameters, extracted from the Mössbauer spectra, confirm a high-spin iron(III) state with S =5/2. In contrast to the undoped and Ba-doped samples, the narrower distribution of the hyperfine magnetic fields, observed in the Ca-doped perovskite can be ascribed to the larger particles. Compared to the undoped sample, the field of maximum probability is higher in the Ca-substituted perovskite while it is reduced in the Ba-doped sample because of the effects of the chemical compression and expansion, respectively. In addition, the Ca-doped sample exhibits more negative Weiss temperature (Θ=-105K) than that found for the Ba-substituted

  4. Fe substitution for Mn in PrSrCaMnO - The electrical and dielectrical properties of Pr0.6Sr0.3Ca0.1Mn1-xFexO3 perovskite

    NASA Astrophysics Data System (ADS)

    Cherif, B.; Jemai, R.; Rahmouni, H.; Baazaoui, M.; Khirouni, K.

    2016-09-01

    We have performed admittance spectroscopy measurements on a series of Pr_{0.6}Sr_{0.3}Ca_{0.1}Mn_{1-x}FexO3 (PSCMO) compounds with x=0, 0.025, 0.050 and 0.075. The results show that all samples exhibit a metal-insulator transition at a temperature which decreases with the iron content. The conduction mechanism is described by thermally activated hopping of small polaron. Activation energy changes at specific temperature T s, probably due to the contribution of the polarization effect to the conductivity. The dielectric permittivity increases with the temperature until a temperature T d near the specific temperature T s and then begins to decrease. This is explained by the fact that at a certain temperature, the free carriers acquire sufficient energy to overcome potential barriers, and so they enhance the conductivity and decrease the polarization. The dielectric permittivity measurements are well described by a modified Curie-Weiss law.

  5. Cenozoic seawater Sr/Ca evolution

    NASA Astrophysics Data System (ADS)

    Sosdian, Sindia M.; Lear, Caroline H.; Tao, Kai; Grossman, Ethan L.; O'Dea, Aaron; Rosenthal, Yair

    2012-10-01

    Records of seawater chemistry help constrain temporal variations in geochemical processes that impact the global carbon cycle and climate through Earth's history. Here we reconstruct Cenozoic seawater Sr/Ca (Sr/Casw) using fossil Conus and turritellid gastropod Sr/Ca. Combined with an oxygen isotope paleotemperature record from the same samples, the gastropod record suggests that Sr/Caswwas slightly higher in the Eocene (˜11.4 ± 3 mmol/mol) than today (˜8.54 mmol/mol) and remained relatively stable from the mid- to late Cenozoic. We compare our gastropod Cenozoic Sr/Casw record with a published turritellid gastropod Sr/Casw record and other published biogenic (benthic foraminifera, fossil fish teeth) and inorganic precipitate (calcite veins) Sr/Caswrecords. Once the uncertainties with our gastropod-derived Sr/Casw are taken into account the Sr/Casw record agrees reasonably well with biogenic Sr/Caswrecords. Assuming a seawater [Ca] history derived from marine evaporite inclusions, all biogenic-based Sr/Casw reconstructions imply decreasing seawater [Sr] through the Cenozoic, whereas the calcite vein Sr/Casw reconstruction implies increasing [Sr] through the Cenozoic. We apply a simple geochemical model to examine the implications of divergence among these seawater [Sr] reconstructions and suggest that the interpretation and uncertainties associated with the gastropod and calcite vein proxies need to be revisited. Used in conjunction with records of carbonate depositional fluxes, our favored seawater Sr/Ca scenarios point to a significant increase in the proportion of aragonite versus calcite deposition in shelf sediments from the Middle Miocene, coincident with the proliferation of coral reefs. We propose that this occurred at least 10 million years after the seawater Mg/Ca threshold was passed, and was instead aided by declining levels of atmospheric carbon dioxide.

  6. Raman spectra of (Bi,Pb) sub 2 Sr sub 2 CaCu sub 2 O sub 8+ y single crystals and the role of lead substitution

    SciTech Connect

    Sapriel, J.; Schneck, J.; Scott, J.F.; Toledano, J.C.; Pierre, L.; Chavignon, J.; Daguet, C. ); Chaminade, J.P. ); Boyer, H. )

    1991-03-01

    We report the Raman spectra of chemically characterized (Bi{sub 2{minus}{ital x}}Pb{sub {ital x}})Sr{sub 2}CaCu{sub 2}O{sub 8+{ital y}} single crystals for 0{lt}{ital x}{lt}0.4. Significant modifications of the spectra, becoming more pronounced with increasing {ital x}, are noted with respect to the lead-free crystals in the ranges of the 117-cm{sup {minus}1}, (460--530)-cm{sup {minus}1}, and (630--650)-cm{sup {minus}1} lines. The interpretation of these modifications provides an important confirmation of recent speculations concerning the lattice dynamics of this family of superconductors and the role of lead in modifying their structure and their microstructure.

  7. Computational insights on crystal structures of the oxygen-evolving complex of photosystem II with either Ca²⁺ or Ca²⁺ substituted by Sr²⁺

    DOE PAGES

    Vogt, Leslie; Ertem, Mehmed Z.; Pal, Rhitankar; Brudvig, Gary W.; Batista, Victor S.

    2015-01-15

    The oxygen-evolving complex of photosystem II can function with either Ca²⁺ or Sr²⁺ as the heterocation, but the reason for differing turnover rates remains unresolved despite reported X-ray crystal structures for both forms. Using quantum mechanics/molecular mechanics (QM/MM) calculations, we optimize structures with each cation in both the resting state (S₁) and in a series of reduced states (S₀, S₋₁, and S-₂). Through comparison with experimental data, we determine that X-ray crystal structures with either Ca²⁺ or Sr²⁺ are most consistent with the S-₂ state, Mn₄[III,III,III,II] with O4 and O5 protonated. As expected, the QM/MM models show that Ca²⁺/Sr²⁺ substitutionmore » results in elongation of the heterocation bonds and displaces terminal waters W3 and W4. The optimized structures also show that hydrogen-bonded W5 is displaced in all S states with Sr²⁺ as the heterocation, suggesting that this water may play a critical role during water oxidation.« less

  8. Controls on Sr/Ca in Scleractinian Corals: The Effects of Ca-ATPase and Ca channels on Skeletal Chemistry

    NASA Astrophysics Data System (ADS)

    Allison, N.; Cohen, I.; Finch, A. A.; Erez, J.

    2010-12-01

    Coral skeletal Sr/Ca is a commonly used palaeothermometer and has been used to estimate past sea surface temperatures. However the processes controlling Sr incorporation in coral aragonite are poorly understood. The Sr/Ca chemistry of the massive Porites spp. corals typically used for palaeoenvironmental reconstruction is dominated by short-term (weekly-monthly) oscillations of ~10% which do not reflect seawater temperature. This heterogeneity may reflect variations in the composition of the fluid used for calcification. Coral skeletons precipitate from an extracellular calcifying fluid enclosed in a semi-isolated space between the skeleton and the calicoblastic epithelium (the tissue layer at the base of the coral organism). Seawater diffuses directly to the calcification site and the calcification fluid has a composition derived from that of seawater but modified by other transport processes. In zooxanthellate corals, Ca2+ is transported transcellularly to the calcification site by both calcium channels and by the carrier protein Ca-ATPase. Sr2+ has a similar ionic radius to Ca2+, but it is not clear if Sr2+ can substitute for Ca2+ in these transport mechanisms. Variations in the relative contributions of each of the transport mechanisms to the calcification fluid and the efficiencies with which each process transports Sr2+ and Ca2+ could explain the Sr/Ca heterogeneity observed in coral skeletons. To test the impact of transcellular Ca transport processes on skeletal Sr/Ca and Mg/Ca we cultured Pocillopora damicornis corals in the presence of inhibitors of Ca-ATPase (ruthenium red) and Ca channels (verapamil). The photosynthesis, respiration and calcification rates of the colonies were monitored throughout the experiment. The skeleton subsequently deposited was identified (by 42Ca spike) and analysed by secondary ion mass spectrometry. The Sr/Ca and Mg/Ca of the aragonite deposited in the presence of either of the inhibitors was not significantly different from

  9. Anisotropic scattering rate in Fe-substituted Bi2Sr2Ca(Cu1-xFex)2O8+δ

    DOE PAGES

    Naamneh, M.; Lubashevsky, Y.; Lahoud, E.; Gu, G.; Kanigel, A.

    2015-05-27

    We measured the electronic structure of Fe substituted Bi2212 using Angle Resolved Photoemission Spectroscopy (ARPES). We find that the substitution does not change the momentum dependence of the superconducting gap but induces a very anisotropic enhancement of the scattering rate. A comparison of the effect of Fe substitution to that of Zn substitution suggests that the Fe reduces Tc so effectively because it supresses very strongly the coherence weight around the anti-nodes.

  10. Effect of Sr and Ca solid-solution behaviour on superconductive properties as determined by microstructure analysis

    NASA Astrophysics Data System (ADS)

    Hong, Zhanglian; Wang, Minquan; Xiong, Guohong; Fan, Xianping

    1997-02-01

    The effects of the Sr and Ca composition and site-selection in a solid solution of a Bi-system superconductor on the superconductive properties were studied. Results showed that the Sr and Ca solid-solution behaviour had a remarkable effect on the superconductive properties. Further analysis indicated that this effect originated from varied hole concentration which was determined by the content of Sr atoms substituting for Bi atoms within the BiO layers. This substitution was influenced by the Sr and Ca solid-solution behaviour. This result offers a new mechanism for clarifying why the bivalent Sr and Ca cations affect the superconductive properties.

  11. Hydrothermal synthesis and characterization of Si and Sr co-substituted hydroxyapatite nanowires using strontium containing calcium silicate as precursors.

    PubMed

    Zhang, Na; Zhai, Dong; Chen, Lei; Zou, Zhaoyong; Lin, Kaili; Chang, Jiang

    2014-04-01

    In the absence of any organic surfactants and solvents, the silicon (Si) and strontium (Sr) co-substituted hydroxyapatite [Ca10(PO4)6(OH)2, Si/Sr-HAp] nanowires were synthesized via hydrothermal treatment of the Sr-containing calcium silicate (Sr-CS) powders as the precursors in trisodium phosphate (Na3PO4) aqueous solution. The morphology, phase, chemical compositions, lattice constants and the degradability of the products were characterized. The Si/Sr-HAp nanowires with diameter of about 60nm and up to 2μm in length were obtained after hydrothermal treatment of the Sr-CS precursors. The Sr and Si substitution amount of the HAp nanowires could be well regulated by facile tailoring the Sr substitution level of the precursors and the reaction ratio of the precursor/solution, respectively. The SiO4 tetrahedra and Sr(2+) ions occupied the crystal sites of the HAp, and the lattice constants increased apparently with the increase of the substitution amount. EDS mapping also suggested the uniform distribution of Si and Sr in the synthetic nanowires. Moreover, the Si/Sr-substitution apparently improved the degradability of the HAp materials. Our study suggested that the precursor transformation method provided a facile approach to synthesize the Si/Sr co-substituted HAp nanowires with controllable substitution amount, and the synthetic Si/Sr-HAp nanowires might be used as bioactive materials for hard tissue regeneration applications. PMID:24582251

  12. Hydrothermal synthesis and characterization of Si and Sr co-substituted hydroxyapatite nanowires using strontium containing calcium silicate as precursors.

    PubMed

    Zhang, Na; Zhai, Dong; Chen, Lei; Zou, Zhaoyong; Lin, Kaili; Chang, Jiang

    2014-04-01

    In the absence of any organic surfactants and solvents, the silicon (Si) and strontium (Sr) co-substituted hydroxyapatite [Ca10(PO4)6(OH)2, Si/Sr-HAp] nanowires were synthesized via hydrothermal treatment of the Sr-containing calcium silicate (Sr-CS) powders as the precursors in trisodium phosphate (Na3PO4) aqueous solution. The morphology, phase, chemical compositions, lattice constants and the degradability of the products were characterized. The Si/Sr-HAp nanowires with diameter of about 60nm and up to 2μm in length were obtained after hydrothermal treatment of the Sr-CS precursors. The Sr and Si substitution amount of the HAp nanowires could be well regulated by facile tailoring the Sr substitution level of the precursors and the reaction ratio of the precursor/solution, respectively. The SiO4 tetrahedra and Sr(2+) ions occupied the crystal sites of the HAp, and the lattice constants increased apparently with the increase of the substitution amount. EDS mapping also suggested the uniform distribution of Si and Sr in the synthetic nanowires. Moreover, the Si/Sr-substitution apparently improved the degradability of the HAp materials. Our study suggested that the precursor transformation method provided a facile approach to synthesize the Si/Sr co-substituted HAp nanowires with controllable substitution amount, and the synthetic Si/Sr-HAp nanowires might be used as bioactive materials for hard tissue regeneration applications.

  13. Characterization of Sr-substituted hydroxyapatite thin film by sputtering technique from mixture targets of hydroxyapatite and strontium apatite.

    PubMed

    Ozeki, K; Goto, T; Aoki, H; Masuzawa, T

    2014-01-01

    Sr-substituted hydroxyapatite thin films were prepared by sputtering technique from mixture targets of hydroxyapatite (HA) and strontium apatite (SrAp). The HA and SrAp powders were mixed at 0-100% Sr/(Sr+Ca) target ratios. The coated films were recrystallized by a hydrothermal treatment to reduce film dissolution. The films were then characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectrometry (ICP). The osteocompatiblity of the films was also evaluated by the size of the bone formation area in osteoblast cells.In the XRD patterns, peaks shifted to lower 2θ values with increasing Sr/(Sr+Ca) target ratios, which indicated Sr incorporation into the HA lattice. In the SEM observation of the hydrothermally treated films, the surface was covered with globular particles, and the size of the globular particles increased from Sr0 to Sr40, and then the size decreased from Sr60 to Sr100. The ICP analysis showed that the Sr/(Sr+Ca) film ratios were almost the same as the target ratios. In the cell culture, the bone formation area on the Sr-substituted HA films increased with increasing Sr concentration, and saturated at Sr60. PMID:24642972

  14. The effect of Yttrium on the Ca and Sr planes of Y-doped Bi 2Sr 2Ca 1Cu 2O 8

    NASA Astrophysics Data System (ADS)

    Alméras, P.; Berger, H.; Margaritondo, G.

    1993-08-01

    Photoemission spectromicroscopy experiments on a series of Y-doped Bi 2Sr 2Ca 1Cu 2O 8 single crystals show that the doping changes the valence of copper as required for the observed modification of the critical temperature. The doping, however, affects with substitutional reactions not only the CaO planes, but also the SrO planes. Des expériences de photoémission sur une série de monocristaux de Bi 2Sr 2Ca 1Cu 2O 8 dopés avec de l'yttrium montrent que le dopage change la valence du cuivre, comme on dopage, pourtant, ne modifie pas seulement les plans CaO par des réactions de substitution, mais également les plans SrO. Esperimenti di fotoemissione condotti su una serie di monocristalli di Bi 2Sr 2Ca 2O 8 con impurezze di Y mostrano che tali impurezze modificano la valenza del rame, com'é indipendentemente reso necessario dal fatto che si osservano dei cambiamenti della temperature di transizione. Si nota peraltro che le impurezze non modificano solamente i piani CaO mediante reazioni di sostituzione, ma anche i piani SrO.

  15. Electronic structure of Ca, Sr, and Ba under pressure.

    NASA Technical Reports Server (NTRS)

    Animalu, A. O. E.; Heine, V.; Vasvari, B.

    1967-01-01

    Electronic band structure calculations phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure

  16. Induction of CaSR expression circumvents the molecular features of malignant CaSR null colon cancer cells.

    PubMed

    Singh, Navneet; Chakrabarty, Subhas

    2013-11-15

    We recently reported on the isolation and characterization of calcium sensing receptor (CaSR) null human colon cancer cells (Singh et al., Int J Cancer 2013; 132: 1996-2005). CaSR null cells possess a myriad of molecular features that are linked to a highly malignant and drug resistant phenotype of colon cancer. The CaSR null phenotype can be maintained in defined human embryonic stem cell culture medium. We now show that the CaSR null cells can be induced to differentiate in conventional culture medium, regained the expression of CaSR with a concurrent reversal of the cellular and molecular features associated with the null phenotype. These features include cellular morphology, expression of colon cancer stem cell markers, expression of survivin and thymidylate synthase and sensitivity to fluorouracil. Other features include the expression of epithelial mesenchymal transition linked molecules and transcription factors, oncogenic miRNAs and tumor suppressive molecule and miRNA. With the exception of cancer stem cell markers, the reversal of molecular features, upon the induction of CaSR expression, is directly linked to the expression and function of CaSR because blocking CaSR induction by shRNA circumvented such reversal. We further report that methylation and demethylation of the CaSR gene promoter underlie CaSR expression. Due to the malignant nature of the CaSR null cells, inclusion of the CaSR null phenotype in disease management may improve on the mortality of this disease. Because CaSR is a robust promoter of differentiation and mediates its action through diverse mechanisms and pathways, inactivation of CaSR may serve as a new paradigm in colon carcinogenesis.

  17. Regional and interspecific variation in Sr, Ca, and Sr/Ca ratios in avian eggshells from the USA.

    PubMed

    Mora, Miguel A; Brattin, Bryan; Baxter, Catherine; Rivers, James W

    2011-08-01

    To examine regional variation in strontium (Sr), which at high concentrations may reduce eggshell quality, increase egg breakage and reproductive failure, we analyzed Sr, and calcium (Ca) concentrations and Sr/Ca ratios in eggshells from 20 avian species from California, Texas, Idaho, Kansas, and Michigan. In addition, we included data previously reported from Arizona to expand the regional comparisons and to better establish patterns of Sr, and Sr/Ca ratios in bird species across the United States. We found Sr concentrations varied significantly among regions, among species, and among foraging guilds; this variability is strongly influenced by the Sr/Ca ratios in surface water from locations close to the region where the eggshells were collected. Sr concentrations and Sr/Ca ratios were significantly higher in bird eggshells from the Volta wildlife region in the San Joaquin Valley, California and in various locales from Arizona. Sr concentrations and Sr/Ca ratios in bird eggshells from other locations in the USA were lower than those detected in these two regions. Among foraging guilds, invertivores had the highest Sr concentrations and Sr/Ca ratios and carnivores had the lowest. In general, the Sr/Ca ratio increased strongly with increasing Sr concentrations (R(2) = 0.99, P < 0.0001). There was a significant correlation (R(2) = 0.58, P < 0.0001) between Sr/Ca ratios in water and the average Sr/Ca ratios in eggshells suggesting that these values could be determined from Sr/Ca ratios in water. Eggshell thickness was poorly correlated with Sr (R(2) = 0.03) but had a significant and positive correlation with Ca and was more properly correlated by a quadratic equation (R(2) = 0.50, Thickness = 2.13 - 0.02Ca - 3.07 * 10(-5)Ca(2)). Our study provides further evidence that Sr accumulates significantly in the avian eggshell, in some regions at concentrations which could be of concern for potential negative effects on reproduction. We suggest that when assessing the effects

  18. Regional and interspecific variation in Sr, Ca, and Sr/Ca ratios in avian eggshells from the USA.

    PubMed

    Mora, Miguel A; Brattin, Bryan; Baxter, Catherine; Rivers, James W

    2011-08-01

    To examine regional variation in strontium (Sr), which at high concentrations may reduce eggshell quality, increase egg breakage and reproductive failure, we analyzed Sr, and calcium (Ca) concentrations and Sr/Ca ratios in eggshells from 20 avian species from California, Texas, Idaho, Kansas, and Michigan. In addition, we included data previously reported from Arizona to expand the regional comparisons and to better establish patterns of Sr, and Sr/Ca ratios in bird species across the United States. We found Sr concentrations varied significantly among regions, among species, and among foraging guilds; this variability is strongly influenced by the Sr/Ca ratios in surface water from locations close to the region where the eggshells were collected. Sr concentrations and Sr/Ca ratios were significantly higher in bird eggshells from the Volta wildlife region in the San Joaquin Valley, California and in various locales from Arizona. Sr concentrations and Sr/Ca ratios in bird eggshells from other locations in the USA were lower than those detected in these two regions. Among foraging guilds, invertivores had the highest Sr concentrations and Sr/Ca ratios and carnivores had the lowest. In general, the Sr/Ca ratio increased strongly with increasing Sr concentrations (R(2) = 0.99, P < 0.0001). There was a significant correlation (R(2) = 0.58, P < 0.0001) between Sr/Ca ratios in water and the average Sr/Ca ratios in eggshells suggesting that these values could be determined from Sr/Ca ratios in water. Eggshell thickness was poorly correlated with Sr (R(2) = 0.03) but had a significant and positive correlation with Ca and was more properly correlated by a quadratic equation (R(2) = 0.50, Thickness = 2.13 - 0.02Ca - 3.07 * 10(-5)Ca(2)). Our study provides further evidence that Sr accumulates significantly in the avian eggshell, in some regions at concentrations which could be of concern for potential negative effects on reproduction. We suggest that when assessing the effects

  19. The structure and activation of substrate water molecules in Sr(2+)-substituted photosystem II.

    PubMed

    Chatterjee, Ruchira; Milikisiyants, Sergey; Coates, Christopher S; Koua, Faisal H M; Shen, Jian-Ren; Lakshmi, K V

    2014-10-14

    The mechanism of solar water oxidation by photosystem II (PSII) is of fundamental interest and it is the object of extensive studies both in the past and present. The solar water oxidation reaction of PSII occurs in the oxygen-evolving complex (OEC). The OEC consists of a tetranuclear manganese calcium-oxo (Mn4Ca-oxo) cluster that is surrounded by amino acid residues and inorganic cofactors. The role of the Ca(2+) ion in the water oxidation reaction is one of the most interesting questions that is yet to be answered. In this study, we probe the structural and functional differences induced by metal ion substitution in the Mn4Ca-oxo cluster by substituting the Ca(2+) ion in the OEC by a Sr(2+) ion. We apply two-dimensional (2D) hyperfine sublevel correlation (HYSCORE) spectroscopy to detect weak magnetic interactions between the paramagnetic Mn4Sr-oxo cluster and the surrounding protons in the S2 state of the OEC of Sr(2+)-substituted PSII. We identify three groups of protons that are magnetically interacting with the Mn4Sr-oxo cluster. Using the recently reported 1.9 Å resolution X-ray structure of the OEC in the S1 state [Umena et al.] and the high-resolution 2D HYSCORE spectroscopy studies of the S2 state of the OEC of Ca(2+)-containing PSII [Milikisiyants et al., Energy Environ. Sci., 2012, 5, 7747], we discuss the assignments of the three groups of protons that are magnetically coupled to the Mn4Sr-oxo cluster. Since hyperfine interactions are highly sensitive to small perturbations in the electronic and geometric structure of paramagnetic centers, a comparison of the 2D HYSCORE spectra of Sr(2+)-substituted and Ca(2+)-containing PSII allows us to draw important conclusions with respect to the structure of the substrate water molecules in the OEC and the role of the Ca(2+) ion in the water oxidation reaction. In addition, for the first time, we determine the experimental value of the spin projection factor for the Mn(III) ion of the Mn4Ca-oxo cluster as ρ1

  20. Interstitial and substitutional Zr in SrTiO3

    NASA Astrophysics Data System (ADS)

    Jaffe, John; van Ginhoven, Renee; Jiang, Weilin

    2011-03-01

    We investigate Zr in SrTi O3 (STO) as an electronic dopant and as a model for nuclear waste forms in which radioactive Sr decays to Y and then to stable Zr through beta emission. Density functional theory (DFT) within the supercell model is used to predict the thermodynamic stability and electronic states of interstitial and Sr- or Ti-substituted Zr atoms in the STO lattice. Native point defects such as vacancies and antisites are also considered. When Zr replaces Sr, its most stable configuration is to simply occupy the Sr site (instead of, for example, replacing a Ti and displacing the Ti to the Sr site.) For Zr added to the lattice, its most stable configuration is to replace a Ti, making a Zr Ti impurity plus a Ti interstitial (as opposed to the Zr just remaining as an interstitial atom.) Zr Sr is predicted to be a double electron donor, Zr Ti is electrically inactive and interstitial Zr and Ti are predicted to be quadruple donors, with all donor levels in the conduction band. Zr Sr and the tetravalent interstitials are all predicted to increase the crystal volume, and the interstitials also are predicted to lead to a tetragonal distortion of the lattice. Experiments with injection of Zr atoms into STO qualitatively confirm these predictions of crystal structural changes. Supported by U.S. Department of Energy Waste Form Campaign.

  1. Late Quaternary Productivity Records from Coccolith Sr/Ca

    NASA Astrophysics Data System (ADS)

    Stoll, H. M.; Burke, A.; Mejia Ramirez, L. M.; Shimizu, N.; Ziveri, P. P. I.

    2014-12-01

    The Sr/Ca of coccoliths has been proposed as an indicator of productivity on the basis of correlation with export production in sediment traps and across upwelling productivity gradients, although the mechanism responsable for this relationship is not clear. For diverse oceanographic settings in the Late Quaternary, we compare coccolith Sr/Ca productivity records with those of other productivity indicators and proxies for mechanisms of productivity forcing. For the Somalia Basin in the Arabian Sea, coccolith Sr/Ca shows a large variation coherent with precessional forcing of wind strength as a mechanism for productivity regulation. During the glacial, the Sr/Ca peak is decoupled from productivity indicators based on organic C accumulation rate. For the Northern Bay of Bengal, coccolith Sr/Ca, Ba/Ti, and relative abundance of G. bulloides, all suggest greater productivity during the interglacial periods, consisted with Nd isotopic evidence for greater riverine nutrient inputs. In the Andaman Sea, coccolith Sr/Ca is highest during precessional maxima in the summer monsoon, consistent with proxies for chemical weathering in the Irawaddy rivershed. In the Eastern Mediterranean, coccolith Sr/Ca is on average low, and peaks during the E. Holocene interval characterized by deposition of sapropel S1. The peak in Sr/Ca however is comparable to the level maintained throughout the Holocene in the Western Mediterranean, where no sapropel occurs, implicating deepwater oxygen levels as a significant contributor to sapropel formation. Finally, on the Agulhas Bank, minima in coccolith Sr/Ca occur during obliquity minima which are periods of anomalous equatorward deposition of IRD in the Southern Ocean. Northward explansion of the westerly wind field during these cold intervals, block upwelling on the Agulhas Bank and result in low productivity.

  2. Biocompatibility and biodegradability of Mg-Sr alloys: the formation of Sr-substituted hydroxyapatite.

    PubMed

    Bornapour, M; Muja, N; Shum-Tim, D; Cerruti, M; Pekguleryuz, M

    2013-02-01

    Magnesium is an attractive material for use in biodegradable implants due to its low density, non-toxicity and mechanical properties similar to those of human tissue such as bone. Its biocompatibility makes it amenable for use in a wide range of applications from bone to cardiovascular implants. Here we investigated the corrosion rate in simulated body fluid (SBF) of a series of Mg-Sr alloys, with Sr in the range of 0.3-2.5%, and found that the Mg-0.5 Sr alloy showed the slowest corrosion rate. The degradation rate from this alloy indicated that the daily Sr intake from a typical stent would be 0.01-0.02 mg day⁻¹, which is well below the maximum daily Sr intake levels of 4 mg day⁻¹. Indirect cytotoxicity assays using human umbilical vascular endothelial cells indicated that Mg-0.5 Sr extraction medium did not cause any toxicity or detrimental effect on the viability of the cells. Finally, a tubular Mg-0.5 Sr stent sample, along with a WE43 control stent, was implanted into the right and left dog femoral artery. No thrombosis effect was observed in the Mg-0.5 Sr stent after 3 weeks of implantation while the WE43 stent thrombosed. X-ray diffraction demonstrated the formation of hydroxyapatite and Mg(OH)₂ as a result of the degradation of Mg-0.5 Sr alloy after 3 days in SBF. X-ray photoelectron spectroscopy further showed the possibility of the formation of a hydroxyapatite Sr-substituted layer that presents as a thin layer at the interface between the Mg-0.5 Sr alloy and the corrosion products. We believe that this interfacial layer stabilizes the surface of the Mg-0.5 Sr alloy, and slows down its degradation rate over time. PMID:22871640

  3. Kinetics of Sr/Ba and Sr/Ca ion exchange in synthetic zeolite A

    SciTech Connect

    Gaus, H.; Lutze, W.

    1981-01-08

    The isotopic exchange kinetics of Sr, Ba, and Ca have been measured in zeolites with different compositions and found to be describable as self-diffusion. The self-diffusion coefficients are strongly dependent on the composition. Also the Sr/Ba and Sr/Ca ion exchanges are measured in both directions and described as interdiffusion. While for Sr/Ba tolerable agreement is reached, for Sr/Ca a modification is necessary. The interdiffusion coefficient is multiplied by a factor which takes into account the activity, i.e., the selectivity of the zeolite. As a continuation of an earlier paper the zeolite is described as a mixture of microcells and free water. The above-mentioned factor must be calculated for a nonequilibrium state with respect to the water content in order to get agreement with the measurements.

  4. Electronic structure and properties of isoelectronically substituted compounds Y{sub 1}Ba{sub 2-m}M{sub m}Cu{sub 3}O{sub 7} and Y{sub 1}Ba{sub 2-m}M{sub m}Cu{sub 4}O{sub 8} (M = Be, Mg, Ca, Sr, Ba, Ra)

    SciTech Connect

    Ermakov, A.I.; Zharikova, E.A.; Markushin, N.A.

    1994-09-01

    According to cluster calculations, the electronic structures of compounds based on Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} and Y{sub 1}Ba{sub 2}Cu{sub 4}O{sub 8} with isoelectronically substituted barium have some qualitative distinctions. These compounds behave differently upon barium substitution by other elements due to differences in the character of their highest occupied and lowest unoccupied molecular orbitals. Substitution of barium by radium is expected to lead to an increase in oxygen stability without a significant decrease in the critical temperature of superconduction transition T{sub s}. In order to raise T{sub s}, it is of interest to study the systems YBa{sub 2-m}(Be or Mg){sub m}Cu{sub 3}O{sub x} and YBa{sub 2-m}(Ca, Sr){sub m}Cu{sub 3}O{sub x}. On partial substitution of barium by calcium in YBa{sub 2}Cu{sub 4}O{sub 8}, the mechanism of T{sub s} elevation may involve contraction of the forbidden band due to oxygen sublattice distortions in the vicinity of Ba centers.

  5. Negative feedback from CaSR signaling to aquaporin-2 sensitizes vasopressin to extracellular Ca2.

    PubMed

    Ranieri, Marianna; Tamma, Grazia; Di Mise, Annarita; Russo, Annamaria; Centrone, Mariangela; Svelto, Maria; Calamita, Giuseppe; Valenti, Giovanna

    2015-07-01

    We previously described that high luminal Ca(2+) in the renal collecting duct attenuates short-term vasopressin-induced aquaporin-2 (AQP2) trafficking through activation of the Ca(2+)-sensing receptor (CaSR). Here, we evaluated AQP2 phosphorylation and permeability, in both renal HEK-293 cells and in the dissected inner medullary collecting duct, in response to specific activation of CaSR with NPS-R568. In CaSR-transfected cells, CaSR activation drastically reduced the basal levels of AQP2 phosphorylation at S256 (AQP2-pS256), thus having an opposite effect to vasopressin action. When forskolin stimulation was performed in the presence of NPS-R568, the increase in AQP2-pS256 and in the osmotic water permeability were prevented. In the freshly isolated inner mouse medullar collecting duct, stimulation with forskolin in the presence of NPS-R568 prevented the increase in AQP2-pS256 and osmotic water permeability. Our data demonstrate that the activation of CaSR in the collecting duct prevents the cAMP-dependent increase in AQP2-pS256 and water permeability, counteracting the short-term vasopressin response. By extension, our results suggest the attractive concept that CaSR expressed in distinct nephron segments exerts a negative feedback on hormones acting through cAMP, conferring high sensitivity of hormone to extracellular Ca(2+). PMID:25977473

  6. CaMKII-dependent SR Ca leak contributes to doxorubicin-induced impaired Ca handling in isolated cardiac myocytes

    PubMed Central

    Sag, Can M.; Köhler, Anne C.; Anderson, Mark E.; Backs, Johannes; Maier, Lars S.

    2011-01-01

    Objective Doxorubicin (DOX) is one of the most effective chemotherapeutic agents, but cardiotoxicity limits DOX therapy. Although the mechanisms are not entirely understood, reactive oxygen species (ROS) appear to be involved in DOX cardiotoxicity. Ca/calmodulin dependent protein kinase II (CaMKII) can be activated by ROS through oxidation and is known to contribute to myocardial dysfunction through Ca leakage from the sarcoplasmic reticulum (SR). Rationale We hypothesized that CaMKII contributes to DOX-induced defects in intracellular Ca ([Ca]i) handling. Methods Cardiac myocytes were isolated from wild-type (WT) adult rat hearts and from mouse hearts lacking the predominant myocardial CaMKII isoform (CaMKIIδ−/−, KO) vs. WT. Isolated cardiomyocytes were investigated 30 min after DOX (10 µmol/L) superfusion, using epifluorescence and confocal microscopy. Intracellular ROS-generation ([ROS]i) and [Ca]i handling properties were assessed. In a subset of experiments, KN-93 or AIP (each 1 µmol/L) were used to inhibit CaMKII. Melatonin (Mel, 100 µmol/L) served as ROS-scavenger. Western blots were performed to determine the amount of CaMKII phosphorylation and oxidation. Results DOX increased [ROS]i and led to significant diastolic [Ca]i overload in rat myocytes. This was associated with reduced [Ca]i transients, a 5.8-fold increased diastolic SR Ca leak and diminished SR Ca content. ROS-scavenging partially rescued Ca handling. Western blots revealed increased CaMKII phosphorylation, but not CaMKII oxidation after DOX. Pharmacological CaMKII inhibition attenuated diastolic [Ca]i overload after DOX superfusion and led to partially restored [Ca]i transients and SR Ca content, presumably due to reduced Ca spark frequency. In line with this concept, isoform-specific CaMKIIδ-KO attenuated diastolic [Ca]i overload and Ca spark frequency. Conclusions DOX exposure induces CaMKII-dependent SR Ca leakage, which partially contributes to impaired cellular [Ca]i homeostasis

  7. Controls on Sr/Ca and Mg/Ca in scleractinian corals: The effects of Ca-ATPase and transcellular Ca channels on skeletal chemistry

    NASA Astrophysics Data System (ADS)

    Emif Allison, Nicola; Cohen, Itay; Finch, Adrian A.; Erez, Jonathan

    2011-11-01

    The Sr/Ca of aragonitic coral skeletons is a commonly used palaeothermometer. However skeletal Sr/Ca is typically dominated by weekly-monthly oscillations which do not reflect temperature or seawater composition and the origins of which are currently unknown. To test the impact of transcellular Ca2+ transport processes on skeletal Sr/Ca, colonies of the branching coral, Pocillopora damicornis, were cultured in the presence of inhibitors of Ca-ATPase (ruthenium red) and Ca channels (verapamil hydrochloride). The photosynthesis, respiration and calcification rates of the colonies were monitored throughout the experiment. The skeleton deposited in the presence of the inhibitors was identified (by 42Ca spike) and analysed for Sr/Ca and Mg/Ca by secondary ion mass spectrometry. The Sr/Ca of the aragonite deposited in the presence of either of the inhibitors was not significantly different from that of the solvent (dimethyl sulfoxide) control, although the coral calcification rate was reduced by up to 66% and 73% in the ruthenium red and verapamil treatments, respectively. The typical precision (95% confidence limits) of mean Sr/Ca determinations within any treatment was <±1% and differences in skeletal Sr/Ca between treatments were correspondingly small. Either Ca-ATPase and Ca channels transport Sr2+ and Ca2+ in virtually the same ratio in which they are present in seawater or transcellular processes contribute little Ca2+ to the skeleton and most Ca is derived from seawater transported directly to the calcification site. Variations in the activities of Ca-ATPase and Ca-channels are not responsible for the weekly-monthly Sr/Ca oscillations observed in skeletal chronologies, assuming that the specificities of Ca transcellular transport processes are similar between coral genera.

  8. Controls on Sr/Ca and Mg/Ca in scleractinian corals: The effects of Ca-ATPase and transcellular Ca channels on skeletal chemistry

    NASA Astrophysics Data System (ADS)

    Allison, Nicola; Cohen, Itay; Finch, Adrian A.; Erez, Jonathan; EMIF

    2011-11-01

    The Sr/Ca of aragonitic coral skeletons is a commonly used palaeothermometer. However skeletal Sr/Ca is typically dominated by weekly-monthly oscillations which do not reflect temperature or seawater composition and the origins of which are currently unknown. To test the impact of transcellular Ca 2+ transport processes on skeletal Sr/Ca, colonies of the branching coral, Pocillopora damicornis, were cultured in the presence of inhibitors of Ca-ATPase (ruthenium red) and Ca channels (verapamil hydrochloride). The photosynthesis, respiration and calcification rates of the colonies were monitored throughout the experiment. The skeleton deposited in the presence of the inhibitors was identified (by 42Ca spike) and analysed for Sr/Ca and Mg/Ca by secondary ion mass spectrometry. The Sr/Ca of the aragonite deposited in the presence of either of the inhibitors was not significantly different from that of the solvent (dimethyl sulfoxide) control, although the coral calcification rate was reduced by up to 66% and 73% in the ruthenium red and verapamil treatments, respectively. The typical precision (95% confidence limits) of mean Sr/Ca determinations within any treatment was <±1% and differences in skeletal Sr/Ca between treatments were correspondingly small. Either Ca-ATPase and Ca channels transport Sr 2+ and Ca 2+ in virtually the same ratio in which they are present in seawater or transcellular processes contribute little Ca 2+ to the skeleton and most Ca is derived from seawater transported directly to the calcification site. Variations in the activities of Ca-ATPase and Ca-channels are not responsible for the weekly-monthly Sr/Ca oscillations observed in skeletal chronologies, assuming that the specificities of Ca transcellular transport processes are similar between coral genera.

  9. What does the Sr-substituted 2.1 Å resolution crystal structure of photosystem II reveal about the water oxidation mechanism?

    PubMed

    Terrett, Richard; Petrie, Simon; Pace, Ron J; Stranger, Robert

    2014-03-25

    A density functional study of the Sr-substituted photosystem II water oxidising complex demonstrates that its recent X-ray crystal structure is consistent with a (Mn(III))4 oxidation state pattern, and with a Sr-bound hydroxide ion. The Sr-water-hydroxide interactions rationalize differences in the exchange rates of substrate water and kinetics of dioxygen bond formation relative to the Ca-containing structure.

  10. What does the Sr-substituted 2.1 Å resolution crystal structure of photosystem II reveal about the water oxidation mechanism?

    PubMed

    Terrett, Richard; Petrie, Simon; Pace, Ron J; Stranger, Robert

    2014-03-25

    A density functional study of the Sr-substituted photosystem II water oxidising complex demonstrates that its recent X-ray crystal structure is consistent with a (Mn(III))4 oxidation state pattern, and with a Sr-bound hydroxide ion. The Sr-water-hydroxide interactions rationalize differences in the exchange rates of substrate water and kinetics of dioxygen bond formation relative to the Ca-containing structure. PMID:24519750

  11. The influence of SrO and CaO in silicate and phosphate bioactive glasses on human gingival fibroblasts.

    PubMed

    Massera, J; Kokkari, A; Närhi, T; Hupa, L

    2015-06-01

    In this paper, we investigate the effect of substituting SrO for CaO in silicate and phosphate bioactive glasses on the human gingival fibroblast activity. In both materials the presence of SrO led to the formation of a CaP layer with partial Sr substitution for Ca. The layer at the surface of the silicate glass consisted of HAP whereas at the phosphate glasses it was close to the DCPD composition. In silicate glasses, SrO gave a faster initial dissolution and a thinner reaction layer probably allowing for a continuous ion release into the solution. In phosphate glasses, SrO decreased the dissolution process and gave a more strongly bonded reaction layer. Overall, the SrO-containing silicate glass led to a slight enhancement in the activity of the gingival fibroblasts cells when compared to the SrO-free reference glass, S53P4. The cell activity decreased up to 3 days of culturing for all phosphate glasses containing SrO. Whereas culturing together with the SrO-free phosphate glass led to complete cell death at 7 days. The glasses containing SrO showed rapid cell proliferation and growth between 7 and 14 days, reaching similar activity than glass S53P4. The addition of SrO in both silicate and phosphate glasses was assumed beneficial for proliferation and growth of human gingival fibroblasts due to Sr incorporation in the reaction layer at the glass surface and released in the cell culture medium.

  12. Anisotropic scattering rate in Fe-substituted Bi2Sr2Ca(Cu1-xFex)2O8+δ

    SciTech Connect

    Naamneh, M.; Lubashevsky, Y.; Lahoud, E.; Gu, G.; Kanigel, A.

    2015-05-27

    We measured the electronic structure of Fe substituted Bi2212 using Angle Resolved Photoemission Spectroscopy (ARPES). We find that the substitution does not change the momentum dependence of the superconducting gap but induces a very anisotropic enhancement of the scattering rate. A comparison of the effect of Fe substitution to that of Zn substitution suggests that the Fe reduces Tc so effectively because it supresses very strongly the coherence weight around the anti-nodes.

  13. A systematic study of superconductivity in BiPb(Sn)-Sb Sr-Ca-Cu-O systems

    NASA Technical Reports Server (NTRS)

    Akbar, Sheikh A.; Botelho, M. J.; Wong, M. S.; Alauddin, M.

    1990-01-01

    Superconducting transition above 160 K has been reported in the Bi-Pb-Sb-Sr-Ca-Cu-O system. Results of a systematic study emphasizing the correlations between the type and amount of dopant, and superconducting transition is presented. The effect of Sn (instead of Pb) substitution is also highlighted.

  14. Synthesis of BiPbSrCaCuO superconductor

    DOEpatents

    Hults, W.L.; Kubat-Martin, K.A.; Salazar, K.V.; Phillips, D.S.; Peterson, D.E.

    1994-04-05

    A process and a precursor composition for preparing a lead-doped bismuth-strontium-calcium-copper oxide superconductor of the formula Bi[sub a]Pb[sub b]Sr[sub c]Ca[sub d]Cu[sub e]O[sub f] wherein a is from about 1.7 to about 1.9, b is from about 0.3 to about 0.45, c is from about 1.6 to about 2.2, d is from about 1.6 to about 2.2, e is from about 2.97 to about 3.2 and f is 10[+-]z by reacting a mixture of Bi[sub 4]Sr[sub 3]Ca[sub 3]Cu[sub 4]O[sub 16[+-]z], an alkaline earth metal cuprate, e.g., Sr[sub 9]Ca[sub 5]Cu[sub 24]O[sub 41], and an alkaline earth metal plumbate, e.g., Ca[sub 2[minus]x]Sr[sub x]PbO[sub 4] wherein x is about 0.5, is disclosed.

  15. Synthesis of BiPbSrCaCuO superconductor

    DOEpatents

    Hults, William L.; Kubat-Martin, Kimberly A.; Salazar, Kenneth V.; Phillips, David S.; Peterson, Dean E.

    1994-01-01

    A process and a precursor composition for preparing a lead-doped bismuth-strontium-calcium-copper oxide superconductor of the formula Bi.sub.a Pb.sub.b Sr.sub.c Ca.sub.d Cu.sub.e O.sub.f wherein a is from about 1.7 to about 1.9, b is from about 0.3 to about 0.45, c is from about 1.6 to about 2.2, d is from about 1.6 to about 2.2, e is from about 2.97 to about 3.2 and f is 10.+-.z by reacting a mixture of Bi.sub.4 Sr.sub.3 Ca.sub.3 Cu.sub.4 O.sub.16.+-.z, an alkaline earth metal cuprate, e.g., Sr.sub.9 Ca.sub.5 Cu.sub.24 O.sub.41, and an alkaline earth metal plumbate, e.g., Ca.sub.2-x Sr.sub.x PbO.sub.4 wherein x is about 0.5, is disclosed.

  16. Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements

    NASA Astrophysics Data System (ADS)

    Hathorne, Ed C.; Gagnon, Alex; Felis, Thomas; Adkins, Jess; Asami, Ryuji; Boer, Wim; Caillon, Nicolas; Case, David; Cobb, Kim M.; Douville, Eric; deMenocal, Peter; Eisenhauer, Anton; Garbe-Schönberg, Dieter; Geibert, Walter; Goldstein, Steven; Hughen, Konrad; Inoue, Mayuri; Kawahata, Hodaka; Kölling, Martin; Cornec, Florence L.; Linsley, Braddock K.; McGregor, Helen V.; Montagna, Paolo; Nurhati, Intan S.; Quinn, Terrence M.; Raddatz, Jacek; Rebaubier, Hélène; Robinson, Laura; Sadekov, Aleksey; Sherrell, Rob; Sinclair, Dan; Tudhope, Alexander W.; Wei, Gangjian; Wong, Henri; Wu, Henry C.; You, Chen-Feng

    2013-09-01

    The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.

  17. Ge/Si, Ca/Sr and 87Sr/86Sr tracers of biogeochemical sources and cycling of Si and Ca at the Shale Hills CZO

    NASA Astrophysics Data System (ADS)

    Derry, L. A.; Meek, K.; Sparks, J. P.

    2014-12-01

    Plant uptake and cycling of nutrients is commonly the largest flux of nutrients in terrestrial ecosystems. Hydrologic and other losses are offset by inputs from atmospheric deposition and weathering. We measured elemental and isotopic compositions from soil solution, soil exchange complex, leaves and sapwater from two canopy species, soil and rock samples, and stream and ground waters at the Shale Hills CZO. Xylem fluid and leaf samples have similar Ge/Si < 1 μmo/mol, consistent with fractionation at the root-soil water interface. Ge/Si in soil waters is higher Ge/Si near the surface and increases over the growing season, indicating preferential uptake of Si. Ca/Sr in leaves of Quercus are significantly higher (450±150) than for Acer (200±100), and Ca/Sr is generally higher in leaves than in xylem, consistent with Ca uptake during transpiration. 87Sr/86Sr in both are similar for a given site, implying that the trees access similar pools of Sr and Ca, although there are site-to-site differences. Data on litterfall rates and transpiration rates yield similar estimates of plant cycling of Ca and Si. 87Sr/86Sr in soil solutions from ridgtop and swale sites are well explained by mixing Sr derived from shale and atmospheric deposition. Valley bottom soil solutions and stream and groundwater samples include Sr and Ca derived from dissolution of diagenetic carbonates, found in drill cuttings. A preliminary estimate of the Sr and Ca stream fluxes and isotopic mass balances imply propagation of a carbonate weathering front of ca. 200 m/Ma, faster than previously reported regolith weathering advance rates based on on cosmogenic nuclides and U series (Jin et al., 2010; Ma et al., 2010). These rates are not strictly comparable and differences are at least in part consistent with the greater depth of the carbonate weathering front (Brantley et al, 2013). The data for Ca, Sr, Si and Ge in soil, soil solutions and stream waters reflects the interaction of slower weathering

  18. Quantifying Saline Groundwater Discharge to the Rio Grande using 87Sr/86Sr and [Ca]/[Sr] Ratios

    NASA Astrophysics Data System (ADS)

    Hogan, J. F.; Phillips, F. M.; Mills, S. K.; Ruiz, J.; Chesley, J. T.

    2002-12-01

    Issues of water quality, especially salinity, limit the use of water resources from the Rio Grande. Identification and quantification of salinity sources is critical for improved river management. We have conducted winter and summer synoptic sampling of the Rio Grande from the headwaters in Colorado to south of El Paso, Texas. The total dissolved solids content (TDS) of the Rio Grande increases from less than 50 mg/L in headwater regions of Colorado to greater than 2000 mg/L south of El Paso, Texas. Increases in salinity are not a simple function of distance downriver, but rather occur in a series of steps. Many of these increases are located at the lower end of sedimentary basins leading to the hypothesis that they are the result of discharge of deep, saline, groundwaters. Of particular interest is the Albuquerque and Socorro basins where, in three distinct steps, the TDS of the river doubles from ~ 150 mg/L to ~ 300 mg/L. With little change in river discharge for this reach, this represents a significant increase in the solute burden of the river. We have used 87Sr/86Sr and [Ca]/[Sr] ratios to "fingerprint" and quantify saline groundwater discharge. The Rio Grande entering the Albuquerque basin has an 87Sr/86Sr ratio of 0.7096and a [Ca]/[Sr] ratio of 80. These values are consistent with a mixture of atmospheric deposition and weathering of basalt rock found upstream. Traveling through the Albuquerque and Socorro basin the Rio Grande shifts to a 87Sr/86Sr ratio of 0.7102 and a [Ca]/[Sr] ratio of 30, values which are consistent with saline groundwater discharge. Mixing relationships indicate only two solute sources are required, and that a total saline groundwater discharge rate of ~ 50 cfs is sufficient to explain the observed salinity increases.

  19. Growth rate effects on Mg/Ca and Sr/Ca ratios constrained by belemnite calcite

    NASA Astrophysics Data System (ADS)

    Vinzenz Ullmann, Clemens

    2016-04-01

    Multiple temperature proxies from single species are important to achieve robust palaeotemperature estimates. Besides the commonly employed oxygen isotope thermometer, also Mg/Ca and Sr/Ca ratios perform well as proxies for calcification temperature in the shells of some species. While salinity changes affect the ratios of earth alkaline elements much less than the δ18O thermometer, metabolic effects may exert a strong control on the expression of element ratios. Such effects are hard to study because biomineralization experiments have to overcome large intraspecific variability and can hardly ever isolate the controls of a single parameter on shell geochemistry. The unique geometry of the belemnite rostrum constitutes an exception to this rule. Its shape, large size, and the visibility of growth increments as bands enable the analysis of multiple, correlatable, high resolution geochemical profiles in a single fossil. The effects of the growth rate variability amongst these profiles on Mg/Ca and Sr/Ca ratios has been tested here. Within a specimen of Passaloteuthis bisulcata (Early Toarcian, Cleveland Basin, UK), Mg/Ca and Sr/Ca data were obtained from four profiles. With respect to growth rate in the first profile, which was taken as a reference, the relative growth rates in the remaining three profiles varied by a factor of 0.9 to 2.7. Results suggest that relative growth rate is linearly correlated with Mg/Ca and Sr/Ca, with a decrease of Mg/Ca by 8 % and increase of Sr/Ca by 6 % per 100 % increase in relative growth rate. The observed trends are consistent with abiogenic precipitation experiments and suggest that crystal precipitation rate exerts a significant, predictable control on the element distribution in biogenic calcite.

  20. Mechanochemical synthesis of MgF2 - MF2 composite systems (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Scholz, G.; Breitfeld, S.; Krahl, T.; Düvel, A.; Heitjans, P.; Kemnitz, E.

    2015-12-01

    The capability of mechanochemical synthesis for the formation of MgF2-MF2 (M: Ca, Sr, Ba) composites, solid solutions or well-defined compounds was tested applying a fluorination of different fluorine-free metal sources with NH4F directly at milling. No evidence was found for a substitution of Mg2+ with Ca2+ (Sr2+, Ba2+) ions, or vice versa, in rutile or fluorite structure. However, an equimolar ratio of Mg2+ to the second cation allows the mechanochemical synthesis of tetrafluoromagnesates, MMgF4, which is more and more hampered the smaller the radius of the cation M2+ is. BaMgF4 is formed even phase pure from the acetates, SrMgF4 can only be observed in a mixture accompanied by the binary fluorides. In addition, 19F MAS NMR spectra along with calculations of 19F isotropic chemical shift values according to the superposition model point to the formation of a metastable phase of CaMgF4, which disappears at thermal treatment and decomposes into the binary fluorides CaF2 and MgF2.

  1. Ca/Ba/Sr-induced conformational changes of ciliary axonemes.

    PubMed

    Tamm, S; Tamm, S

    1990-01-01

    Macrocilia of the ctenophore Beroë undergo Ca/Ba/Sr-dependent activation of ciliary beating and microtubule sliding disintegration [Tamm, J. Comp. Physiol. A163:23-31, 1988a; Tamm, Cell Motil. Cytoskeleton 11:126-138, 1988b; Tamm, Cell Motil. Cytoskeleton 12:104-112, 1989; Tamm and Tamm, Proc. Natl. Acad. Sci. U.S.A. 86:6987-6991, 1989]. Here we report that detergent-extracted macrocilia show an ATP-independent conformational change in response to high concentrations of Ca, Ba, or Sr ions. When applied locally by iontophoresis, these ions induce a rapid planar curvature of the distal end of the macrociliary shaft, followed by a slower relaxation to the rest position. Tip curling occurs in a direction opposite to the physiological Ca/Ba/Sr response. When applied uniformly in the bath, a threshold concentration of 10(-1) M Sr is required to induce curling of the tip, and the distal ends remain curved. Calmodulin antagonists do not inhibit the tip curling response. Previous workers found that Ca induces changes in the helical shape of isolated doublet microtubules [Miki-Noumura and Kamiya, Exp. Cell Res. 97:451-453, 1976; Miki-Noumura and Kamiya, J. Cell Biol. 81:355-360, 1979; Takasaki and Miki-Noumura, J. Mol. Biol. 158:317-324, 1982] and sperm axonemes [Okuno and Brokaw, Cell Motil. 1:349-362, 1981] and suggested that conformational changes in microtubules may play a role in Ca regulation of ciliary motility. We propose that the Ca/Ba/Sr-induced curling of the macrociliary tip is due to similar helical changes of doublet microtubules, some of which in macrocilia are prevented from sliding by permanent connections (compartmenting lamellae) between adjacent axonemes within the shaft. Although the tip curling response does not appear to be directly relevant to the physiological Ca response of macrocilia, it provides a novel system for investigating Ca-induced conformational changes of microtubules independent of dynein-powered active sliding.

  2. Processing & properties La{sub 1-x}A{sub x}Co{sub 1-y}Fe{sub y}O{sub 3}(A = Sr, Ca) perovskites

    SciTech Connect

    Stevenson, J.W.; Armstrong, T.R.; Pederson, L.R.

    1995-04-01

    Selected compositions within the system La{sub 1-x}A{sub x}Co{sub 1-y}Fe{sub y}O{sub 3-{delta}}(A = Sr, Ca) were prepared by combustion synthesis and characterized by XRD, TGA, electrical conductivity, and oxygen permeation measurements. Substantial weight loss (due to loss of lattice oxygen) was observed in some compositions at high temperatures. For Sr containing materials, this weight loss increased with increasing Sr content. A substantial decrease in electronic conductivity was observed at high temperatures in Sr doped materials; this decrease was related to the decreased oxygen stoichiometry at these temperatures. In Sr doped compositions, oxygen flux increased with increasing Sr content. Calculated values of ionic conductivity were greater than the conductivity of yttria stabilized zirconia. Substitution of Ca for Sr resulted in substantially lower fluxes.

  3. La and Sr substituted Pr{sub 2}NiO{sub 4+{delta}}: Oxygenation and electrical properties

    SciTech Connect

    Allancon, C.; Odier, P.; Loup, J.P.; Bassat, J.M.

    1997-06-01

    We report herein results concerning the solid solutions Pr{sub 2-x}M{sub x}NiO{sub 4+{delta}}, M = La, Sr. These two cations are larger than praseodymium and lead to a structural stabilization. The oxygen excess {delta} decreases with x for La and Sr substituted Pr{sub 2}NiO{sub 4+{delta}}. Both cases suggest that structural strain is a leading factor for the oxygenation ability of the title compounds. From the evolution of cell parameters, we suggest a phase transition for La substituted compounds occurring for x {approximately} 1-1.2. Surprisingly, this transition has a negligible effect on transport properties. On the other hand, a charge localization linked to the presence of praseodymium is observed. Owing to charge compensation, the Sr substituted compounds have a quasi-constant hole concentration (formally 50%) for x < 0.5. The Pr{sub 2-x}Sr{sub x}NiO{sub 4+{delta}} solid solution shows an anomalous behavior for x = 0.5 corresponding to Ni{sup 2+}/Ni{sup 3+} = 1. This anomaly combines an enhancement of the c/a ratio, a larger resistivity, and a peak for the activation energy of the resistivity versus T.

  4. CaCO3 and SrCO3 bioprecipitation by fungi isolated from calcareous soil.

    PubMed

    Li, Qianwei; Csetenyi, Laszlo; Paton, Graeme Iain; Gadd, Geoffrey Michael

    2015-08-01

    The urease-positive fungi Pestalotiopsis sp. and Myrothecium gramineum, isolated from calcareous soil, were examined for their properties of CaCO3 and SrCO3 biomineralization. After incubation in media amended with urea and CaCl2 and/or SrCl2 , calcite (CaCO3 ), strontianite (SrCO3 ), vaterite in different forms [CaCO3 , (Cax Sr1-x )CO3 ] and olekminskite [Sr(Sr,Ca)(CO3 )2 ] were precipitated, and fungal 'footprints' were observed on mineral surfaces. The amorphous precipitate mediated by Pestalotiopsis sp. grown with urea and equivalent concentrations of CaCl2 and SrCl2 was identified as hydrated Ca and Sr carbonates by Fourier transform infrared spectroscopy. Liquid media experiments showed M. gramineum possessed the highest Sr(2+) removal ability, and ∼ 49% of supplied Sr(2+) was removed from solution when grown in media amended with urea and 50 mM SrCl2 . Furthermore, this organism could also precipitate 56% of the available Ca(2+) and 28% of the Sr(2+) in the form of CaCO3 , SrCO3 and (Cax Sr1-x )CO3 when incubated in urea-amended media and equivalent CaCl2 and SrCl2 concentrations. This is the first report of biomineralization of olekminskite and coprecipitation of Sr into vaterite mediated by fungi. These findings suggest that urease-positive fungi could play an important role in the environmental fate, bioremediation or biorecovery of Sr or other metals and radionuclides that form insoluble carbonates.

  5. Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite

    NASA Astrophysics Data System (ADS)

    Zougrou, I. M.; Katsikini, M.; Brzhezinskaya, M.; Pinakidou, F.; Papadopoulou, L.; Tsoukala, E.; Paloura, E. C.

    2016-08-01

    Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

  6. Analysis of coupled Sr/Ca and 87Sr/ 86Sr variations in enamel using laser-ablation tandem quadrupole-multicollector ICPMS

    NASA Astrophysics Data System (ADS)

    Balter, Vincent; Telouk, Philippe; Reynard, Bruno; Braga, José; Thackeray, Francis; Albarède, Francis

    2008-08-01

    We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and 87Sr/ 86Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST "SRM1400 Bone Ash" with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and 87Sr/ 86Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas 87Sr/ 86Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the 87Sr/ 86Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating.

  7. Superconductivity and chemical composition of the high-Tc phase (Tc = 111 K) in the Sb-Pb-Bi-Sr-Ca-Cu-O system

    NASA Astrophysics Data System (ADS)

    Kijima, Naota; Gronsky, Ronald; McKernan, Steffen K.; Endo, Hozumi; Oguri, Yasuo

    1991-01-01

    A superconducting phase with a critical temperature of 111 K in the Sb-Pb-Bi-Sr-Ca-Cu-O system has been synthesized by means of a long firing period. Its crystal structure is similar to the high-Tc phase (107 K) in the Pb-Bi-Sr-Ca-Cu-O system, and its average chemical composition is 4.3, 2.6, 19.2, 21.4, 15.8 and 36.9 percent for Sb, Pb, Bi, Sr, Ca, and Cu, respectively. The summation of the Sb concentration and the Ca concentration is approximately the same for all the samples of this phase, implying that Sb substitutes for Ca, and oxygen atoms are introduced to compensate the oxygen deficiency in the central Cu-O layer sandwiched by the two Ca layers in the crystal structure of the high-Tc phase.

  8. Evolution of superconductivity in SrFe2As2 with Ni and Pt substitution

    NASA Astrophysics Data System (ADS)

    Saha, S. R.; Drye, T.; Kirshenbaum, K.; Butch, N. P.; Zhang, X.; Greene, R.; Paglione, J.

    2010-03-01

    The superconducting state in the iron pnictide compounds with tetragonal ThCr2Si2 crystal structure has attracted much interest. Transition metal substitution is known to suppress the antiferromagnetic phase of the parent compounds, yielding superconductivity with maximum Tc values approaching ˜20-25 K when Co, Ni, Ru, Rh, Pd, or Ir are used to replace Fe. However, this trend is known to be broken in the case of SrFe2-xNixAs2 and SrFe2-xPdxAs2, which both exhibit reduced maximum Tc values of order 10 K. We will present the effects of Ni and Pt substitution in single crystalline SrFe2As2 as measured by resistivity, magnetic susceptibility and specific heat, and discuss how our results relate to the isoelectronic case of Pd substitution as well as other neighboring transition metal substitution series.

  9. Seawater strontium and Sr/Ca variability in the Atlantic and Pacific oceans

    NASA Astrophysics Data System (ADS)

    de Villiers, Stephanie

    1999-09-01

    Seawater Sr and Sr/Ca exhibit spatial gradients of 2-3% globally, with the deep ocean more enriched relative to the surface. In latitudinal transects, the highest surface values are found at high latitudes and associated with areas of upwelling. A pronounced upper ocean vertical Sr gradient is attributable to the production of celestite skeletons by surface-dwelling acantharia, coupled to a shallow dissolution cycle. The upper ocean residence time of Sr with respect to celestite cycling is much shorter than its global oceanic residence time. Although the magnitude of seawater Sr/Ca variability is relatively small, it is significant with respect to high-precision paleoceanographic applications. Sr/Ca gradients in the contemporary ocean also complicates evaluating Quaternary changes in seawater Sr/Ca that may have resulted from other processes, such as aragonite recrystallization during sea-level low stands.

  10. The Sr/Ca-temperature relationship in coralline aragonite: Influence of variability in (Sr/Ca)[sub seawater] and skeletal growth parameters

    SciTech Connect

    de Villiers, S.; Shen, G.T.; Nelson, B.K. )

    1994-01-01

    This paper provides an evaluation of two of the most likely pitfalls of Sr/Ca thermometry, i.e., the effect of biogenic cycling of Sr vs. Ca in the surface ocean and the effect of variable extension rate on Sr incorporation in coralline aragonite. The authors also report calibration of the Sr/Ca-temperature relationship for three coral species, Porites lobata, Pocillopora eydouxi, and Pavona clavus, collected for the Hawaiian and Galapagos islands. Analyses of seawater samples show significant spatial and depth variability in the Sr:Ca ratio. The uncertainty introduced by this effect is estimated to be <0.2[degrees]C for corals located in tropical oligotrophic waters, and potentially larger for corals located in upwelling areas. Sr/Ca along two different growth axes of a Galapagos Pavona clavus, with annual extension rates of [approximately]6 and 12 mm/y, respectively, indicate an offset of 1-2[degrees]C, with higher Sr/Ca values associated with slower extension rates. The offset observed between the two growth axes may be the result of variations in extension and/or calcification rate. These results are important in determining past sea surface temperatures for reconstruction of paleoclimates.

  11. Determination of Sr and Ca sources in small tropical catchments (La Selva, Costa Rica) - A comparison of Sr and Ca isotopes

    NASA Astrophysics Data System (ADS)

    Wiegand, B. A.; Schwendenmann, L.

    2013-04-01

    SummaryA comparative study of Sr and Ca isotopes was conducted to assess solute sources and effects of biogeochemical processes on surface water and groundwater in four small tropical catchments located at La Selva Biological Station, Costa Rica. Variable concentrations of dissolved Sr2+ and Ca2+ in the catchments are related to mixing of waters from different origin. Three catchments are influenced by high-solute bedrock groundwater, while another catchment is primarily supplied by local recharge. 87Sr/86Sr ratios were employed to discriminate contributions from mineral weathering and atmospheric sources. Solutes in bedrock groundwater have a predominant geogenic origin, whereas local recharge is characterized by low-solute inputs from rainwater and minor in situ weathering releases from nutrient-depleted soils. Bedrock groundwater contributes more than 60% of dissolved Sr2+ to surface discharge in the Salto, Saltito, and Arboleda catchments, whereas the Taconazo catchment receives more than 95% of dissolved Sr2+ from rainwater. δ44/40Ca values of dissolved Ca2+ vary greatly in the catchments, mainly as a result of heterogeneous Ca isotope compositions of the contributing sources. Based on differences in δ44/40Ca values, two distinct bedrock groundwaters discharging at the Salto and the Arboleda catchments are suggested. Effects of biological processes in the plant-soil system on solute generation in the catchments are indicated by variable Ca/Sr ratios. However, these effects cannot clearly be assessed by Ca isotopes due to the strong heterogeneity of δ44/40Ca values of Ca2+ sources and high Ca2+ concentrations in bedrock groundwater.

  12. Patterns of Ca/Sr and 87Sr/ 86Sr variation before and after a whole watershed CaSiO 3 addition at the Hubbard Brook Experimental Forest, USA

    NASA Astrophysics Data System (ADS)

    Nezat, Carmen A.; Blum, Joel D.; Driscoll, Charles T.

    2010-06-01

    Forty-one metric tons of the mineral wollastonite (CaSiO 3) was applied to an 11.8 hectare watershed at the Hubbard Brook Experimental Forest (HBEF; White Mountains, New Hampshire, USA) with the goal of restoring the Ca estimated to have been depleted from the soil exchange complex by acid deposition. This experiment provided an opportunity to gain qualitative information on whole watershed hydrologic flow paths by studying the response of stream water chemistry to the addition of Ca. Because the Ca/Sr and 87Sr/ 86Sr ratios of wollastonite strongly contrast that of other Ca sources in the watershed, the wollastonite-derived Ca can be identified and its amount estimated in various ecosystem components. Stream water chemistry at the HBEF varies seasonally due to shifts in the proportion of base flow and interflow. Prior to the wollastonite application, seasonal variations in 87Sr/ 86Sr ratios indicated that 87Sr/ 86Sr was higher during base flow than interflow, due largely to greater amounts of biotite weathering along deeper flow paths. After the application, Ca/Sr and 87Sr/ 86Sr changed markedly as the high Ca/Sr and low 87Sr/ 86Sr wollastonite dissolved and mixed with stream water. The Ca addition provided information on the response times of various flow paths and ion exchange processes to Ca addition in this small upland watershed. During the first year after the addition, wollastonite applied to the near stream zone dissolved and was partially immobilized by cation exchange sites in the hyporheic zone. In the second and third years after the addition we infer that much of this Ca and Sr was subsequently desorbed from the hyporheic zone and was exported from the watershed in stream flow. In the fourth through ninth years after the addition, Ca and Sr from wollastonite that had dissolved in upland soils was transported to the stream by interflow during wet periods when the ground water table was elevated. Between years three and nine the minimum annual Ca/Sr

  13. Sr/Ca and Mg/Ca in Aragonitic Bivalves: Do They Record Temperature?

    NASA Astrophysics Data System (ADS)

    Gillikin, D. P.; Ulens, H.; Dehairs, F.; Baeyens, W.; Navez, J.; Andre, L.; Keppens, E.; Calmars Group,.

    2003-12-01

    The chemical or isotopic composition of calcareous skeletons have long been recognized as archives of past and present environmental conditions. Oxygen isotopes (d18O) of biogenic carbonates are a powerful proxy of SST, however, although usually dominated by SST, salinity (SSS) also significantly effects the oxygen isotopic signal recorded in the carbonate. This has led researchers to explore new proxies, which are independent of SSS. Generally, Sr/Ca and Mg/Ca of seawater remains unchanged above salinities of 10 and marine animals will commonly live in habitats that do not fluctuate below this salinity. To solve the issue of SSS complicating paleotemperature records, these "new" proxies must be at least as reliable as d18O. If an environmental control is dominant, the proxies should be reproducible between specimens growing under the same field conditions. Both Sr and Mg have been used as paleotemperature proxies in corals and foraminifera, whereas a fewer attempts have been made to use these proxies in bivalves. Some report a clear seasonal periodicity in Sr/Ca profiles of bivalves, which covaries with d18O (i.e., temperature), whereas others have found no clear periodicity. We test the robustness of these proxies by analyzing the shell material from three species of aragonitic clams from around the world using a LA-ICP-MS. Three individuals of M. mercenaria from North Carolina, USA, three individuals of Saxidomus giganteus from Washington, USA and one Arctica islandica from Norway have been analyzed. As expected, there is excellent reproducibility of d18O between specimens (both M. mercenaria and S. giganteus) indicating external environmental conditions control this proxy (i.e. SST and SSS). Preliminary data analysis show that Sr and Mg are not reproducible between specimens from the same site nor do they exhibit a clear seasonal cyclicity, indicating individual metabolic effects (i.e., vital effects) dominate the incorporation of these elements. A. islandica

  14. Climate proxies from Sr/Ca of coccolith calcite: calibrations from continuous culture of Emiliania huxleyi

    NASA Astrophysics Data System (ADS)

    Stoll, Heather M.; Rosenthal, Yair; Falkowski, Paul

    2002-03-01

    Continuous culture of the coccolithophorid Emiliania huxleyi reveals that coccolith Sr/Ca ratios depend on temperature and growth rate. At a constant temperature of 18°C, coccolith Sr/Ca ratios increased nearly 15% as growth rate increased from 0.1 to 1.5 divisions per day and calcification rate increased from 1.5 to 50 pg calcite per cell per day. When temperature increased from 7 to 26°C, Sr/Ca ratios increased by more than 25% (i.e., 1%/1°C), although the range in growth and calcification rates was the same as for experiments at constant temperature. The temperature dependence of Sr/Ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic calcites, suggesting that it is controlled by thermodynamic processes. However, the positive correlation of coccolith Sr/Ca with temperature contrasts with field studies in the equatorial Pacific, where Sr/Ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures. This paradox may reflect different calcification rate effects between E. huxleyi and the other species dominating assemblages in the equatorial Pacific sediments, which may be resolved by new techniques for separation of monospecific coccolith samples from sediments. Models of crystal growth indicate that kinetic effects on Sr partitioning in calcite due to surface enrichment could explain the Sr/Ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial Pacific sediments. Despite the dual influence of temperature and growth rate on coccolith Sr/Ca, coccolith Sr/Ca correlates with "b," the slope of the dependence of carbon isotope fractionation in biomarkers (ɛ p) on CO 2(aq) at a range of growth rates and temperatures. Consequently, using coccolith Sr/Ca in combination with alkenone ɛ p may improve paleo-CO 2 determinations.

  15. Surface characterization, in vitro and in vivo biocompatibility of Mg-0.3Sr-0.3Ca for temporary cardiovascular implant.

    PubMed

    Bornapour, M; Mahjoubi, H; Vali, H; Shum-Tim, D; Cerruti, M; Pekguleryuz, M

    2016-10-01

    Magnesium-based alloys are attractive candidate materials for medical applications. Our earlier work showed that the ternary Mg-0.3Sr-0.3Ca alloy exhibits slower degradation rates than both binary Mg-Sr and Mg-Ca alloys. The ternary alloy immersed in simulated body fluid (SBF) forms a compact surface layer of corrosion products that we hypothesized to be a Sr-substituted hydroxyapatite (HA). The main objectives of the current work are to understand the bio-degradation mechanism of Mg-0.3Sr-0.3Ca, to identify the exact nature of its protective layer and to evaluate the in vitro and in vivo biocompatibility of the alloy for cardiovascular applications. To better simulate the physiological environment, the alloy was immersed in SBF which was daily refreshed. Raman spectroscopy and X-Ray photoelectron spectroscopy (XPS) confirmed the formation of a thin, Sr-substituted HA layer at the interface between the alloy and the corrosion products. In vitro biocompatibility evaluated via indirect cytotoxicity assays using HUVECs showed no toxicity effect and ions extracted from Mg-0.3Sr-0.3Ca in fact increased the viability of HUVECs after one week. In vivo tests were performed by implanting a tubular Mg-0.3Sr-0.3Ca stent along with a WE43 control stent into the right and left femoral artery of a dog. Post implantation and histological analyses showed no thrombosis in the artery with Mg-0.3Sr-0.3Ca stent after 5weeks of implantation while the artery implanted with WE43 stent was extensively occluded and thrombosed. Microscopic observation of the Mg-0.3Sr-0.3Ca implant-tissue interface confirmed the in situ formation of Sr-substituted HA on the surface during in vivo test. These results show that the interfacial layer protects the surface of the Mg-0.3Sr-0.3Ca alloy both in vitro and in vivo, and is the key factor in the bio-corrosion resistance of the alloy. PMID:27287101

  16. Review of high-temperature superconductivity and the effect of chemical modifications on Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10. Technical report

    SciTech Connect

    Jones, T.E.; McGinnis, W.C.; Boss, R.D.

    1991-08-01

    Perform chemical modifications to existing materials that may enhance their superconducting properties and provide insight into the mechanisms responsible for high-temperature superconductivity. This report presented a review of high-temperature superconductivity. An overview of superconductivity from its original discovery to the present is also given. Synthesized two sets of samples. One set was based on the structure Bi2Sr2CaCu2O8 and the other on Bi2Sr2Ca2Cu3O10. In both cases, the copper was partially replaced with elements from the first transition row of elements. The replacement was at the level of 5 mol.-% of the transition element for copper. The transition elements used were vanadium (V), manganese (Mn), titanium (Ti), nickel (Ni), zinc (Zn), cobalt (Co), and iron (Fe) and determined the effect of the substitutions on the crystal structure.

  17. Synthesis and study of Sr-substituted misfit layer sulfides

    SciTech Connect

    Grippa, A.Yu. . E-mail: grippa@icr.chem.msu.ru; Lidin, S.; D'yachenko, O.G.; Rupasov, D.P.; Antipov, E.V.

    2005-01-04

    Two series of [(Ln{sub 1/3}Sr{sub 2/3}S){sub 1.5}]{sub 1.15}NbS{sub 2} (1.5Q/1H) and (Ln{sub 1-x}Sr{sub x}S){sub 1+y}NbS{sub 2} (1Q/1H) misfit layer sulfides have been synthesised and studied by X-ray powder and single crystal diffraction, EDX-analysis and magnetic measurements. For the early lanthanides (Ln = La, Ce) only the (Ln{sub 1-x}Sr{sub x}S){sub 1+y}NbS{sub 2} (x < 0.40-0.45, y = 0.15-0.17) compounds were formed whereas for late lanthanides (Ln = Pr, Nd, Sm, Gd-Er, Yb, Lu), and yttrium, both types of phases can be obtained. The crystal structure of (Pr{sub 0.55}Sr{sub 0.45}S){sub 1.15}NbS{sub 2} has been refined on the basis of X-ray single crystal data using the superspace approach. It consists of double layers [Pr{sub 0.55}Sr{sub 0.45}S] of NaCl-type (Q-part: a = 5.799(3) A, b = 5.810(2) A, c = 23.331(9) A, z = 4) and NbS{sub 2}-sandwiches (H-part: a = 3.332(3) A), z = 8, yielding a q-vector q = ({alpha} 0 0), {alpha} = 0.74) alternating along the c-direction. The superspace group pair is Fm2m ({alpha} 0 0):Fm2m ({alpha} 0 0) (No. 42.7). The refinement converged to R{sub w(obs)} = 0.069. According to the structure refinement and EDX-analysis data in the [Pr{sub 0.55}Sr{sub 0.45}S]-slab almost half of the Pr-atoms are randomly replaced by Sr. The minimal formal value of charge transfer from the Q- to the H-part of the structure necessary to stabilise the misfit Nb-based layer sulfides has been estimated as about 0.6 e per Nb atom.

  18. Moderate intensity of regular exercise improves cardiac SR Ca2+ uptake activity in ovariectomized rats.

    PubMed

    Bupha-Intr, Tepmanas; Laosiripisan, Jitanan; Wattanapermpool, Jonggonnee

    2009-10-01

    The impact of regular exercise in protecting cardiac deteriorating results of female sex hormone deprivation was evaluated by measuring changes in intracellular Ca2+ removal activity of sarcoplasmic reticulum (SR) in ovariectomized rats following 9-wk treadmill running exercise at moderate intensity. Despite induction of cardiac hypertrophy in exercised groups of both sham-operated and ovariectomized rats, exercise training had no effect on SR Ca2+ uptake and SR Ca(2+)-ATPase (SERCA) in hormone intact rat heart. However, exercise training normalized the suppressed maximum SR Ca2+ uptake and SERCA activity in ovariectomized rat heart. While exercise training normalized the leftward shift in pCa (-log[Ca2+])-SR Ca2+ uptake relation in ovariectomized rats, no effect was detected in exercised sham-operated rats. Similar phenomena were also observed on SERCA and on phospholamban (PLB) phosphorylation levels; exercise training in ovariectomized rats enhanced SERCA expression to reach the level as that in sham-operated rats, in which there were no differences in SERCA and phospho-PLB levels between sedentary and exercised groups. In addition, the reduction in phospho-Thr(17) PLB in myocardium of ovariectomized rats was abolished by exercise training. These results showed that regular exercise maintains the molecular activation of cardiac SR Ca2+ uptake under normal physiological conditions and is able to induce a protective impact on cardiac SR Ca2+ uptake in ovarian sex hormone-deprived status.

  19. Migration and rearing histories of chinook salmon (Oncorhynchus tshawytscha) determined by ion microprobe Sr isotope and Sr/Ca transects of otoliths

    USGS Publications Warehouse

    Bacon, C.R.; Weber, P.K.; Larsen, K.A.; Reisenbichler, R.; Fitzpatrick, J.A.; Wooden, J.L.

    2004-01-01

    Strontium isotope and Sr/Ca ratios measured in situ by ion microprobe along radial transects of otoliths of juvenile chinook salmon (Oncorhynchus tshawytscha) vary between watersheds with contrasting geology. Otoliths from ocean-type chinook from Skagit River estuary, Washington, had prehatch regions with 87Sr/86Sr ratios of ???0.709, suggesting a maternally inherited marine signature, extensive fresh water growth zones with 87Sr/86Sr ratios similar to those of the Skagit River at ???0.705, and marine-like 87Sr/86Sr ratios near their edges. Otoliths from stream-type chinook from central Idaho had prehatch 87Sr/86Sr ratios ???0.711, indicating that a maternal marine Sr isotopic signature is not preserved after the ???1000- to 1400-km migration from the Pacific Ocean. 87Sr/86Sr ratios in the outer portions of otoliths from these Idaho juveniles were similar to those of their respective streams (???0.708-0.722). For Skagit juveniles, fresh water growth was marked by small decreases in otolith Sr/Ca, with increases in Sr/Ca corresponding to increases in 87Sr/86Sr with migration into salt water. Otoliths of Idaho fish had Sr/Ca radial variation patterns that record seasonal fluctuation in ambient water Sr/Ca ratios. The ion microprobe's ability to measure both 87Sr/86Sr and Sr/Ca ratios of otoliths at high spatial resolution in situ provides a new tool for studies of fish rearing and migration. ?? 2004 NRC Canada.

  20. Cenozoic Seawater Sr/Ca ratios: Implications for coral reef development through ocean de-acidification

    NASA Astrophysics Data System (ADS)

    Sosdian, S. M.; Grossman, E. L.; Lear, C. H.; Tao, K.; Rosenthal, Y.

    2010-12-01

    Records of seawater chemistry help constrain the temporal variation in geochemical processes that impact the global carbon cycle and global climate across Earth’s history. To date, various attempts to reconstruct Cenozoic seawater Sr/Ca ratios have produced markedly different results, with estimated Paleogene seawater Sr/Ca ranging from ~50% higher than today to 70% lower. We reconstruct seawater Sr/Ca using Eocene to Pliocene fossil mollusks collected from US Gulf Coast (Mississippi, Alabama, and Florida). We use Conus spp. and Turritella, taxa for which the Sr/Ca distribution coefficients have been determined as a function of temperature in modern specimens [1, 2]. Specimens were serially sampled perpendicular to growth to produce seasonal records of Sr/Ca. Fossil Conus shells show pronounced seasonal Sr/Ca cycles with a strong inverse correlation between Sr/Ca and δ18O, similar to those observed in modern specimens [1]. The fossil Turritella also show similar Sr/Ca cyclicity as modern specimens [2]. We calculate seawater Sr/Ca ratios using our Sr/Ca record, modern Sr/Ca-temperature calibrations for Conus and Turritella [1, 2], and a paleotemperature record based on oxygen isotopes from the same samples [3]. Seawater Sr/Ca increased from ~11.5 to 13.9 mmol/mol between the mid-Eocene (42 Ma) and early Oligocene (33 Ma) and decreased substantially from the mid-Miocene (11 mmol/mol) to the Pliocene (9 mmol/mol) and modern (8.5 mmol/mol). A mass balance model of variations in seawater Sr concentrations suggests a long-term decrease through the Neogene, which we attribute to a significant increase in the proportion of aragonite versus calcite deposition in shallow waters. The largest change is coincident with the proliferation of coral reefs, which occurred after the calcite-aragonite sea transition, and was likely ultimately driven by ocean de-acidification. [1] Sosdian et al. (2006) Geochemistry, Geophysics, Geosystems (G3) 7, Q11023, doi:10.1029/2005GC001233; [2

  1. Formation of infinite-layered (Ca(1-x)Sr(x)) CuO2 and NaCuO2-type (Ca(1-y)Na(y))(0.85)CuO2 in tartrate route

    NASA Astrophysics Data System (ADS)

    Kikkawa, Shinichi; Kato, Namie; Taya, Noriko; Tada, Masakazu; Kanamaru, Fumikazu

    1995-05-01

    Both NaCuO2-type Ca(0.85)CuO2 and infinite-layered (Ca(1 - x)Sr(x))CuO2 could be prepared much more easily by firing the dried solids from mixed acetate aqueous solutions titrated with tartaric acid than by normal calcination. The presence of a narrow solid-solution composition range of 0.10 less than x less than 0.16 was confirmed in infinite-layered (Ca(1 - x)Sr(x))CuO2 in the preparation using the tartrate route. The calcium could also be substituted by sodium in a range of y less than 0.15 in NaCuO2-type (Ca(1 - y)Na(y))(0.85)CuO(2) using the same route. Further substitution of Ca(2+)/ with Y(3+)/ might also be possible in infinite-layered (Ca(1 - x)Sr(x))CuO2, but resulted in the NaCuO2-type compound in the substitution with Na(+).

  2. Preparation and characterisation of nanophase Sr, Mg, and Zn substituted hydroxyapatite by aqueous precipitation.

    PubMed

    Cox, Sophie C; Jamshidi, Parastoo; Grover, Liam M; Mallick, Kajal K

    2014-02-01

    Hydroxyapatite (HA) substituted with 2 mol% Sr, 10 mol% Mg, and 2 mol% Zn were precipitated under identical alkaline conditions (pH 11) at 20°C from an aqueous solution. As-synthesised materials were confirmed to be phase pure by XRD and samples prepared in air contained surface adsorbed CO2 as observed by FTIR. SEM studies revealed a globular morphology and agglomeration behaviour, typical of precipitated nHA. EDS spectra confirmed nominal compositions and substitution of Sr, Mg and Zn. At the levels investigated cationic doping was not found to radically influence particle morphology. An indication of the potential in-vivo bioactivity of samples was achieved by analysing samples immersed in SBF for up to 28 days by interferometry and complementary SEM micrographs. Furthermore, a live/dead assay was used and confirmed the viability of seeded MC3T3 osteoblast precursor cells on HA and substituted HA substrates up to 7 days of culture.

  3. Evidence for the non-influence of salinity variability on the coral Sr/Ca paleothermometer

    NASA Astrophysics Data System (ADS)

    Moreau, M.; Corrège, T.; Dassié, E. P.; Le Cornec, F.

    2014-04-01

    The influence of salinity in the incorporation of trace elements in the skeleton of calcareous organisms is still poorly known. Studies on foraminiferal Mg/Ca thermometry have suggested a bias due to Sea Surface Salinity (SSS) variations, leading to potential erroneous estimation of Mg/Ca-based Sea Surface Temperature (SST). Culture experiments seem to indicate that in three coral species (not including the widely used Porites genus), salinity does not influence the Sr/Ca thermometer. In this study, we test the salinity effect on coral Sr/Ca-based SST reconstructions at monthly and interannual timescales in open-ocean environmental conditions, using a large spatial compilation of published coral data (mainly based on the Porites genus) originating from the Western Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the China Sea and the Red Sea and adding a new Eastern Pacific coral Sr/Ca record from the Clipperton atoll. We use simple and multiple regressions between Sr/Ca on one hand and SST and SSS on the other hand at the various sites. We find no evidence for a salinity bias on the Sr/Ca SST proxy for the two studied timescales. This study reinforces the use of coral Sr/Ca as a reliable paleothermometer.

  4. Phase formation in a Bi-Sr-Ca-Cu oxide superconductor

    NASA Astrophysics Data System (ADS)

    Mei, Yu; Green, S. M.; Jiang, C.; Luo, H. L.

    1988-12-01

    The formation of different superconducting phases in the Bi-Sr-Ca-Cu-oxide system sensitively depends on the preparation procedures, particularly the firing temperatures. The tangled X-ray powder diffraction patterns of coexisting Bi2Sr2CaCu2O(y) and Bi2Sr2Ca2Cu3O(y) have been completely identified. The basic unit cells are of approximate tetragonal symmetry. The lattice constants of the latter have been determined to be 5.40 x 5.40 x 37.09 cu A.

  5. L-type Ca2+ channels serve as a sensor of the SR Ca2+ for tuning the efficacy of Ca2+-induced Ca2+ release in rat ventricular myocytes

    PubMed Central

    Takamatsu, Hajime; Nagao, Taku; Ichijo, Hidenori; Adachi-Akahane, Satomi

    2003-01-01

    In cardiac excitation-contraction coupling, Ca2+-induced Ca2+ release (CICR) from ryanodine receptors (RyRs), triggered by Ca2+ entry through the nearby L-type Ca2+ channel, induces Ca2+-dependent inactivation (CDI) of the Ca2+ channel. Aiming at elucidating the physiological role of CDI produced by CICR (CICR-dependent CDI), we investigated the contribution of the CICR-dependent CDI to action potential (AP) waveform and the amount of Ca2+-influx through Ca2+ channels during AP in rat ventricular myocytes. The elimination of the CICR-dependent CDI, by depletion of the SR Ca2+ with thapsigargin, significantly prolonged AP duration (APD). APD changed in parallel with the magnitude of CICR during the recovery of the SR Ca2+ content after transient depletion by caffeine. Such CICR-dependent change of APD persisted under the highly Ca2+ buffered condition where the Ca2+ signalling was restricted to nanoscale domains. Blockers of the Ca2+-dependent Cl− channel or the BK channel did not affect AP waveform. The amount of Ca2+-influx through Ca2+ channels during the SR-depleted type AP waveform, measured in the SR-depleted myocyte, was increased by 40% over that during the SR-intact type AP waveform measured in the SR-intact myocyte. The protein kinase A stimulation further enhanced the Ca2+-influx during AP under the SR-depleted condition to 70% of that under the SR-intact condition. These results indicate that the CICR-dependent CDI of L-type Ca2+ channels, under control of the privileged cross-signalling between L-type Ca2+ channels and RyRs, play important roles for monitoring and tuning the SR Ca2+ content via changes of AP waveform and the amount of Ca2+-influx during AP in ventricular myocytes. PMID:14561825

  6. Ambient pressure structural quantum critical point in the phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13).

    PubMed

    Goh, S K; Tompsett, D A; Saines, P J; Chang, H C; Matsumoto, T; Imai, M; Yoshimura, K; Grosche, F M

    2015-03-01

    The quasiskutterudite superconductor Sr_{3}Rh_{4}Sn_{13} features a pronounced anomaly in electrical resistivity at T^{*}∼138  K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centered around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T^{*} as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., x_{c}=0.9). This establishes the (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13} series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures. PMID:25793843

  7. Superconductivity in Ru-BASED Cuprate Ru(Sr1.5Ca0.5)PbCu2O8 Prepared by Sol-Gel Route

    NASA Astrophysics Data System (ADS)

    Yeoh, L. M.; Ahmad, M.; Abd-Shukor, R.

    Pb containing ruthenium-based superconducting cuprates Ru(Sr1.5Ca0.5)PbCu2O8 (Ru-1212 type) have been successfully synthesized through the sol-gel route. The optimum annealing temperature for the ruthenium-based cuprate superconductor was found to be 890°C. The crystal structure determined by X-ray powder diffraction method showed a single Ru-1212 type phase with tetragonal symmetry with lattice parameters a = b = 3.920 Å, and c = 11.76 Å. The Ru(Sr1.5Ca0.5)PbCu2O8 material showed onset temperature, Tc-onset at 35 K and zero resistant temperature, Tc-zero at 20 K. Pb together with the partial substitution of Sr with Ca lowered the formation temperature of the Ru-1212 type phase.

  8. Calcium-sensing receptor (CaSR) as a novel target for ischemic neuroprotection

    PubMed Central

    Kim, Jong Youl; Ho, Hanson; Kim, Nuri; Liu, Jialing; Tu, Chia-Ling; Yenari, Midori A; Chang, Wenhan

    2014-01-01

    Object Ischemic brain injury is the leading cause for death and long-term disability in patients who suffer cardiac arrest and embolic stroke. Excitotoxicity and subsequent Ca2+-overload lead to ischemic neuron death. We explore a novel mechanism concerning the role of the excitatory extracellular calcium-sensing receptor (CaSR) in the induction of ischemic brain injury. Method Mice were exposed to forebrain ischemia and the actions of CaSR were determined after its genes were ablated specifically in hippocampal neurons or its activities were inhibited pharmacologically. Since the CaSR forms a heteromeric complex with the inhibitory type B γ-aminobutyric acid receptor 1 (GABABR1), we compared neuronal responses to ischemia in mice deficient in CaSR, GABABR1, or both, and in mice injected locally or systemically with a specific CaSR antagonist (or calcilytic) in the presence or absence of a GABABR1 agonist (baclofen). Results Both global and focal brain ischemia led to CaSR overexpression and GABABR1 downregulation in injured neurons. Genetic ablation of Casr genes or blocking CaSR activities by calcilytics rendered robust neuroprotection and preserved learning and memory functions in ischemic mice, partly by restoring GABABR1 expression. Concurrent ablation of Gabbr1 gene blocked the neuroprotection caused by the Casr gene knockout. Coinjection of calcilytics with baclofen synergistically enhanced neuroprotection. This combined therapy remained robust when given 6 h after ischemia. Interpretation Our study demonstrates a novel receptor interaction, which contributes to ischemic neuron death through CaSR upregulation and GABABR1 downregulation, and feasibility of neuroprotection by concurrently targeting these two receptors. PMID:25540800

  9. Effects of low-level Ag doping on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}

    SciTech Connect

    Deis, T.A.; Eror, N.G.; Krishnaraj, P.; Prorok, B.C.; Lelovic, M.; Balachandran, U.

    1995-07-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} has been doped with silver, up to 10,000 ppm, in three ways: excess additions, substitution of Ag for Bi, and substitution of Ag for Sr. Effects of doping on the c-axis lattice parameter and critical temperature ({Tc}) were measured. Effects from doing were only observed in slow-cooled [10{degree}/hr] oxygen equilibrated samples. Doping by excess additions caused a small decrease in {Tc} and an increase in the c-axis length of the lattice. Doping by substitution, compared to excess Ag additions, caused a larger decrease in {Tc} and higher c-axis values for doping levels up to 1,000 ppm. Doping by substitution at higher levels (1,000--10,000 ppm) caused {Tc} to increase and the c-axis to decrease. Samples with similar substitutional doping levels exhibited comparable {Tc} values and samples with Ag substituted for Sr consistently exhibited higher c-axis values than samples that had equivalent amounts of Ag substituted for Bi.

  10. Study of the superconducting properties of the Bi-Ca-Sr-Cu-O system

    NASA Technical Reports Server (NTRS)

    Khan, Musheer H.; Naqvi, S. M. M. R.; Zia-Ul-haq, S. M.

    1991-01-01

    High Temperature Superconductivity in the Bi-Ca-Sr-Cu-O System has been observed and has attracted considerable attention in 1988. The 80 K superconductivity phase has been identified to have a composition of Bi2CaSr2Cu2Ox, while the 110 K phase as reported in the literature has a possible composition of Bi2Ca2Sr2Cu3O(x). Researchers present here a study of the electrical properties of bulk samples of the slowly cooled and rapidly quenched 2:1:2:2 system. The samples used in this study were prepared from appropriate amounts of Bi2O3, CuO, SrCO3, CaCO3.

  11. HREM and Simulation Study in the Bi-Sr-Ca-Cu-O System

    NASA Astrophysics Data System (ADS)

    Boussiri, K. El.; Snoeck, E.; Clin, M.; Toledano, J. C.; Rais, T.

    1997-08-01

    We have studied the Bi-Sr-Ca-Cu-O family by high resolution electron microscopy (HREM). We have simulated the HREM images using a phenomenological model. The experimental and calculated results agree quite well.

  12. Sintering of bulk high-{Tc} superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B.; Nash, A.S.

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  13. Sintering of bulk high- Tc superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. ); Nash, A.S. )

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  14. Study of the superconducting properties of the Bi-Ca-Sr-Cu-O system

    NASA Technical Reports Server (NTRS)

    Khan, Musheer H.; Qidwai, A. A.; Zia-Ul-haq, S. M.; Binsaif, Rashid

    1990-01-01

    High Temperature Superconductivity in the Bi-Ca-Sr-Cu-O System has been observed and has attracted considerable attention in 1988. The 80 K superconductivity phase has been identified to have a composition of Bi2CaSr2Cu2Ox, while the 110 K phase as reported in the literature has a possible composition of Bi2Ca2Sr2Cu3Ox. Researchers present here a study of the electrical properties of bulk samples of the slowly cooled and rapidly quenched 2:1:2:2 system. The samples used in this study were prepared from appropriate amounts of Bi2O3, CuO, SrCO3, CaCO3.

  15. Thin films of the Bi2Sr2Ca2Cu3O(x) superconductor

    NASA Technical Reports Server (NTRS)

    Mei, YU; Luo, H. L.; Hu, Roger

    1990-01-01

    Using RF sputtering technique, thin films of near single phase Bi2Sr2Ca2Cu3O(x) were successfully prepared on SrTiO3(100), MgO(100), and LaAlO3(012) substrates. Zero resistance of these films occurred in the range of 90-105 K.

  16. Are SR Ca content fluctuations or SR refractoriness the key to atrial cardiac alternans?: insights from a human atrial model.

    PubMed

    Lugo, Carlos A; Cantalapiedra, Inma R; Peñaranda, Angelina; Hove-Madsen, Leif; Echebarria, Blas

    2014-06-01

    Despite the important role of electromechanical alternans in cardiac arrhythmogenesis, its molecular origin is not well understood. The appearance of calcium alternans has often been associated to fluctuations in the sarcoplasmic reticulum (SR) Ca loading. However, cytosolic calcium alternans observed without concurrent oscillations in the SR Ca content suggests an alternative mechanism related to a dysfunction in the dynamics of the ryanodine receptor (RyR2). We have investigated the effect of SR release refractoriness in the appearance of alternans, using a mathematical model of a single human atrial cell, based on the model by Nygren et al. (30), where we modified the dynamics of the RyR2 and of SR Ca release. The genesis of calcium alternans was studied stimulating the cell for different periods and values of the RyR2 recovery time from inactivation. At fast rates cytosolic calcium alternans were obtained without concurrent SR Ca content fluctuations. A transition from regular response to alternans was also observed, changing the recovery time from inactivation of the RyR2. This transition was found to be hysteretic, so for a given set of parameters different responses were observed. We then studied the relevance of RyR2 refractoriness for the generation of alternans, reproducing the same protocols as in recent experiments. In particular, restitution of Ca release during alternans was studied with a S1S2 protocol, obtaining a different response if the S2 stimulation was given after a long or a short release. We show that the experimental results can be explained by RyR2 refractoriness, arising from a slow RyR2 recovery from inactivation, stressing the role of the RyR2 in the genesis of alternans.

  17. Thermoelectric properties of n-type double substituted SrTiO3 bulk materials.

    PubMed

    Cui, Yanjie; He, Jian; Amow, Gisele; Kleinke, Holger

    2010-01-28

    A series of La, Ta double substituted Sr(1-x)La(x)Ti(1-x)Ta(x)O(3), with x = 0.01, 0.05 and 0.10, and La, Nb double substituted Sr(0.90)La(0.10)Ti(0.90)Nb(0.10)O(3) for comparison were investigated in this project. Rietveld refinements were performed to check for purity and symmetry reduction. Electronic structure calculations indicate n-type conduction with steep and flat bands in the vicinity of the Fermi level for x = 0.125. Seebeck coefficient, electrical conductivity, and thermal conductivity measurements on hot-pressed and spark-plasma-sintered samples were performed over a wide range of temperatures. Best results were obtained by spark-plasma-sintering of double substituted Sr(0.99)La(0.01)Ti(0.99)Ta(0.01)O(3) with a thermoelectric figure-of-merit of 0.13 at 660 K.

  18. Migration behaviour of twaite shad Alosa fallax assessed by otolith Sr:Ca and Ba:Ca profiles.

    PubMed

    Magath, V; Marohn, L; Fietzke, J; Frische, M; Thiel, R; Dierking, J

    2013-06-01

    Individual migration behaviour during the juvenile and adult life phase of the anadromous twaite shad Alosa fallax in the Elbe estuary was examined using otolith Sr:Ca and Ba:Ca profiles. Between hatching and the end of the first year of life, juveniles showed two migration patterns. Pattern one exhibited a single downstream migration from fresh water to the sea with no return into fresh water. In contrast, pattern two showed a first migration into the sea, then a return into fresh water and, finally, a second downstream migration into marine water. This first report of migration plasticity for A. fallax points to different exposure times to estuarine threats depending on the migration strategy. In adults, high Sr:Ca and low Ba:Ca in the majority of individuals confirmed prior reports of a primarily marine habitat use. Patterns reflecting spawning migrations were rarely observed on otoliths, possibly due to the short duration of visits to fresh water.

  19. High-pressure densified solid solutions of alkaline earth hexaborides (Ca/Sr, Ca/Ba, Sr/Ba) and their high-temperature thermoelectric properties

    SciTech Connect

    Gürsoy, M.; Takeda, M.; Albert, B.

    2015-01-15

    Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB{sub 6}, SrB{sub 6}, BaB{sub 6} and the ternary hexaborides Ca{sub x}Sr{sub 1−x}B{sub 6}, Ca{sub x}Ba{sub 1−x}B{sub 6}, Sr{sub x}Ba{sub 1−x}B{sub 6} (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB{sub 6} (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process. - Highlights: • Solid solutions of alkaline earth hexaborides were synthesized. • High-temperature thermoelectric properties of mixed calcium borides are excellent. • Spark plasma source densification results in high ZT values. • Borides are rare-earth free and refractory materials.

  20. Phase, Microstructure, and Microwave Dielectric Properties of NaCa4- x Sr x Nb5O17 ( x = 0 to 4) Ceramics

    NASA Astrophysics Data System (ADS)

    Iqbal, Y.; Muhammad, R.

    2013-03-01

    A series of A5B5O17-type NaCa4- x Sr x Nb5O17 ( x = 0 to 4) compounds were processed through a solid-state mixed-oxide route. All the compositions formed dense single-phase ceramics within the detection limit of an in-house x-ray diffraction facility when sintered at 1300°C. The substitution of Sr for Ca changed the crystal symmetry from monoclinic ( x = 0) to orthorhombic ( x = 1 to 4) along with a slight increase in molar cell volume due to the relatively larger ionic radius of Sr. The relative permittivity ( ɛ r) and temperature coefficient of resonance frequency (TCF) increased from 46 to 84 and from -117 ppm/°C to +377 ppm/°C, respectively, while the quality factor ( Q × f) decreased from 11,063 GHz to 559 GHz with an increase in x from 0 to 4. Optimum properties were achieved for NaCa3SrNb5O17, which exhibited ɛ r = 57, Q × f = 4628 GHz, and TCF = -41 ppm/°C. Compounds in the NaCa4- x Sr x Nb5O17 series exhibited high ɛ r and Q × f with adjustable TCF; however, further work is required for simultaneous optimization of all three properties.

  1. Tracing coastal waster masses with Sr/Ca ratio and salinity in Nanwan Bay, Taiwan

    NASA Astrophysics Data System (ADS)

    Shen, C.; Liu, K.; Lee, M.; Lee, T.; Wang, C.

    2002-12-01

    We propose a method of using two tracers, water Sr/Ca ratio (with a precision of better one per mil), and salinity, to differentiate the freshwater and marine sources of oceanic water for coastal areas with strong upwelling. In general, water column Sr/Ca ratios increase from a surface value of 8.50 mmol/mol to 8.64 mmol/mol, found below 1000 m in the Equatorial Pacific. The fresh water Sr and Ca concentrations are over ten times lower than those in seawater and its input to the ocean will not significantly change the seawater Sr/Ca ratio. The regional water Sr/Ca value, therefore, is essentially controlled by the mixing of surface and deeper seawaters. However, the variation of seawater salinity is dominated by fresh water input. We used a Sr/Ca-salinity diagram to determine the end-member composition of the surface seawater in a semi-enclosed bay (Nanwan Bay located in the southernmost Taiwan) with well-known tidally induced upwelling. We divided the sources of the Nanwan water into two components during the dry season: 69% upwelled water from a deep ocean source, and 31% offshore surface water. During the 1994 wet season an additional 2-2.5 % fresh water, mainly from rainfall, was added to the bay. A residence time of 30-40 days is estimated for the Nanwan water. These results are supported by the relation between seasonal variations of seawater oxygen isotope value, salinity and precipitation and demonstrate the practicality of a Sr/Ca-salinity diagram in distinguishing the freshwater and oceanic water contributions to the geochemistry of the surface seawater in an enclosed bay that exhibits strong upwelling. This comparison could also be applied to other regions of strong upwelling.

  2. Effects of v- or Cr-DOPING on Phase Formation, Electric Properties and Superconductivity of the 3212-TYPE Phase Pb2Sr2(Ca0.5Y0.5)Cu3Oz

    NASA Astrophysics Data System (ADS)

    Chen, Z. Y.; Qian, Y. T.; Luo, H. M.; Qu, B.; Sheng, Z. Z.; Wang, L. M.

    The effects of vanadium or chromium on the formation, electric properties and superconductivity of Pb-3212 phase (Pb2Cu)Sr2(Ca0.5Y0.5)Cu2Oz are studied. The sites of V or Cr in PbO-CuOδ-PbO structure unit for Pb-3212 phase is also investigated. Compared with the effects of Cr-doping, V can totally substitute Ca to form a new compound Pb2Sr2(V0.5Y0.5)Cu3Oz, and V has relatively greater substitution amount in (Pb2-xMx)Sr2(Ca0.5Y0.5)Cu3Oz (M = Cr or V). Moreover, the resistivity and superconductivity of the above samples decrease with increasing V or Cr amount. Among them, the effects of V is greater, and its location (in Pb or Ca site) also affects greatly the superconductivity.

  3. Characterization of the Sr(2+)- and Cd(2+)-Substituted Oxygen-Evolving Complex of Photosystem II by Quantum Mechanics/Molecular Mechanics Calculations.

    PubMed

    Pitari, Fabio; Bovi, Daniele; Narzi, Daniele; Guidoni, Leonardo

    2015-09-29

    The Mn4CaO5 cluster in the oxygen-evolving complex is the catalytic core of the Photosystem II (PSII) enzyme, responsible for the water splitting reaction in oxygenic photosynthesis. The role of the redox-inactive ion in the cluster has not yet been fully clarified, although several experimental data are available on Ca2+-depleted and Ca2+-substituted PSII complexes, indicating Sr2+-substituted PSII as the only modification that preserves oxygen evolution. In this work, we investigated the structural and electronic properties of the PSII catalytic core with Ca2+ replaced with Sr2+ and Cd2+ in the S2 state of the Kok−Joliot cycle by means of density functional theory and ab initio molecular dynamics based on a quantum mechanics/ molecular mechanics approach. Our calculations do not reveal significant differences between the substituted and wild-type systems in terms of geometries, thermodynamics, and kinetics of two previously identified intermediate states along the S2 to S3 transition, namely, the open cubane S2 A and closed cubane S2 B conformers. Conversely, our calculations show different pKa values for the water molecule bound to the three investigated heterocations. Specifically, for Cd-substituted PSII, the pKa value is 5.3 units smaller than the respective value in wild type Ca-PSII. On the basis of our results, we conclude that, assuming all the cations sharing the same binding site, the induced difference in the acidity of the binding pocket might influence the hydrogen bonding network and the redox levels to prevent the further evolution of the cycle toward the S3 state.

  4. Loparite, a rare-earth ore (Ce, Na, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3

    USGS Publications Warehouse

    Hedrick, James B.; Sinha, Shyama P.; Kosynkin, Valery D.

    1997-01-01

    The mineral loparite (Ce, NA, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3 is the principal ore of the light-group rare-earth elements (LREE) in Russia. The complex oxide has a perovskite (ABO3) structure with coupled substitutions, polymorphism, defect chemistry and a tendency to become metamict. The A site generally contains weakly bonded, easily exchanged cations of the LREE, Na and Ca. The B site generally contains smaller, highly charged cations of Ti, Nb or Fe+3. Mine production is from Russia's Kola Peninsula. Ore is beneficiated to produce a 95% loparite concentrate containing 30% rare-earth oxides. Loparite concentrate is refined by either a chlorination process or acid decomposition process to recover rare-earths, titanium, niobium and tantalum. Rare-earths are separated by solvent extraction and selective precipitation/dissolution. The concentrate is processed at plants in Russia, Estonia and Kazakstan.

  5. Magnetism, superconductivity, and the volume collapse transition in (Ca0.67Sr0.33)Fe2As2 under pressure

    NASA Astrophysics Data System (ADS)

    Jeffries, Jason; Butch, N. P.; Saha, S. R.; Kirshenbaum, K.; Weir, S. T.; Vohra, Y. K.; Paglione, J.

    2012-02-01

    The alkaline earth site of CaFe2As2 can be chemically substituted with Sr, forming a homogeneous solid solution series ending with SrFe2As2. It is found that (Ca0.67Sr0.33)Fe2As2 exhibits a pressure-temperature phase diagram intermediate between the two end members of the series, shifting the phase lines for the suppression of magnetism, the development of superconductivity, and the occurrence of a volume collapse transition to higher pressures. The overall shift in the pressure-temperature phase diagram permits the study of each phase field, yielding valuable information about the correlations between local atomic structure, magnetism, superconductivity, and the volume collapse transition. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

  6. Hanford 100N Area Apatite Emplacement: Laboratory Results of Ca-Citrate-PO4 Solution Injection and Sr-90 Immobilization in 100N Sediments

    SciTech Connect

    Szecsody, James E.; Burns, Carolyn A.; Moore, Robert C.; Fruchter, Jonathan S.; Vermeul, Vincent R.; Williams, Mark D.; Girvin, Donald C.; McKinley, James P.; Truex, Michael J.; Phillips, Jerry L.

    2007-10-01

    This report summarizes laboratory scale studies investigating the remediation of Sr-90 by Ca-citrate-PO4 solution injection/infiltration to support field injection activities in the Hanford 100N area. This study is focused on experimentally testing whether this remediation technology can be effective under field scale conditions to mitigate Sr-90 migration 100N area sediments into the Columbia River. Sr-90 is found primarily adsorbed to sediments by ion exchange (99% adsorbed, < 1% in groundwater) in the upper portion of the unconfined aquifer and lower vadose zone. Although primarily adsorbed, Sr-90 is still considered a high mobility risk as it is mobilized by seasonal river stage increases and by plumes of higher ionic strength relative to groundwater. This remediation technology relies upon the Ca-citrate-PO4 solution forming apatite precipitate [Ca6(PO4)10(OH)2], which incorporates some Sr-90 during initial precipitation and additionally slowly incorporates Sr-90 by solid phase substitution for Ca. Sr substitution occurs because Sr-apatite is thermodynamically more stable than Ca-apatite. Once the Sr-90 is in the apatite structure, Sr-90 will decay to Y-90 (29.1 y half-life) then Zr-90 (64.1 h half-life) without the potential for migration into the Columbia River. For this technology to be effective, sufficient apatite needs to be emplaced in sediments to incorporate Sr and Sr-90 for 300 years (~10 half-lives of Sr-90), and the rate of incorporation needs to exceed the natural groundwater flux rate of Sr in the 100N area. A primary objective of this study is to supply an injection sequence to deliver sufficient apatite into subsurface sediments that minimizes initial mobility of Sr-90, which occurs because the injection solution has a higher ionic strength compared to groundwater. This can be accomplished by sequential injections of low, then high concentration injection of Ca-citrate-PO4 solutions. Assessment of low concentration Ca-citrate-PO4, citrate-PO4

  7. Synchrony of Cardiomyocyte Ca2+ Release is Controlled by t-tubule Organization, SR Ca2+ Content, and Ryanodine Receptor Ca2+ Sensitivity

    PubMed Central

    Øyehaug, Leiv; Loose, Kristian Ø.; Jølle, Guro F.; Røe, Åsmund T.; Sjaastad, Ivar; Christensen, Geir; Sejersted, Ole M.; Louch, William E.

    2013-01-01

    Recent work has demonstrated that cardiomyocyte Ca2+release is desynchronized in several pathological conditions. Loss of Ca2+ release synchrony has been attributed to t-tubule disruption, but it is unknown if other factors also contribute. We investigated this issue in normal and failing myocytes by integrating experimental data with a mathematical model describing spatiotemporal dynamics of Ca2+ in the cytosol and sarcoplasmic reticulum (SR). Heart failure development in postinfarction mice was associated with progressive t-tubule disorganization, as quantified by fast-Fourier transforms. Data from fast-Fourier transforms were then incorporated in the model as a dyadic organization index, reflecting the proportion of ryanodine receptors located in dyads. With decreasing dyadic-organization index, the model predicted greater dyssynchrony of Ca2+ release, which exceeded that observed in experimental line-scan images. Model and experiment were reconciled by reducing the threshold for Ca2+ release in the model, suggesting that increased RyR sensitivity partially offsets the desynchronizing effects of t-tubule disruption in heart failure. Reducing the magnitude of SR Ca2+ content and release, whether experimentally by thapsigargin treatment, or in the model, desynchronized the Ca2+ transient. However, in cardiomyocytes isolated from SERCA2 knockout mice, RyR sensitization offset such effects. A similar interplay between RyR sensitivity and SR content was observed during treatment of myocytes with low-dose caffeine. Initial synchronization of Ca2+ release during caffeine was reversed as SR content declined due to enhanced RyR leak. Thus, synchrony of cardiomyocyte Ca2+ release is not only determined by t-tubule organization but also by the interplay between RyR sensitivity and SR Ca2+ content. PMID:23601316

  8. Catalytic partial oxidation of n-tetradecane using pyrochlores: Effect of Rh and Sr substitution

    SciTech Connect

    Haynes, D.; Berry, D.; Shekhawat, D.; Spivey, J.

    2008-01-01

    The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2 y)O(7-j,) (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2 x)SrxRhyZr(2 y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had

  9. Catalytic Partial oxidation of n-Tetradecane Using Pyrochlores: Effect of Rh and Sr Substitution

    SciTech Connect

    Haynes, D.J.; Berry, D.A.; Shekhawat, Dushyant; Spivey, J.J.

    2008-07-31

    The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2 y)O(7-j,) (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2 x)SrxRhyZr(2 y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had

  10. Sr, Ca, and C isotope systematic in small tropical catchments, La Selva, Costa Rica

    NASA Astrophysics Data System (ADS)

    Wiegand, B. A.; Schwendenmann, L.

    2010-12-01

    Sr, Ca, and C isotopes were analyzed to assess sources and biogeochemical processes affecting surface and groundwater composition of four small catchments located at La Selva Biological Station, Costa Rica. 87Sr/86Sr ratios were employed to quantify inputs from mineral weathering and atmospheric sources. δ13C values of dissolved organic carbon (DOC) and δ44Ca values provide information on biological processes that affect water chemistry. Sr2+ and Ca2+ concentrations of surface and groundwater show large variations due to intermixture of bedrock groundwater with local groundwater [1]. Low 87Sr/86Sr ratios suggest weathering of volcanic rocks as the primary solute source in bedrock groundwater, while atmospheric and in situ weathering contributions are predominant in local groundwater. Contributions of bedrock groundwater constitute > 60 % in the Salto, Saltito and Arboleda catchments, whereas the Taconazo catchment receives atmospheric inputs of > 95 % in addition to local weathering contributions. Surface water and groundwater wells show δ13C-DOC values between -24 ‰ and -30 ‰ due to transfer of organic carbon from the soil zone. δ44Ca values of dissolved Ca2+ in surface and groundwater are considerably fractionated from the input sources rainwater and bedrock groundwater. Light δ44Ca values are preferentially distributed in stream water and shallow groundwater horizons and contrast with heavy Ca isotopes in deeper groundwater wells. Biological processes including plant uptake and decomposition in combination with cation exchange processes in the soils may explain the fractionation of Ca isotopes. [1]Genereux et al., 2009. Water Resour. Res, 45, W08413, doi:10.1029/2008WR007630

  11. Is otolith microchemistry (Sr: Ca and Ba:Ca ratios) useful to identify Mugil curema populations in the southeastern Caribbean Sea?

    PubMed

    Avigliano, E; Callicó-Fortunato, R; Buitrago, J; Volpedo, A V

    2015-11-01

    The aim of the present study was to evaluate the potential use of otolith microchemistry (Sr:Ca and Ba:Ca ratios) to identify silver mullet, Mugil curema, populations in Southeastern Caribbean Sea. Fish samples were collected in 7 areas of Nueva Esparta State (Venezuela). The otolith Sr:Ca and Ba:Ca ratios and water Sr:Ca were determined (by ICP-OES and EDTA volumetric method). Otoliths Sr:Ca and Ba:Ca ratios and Sr:Ca partition coefficient of mullets in Cubagua island (south of the State) were significantly different from ratios in La Guardia (north of the State). A discriminant analysis of otolith Sr:Ca and Ba:Ca ratios separated Cubagua Island from La Guardia values. These results suggest the existence of different mullet groups in the Southeastern Caribbean Sea. For this, the simultaneous use of Sr:Ca and Ba:Ca ratios could be a potential tool to identify populations in the study area. PMID:26628220

  12. Is otolith microchemistry (Sr: Ca and Ba:Ca ratios) useful to identify Mugil curema populations in the southeastern Caribbean Sea?

    PubMed

    Avigliano, E; Callicó-Fortunato, R; Buitrago, J; Volpedo, A V

    2015-11-01

    The aim of the present study was to evaluate the potential use of otolith microchemistry (Sr:Ca and Ba:Ca ratios) to identify silver mullet, Mugil curema, populations in Southeastern Caribbean Sea. Fish samples were collected in 7 areas of Nueva Esparta State (Venezuela). The otolith Sr:Ca and Ba:Ca ratios and water Sr:Ca were determined (by ICP-OES and EDTA volumetric method). Otoliths Sr:Ca and Ba:Ca ratios and Sr:Ca partition coefficient of mullets in Cubagua island (south of the State) were significantly different from ratios in La Guardia (north of the State). A discriminant analysis of otolith Sr:Ca and Ba:Ca ratios separated Cubagua Island from La Guardia values. These results suggest the existence of different mullet groups in the Southeastern Caribbean Sea. For this, the simultaneous use of Sr:Ca and Ba:Ca ratios could be a potential tool to identify populations in the study area.

  13. Structure electronic and ionic conductivity study versus Ca content in Ca{sub 10-x}Sr{sub x}(PO{sub 4}){sub 6}F{sub 2} apatites

    SciTech Connect

    Sghir, B.; Hlil, E.K.; Laghzizil, A.; Boujrhal, F.Z.; Cherkaoui El Moursli, R.; Fruchart, D.

    2009-07-01

    Substitution effect on the crystallographic structure in Ca{sub 10-x}Sr{sub x}(PO{sub 4}){sub 6}F{sub 2} solid solution are studied by X-ray diffraction patterns and Rietveld refinements. Full potential electronic structure calculations based on LCAO (linear combination atomic orbital) are also performed using the obtained crystallographic parameters. DOS modification and the charge transfer are estimated versus the calcium content. According to the complex impedance method, ionic conductivity changes are explained.

  14. Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic calcite formation: III. Impact of salinity/ionic strength

    PubMed Central

    Tang, Jianwu; Niedermayr, Andrea; Köhler, Stephan J.; Böhm, Florian; Kısakürek, Basak; Eisenhauer, Anton; Dietzel, Martin

    2012-01-01

    In order to apply Sr/Ca and 44Ca/40Ca fractionation during calcium carbonate (CaCO3) formation as a proxy to reconstruct paleo-environments, it is essential to evaluate the impact of various environmental factors. In this study, a CO2 diffusion technique was used to crystallize inorganic calcite from aqueous solutions at different ionic strength/salinity by the addition of NaCl at 25 °C. Results show that the discrimination of Sr2+ versus Ca2+ during calcite formation is mainly controlled by precipitation rate (R in μmol/m2/h) and is weakly influenced by ionic strength/salinity. In analogy to Sr incorporation, 44Ca/40Ca fractionation during precipitation of calcite is weakly influenced by ionic strength/salinity too. At 25 °C the calcium isotope fractionation between calcite and aqueous calcium ions (Δ44/40Cacalcite-aq = δ44/40Cacalcite − δ44/40Caaq) correlates inversely to log R values for all experiments. In addition, an inverse relationship between Δ44/40Cacalcite-aq and log DSr, which is independent of temperature, precipitation rate, and aqueous (Sr/Ca)aq ratio, is not affected by ionic strength/salinity either. Considering the log DSr and Δ44/40Cacalcite-aq relationship, Sr/Ca and δ44/40Cacalcite values of precipitated calcite can be used as an excellent multi-proxy approach to reconstruct environmental conditions (e.g., temperature, precipitation rate) of calcite growth and diagenetic alteration. PMID:22347722

  15. Controls on shell Mg/Ca and Sr/Ca in cultured planktonic foraminiferan, Globigerinoides ruber (white)

    NASA Astrophysics Data System (ADS)

    Kısakürek, B.; Eisenhauer, A.; Böhm, F.; Garbe-Schönberg, D.; Erez, J.

    2008-09-01

    Mg/Ca and Sr/Ca ratios were determined on a single species of planktonic foraminiferan, Globigerinoides ruber (white), collected from the Gulf of Eilat and cultured in seawater at five different salinities (32 to 44), five temperatures (18 to 30 °C) and four pH values (7.9 to 8.4). The Mg/Ca-temperature calibration of cultured G. ruber (with an exponential slope of 8 ± 3%/°C) agrees well with previously published calibrations from core-tops and sediment traps. However, the dependence of Mg/Ca on salinity (with an exponential slope of 5 ± 3%/psu) is also significant and should be included in the calibration equation. With this purpose, we calculated a calibration equation for G. ruber dependent on both temperature and salinity within the 95% confidence limits: Mg/Ca(mmol/mol)=exp[0.06(±0.02)∗S(psu)+0.08(±0.02)∗T(°C)-2.8(±1.0)],R=0.95 The influence of pH on Mg/Ca ratios is negligible at ambient seawater pH (8.1 to 8.3). However, we observe a dominating pH control on shell Mg/Ca when the pH of seawater is lower than 8.0. Sr/Ca in G. ruber shows a significant positive correlation with average growth rate. Presumably, part of the variability in shell Sr/Ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions.

  16. 44/40Ca and 87Sr/86Sr isotopes as tracers of silicate weathering in small catchments of the Massif Central, France

    NASA Astrophysics Data System (ADS)

    Négrel, Philippe; Guerrot, Catherine; Millot, Romain; Petelet-Giraud, Emmanuelle; Bullen, Thomas

    2013-04-01

    We present calcium stable isotope and strontium radiogenic isotope data for soils and sediments developed on volcanic and igneous rocks forming small catchments in the Massif Central (France). Measurements of 44/40Ca isotope ratios (44/40Ca measured by the double spike method on TIMS and normalized to the value for seawater Ca in delta units) in rocks, sediments and soils from silicate catchments (e.g. granite and basalts) together with 87Sr/86Sr isotope ratios permit an examination of the relationships of these isotope systematics during weathering of silicate rocks. We have analysed the granite, weathered granite (arene) and saprolite, sediment and soil overlying the granite on one hand and the basanite, sediment and soil overlying the basanite on the other. The main bedrock in the volcanic zone (e.g. Allanche catchment) is 11 to 2.5 Ma basanite (nephelinitic to leucitic basalts) having SiO2 between 41-45 wt. %, Na2O + K2O <5%, modal or normative nepheline or leucite and a ground mass of clinopyroxene and plagioclase. Surrounding rocks are feldspathic basalts having SiO2 between 46-49 wt. %, Na2O + K2O <5%, normative nepheline, hyperstene and olivine, with plagioclase as the main crystalline phase. The granite massif (e.g. Margeride, 332 ± 12Ma) consists of light and dark facies as a result of the fractional crystallisation of a crustal magma in a sub-horizontal laccolith, with leucogranites dated at 298±2 Ma intruding this granite. The average mineral composition is 37% quartz, 30% oligoclase, 23% K-feldspar and 10% biotite (light facies) and 31% quartz, 30% andesine, 20% K-feldspar and 19% biotite (dark facies). Sr isotope ratios in the arene, sediment and soil diverge strongly from those in the granite bedrock and are positively correlated with Rb/Sr ratios. The 87Sr/86Sr and Rb/Sr ratios both increase from the whole rock to the arene, reflecting the weathering of low 87Sr/86Sr, low-Rb/Sr minerals such as plagioclase and apatite. Sediments collected on a

  17. Measurement of Ca, Zn and Sr in enamel of human teeth by XRF

    SciTech Connect

    Wielopolski, L.; Featherstone, J.D.B.; Cohn, S.H.

    1984-01-01

    Energy dispersive x-ray fluorescence (EDXRF) has been employed to measure Ca, Zn, and Sr in enamel of human teeth. The calibration of the EDXRF system was performed by comparing Sr/Ca ratios with values obtained by atomic absorption analysis of acid etched biopsies of the enamel surface. Two calibration lines were obtained, one line for untreated teeth and the second line for teeth immersed (treated) in solutions containing Sr. A simple analytical model demonstrated that the two calibration lines were the result of the difference in the depth of the enamel sampled by EDXRF and by the acid-etched biopsy. The multi-elemental, non-destructive and quantitative aspects of EDXRF permit the sequential monitoring of the effects of Sr and Zn ions on the mineralization and demineralization processes in human enamel. The portability of the system and adaptability to non-invasive measurements makes it suitable for field studies. 26 references, 4 figures.

  18. Dimensional 3D-2D cross-over under magnetic field in Bi2Sr2-xLaxCuOy induced by La/Sr substitution

    NASA Astrophysics Data System (ADS)

    Murrills, C. D.; Li, Z. Z.; Raffy, H.

    2015-06-01

    The single CuO2 layer Bi2Sr2CuO6 (Bi-2201) is characterized by a low anisotropy under magnetic field. We show that this anisotropy increases exponentially from 4 to 400 with La/Sr substitution in Bi2Sr2-xLaxCu06 (Bi(La)-2201). We present a phase diagram showing the change in transport properties from 3D to 2D when the La concentration is increased, deduced from angular transport measurements in the mixed state of c-axis oriented epitaxial Bi(La)-2201 thin films with columnar pinning centers parallel to the c-axis. We attribute this anisotropy increase to the decrease of the distortion of CuO2 planes by La/Sr substitution.

  19. Sr isotopic fractionation in Ca-Al inclusions from the Allende meteorite

    USGS Publications Warehouse

    Patchett, P.J.

    1980-01-01

    True relative Sr isotopic compositions, determined by double spiking on Ca-Al inclusions from the Allende meteorite show up to 1.5??? per mass unit mass fractionation relative to the Earth and bulk chondrites. All abnormal inclusions are light-isotope enriched. A lack of isotopically heavy Sr in inclusions would place constraints on the time, place and mechanism of origin of these objects. ?? 1980 Nature Publishing Group.

  20. Preparation and characterisation of nanophase Sr, Mg, and Zn substituted hydroxyapatite by aqueous precipitation.

    PubMed

    Cox, Sophie C; Jamshidi, Parastoo; Grover, Liam M; Mallick, Kajal K

    2014-02-01

    Hydroxyapatite (HA) substituted with 2 mol% Sr, 10 mol% Mg, and 2 mol% Zn were precipitated under identical alkaline conditions (pH 11) at 20°C from an aqueous solution. As-synthesised materials were confirmed to be phase pure by XRD and samples prepared in air contained surface adsorbed CO2 as observed by FTIR. SEM studies revealed a globular morphology and agglomeration behaviour, typical of precipitated nHA. EDS spectra confirmed nominal compositions and substitution of Sr, Mg and Zn. At the levels investigated cationic doping was not found to radically influence particle morphology. An indication of the potential in-vivo bioactivity of samples was achieved by analysing samples immersed in SBF for up to 28 days by interferometry and complementary SEM micrographs. Furthermore, a live/dead assay was used and confirmed the viability of seeded MC3T3 osteoblast precursor cells on HA and substituted HA substrates up to 7 days of culture. PMID:24411358

  1. Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state

    NASA Technical Reports Server (NTRS)

    Chiang, C. K.; Freiman, S. W.; Wong-Ng, W.; Hwang, N. M.; Shapiro, A. J.; Hill, M. D.; Cook, L. P.; Shull, R. D.; Swartzendruber, L. J.; Bennett, L. H.

    1990-01-01

    Researchers produced superconducting ceramics of the Bi-Pb-Sr-Ca-Cu-O system started from a glass. To form the glass, the mixed oxide powder was melted at 1200 C in air. The liquid was quenched rapidly by pouring it onto an aluminum plate and rapidly pressing with another plate. The quenched compound was in the form of black amorphous solid, whose x-ray powder pattern has no crystalline peaks. After heat treatment at high temperatures, the glass crystallized into a superconductor. The crystalline phases in the superconductor identified using x-ray diffraction patterns. These phases were that associated with the superconducting phases of T(sub c) = 80 K (Bi2Ca1Sr2Cu2Ox) and of T(sub c) = 110 K (Bi2Ca2Sr2Cu3Ox). The dc resistivity and the ac susceptibility of these superconductors were studied.

  2. K-Ca and Rb-Sr Dating of Lunar Granite 14321 Revisited

    NASA Technical Reports Server (NTRS)

    Simon, Justin I.; Shih, C.-Y.; Nyquist, L. E.

    2011-01-01

    K-Ca and Rb-Sr age determinations were made for a bulk feldspar-rich portion of an Apollo rock fragment of the pristine lunar granite clast (14321,1062), an acid-leached split of the sample, and the leachate. K-Ca and Rb-Sr data were also obtained for a whole rock sample of Apollo ferroan anorthosite (FAN, 15415). The recent detection [1] of widespread intermediate composition plagioclase indicates that the generation of a diversity of evolved lunar magmas maybe more common and therefore more important to our understanding of crust formation than previously believed. Our new data strengthen the K-Ca and Rb-Sr internal isochrons of the well-studied Apollo sample 14321 [2], which along with a renewed effort to study evolved lunar magmas will provide an improved understanding of the petrogenetic history of evolved rocks on the Moon.

  3. Reduced pressure MOCVD of C-axis oriented BiSrCaCuO thin films

    NASA Technical Reports Server (NTRS)

    Hamaguchi, Norihito; Vigil, J.; Gardiner, R.; Kirlin, P. S.

    1990-01-01

    BiSrCaCuO thin films were deposited on MgO (100) single-crystal substrates by metalorganic chemical vapor deposition at 500 C and 2 torr using fluorinated beta-diketonate complexes of Sr, Ca, and Cu and triphenylbismuth. An inverted vertical reaction chamber allowed uniform film growth over large areas (7.7 cm diameter). The as-deposited films were amorphous mixtures of oxides and fluorides; a two-step annealing protocol (750 C + 850-870 C) was developed which gives c-axis oriented films of Bi2Sr2Ca1Cu2O(x). The postannealed films showed onsets in the resistive transition of 110 K, and zero resistivity was achieved by 83 K. Critical current densities as high as 11,000 A/sq cm were obtained at 25 K.

  4. Enhancement of the critical current density in single-crystal Bi2Sr2CaCu2O8 superconductors by chemically induced disorder.

    PubMed Central

    Wang, Y L; Wu, X L; Chen, C C; Lieber, C M

    1990-01-01

    The effect of metal substitution on the critical current densities of single-crystal PbxBi2-xSr2CaCu2O8 (x = 0 or x = 0.7) superconductors has been investigated. Substitution of lead was found to increase the average critical current density from 1 x 10(5) A/cm2 to 2 x 10(6) A/cm2 at 5 K in an applied magnetic field of 10 kilooersteds (1 oersted = 80 A/m). The order of magnitude increase in the critical current density was observed for temperatures up to the flux vortex lattice melting point; the flux lattice melting point was also found to increase to 30 K (from 22 K) in the lead-substituted materials. Diffraction and microscopy investigations of the structural parameters indicate that the fundamental atomic lattices are virtually the same for both materials. Scanning tunneling microscopy images demonstrate, however, that lead substitution causes significant disorder (or defects) in the one-dimensional superstructure found in Bi2Sr2CaCu2O8. Since crystal defects can increase the critical current density by pinning the motion of flux vortices, it is likely that this lead-induced disorder enhances vortex pinning. The lead-induced disorder is specific to the nonsuperconducting Bi-O layers, and thus our results suggest that chemical substitutions may be utilized to control selectively flux pinning and the critical current density in these materials. Images PMID:11607103

  5. Superconductivity in the high-Tc Bi-Ca-Sr-Cu-O system - Phase identification

    NASA Technical Reports Server (NTRS)

    Hazen, R. M.; Prewitt, C. T.; Angel, R. J.; Ross, N. L.; Finger, L. W.

    1988-01-01

    Four phases are observed in superconducting Bi-Ca-Sr-Cu-O samples. The superconducting phase, with onset temperature near 120 K, is a 15.4-A-layered compound with composition near Bi2Ca1Sr2Cu2O9 and an A-centered orthorhombic unit subcell 5.41 x 5.44 x 30.78 A. X-ray diffraction and electron microscopy data are consistent with a structure of alternating perovskite and Bi2O2 layers. High-resolution transmission electron microscopy images reveal a b-axis superstructure of 27.2 A, numerous (001) stacking faults, and other defects.

  6. Synthesis of highly phase pure (Bi, Pb)-Sr-Ca-Cu-O superconductor

    DOEpatents

    Dorris, S.E.; Poeppel, R.B.; Prorok, B.C.; Lanagan, M.T.; Maroni, V.A.

    1994-10-11

    An article and method of manufacture of (Bi,Pb)-Sr-Ca-Cu-O superconductor are disclosed. The superconductor is manufactured by preparing a first powdered mixture of bismuth oxide, lead oxide, strontium carbonate, calcium carbonate and copper oxide. A second powdered mixture is then prepared of strontium carbonate, calcium carbonate and copper oxide. The mixtures are calcined separately with the two mixtures then combined. The resulting combined mixture is then subjected to a powder in tube deformation and thermal processing to produce a substantially phase pure (Bi,Pb)-Sr-Ca-Cu-O superconductor. 5 figs.

  7. Synthesis of highly phase pure (Bi, Pb)-Sr-Ca-Cu-O superconductor

    DOEpatents

    Dorris, Stephen E.; Poeppel, Roger B.; Prorok, Barton C.; Lanagan, Michael T.; Maroni, Victor A.

    1994-01-01

    An article and method of manufacture of (Bi,Pb)-Sr-Ca-Cu-O superconductor. The superconductor is manufactured by preparing a first powdered mixture of bismuth oxide, lead oxide, strontium carbonate, calcium carbonate and copper oxide. A second powdered mixture is then prepared of strontium carbonate, calcium carbonate and copper oxide. The mixtures are calcined separately with the two mixtures then combined. The resulting combined mixture is then subjected to a powder in tube deformation and thermal processing to produce a substantially phase pure (Bi,Pb)-Sr-Ca-Cu-O superconductor.

  8. Superconductivity in Pb-doped Bi-Ca-Sr-Cu-O system

    SciTech Connect

    Xia, J.S.; Fan, M.H.; He, Z.H.; Zhang, Q.R. ); Chen, J.; Chen, Z.Y.; Qian, Y.T. )

    1989-03-20

    A new superconducting transition near 100 {Kappa} was observed in the Pb-doped Bi-Ca-Sr-Cu-O samples. Compared with the 107 {Kappa} and 65 {Kappa} phases, the volume fraction of this superconducting phase is very small, but forms an effective connection between the grains of other two phases. It is suggested that the new phase plays an important role for T/sub c/ above 100 {Kappa} in the Bi/sub 2-chi/Pb/sub chi/Ca/sub 2/Sr/sub 2/Cu/sub 3/O/sub y/ system.

  9. Investigation of thermoluminescence characteristics of CaSrS: Ce nanophosphors

    NASA Astrophysics Data System (ADS)

    Sharma, Geeta; Lochab, S. P.; Singh, Nafa

    2010-11-01

    Thermoluminescence characteristics of Ca 0.75Sr 0.25S: Ce nanophosphors exposed to UV radiations have been investigated. Solid state diffusion method was employed to synthesize the nanophosphors. The confirmation for the formation of the mixed lattice was done by XRD. The particles formed were found to have 45 nm size as calculated by the Debye Scherrer formula. TEM results were in close agreement with the XRD as the nanoparticles formed possess capsule like structure with an average diameter of 50 nm. TL glow curves for the low doses (110-1680 mJ/cm 2) of UV show a main peak around 381 K and another peak of very low intensity around 570 K. The TL intensity increases up to 450 mJ/cm 2 of UV exposure. At higher doses (3.5-80 J/cm 2) the peak position varies slightly but the high temperature peak becomes more intense. Thermoluminescence characteristics of UV irradiated Ca 1- xSr xS: Ce as a function of x (0.25, 0.50, and 0.75) have also been investigated. TL glow curves of Ca 1- xSr xS: Ce (0.25, 0.50, and 0.75) recorded after 450 mJ/cm 2 of exposure of UV radiations show almost similar structure except slight variation in the peak position. Ca 0.25Sr 0.75S: Ce and Ca 0.50Sr 0.50S: Ce have single peak at 373 and 367 K, respectively, while Ca 0.75Sr 0.25S: Ce has a main peak at 381 K and a less intense peak at 570 K. Ca 0.75Sr 0.25S: Ce shows the most intense TL peak. The trap parameters namely, activation energy ( E), order of kinetics ( b), and frequency factor ( s) of Ca 0.75Sr 0.25S: Ce have been determined using Chen’s peak shape method and GCD function suggested by Kitis for second order kinetics.

  10. Measurements of Sr/Ca in bones to evaluate differences in temperature

    NASA Astrophysics Data System (ADS)

    Santos, P. R.; Added, N.; Aburaya, J. H.; Rizzutto, M. A.

    2008-04-01

    Analysis of aragonite from sea shells and coral skeletons showed a clear correlation between the strontium and calcium concentrations for these crystals (Sr/Ca ratio) and seawater temperature obtained by satellites and ship readings. In this work we present the results of a study that correlates Sr/Ca ratio with formation temperature of another calcium crystal, the hydroxyapatite (Ca10(PO4)6(OH)2), main mineral compound of teeth and bones from vertebrates. These animals, independent of its thermoregulation pattern (endothermic or ectothermic) have variations of internal temperature along the body. One interesting application of this work is to differentiate warm-blooded animals from cold-blooded ones just by measuring Sr/Ca ratio in their bones. Bones from a crocodile from Caiman yacare species and two dogs, a poodle and a non defined race, were analyzed using PIXE technique and thick target correction. A 1.78 (18) MeV external proton beam was used in LAMFI-USP with an accumulated charge of about 10 μC for probing the samples. Emitted X-rays were collected using Si-PIN detectors (140 keV for Fe). As in coral skeletons, the Sr/Ca ratio of animals is lower in the body's warmer parts and higher in colder parts.

  11. Comparison of equatorial Pacific sea surface temperature variability and trends with Sr/Ca records from multiple corals

    NASA Astrophysics Data System (ADS)

    Alpert, Alice E.; Cohen, Anne L.; Oppo, Delia W.; DeCarlo, Thomas M.; Gove, Jamison M.; Young, Charles W.

    2016-02-01

    Coral Sr/Ca is widely used to reconstruct past ocean temperatures. However, some studies report different Sr/Ca-temperature relationships for conspecifics on the same reef, with profound implications for interpretation of reconstructed temperatures. We assess whether these differences are attributable to small-scale oceanographic variability or "vital effects" associated with coral calcification and quantify the effect of intercolony differences on temperature estimates and uncertainties. Sr/Ca records from four massive Porites colonies growing on the east and west sides of Jarvis Island, central equatorial Pacific, were compared with in situ logger temperatures spanning 2002-2012. In general, Sr/Ca captured the occurrence of interannual sea surface temperature events but their amplitude was not consistently recorded by any of the corals. No long-term trend was identified in the instrumental data, yet Sr/Ca of one coral implied a statistically significant cooling trend while that of its neighbor implied a warming trend. Slopes of Sr/Ca-temperature regressions from the four different colonies were within error, but offsets in mean Sr/Ca rendered the regressions statistically distinct. Assuming that these relationships represent the full range of Sr/Ca-temperature calibrations in Jarvis Porites, we assessed how well Sr/Ca of a nonliving coral with an unknown Sr/Ca-temperature relationship can constrain past temperatures. Our results indicate that standard error of prediction methods underestimate the actual error as we could not reliably reconstruct the amplitude or frequency of El Niño-Southern Oscillation events as large as ± 2°C. Our results underscore the importance of characterizing the full range of temperature-Sr/Ca relationships at each study site to estimate true error.

  12. Physical properties of Rh substituted CaFe2As2 tuned by annealing/quenching

    NASA Astrophysics Data System (ADS)

    Ran, Sheng; Bud'Ko, Sergey; Canfield, Paul

    2014-03-01

    Our previous work on CaFe2As2 single crystal grown out of FeAs flux has shown that a process of annealing and quenching can be used as an additional control parameter which can tune the ground state of CaFe2As2 systematically. We have also shown that CaFe2As2 is very pressure sensitive. Therefore, unlike the BaFe2As2 system, the effect of 4d transition metal substitution on CaFe2As2 is expected to be largely different from that of 3d transition metal substitution (e.g. cobalt or nickel substitution). In this talk we will present results of measurements on a Rh substituted CaFe2As2 system with different annealing/quenching temperatures. Phase diagrams with substitution level and annealing/quenching temperature as independent parameters are constructed and compared with that of other transition metal substitutions. Supported by the U.S. Department of Energy Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

  13. Behaviour of Sr, Ca, Nd and Li Isotopes During Granite Weathering: the Margeride Massif, France

    NASA Astrophysics Data System (ADS)

    Negrel, P.; Bullen, T. D.; Millot, R.

    2008-12-01

    The Massif Central region of France contains numerous mineral water springs with salinities up to 6 g/L. These high salinities develop due to water-rock interaction processes accompanying weathering of granitic rocks such as the Margeride massif, a 5 km-deep laccolith having an age of 323 ± 12 Ma and consisting mainly of granitoid and gneiss. In order to better constrain weathering processes, we have determined the Sr, Nd, Ca and Li-isotope compositions of the Margeride granite, weathered granite (arene) and saprolite, sediment and soil overlying the granite, and groundwater samples (e.g., mineral water springs) associated with the massif. 87Sr/86Sr ratios increase in the order apatite-plagioclase-K-feldspar-arene- sediments and soils-biotite, and are well correlated with Rb/Sr ratios. Mineral waters have 87Sr/86Sr ratios similar to that of plagioclase, but have higher Rb/Sr ratios. 44Ca/40Ca ratios of plagioclase and apatite are similar to that of the whole rock, while those of K-feldspar and biotite are significantly less. 44Ca/40Ca ratios of arene, soil and sediment are similar to or less than that of K- feldspar, reflecting complete loss of Ca from plagioclase and apatite during weathering. In contrast, 44Ca/40Ca ratios for the mineral waters are similar to or substantially greater than that of plagioclase, reflecting extensive calcium carbonate precipitation during ascent of the waters along the rock fracture network. 44Ca/40Ca ratios of the waters are as much as 3.5 per mil greater than that of seawater, and thus contain the heaviest Ca yet reported for terrestrial materials. 7Li/6Li ratios differ by a few per mil among the granite minerals; of the weathering products, arene and soils have the least 7Li/6Li ratios, while river bank sediment and arene surface sediment have progressively greater ratios. 7Li/6Li ratios of the mineral waters have the greatest values, reflecting preferential retention of 6Li in the weathering products. 143Nd/144Nd ratios are

  14. Accelerated formation of 110 K high T sub c phase in the Ca- and Cu-rich Bi-Pb-Sr-Ca-Cu-O system

    SciTech Connect

    Huang, Y.T.; Liu, R.G.; Lu, S.W.; Wu, P.T. ); Wang, W.N. )

    1990-02-19

    The crystal structure and superconducting properties of the Bi-Pb-Sr-Ca-Cu-O system with Ca- and Cu-rich nominal composition were investigated. A nearly single-phased 110 K high {ital T}{sub {ital c}} superconductor can be obtained with 852 {degree}C/20 h sintering from the starting composition of Bi{sub 1.7}Pb{sub 0.4}Sr{sub 1.6}Ca{sub 2.4}Cu{sub 3.6}O{sub {ital y}}. X-ray diffraction patterns, resistivity measurement, diamagnetic susceptibility results, and scanning electron micrographs all indicate that the Ca- and Cu-rich nominal composition would result in better superconducting properties than those of Ca:Sr=1:1 Bi-Pb-Sr-Ca-Cu-O compounds in a much shorter sintering time.

  15. Coprecipitation of Sr, Ni and U with CaCO{sub 3}: An experimental study

    SciTech Connect

    Carlsson, T.; Aalto, H.

    1996-08-01

    At the Finnish candidate sites for a nuclear waste repository, calcite (CaCO{sub 3}) is a common fracture mineral that may participate in coprecipitation processes. The objective of this preliminary work was to study the coprecipitation of the trace elements Sr, Ni, and U with CaCO{sub 3} under controlled conditions. The experiments were made in a titration vessel at room temperature under pure N{sub 2} or a 0.1% CO{sub 2}/N{sub 2} mixture. The water phase contained CaCl{sub 2} (0.01M) and NaCl (0.05 M) to which trace amounts of Ni{sup 2+}, Sr{sup 2+} and UO{sub 2}{sup 2+} were initially added. CaCO{sub 3} was precipitated by the addition of Na{sub 2}CO{sub 3} and the use of CaCO{sub 3} seed crystals. When about 10{sup {minus}4} mol of precipitate had formed, the solution and solid phases were analyzed with ICP-MS. The results seem to indicate that Ni coprecipitated with CaCO{sub 3} under the experimental conditions, while U did not. In the case of Sr, further data are needed in order to make any conclusions from the experiments.

  16. Enhancement of ferromagnetism by oxygen isotope substitution in strontium ruthenate SrRuO3

    NASA Astrophysics Data System (ADS)

    Kawanaka, Hirofumi; Aiura, Yoshihiro; Hasebe, Takayuki; Yokoyama, Makoto; Masui, Takahiko; Nishihara, Yoshikazu; Yanagisawa, Takashi

    2016-10-01

    The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature Tc of 160 K is studied. We observed for the first time a shift of ∆Tc ~ 1 K by oxygen isotope substitution of 16O → 18O in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient α = ‑∂ lnTc/∂ lnM. The Raman spectra indicate that the main vibration frequency of 16O at 363 cm‑1 shifts to 341 cm‑1 following oxygen isotope substitution 18O. This shift is remarkably consistent with the Debye frequency being proportional to ∝ 1√M where M is the mass of an oxygen atom. The positive isotope shift of ∆Tc can be understood by taking account of the electron-phonon interaction.

  17. Catalytic partial oxidation of n-tetradecane on Rh and Sr substituted pyrochlores

    SciTech Connect

    Haynes, D.J.; Berry, D.A.; Shekhawat, Dushyant; Gardner, T.H.; Spivey, J.J.

    2007-10-01

    Catalyst deactivation by high levels of sulfur and aromatics limits the catalytic partial oxidation (CPOX) of diesel fuel into a H2-rich stream for fuel cells. These species poison traditional supported metal catalysts because they adsorb strongly to electron dense metal clusters and promote the formation of carbon on the surface. In this work, Rh + Sr are substituted into lanthanum zirconate (LZ) pyrochlore (La2Zr2O7) to give an La(2-x)SrxRhyZr(2-y)O(7- î) (LSRZ) catalyst. The resistance to deactivation and carbon formation were examined by the CPOX of a mixture of 5 wt% 1-methylnaphthalene + 1000 ppmw dibenzothiophene in n-tetradecane. The results were compared to a commercial Rh/ã-Al2O3 catalyst. In the presence of these contaminants, the activity of the LSRZ was only kinetically inhibited, which is thought to be attributable to the oxygen-ion conductivity that results from Sr substitution into the pyrochlore structure. Rh/ã-Al2O3 was deactivated, likely due to significant carbon accumulation on/near the Rh metal

  18. Enhancement of ferromagnetism by oxygen isotope substitution in strontium ruthenate SrRuO3

    PubMed Central

    Kawanaka, Hirofumi; Aiura, Yoshihiro; Hasebe, Takayuki; Yokoyama, Makoto; Masui, Takahiko; Nishihara, Yoshikazu; Yanagisawa, Takashi

    2016-01-01

    The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature Tc of 160 K is studied. We observed for the first time a shift of ∆Tc ~ 1 K by oxygen isotope substitution of 16O → 18O in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient α = −∂ lnTc/∂ lnM. The Raman spectra indicate that the main vibration frequency of 16O at 363 cm−1 shifts to 341 cm−1 following oxygen isotope substitution 18O. This shift is remarkably consistent with the Debye frequency being proportional to ∝ 1√M where M is the mass of an oxygen atom. The positive isotope shift of ∆Tc can be understood by taking account of the electron-phonon interaction. PMID:27739475

  19. Superconducting glass-ceramics in the Bi-Sr-Ca-Cu-O system

    NASA Technical Reports Server (NTRS)

    De Guire, Mark R.; Kim, Cheol J.; Bausal, Narottam P.

    1990-01-01

    Differential thermal analysis, XRD, SEM, and resistivity measurements, have been used to study the recrystallization during various heat treatments of a Bi1.5SrCaCu2O(z) glass obtained by rapid quenching from the melt. Heating at 450 C formed the Bi(2+x)Sr(2-x)-CuO(z) solid solution designated 'R'. Between 765 and 845 C, R reacts slowly with the glass to form the 80 K superconductor Bi2(Sr,Ca)3Cu2O(z), together with CuO. Heating for 7 days at the higher temperature, followed by slow cooling, raised the temperature of zero resistance to 77 K.

  20. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

    PubMed

    Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  1. Preparation of Bi-Sr-Ca-Cu-O superconductors from oxide-glass precursors

    DOEpatents

    Hinks, David G.; Capone, II, Donald W.

    1992-01-01

    A superconductor and precursor therefor from oxide mixtures of Ca, Sr, Bi and Cu. Glass precursors quenched to elevated temperatures result in glass free of crystalline precipitates having enhanced mechanical properties. Superconductors are formed from the glass precursors by heating in the presence of oxygen to a temperature below the melting point of the glass.

  2. Superconducting behavior in the Bi-In-Sr-Ca-Cu-Pb-O system

    NASA Astrophysics Data System (ADS)

    Okada, M.; Homma, M.; Murakami, T.; Matsuoka, D.; Cross, K.

    1990-09-01

    The superconducting behavior of the nominal composition of (Bi/1-x/In/x/)2Sr2Ca2Cu3Pb/0.6/O/y/ was studied. It was found that the samples with x equal to or less than 0.90 fired at 850 C for 50 h in air showed zero resistance above 60 K. The sample with x = 0.25 showed the highest zero resistance transition temperature of 92 K and an onset temperature of 110 K. It was found that the grains with the composition of Bi2Sr2Ca2Cu3O/y/ for the sample with x = 0.25 contained 9 percent In for the amount of Bi. The surface of the sample with x = 0.90, which showed zero resistance above 60 K, was covered with Bi2Sr2Ca1Cu2O/y/ because the In oxide is volatile from its surface over 850 C. The addition of In to the system has no effect on the critical temperatures, but is effective in increasing the volume fraction of the Bi2Sr2Ca2Cu3O10 compound.

  3. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr

    PubMed Central

    Li, H. F.; Xie, X. H.; Zheng, Y. F.; Cong, Y.; Zhou, F. Y.; Qiu, K. J.; Wang, X.; Chen, S. H.; Huang, L.; Tian, L.; Qin, L.

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  4. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

    PubMed

    Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

    2015-05-29

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals.

  5. Tracing thermal aquifers of El Chichón volcano-hydrothermal system (México) with 87Sr/ 86Sr, Ca/Sr and REE

    NASA Astrophysics Data System (ADS)

    Peiffer, L.; Taran, Y. A.; Lounejeva, E.; Solís-Pichardo, G.; Rouwet, D.; Bernard-Romero, R. A.

    2011-08-01

    The volcano-hydrothermal system of El Chichón volcano, Chiapas, Mexico, is characterized by numerous thermal manifestations including an acid lake, steam vents and boiling springs in the crater and acid and neutral hot springs and steaming ground on the flanks. Previous research on major element chemistry reveals that thermal waters of El Chichón can be divided in two groups: (1) neutral waters discharging in the crater and southern slopes of the volcano with chloride content ranging from 1500 to 2200 mg/l and (2) acid-to-neutral waters with Cl up to 12,000 mg/l discharging at the western slopes. Our work supports the concept that each group of waters is derived from a separate aquifer (Aq. 1 and Aq. 2). In this study we apply Sr isotopes, Ca/Sr ratios and REE abundances along with the major and trace element water chemistry in order to discriminate and characterize these two aquifers. Waters derived from Aq. 1 are characterized by 87Sr/ 86Sr ratios ranging from 0.70407 to 0.70419, while Sr concentrations range from 0.1 to 4 mg/l and Ca/Sr weight ratios from 90 to 180, close to average values for the erupted rocks. Waters derived from Aq. 2 have 87Sr/ 86Sr between 0.70531 and 0.70542, high Sr concentrations up to 80 mg/l, and Ca/Sr ratio of 17-28. Aquifer 1 is most probably shallow, composed of volcanic rocks and situated beneath the crater, within the volcano edifice. Aquifer 2 may be situated at greater depth in sedimentary rocks and by some way connected to the regional oil-gas field brines. The relative water output (l/s) from both aquifers can be estimated as Aq. 1/Aq. 2-30. Both aquifers are not distinguishable by their REE patterns. The total concentration of REE, however, strongly depends on the acidity. All neutral waters including high-salinity waters from Aq. 2 have very low total REE concentrations (< 0.6 μg/l) and are characterized by a depletion in LREE relative to El Chichón volcanic rock, while acid waters from the crater lake (Aq. 1) and acid

  6. Photoluminescence of A- and B-site Eu3+-substituted (SrxBa1-x)2CaWyMo1-yO6 phosphors

    NASA Astrophysics Data System (ADS)

    Sletnes, M.; Lindgren, M.; Valmalette, J. C.; Wagner, N. P.; Grande, T.; Einarsrud, M.-A.

    2016-05-01

    The photoluminescence of two series of A- and B-site Eu3+ substituted (SrxBa1-x)2CaWyMo1-yO6 double perovskite phosphor materials, (SrxBa1-x)1.96Eu0.02K0.02CaWyMo1-yO6 and (SrxBa1-x)2Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, and 1), were studied systematically as a function of stoichiometry and crystal structure. The Eu3+ lattice sites controlled by co-doping with either K or Li were confirmed by Raman spectroscopy. The variation in integrated emission intensity and emission colour over the experimental matrix was examined using statistical tools, and the observed trends were rationalized based on the physical and electronic structure of the phosphors. Phosphors with Eu on B-site with maximum Sr content had remarkably higher emission intensities than all other materials, but the emission was more orange than red due to domination of the 5D0-7F1 (595 nm) transition of Eu3+. The relative intensities of the 5D0-7F2 (615 nm) and 5D0-7F1 transitions of Eu3+, and thus the red-shift of the emission, decreased linearly with increasing Sr content in the A-site Eu-substituted phosphors, and reached a maximum for Sr1.96Eu0.02K0.02CaW0.25Mo0.75O6. A maximum external quantum efficiency of 17% was obtained for the phosphor Sr2Ca0.7Eu0.15Li0.15W0.5Mo0.5O6 with Eu on B-site.

  7. The calibration of D[Sr/Ca]versus sea surface temperature relationship for Porites corals

    NASA Astrophysics Data System (ADS)

    Shen, Chuan-Chou; Lee, Typhoon; Chen, Chi-Yun; Wang, Chung-Ho; Dai, Chang-Feng; Li, Lung-An

    1996-10-01

    Taking advantage of the availability of a continuous sea surface temperature (SST) record at Kenting, southern Taiwan, we have carried out a calibration of D[Sr/Ca]-SST ( D: distribution coefficient) relationships for Porites lobata and P. lutea. Between 22°C ˜ 28°C, the best fitting linear relationships for the two species agree within their respective errors with a maximum deviation less than 0.3°C. Our calibration overlaps with the only published calibration for Porites ( deVilliers et al., 1994) but is somewhat less temperature sensitive. The maximum temperature differences for the two calibrations between 21°C and 27°C are ± 1.2°C. The D-SST relationship calculated using the data of Beck et al. (1992, 1994) and their unpublished seawater data lies between these two calibrations. Our calibration removes some discrepancies previously described in the studies of McCulloch et al. (1994a) on the Great Barrier Reef and of Min et al. (1995) on New Caledonia. We found little growth rate effect on the calibration for P. lutea between 18 mm/yr and 23 mm/yr. We have also monitored the seawater [Sr/Ca] for the entire 1993. The observed variation of 0.033 mmol/mol can cause a temperature artifact of 0.7°C and is thus a dominant error in using this new paleo-thermometer. To carry out this experiment, we have developed a microsurgical technique that can be used to sample corals at better than 0.15 mm resolution. The analytical precision should ultimately allow SST reconstruction of better than 0.2°C. Furthermore, the insensitivity of the calibration against growth rate variation and species differences suggests a promising future for this new thermometer, in contrast to the pessimism of deVilliers et al. (1995). However, inter-laboratory differences and the question of seawater [Sr/Ca] variation need to be addressed first. We recommend a single SST calibration for the Sr/Ca thermometer on coral Porites: Sr/Ca N = 10.286-0.0514 × SST (N: normalized to Hawaii

  8. Structural phase transition in early growth of Bi2Sr2CaCu2O8+x films on SrTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Ariosa, D.; Onellion, M.; Margaritondo, G.; Pavuna, D.

    2002-02-01

    We used pulsed laser deposition, with a Bi2Sr2CaCu2O8+x target, to grow films ranging from (1/4) to 10 unit cells thick. We studied these films, and reference Bi2Sr2CaCu2O8+x single crystal samples, using angle-integrated photoemission, core level photoemission, and x-ray diffraction. The data indicate that all films exhibit a metallic-like Fermi edge in the photoemission data. More strikingly, a structural phase transition occurs at a nominal Bi2Sr2CaCu2O8+x thickness of approximately one unit cell, converting the precursor Bi2O2.33 highly coherent thin film into a Bi2Sr2CaCu2O8+x structure.

  9. Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

    SciTech Connect

    Ingram, B.L.; De Deckker, P.; Chivas, A.R.; Conrad, M.E.; Byrne, A.R.

    2004-10-19

    Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma Marsh over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10-35 {per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5 {per_thousand} between 500 yr BR and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3-4 {per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100-300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600-700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.

  10. Potential and limitations of Sr/Ca ratios in coccolith carbonate: new perspectives from cultures and monospecific samples from sediments.

    PubMed

    Stoll, Heather M; Ziveri, Patricia; Geisen, Markus; Probert, Ian; Young, Jeremy R

    2002-04-15

    The Sr/Ca ratio of coccoliths was recently proposed as a potential indicator of past growth rates of coccolithophorids, marine algae, which play key roles in both the global carbonate and carbon cycles. We synthesize calibrations of this proxy through laboratory culture studies and analysis of monospecific coccolith assemblages from surface sediments. Cultures of coccolithophorids Helicosphaera carteri, Syracosphaera pulchra and Algirospira robusta confirm a 1-2% increase in Sr/Ca per degrees C previously identified in Emiliania huxleyi and Gephyrocapsa oceanica. This effect is not due merely to increases in growth rate with temperature and must be considered in palaeoceanographic studies. In light-limited cultures of E. huxleyi, Calcidiscus leptoporus and G. oceanica at constant temperature, coccolith Sr/Ca ratios vary by 10% across the range of possible growth and calcification rates for a given species. Among different species under similar culture conditions, Sr/Ca ratios vary by 30%. Although the highest ratios are in the cells with highest calcification and organic carbon fixation rates, at lower rates there is much scatter, indicating that different mechanisms control interspecific and intraspecific coccolith Sr/Ca variations. In field studies in the Equatorial Pacific and Somalia coastal region, coccolith Sr/Ca correlates with upwelling intensity and productivity. A more dynamic response is observed in larger coccoliths like C. leptoporus (23-55% variation in Sr/Ca) than in smaller coccoliths of G. oceanica or Florisphaera profunda (6-15% variation in Sr/Ca). This response suggests that, despite temperature effects, coccolith Sr/Ca has potential as an indicator of coccolithophorid productivity. If the variable Sr/Ca response of different species accurately reflects their variable productivity response to upwelling (and not different slopes of Sr/Ca with productivity), coccolith Sr/Ca could provide useful data on past changes in coccolith ecology. The

  11. The comparative kinetics of Ca, Sr, And Ra in a freshwater turtle, Trachemys scripta

    SciTech Connect

    Hinton, T.G.

    1989-01-01

    The accumulation of {sup 45}Ca, {sup 47}Ca, {sup 88}Sr, and {sup 226}Ra was studied in the yellow-bellied slider, a common freshwater turtle of the Southeastern US. The author was particularly interested in testing the hypothesis of competitive inhibition, a concept whereby decreasing the intake of a stable dietary element increases the absorption and retention of chemically similar radionuclides. He established four specific hypotheses and examined the processes of absorption and elimination as a function of stable dietary calcium (2 and 20 mg g{sup {minus}1}), season (summer, fall, winter and spring), and age and sex of the animals (hatchlings, juveniles, adult males, adult females, and gravid females). Turtles were gavaged with radionuclides and the gamma-emitting isotopes were detected during serial whole-body counts performed on the live animals for up to 480 d. The analysis of the beta-emitting {sup 45}Ca was accomplished by chemical separation procedures. Data were fit to a two-component exponential retention model by nonlinear regression. The 10-fold reduction in dietary Ca did not affect the elimination rate constants, and increased the assimilation of Sr and Ra only within juveniles. For all animals the absorption of Ca was significantly greater than Sr, and likewise, Sr was greater than Ra. Mean absorptions were generally higher than values reported for other organisms. Unlike many other organisms, absorption rates did not decline at maturity. He suspects that high Ca demands in constructing and maintaining the massive shell, necessitated by the turtle's survival strategy, may contribute to the high absorption, as well as the lack of a decline at maturity. Elimination rate constants were greatest in the summer and declined to levels that were generally not distinguishable from zero in the spring, winter, and fall seasons.

  12. Mechanochemical synthesis, structure, and properties of solid solutions of alkaline earth metal fluorides: Ma1-xMbxF2 (M: Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Heise, M.; Scholz, G.; Düvel, A.; Heitjans, P.; Kemnitz, E.

    2016-10-01

    The capability of mechanochemical synthesis for the formation of solid solutions of alkaline earth metal fluorides Ma1-xMbxF2 (M: Ca, Sr, Ba) was tested by fluorination of metal acetates and metal hydroxides with ammonium fluoride directly at milling. Evidence was found for a mutual substitution of cations on their lattice positions in Ca1-xSrxF2 and Ba1-xSrxF2 samples. For the Ba/Ca-system this synthesis route is only partially successful. X-ray diffraction and 19F MAS NMR spectroscopy were used to characterize all samples concerning their crystal structure and local fluorine coordination. Calculations of 19F chemical shifts with the superposition model along with probability calculations for the intensity of the individual 19F lines, performed in dependence on the molar composition of the samples, perfectly agree with the experimental findings. The fluoride ion conductivity of as-prepared samples, determined by temperature dependent DC conductivity measurements, is significantly higher than those of crystalline binary fluorides. Moreover, a higher F- ion conductivity is observed for samples with higher mixing grade in the Ca/Sr-and the Ba/Sr-systems.

  13. Regulation of plant immunity through ubiquitin-mediated modulation of Ca(2+) -calmodulin-AtSR1/CAMTA3 signaling.

    PubMed

    Zhang, Lei; Du, Liqun; Shen, Chenjia; Yang, Yanjun; Poovaiah, B W

    2014-04-01

    Transient changes in intracellular Ca(2+) concentration are essential signals for activation of plant immunity. It has also been reported that Ca(2+) signals suppress salicylic acid-mediated plant defense through AtSR1/CAMTA3, a member of the Ca(2+) /calmodulin-regulated transcription factor family that is conserved in multicellular eukaryotes. How plants overcome this negative regulation to mount an effective defense response during a stage of intracellular Ca(2+) surge is unclear. Here we report the identification and functional characterization of an important component of ubiquitin ligase, and the associated AtSR1 turnover. The AtSR1 interaction protein 1 (SR1IP1) was identified by CytoTrap two-hybrid screening. The loss-of-function mutant of SR1IP1 is more susceptible to bacterial pathogens, and over-expression of SR1IP1 confers enhanced resistance, indicating that SR1IP1 acts as a positive regulator of plant defense. SR1IP1 and AtSR1 act in the same signaling pathway to regulate plant immunity. SR1IP1 contains the structural features of a substrate adaptor in cullin 3-based E3 ubiquitin ligase, and was shown to serve as a substrate adaptor that recruits AtSR1 for ubiquitination and degradation when plants are challenged with pathogens. Hence, SR1IP1 positively regulates plant immunity by removing the defense suppressor AtSR1. These findings provide a mechanistic insight into how Ca(2+) -mediated actions are coordinated to achieve effective plant immunity.

  14. Catalytic partial oxidation of n-tetradecane using Rh and Sr substituted pyrochlores: Effects of sulfur

    SciTech Connect

    Haynes, D.; Berry, D.; Shekhawat, D. Spivey, J.

    2009-01-01

    The presence of high levels of organosulfur compounds hinders the catalytic partial oxidation (CPOX) of logistic fuels into a H2-rich gas stream for fuel cells. These species poison traditional supported metal catalysts because the sulfur adsorbs strongly to electron dense metal clusters and promotes the formation of carbon on the surface. To minimize deactivation by sulfur, two substituted lanthanum zirconate (LZ) pyrochlores (La2Zr2O7), identified in a previous study [D.J. Haynes, D.A. Berry, D. Shekhawat, J.J. Spivey, Catal. Today 136 (2008) 206], were investigated: (a) La–Rh–Zr (LRZ) and La–Sr– Rh–Zr (LSRZ). Using unsubstituted lanthanum zirconate and a conventional 0.5 wt% Rh/g-Al2O3 as comparisons, these four catalysts were exposed to a feed containing 1000 ppmw dibenzothiophene (DBT) in n-tetradecane (TD). DBT rapidly deactivated both the 0.5 wt% Rh/g-Al2O3 and LZ. The LRZ catalyst experienced a gradual deactivation, suggesting that Rh substitution into the pyrochlore structure, by itself, cannot completely eliminate deactivation by sulfur. However, the additional substitution of Sr stabilized yields of H2 and CO in the presence of DBT at levels only slightly below those observed without sulfur in the feed. After sulfur was removed from the feed, each catalyst was able to recover some activity. The recovery appears to be linked to carbon formed on active sites. The 0.5 wt% Rh/g-Al2O3, LZ, and LRZ all had comparable amounts of carbon formed on the surface: 0.90, 0.80 and 0.86 gcarbon/gcat, respectively. Of these three catalysts, only the LRZ was able to recover a significant portion of initial activity, suggesting that the carbon formed indiscriminately on the surface, and not solely on the active sites. LSRZ was able to regain almost its initial activity once sulfur was removed from the feed, and had the least amount of carbon on the surface (0.30 gcarbon/gcat). It is hypothesized that oxygen-ion mobility, which results from Sr substitution

  15. Synthesis, structural and vibrational properties of Bi{sub 0.8}La{sub 0.15}A{sub 0.05}FeO{sub 3} (A = Ca, Sr)

    SciTech Connect

    Sharma, Poorva E-mail: poorva.aks@gmail.com; Kumar, Ashwini; Varshney, Dinesh E-mail: poorva.aks@gmail.com

    2015-06-24

    The polycrystalline Bi{sub 0.8}La{sub 0.15}A{sub 0.05}FeO{sub 3} (A = Ca, Sr) was synthesized by solid state reaction route to study the structural and vibrational properties. X-ray diffraction patterns confirmed the formation of single-phase perovskite structure. Rietveld–refined crystal structure parameters revealed the existence of rhombohedral R3c symmetry in the prepared sample. The blue shift of phonon modes is attributed to lower atomic mass of La{sup 3+} and A = (Ca, Sr) substitution at Bi site in BiFeO{sub 3}.

  16. Half-Metallic p-Electron Ferromagnetism in Ca and Sr Pnictides

    NASA Astrophysics Data System (ADS)

    Geshi, Masaaki; Kusakabe, Koichi; Nagara, Hitose; Suzuki, Naoshi

    2007-07-01

    We investigated the magnetism in Ca and Sr pnictides by using the first-principles calculations. These compounds are half-metallic and ferromagnetic (FM) when they assume the zinc-blende structure at the equilibrium lattice constant. Ferromagnetism is induced by the spin polarization of the p-orbitals of the pnictogen atoms; Ca and Sr atoms have no magnetic moments, which is different from that of CrAs or CrSb with a zinc-blende structure. To confirm the mechanism of the ferromagnetism, we have calculated a hypothetical crystal — fcc-As with two additional electrons — and have shown that fcc-As has the same magnetic moment as CaAs with a zinc-blende structure. This means that the role of Ca or Sr atoms is to provide electrons with As atoms at the fcc site and to sustain the distances between the As atoms and crystal symmetry. The FM exchange interactions between the pnictogen atoms are considered to exist in these lattices, which is briefly discussed.

  17. Sr/Ca and Mg/Ca vital effects correlated with skeletal architecture in a scleractinian deep-sea coral and the role of Rayleigh fractionation

    NASA Astrophysics Data System (ADS)

    Gagnon, Alexander C.; Adkins, Jess F.; Fernandez, Diego P.; Robinson, Laura F.

    2007-09-01

    Deep-sea corals are a new tool in paleoceanography with the potential to provide century long records of deep ocean change at sub-decadal resolution. Complicating the reconstruction of past deep-sea temperatures, Mg/Ca and Sr/Ca paleothermometers in corals are also influenced by non-environmental factors, termed vital effects. To determine the magnitude, pattern and mechanism of vital effects we measure detailed collocated Sr/Ca and Mg/Ca ratios, using a combination of micromilling and isotope-dilution ICP-MS across skeletal features in recent samples of Desmophyllum dianthus, a scleractinian coral that grows in the near constant environment of the deep-sea. Sr/Ca variability across skeletal features is less than 5% (2σ relative standard deviation) and variability of Sr/Ca within the optically dense central band, composed of small and irregular aragonite crystals, is significantly less than the surrounding skeleton. The mean Sr/Ca of the central band, 10.6 ± 0.1 mmol/mol (2σ standard error), and that of the surrounding skeleton, 10.58±0.09 mmol/mol, are statistically similar, and agree well with the inorganic aragonite Sr/Ca-temperature relationship at the temperature of coral growth. In the central band, Mg/Ca is greater than 3 mmol/mol, more than twice that of the surrounding skeleton, a general result observed in the relative Mg/Ca ratios of D. dianthus collected from separate oceanographic locations. This large vital effect corresponds to a ˜ 10 °C signal, when calibrated via surface coral Mg/Ca-temperature relationships, and has the potential to complicate paleoreconstructions. Outside the central band, Mg/Ca ratios increase with decreasing Sr/Ca. We explain the correlated behavior of Mg/Ca and Sr/Ca outside the central band by Rayleigh fractionation from a closed pool, an explanation that has been proposed elsewhere, but which is tested in this study by a simple and general relationship. We constrain the initial solution and effective partition

  18. Optical and microwave detection using Bi-Sr-Ca-Cu-O thin films

    NASA Technical Reports Server (NTRS)

    Grabow, B. E.; Sova, R. M.; Boone, B. G.; Moorjani, K.; Kim, B. F.; Bohandy, J.; Adrian, F.; Green, W. J.

    1991-01-01

    Recent progress at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in the development of optical and microwave detectors using high temperature superconducting thin films is described. Several objectives of this work have been accomplished, including: deposition of Bi-Sr-Ca-Cu-O thin films by laser abation processing (LAP); development of thin film patterning techniques, including in situ masking, wet chemical etching, and laser patterning; measurements of bolometric and non-bolometric signatures in patterned Bi-Sr-Ca-Cu-O films using optical and microwave sources, respectively; analysis and design of an optimized bolometer through computer simulation; and investigation of its use in a Fourier transform spectrometer. The focus here is primarily on results from the measurement of the bolometric and non-bolometric response.

  19. Consolidation and plasticity of Bi-Sr-Ca-Cu-O superconductors

    NASA Astrophysics Data System (ADS)

    Nash, A. S.; Goretta, K. C.; Wheeler, R.; Moon, B. M.; Wu, C. T.; Nash, P.

    1991-05-01

    The Bi2Sr2CaCu2O(x) (2212) superconductor consists of platelike grains that grow up very rapidly in two directions at high temperature. The grain growth is so fast that this superconductor can not be sintered by conventional means. Densification can be achieved, however, by hot isostatic pressing by a combination of flat rolling and sintering. Results from 2212 and 2212 + 15 wt. percent Ag specimens produced by these consolidation methods are compared with those from sintering studies. Scanning and transmission electron microscopy were used to assess the mechanisms by which 2212 densifies. The superconducting properties of each type of specimen were measured. It was found that only forms in which the platelike grains exhibited substantial preferred orientation were capable of carrying large amounts of current. This result has important implications to the thermomechanical processing of Bi-Sr-Ca-Cu-O superconductors.

  20. Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state

    NASA Technical Reports Server (NTRS)

    Chiang, C. K.; Wong-Ng, W.; Cook, L. P.; Freiman, S. W.; Hwang, N. M.; Vaudin, M.; Hill, M. D.; Shull, R. D.; Shapiro, A. J.; Swartzendruber, L. J.

    1991-01-01

    The bismuth based high T sub c superconductors can be processed via an amorphous Bi-Pb-Sr-Ca-Cu oxide. The amorphous oxides were prepared by melting the constituent powders in an alumina crucible at 1200 C in air followed by pouring the liquid onto an aluminum plate, and rapidly pressing with a second plate. In the amorphous state, no crystalline phase was identified in the powder x ray diffraction pattern of the quenched materials. After heat treatment at high temperature the amorphous materials crystallized into a glass ceramic containing a large fraction of the Bi2Sr2Ca2Cu3O(x) phase T sub c = 110 K. The processing method, crystallization, and results of dc electrical resistivity and ac magnetic susceptibility measurements are discussed.

  1. The structural and magnetic properties of Sr-doped multiferroic CaMn7O12

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Guang; Ma, Xiao-Chen; Xie, Liang

    2015-10-01

    The structural and magnetic properties of Sr-doped multiferroic CaMn7O12 were investigated by X-ray diffraction (XRD), Raman spectra, X-ray absorption spectroscopy and temperature dependence of magnetization. The XRD indicates that the samples are rhombohedral lattice (space group R3¯) with small additional phase Mn3O4. The refined lattice parameters of the main phase increases by the Sr doping. The Raman spectra demonstrate the phonon vibration direction is affected, which is probably due to the rotation of MnO6 octahedral. However, as the valence state of Sr and Ca is same at +2, the samples with doping show nonvariation of peak position at Mn 2p X-ray absorption spectra, indicating that the ratio of Mn3+ and Mn4+ ions is unchanged. And the magnetic transition temperature both at T1 = 90K and T2 = 42K is also not tunable because the amount of magnetic interaction between Mn3+ and Mn4+ is not influenced by doping Sr ion. Only the enhancement of the magnetization at low temperature is observed, which is the same as the effect caused by external magnetic fields. An unsaturated wasp-waist type hysteresis loop is observed, indicating the competition between ferromagnetic-like and antiferromagnetic order.

  2. Preparation of Bi-Sr-Ca-Cu-O superconductors from oxide-glass precursors

    NASA Astrophysics Data System (ADS)

    Hinks, D. G.; Soderholm, L.; Capone, D. W., II; Dabrowski, B.; Mitchell, A. W.

    1988-08-01

    Efforts to synthesize the new Ca-Sr-Bi-Cu-O superconductors from amorphous glasses are reported. These glasses are produced by quenching melts of the constituent oxides, followed by firing to produce the supercoducting phase. This synthetic route produces denser, more uniform samples than those obtained from firing intimate mixtures of the constituent binary oxides and carbonates. Ultimately, this technique may yield pure materials with enhanced bulk properties.

  3. Effect of doping in the Bi-Sr-Ca-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Akbar, S. A.; Wong, M. S.; Botelho, M. J.; Sung, Y. M.; Alauddin, M.; Drummer, C. E.; Fair, M. J.

    1991-01-01

    The results of the effect of doping on the superconducting transition in the Bi-Sr-Ca-Cu-O system are reported. Samples were prepared under identical conditions with varying types (Pb, Sb, Sn, Nb) and amounts of dopants. All samples consisted of multiple phases, and showed stable and reproducible superconducting transitions. Stabilization of the well known 110 K phase depends on both the type and amount of dopant. No trace of superconducting phase of 150 K and above was observed.

  4. Ca, Sr and Ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence

    USGS Publications Warehouse

    Bullen, Thomas D.; Chadwick, Oliver A.

    2016-01-01

    Nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus (P) and calcium (Ca) from minerals at depth and concentrate those nutrients at the surface. Here we use soil chemistry and stable isotopes of the alkaline earth elements Ca, strontium (Sr) and barium (Ba) to test the hypothesis that biolifting of P has been an important pedogenic process across a soil climosequence developed on volcanic deposits at Kohala Mountain, Hawaii. The geochemical linkage between these elements is revealed as generally positive site-specific relationships in soil mass gains and losses, particularly for P, Ba and Ca, using the ratio of immobile elements titanium and niobium (Ti/Nb) to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials. At sites where P is enriched in surface soils relative to abundances in deeper soils, the isotope compositions of exchangeable Ca, Sr and Ba in the shallowest soil horizons (< 10 cm depth) are lighter than those of the volcanic parent materials and trend toward those of plants growing on fresh volcanic deposits. In contrast the isotope composition of exchangeable Ba in deeper soil horizons (> 10 cm depth) at those sites is consistently heavier than the volcanic parent materials. The isotope compositions of exchangeable Ca and Sr trend toward heavier compositions with depth more gradually, reflecting increasing leakiness from these soils in the order Ba < Sr < Ca and downward transfer of light biocycled Ca and Sr to deeper exchange sites. Given the long-term stability of ecosystem properties at the sites where P is enriched in surface soils, a simple box model demonstrates that persistence of isotopically light exchangeable Ca, Sr and Ba in the shallowest soil horizons requires that the uptake flux to plants from those near-surface layers is less than the recycling flux returned to the surface as

  5. Suppression of superconductivity in orthorhombic La{sub 2-x}M{sub x}CuO{sub 4} (M = Ca,Sr)

    SciTech Connect

    Dabrowski, B.; Wang, Z.; Jorgensen, J.D.; Hitterman, R.L.; Wagner, J.L.; Hunter, B.A.; Radaelli, P.G.; Hinks, D.G.

    1994-05-01

    We have extended the calcium solid-solubility limit in La{sub 2{minus}x} Ca{sub x}CuO{sub 4} to x = 0.2 using synthesis at high oxygen pressure. The superconducting transition temperature increases with doping to 34 K at x = 0.15 and is suppressed for x > 0.15, similar to the Sr-substituted material. At a fixed doping level, the optimum superconducting properties (the highest {Tc}) are found for flat and square CuO{sub 2}planes.

  6. Kinetics on Demand Is a Simple Mathematical Solution that Fits Recorded Caffeine-Induced Luminal SR Ca2+ Changes in Smooth Muscle Cells

    PubMed Central

    Perez-Rosas, Norma C.; Gomez-Viquez, Norma L.; Dagnino-Acosta, Adan; Santillan, Moises; Guerrero-Hernandez, Agustín

    2015-01-01

    The process of Ca2+ release from sarcoplasmic reticulum (SR) comprises 4 phases in smooth muscle cells. Phase 1 is characterized by a large increase of the intracellular Ca2+ concentration ([Ca2+]i) with a minimal reduction of the free luminal SR [Ca2+] ([Ca2+]FSR). Importantly, active SR Ca2+ ATPases (SERCA pumps) are necessary for phase 1 to occur. This situation cannot be explained by the standard kinetics that involves a fixed amount of luminal Ca2+ binding sites. A new mathematical model was developed that assumes an increasing SR Ca2+ buffering capacity in response to an increase of the luminal SR [Ca2+] that is called Kinetics-on-Demand (KonD) model. This approach can explain both phase 1 and the refractory period associated with a recovered [Ca2+]FSR. Additionally, our data suggest that active SERCA pumps are a requisite for KonD to be functional; otherwise luminal SR Ca2+ binding proteins switch to standard kinetics. The importance of KonD Ca2+ binding properties is twofold: a more efficient Ca2+ release process and that [Ca2+]FSR and Ca2+-bound to SR proteins ([Ca2+]BSR) can be regulated separately allowing for Ca2+ release to occur (provided by Ca2+-bound to luminal Ca2+ binding proteins) without an initial reduction of the [Ca2+]FSR. PMID:26390403

  7. High-resolution Sr/Ca records in sclerosponges calibrated to temperature in situ

    NASA Astrophysics Data System (ADS)

    Rosenheim, Brad E.; Swart, Peter K.; Thorrold, Simon R.; Willenz, Philippe; Berry, Lorraine; Latkoczy, Christopher

    2004-02-01

    Ratios of strontium to calcium have been analyzed by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in a skeletal section of the sclerosponge Ceratoporella nicholsoni. The growth period, representative of 3 yr, was stained in the skeleton with a fluorochrome (calcein). Temperatures were recorded at 2 h intervals within the shallow, cryptic reef enclosure that the sclerosponge inhabited on the northern coast of Jamaica, allowing the formulation of a direct empirical relationship between Sr/Ca and temperature. To verify this calibration, Sr/Ca ratios of two sclerosponges of the same species from depths of 67 m and 136 m in Exuma Sound, Bahamas, were analyzed by LA-ICP-MS and compared to the temperatures from these depths over a decade prior to collection. The result is an independently verified, high-resolution empirical calibration for the temperature sensitivity of Sr/Ca ratios in the aragonite skeletons of sclerosponges from Jamaica and the Bahamas. The calibration is a first for C. nicholsoni and indicates that sclerosponges are more sensitive temperature recorders than zooxanthellate corals. It represents an important step in establishing skeletal geochemistry of sclerosponges as a proxy of temperature in the upper 250 m of the ocean.

  8. 110K Bi-Sr-Ca-Cu-O superconductor oxide and method for making same

    DOEpatents

    Veal, B.W.; Downey, J.W.; Lam, D.J.; Paulikas, A.P.

    1992-12-22

    A superconductor is disclosed consisting of a sufficiently pure phase of the oxides of Bi, Sr, Ca, and Cu to exhibit a resistive zero near 110K resulting from the process of forming a mixture of Bi[sub 2]O[sub 3], SrCO[sub 3], CaCO[sub 3] and CuO into a particulate compact wherein the atom ratios are Bi[sub 2], Sr[sub 1.2-2.2], Ca[sub 1.8-2.4], Cu[sub 3]. Thereafter, heating the particulate compact rapidly in the presence of oxygen to an elevated temperature near the melting point of the oxides to form a sintered compact, and then maintaining the sintered compact at the elevated temperature for a prolonged period of time. The sintered compact is cooled and reground. Thereafter, the reground particulate material is compacted and heated in the presence of oxygen to an elevated temperature near the melting point of the oxide and maintained at the elevated temperature for a time sufficient to provide a sufficiently pure phase to exhibit a resistive zero near 110K. 7 figs.

  9. 110K Bi-Sr-Ca-Cu-O superconductor oxide and method for making same

    DOEpatents

    Veal, Boyd W.; Downey, John W.; Lam, Daniel J.; Paulikas, Arvydas P.

    1992-01-01

    A superconductor consisting of a sufficiently pure phase of the oxides of Bi, Sr, Ca, and Cu to exhibit a resistive zero near 110K resulting from the process of forming a mixture of Bi.sub.2 O.sub.3, SrCO.sub.3, CaCO.sub.3 and CuO into aparticulate compact wherein the atom ratios are Bi.sub.2, Sr.sub.1.2-2.2, Ca.sub.1.8-2.4, Cu.sub.3. Thereafter, heating the particulate compact rapidly in the presence of oxygen to an elevated temperature near the melting point of the oxides to form a sintered compact, and then maintaining the sintered compact at the elevated temperature for a prolonged period of time. The sintered compact is cooled and reground. Thereafter, the reground particulate material is compacted and heated in the presence of oxygen to an elevated temperature near the melting point of the oxide and maintained at the elevated temperature for a time sufficient to provide a sufficiently pure phase to exhibit a resistive zero near 110K.

  10. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    PubMed Central

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-01-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis. PMID:26907515

  11. Addition of Zn to the ternary Mg-Ca-Sr alloys significantly improves their antibacterial property

    PubMed Central

    He, Guanping; Wu, Yuanhao; Zhang, Yu; Zhu, Ye; Liu, Yang; Li, Nan; Li, Mei; Zheng, Guan; He, Baohua; Yin, Qingshui; Zheng, Yufeng; Mao, Chuanbin

    2015-01-01

    Most of the magnesium (Mg) alloys possess excellent biocompatibility, mechanical property and biodegradability in orthopedic applications. However, these alloys may suffer from bacterial infections due to their insufficient antibacterial capability. In order to reduce the post-surgical infections, a series of biocompatible Mg–1Ca-0.5Sr-xZn (x=0, 2, 4, 6) alloys were fabricated with the addition of antibacterial Zn with variable content and evaluated in terms of their biocompatibility and antibacterial property. The in vitro corrosion study showed that Mg-1Ca-0.5Sr-6Zn alloys exhibited a higher hydrogen evolution volume after 100 h immersion and resulted in a higher pH value of the immersion solution. Our work indicated that Zn-containing Mg alloys exhibited good biocompatibility with high cell viability. The antibacterial studies reveal that the number of bacteria adhered on all of these Mg alloy samples diminished remarkably compared to the Ti-6Al-4V control group. We also found that the proliferation of the bacteria was inhibited by these Mg alloys extracts. Among the prepared alloys, Mg-1Ca-0.5Sr-6Zn alloy not only exhibited a strong antibacterial effect, but also promoted the proliferation of MC3T3-E1 osteoblasts, suggesting that it is a promising alloy with both good antibacterial property and good biocompatibility for use as an orthopedic implant. PMID:26693010

  12. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    NASA Astrophysics Data System (ADS)

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-02-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis.

  13. Genesis of basalt magmas and their derivatives under the Izu Islands, Japan, inferred from Sr/Ca-Ba/Ca systematics

    NASA Astrophysics Data System (ADS)

    Onuma, Naoki; Hirano, Masataka; Isshiki, Naoki

    1983-10-01

    The Sr/Ca-Ba/Ca systematics defined for a series of volcanic rocks provided by volcanoes of the Izu Islands, Japan, have cast a new light on the origin and evolution of basalt magmas and their derivatives: (1) The mantle material in the source region of primary basalt magmas beneath the Izu Islands shows a chondritic value of Sr/Ca and Ba/Ca ratios. (2) Both the tholeiite magma and the high-alumina/calc-alkali basalt magma are primary with higher degrees (15-20% for the former) and lower degrees (8-11% for the latter) of partial melting of a common mantle material. (3) The primary basalt magmas evolve independently via crystal fractionation process in respective magma chambers at shallower depths each providing a series of andesite and dacite magmas corresponding to respective primary basalt magmas. (4) The crystal fractionation process in magma chamber is controlled mainly by plagioclase and clinopyroxene crystallization in terms of the alkaline earth elements. The plagioclase/clinopyroxene ratio decreases during crystal fractionation process. The chemical environments of magma chambers are similar to each other in the tholeiite series and in the high-alumina basalt/calc-alkali rock series. (5) The end products provided by the crystal fractionation process lie within Bowen's petrogeny's residua system, making a thin, silicic crust under the volcanic islands near the Izu Peninsula. The calc-alkali rhyolites in these islands are derived from the thin silicic crust via melting process by the heat of intruded primary basalt magmas. (6) The regional distribution of degree of partial melting indicates variations from 15 to 20% along the volcanic front and from 8 to 11% in the region behind it. The fact suggests that an interaction between the mantle wedge under the Philippine Sea Plate and the subducting slab of the Pacific Plate beneath the Izu Islands is different from place to place, with respect to temperature distribution and/or water supply from the subducting

  14. Store-operated Ca2+ entry and depolarization explain the anomalous behaviour of myometrial SR: Effects of SERCA inhibition on electrical activity, Ca2+ and force

    PubMed Central

    Noble, Debbie; Borysova, Lyudmyla; Wray, Susan; Burdyga, Theodor

    2014-01-01

    In the myometrium SR Ca2+ depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca2+ sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca2+-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca2+ transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 μM), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca2+]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca2+ spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca2+ and depolarization continued a point was reached when electrical and Ca2+ spikes and phasic contractions ceased, and a maintained, tonic force and Ca2+ was produced. Lanthanum, a non-selective blocker of store-operated Ca2+ entry, but not the L-type Ca2+ channel blocker nifedipine (1–10 μM), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca2+ depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca2+ release is coupled to marked Ca2+ entry, via store operated Ca2+ channels, leading to depolarization and enhanced electrical and mechanical activity. PMID:25084623

  15. Seasonal dripwater Mg/Ca and Sr/Ca variations driven by cave ventilation: Implications for and modeling of speleothem paleoclimate records

    USGS Publications Warehouse

    Wong, C.I.; Banner, J.L.; Musgrove, M.

    2011-01-01

    A 4-year study in a central Texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites. We monitored cave-air compositions, in situ calcite growth, dripwater composition and drip rate every 4-6weeks. Three groups of drip sites are delineated (Groups 1-3) based on geochemical variations in dripwater composition. Quantitative modeling of mineral-solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions. The covariation of Mg/Ca (and Sr/Ca) and Sr isotopes is key in delineating whether Mg/Ca and Sr/Ca variations are dictated by water-rock interaction (i.e., calcite or dolomite recrystallization) or prior calcite precipitation (PCP). Group 1 dripwater compositions reflects a narrow range of the extent of water-rock interaction followed by varying amounts of prior calcite precipitation (PCP). Group 2 dripwater compositions are controlled by varying amounts of water-rock interaction with little to no PCP influence. Group 3 dripwater compositions are dictated by variable extents of both water-rock interaction and PCP. Group 1 drip sites show seasonal variations in dripwater Mg/Ca and Sr/Ca, whereas the other drip sites do not. In contrast to the findings of most previous dripwater Mg/Ca-Sr/Ca studies, these seasonal variations (at Group 1 drip sites) are independent of changes in water flux (i.e., rainfall and/or drip rate), and instead significantly correlate with changes in cave-air CO2 concentrations. These results are consistent with lower cave-air CO2, related to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading to dripwater geochemical evolution via PCP. Group 1 dripwater Mg/Ca and Sr/Ca seasonality and evidence for PCP as a mechanism that can account for that seasonality, have two implications for many other regions where seasonal ventilation of caves

  16. Seasonal dripwater Mg/Ca and Sr/Ca variations driven by cave ventilation: Implications for and modeling of speleothem paleoclimate records

    NASA Astrophysics Data System (ADS)

    Wong, Corinne I.; Banner, Jay L.; Musgrove, MaryLynn

    2011-06-01

    A 4-year study in a central Texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites. We monitored cave-air compositions, in situ calcite growth, dripwater composition and drip rate every 4-6 weeks. Three groups of drip sites are delineated (Groups 1-3) based on geochemical variations in dripwater composition. Quantitative modeling of mineral-solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions. The covariation of Mg/Ca (and Sr/Ca) and Sr isotopes is key in delineating whether Mg/Ca and Sr/Ca variations are dictated by water-rock interaction (i.e., calcite or dolomite recrystallization) or prior calcite precipitation (PCP). Group 1 dripwater compositions reflects a narrow range of the extent of water-rock interaction followed by varying amounts of prior calcite precipitation (PCP). Group 2 dripwater compositions are controlled by varying amounts of water-rock interaction with little to no PCP influence. Group 3 dripwater compositions are dictated by variable extents of both water-rock interaction and PCP. Group 1 drip sites show seasonal variations in dripwater Mg/Ca and Sr/Ca, whereas the other drip sites do not. In contrast to the findings of most previous dripwater Mg/Ca-Sr/Ca studies, these seasonal variations (at Group 1 drip sites) are independent of changes in water flux (i.e., rainfall and/or drip rate), and instead significantly correlate with changes in cave-air CO 2 concentrations. These results are consistent with lower cave-air CO 2, related to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading to dripwater geochemical evolution via PCP. Group 1 dripwater Mg/Ca and Sr/Ca seasonality and evidence for PCP as a mechanism that can account for that seasonality, have two implications for many other regions where seasonal ventilation of

  17. An assessment of the Sr/Ca ratio in shallow water hermatypic corals as a proxy for sea surface temperature

    NASA Astrophysics Data System (ADS)

    Marshall, John F.; McCulloch, Malcolm T.

    2002-09-01

    The high precision measurement of the Sr/Ca ratio in corals has the potential for measuring past sea surface temperatures at very high accuracy. However, the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the Sr/Ca ratio of seawater, and that kinetic effects, such as the calcification rate, can affect the Sr/Ca ratio of corals, and produce inaccuracies of the order of 2-4 °C. In the present study, a number of cores of the massive hermatypic scleractinian coral Porites, from the central Great Barrier Reef, have been analyzed for Sr/Ca at weekly to monthly resolution. Results from a 24 year record from Myrmidon Reef show an overall variation from 22.7 °C to 30.4 °C. The record shows a warming/cooling trend with maximum warming centred on the 1986-1987 summer. While some bleaching was reported to have occurred at Myrmidon Reef in 1982, the Sr/Ca record indicates that subsequent summer temperatures were much higher. The 4.5 year record from Stanley Reef shows a maximum SST of 30 °C during the 1997-1998 El Niño event. The calibrations from Myrmidon and Stanley Reefs are in excellent agreement with previously published calibrations from nearby reefs. While corals do not calcify in equilibrium with seawater due to physiological control on the uptake of Sr and Ca into the lattice of coralline aragonite, it can be argued that, provided only a single genus such as Porites sp. is used, and that the coral is sampled along a major vertical growth axis, then the Sr/Ca ratio should vary uniformly with temperature. Similarly, objections based on the spatial and temporal variability of the Sr/Ca activity ratio of seawater can be countered on the basis that in most areas where coral reefs grow there is a uniformity in the Sr/Ca activity ratio, and there does not appear to be a change in this ratio over the growth period of the coral. Evidence from several corals in this study suggest that stress can be a major

  18. A first principles study on newly proposed (Ca/Sr/Ba)Fe2Bi2 compounds with their parent compounds

    NASA Astrophysics Data System (ADS)

    Sundareswari, M.; Jayalakshmi, D. S.; Viswanathan, E.

    2016-02-01

    The structural, electronic, bonding and magnetic properties of newly proposed iron-based compounds viz., CaFe2Bi2, SrFe2Bi2, BaFe2Bi2 with their Fermi surface topology are reported here for the first time by means of first principles calculation. All these properties of newly proposed compounds are compared and analysed along with their respective parent compounds namely (Ca,Sr,Ba)Fe2As2.

  19. An apparent "vital effect" of calcification rate on the Sr/Ca temperature proxy in the reef coral Montipora capitata

    USGS Publications Warehouse

    Kuffner, Ilsa; Jokiel, Paul L.; Rodgers, Kuulei; Andersson, Andreas; Mackenzie, Fred T.

    2012-01-01

    Measuring the strontium to calcium ratio in coral skeletons reveals information on seawater temperatures during skeletal deposition, but studies have shown additional variables may affect the ratio. Here we measured Sr/Ca in the reef coral, Montipora capitata, grown in six mesocosms continuously supplied with seawater from the adjacent reef flat. Three mesocosms were ambient controls, and three had seawater chemistry simulating "ocean acidification" (OA). We found that Sr/Ca was not affected by the OA treatment, and neither was coral calcification for these small colonies (larger colonies did show an OA effect). The lack of OA effects allowed us to test the hypothesis that coral growth rate can affect Sr/Ca using the natural range in calcification rates of the corals grown at the same temperature. We found that Sr/Ca was inversely related to calcification rate (Sr/Ca = 9.39 - 0.00404 mmol/mol * mg day-1 cm-2, R2 = 0.32). Using a previously published calibration curve for this species, a 22 mg day-1 colony-1 increase in calcification rate introduced a 1°C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9, with mean 26.6 ± 0.9°C SD. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

  20. Structural and magnetic properties of La–Co substituted Sr–Ca hexaferrites synthesized by the solid state reaction method

    SciTech Connect

    Yang, Yujie; Liu, Xiansong Jin, Dali; Ma, Yuqi

    2014-11-15

    Graphical abstract: The change of the remanence (B{sub r}) and intrinsic coercivity (H{sub cj}) with La content (x) and Co content (y) of hexagonal ferrite Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} magnets. - Highlights: • Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} hexaferrites were synthesized by the solid state reaction method. • B{sub r} continuously increases with increasing dopant contents. • H{sub cb}, H{sub cj} and (BH){sub max} for the magnets first increases and then decreases with an increase in the La–Co contents. - Abstract: Hexagonal ferrite Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} (x = 0.05–0.50; y = 0.04–0.40) magnetic powders and magnets were synthesized by the solid state reaction method. X-ray diffraction was employed to determine the phase compositions of the magnetic powders. There is a single magnetoplumbite phase in the magnetic powders with the substitution of La (0.05 ≤ x ≤ 0.15) and Co (0.04 ≤ y ≤ 0.12) contents. For the magnetic powders containing La (x ≥ 0.20) and Co (y ≥ 0.16), magnetic impurities begin to appear in the structure. A field emission scanning electron microscope was used to characterize the micrographs of the magnets. The magnets have formed hexagonal structures. Magnetic properties of the magnets were measured by a magnetic properties test instrument. The remanence continuously increases with increasing dopant contents. Whereas, the magnetic induction coercivity, intrinsic coercivity and maximum energy product for the magnets first increases and then decreases with an increase in the La–Co contents.

  1. Plant uptake of cations under nutrient limitation: An environmental tracer study using Ca/Sr and K/Rb ratios

    NASA Astrophysics Data System (ADS)

    Shi, Z.; Keller, C. K.; Stacks, D.; Grant, M.; Harsh, J. B.; Letourneau, M.; Gill, R. A.; Balogh-Brunstad, Z.; Thomashow, L.; Dohnalkova, A.

    2012-12-01

    Vascular plant growth builds soils and ecosystem nutrient capital by sequestering and partitioning atmospheric CO2 into organic matter and continental runoff and driving terrestrial water and energy balances. Plant root-system functions, e.g. nutrient mobilization and uptake, are altered by environmental stress. However, the stress-response relationships are poorly understood. Chemical tracers have potential for assessing contributions of nutrients from various nutrient pools. Our objective is to quantitatively study how varying degrees of nutrient limitation (and corresponding needs to extract base cations from mineral sources) influence Ca and K uptake functions in a plant-root-mineral system. We are studying plant-driven mineral weathering in column experiments with red pine (Pinus resinosa) seedlings. The columns contain quartz sand amended with anorthite and biotite that constitute the sole mineral sources of Ca and K. These minerals also contain known amounts of Sr and Rb, which exhibit chemical behavior similar to Ca and K, respectively. The solution source of Ca and K was varied by adding 0% (no dissolved Ca and K), 10%, 30%, or 100% of a full strength Ca and K nutrient solution through irrigation water in which both Sr and Rb concentrations were negligible. Selected columns were destructively sampled at 3, 6 and 9 months to harvest biomass and measure plant uptake of cations. We used Ca/Sr and K/Rb ratio results to estimate the contributions of Ca and K from mineral and solution sources. For the 0% nutrient treatment, the Ca/Sr and K/Rb ratios in total biomass at 3 months, compared with those in the mineral phases, suggested preferential uptake of Ca and K over Sr and Rb, respectively, and allowed us to determine uptake discrimination factors for both cations. The K/Rb ratios in total biomass increased with greater K availability in the solution source, as expected, but Ca/Sr ratios did not show any dependence on Ca availability in the solution source

  2. (Sr1-xNax)(Cd1-xMnx)2As2: A new charge and spin doping decoupled diluted magnetic semiconductors with CaAl2Si2-type structure

    NASA Astrophysics Data System (ADS)

    Chen, Bijuan; Deng, Zheng; Li, Wenmin; Gao, Moran; Li, Zhi; Zhao, Guoqiang; Yu, Shuang; Wang, Xiancheng; Liu, Qingqing; Jin, Changqing

    2016-08-01

    We report the synthesis and characterization of a new bulk diluted ferromagnetic semiconductor via Na and Mn co-doping in SrCd2As2 with a hexagonal CaAl2Si2-type structure. Together with carrier doping via (Sr,Na) substitution, spin doping via (Cd,Mn) substitution results in ferromagnetic order with Curie temperature of TC up to 13 K. Negative magnetoresistance is assigned to weak localization at low temperatures, where the magnetization of samples becomes saturated. The hexagonal structure of (Sr1-xNax)(Cd1-xMnx)2As2 can be acted as a promising candidate for spin manipulations owing to its relatively small coercive field of less than 24 Oe.

  3. Trace metal (Mg/Ca and Sr/Ca) analyses of single coccoliths by Secondary Ion Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Prentice, Katy; Jones, Tom Dunkley; Lees, Jackie; Young, Jeremy; Bown, Paul; Langer, Gerald; Fearn, Sarah; EIMF

    2014-12-01

    Here we present the first multi-species comparison of modern and fossil coccolith trace metal data obtained from single liths. We present both trace metal analyses (Sr, Ca, Mg and Al) and distribution maps of individual Paleogene fossil coccoliths obtained by Secondary Ion Mass Spectrometry (SIMS). We use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite. The analysis of coccoliths from deep-ocean sediments spanning the Eocene/Oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments. Instead, where present, diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite. Diagenetic overgrowths on coccoliths are easily distinguished in SIMS analyses on the basis of relatively higher Mg and lower Sr concentrations than co-occurring primary coccolith calcite. This interpretation is confirmed by the comparable SIMS analyses of modern cultured coccoliths of Coccolithus braarudii. Further, with diagenetic calcite overgrowth being the principle source of bias in coccolith-based geochemical records, we infer that lithologies with lower carbonate content, deposited below the palaeo-lysocline, are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate-rich sediments where overgrowth is ubiquitous. The preservation of primary coccolith carbonate in low-carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism.

  4. Luminescence Properties of SrCaS:Cu Thin Film Phosphors

    NASA Astrophysics Data System (ADS)

    Mohammed, Edris; Park, Won; Tong, Wusheng; Stock, Stuart; Summers, Chris

    2000-03-01

    Luminescence Properties of SrxCa1-xS:Cu Thin Film Phosphors E. Mohammed, W. Park, W. Tong, S. Stock and C. J. Summers Phosphor Technology Center of Excellence Georgia Institute of Technology, Atlanta, GA 30332-0560 The luminescence properties of MBE grown thin film SrCaS:Cu phosphors are investigated. 10K photoluminescence (PL) results showed a broad emission band of Cu that shifted between 2.98eV and 2.58eV, with a large increase in linewidth ranging from 0.36eV for CaS:Cu to 0.49eV as the Sr composition was increased. The significant increase in linewidth suggested that the broad emission band of Cu was composed of two closely spaced bands suggesting a possible spin-orbit or Jahn-Teller splitting of the emitting level. Curve fitting of the 10K PL showed that the splitting varied from 100meV for x=0 to 240 meV for x=0.98. In the excitation spectra, the optical absorption edge shifted from 5.1eV to 4.7eV while the energies of the two direct excitation bands of Cu shifted from 4.4 to 4.8eV and 4.0 to 4.2eV respectively. The crystal field parameter 10Dq obtained from experiments showed a linear as the composition of Sr was varied between x=0 to x=0.98 and the result was in excellent agreement with crystal field calculations.

  5. Flux pinning by precipitates in the Bi-Sr-Ca-Cu-O system

    DOEpatents

    Shi, Donglu

    1992-01-01

    A fundamental pinning mechanism has been identified in the Bi-Sr-Ca-Cu-O system. The pinning strength has been greatly increased by the introduction of calcium- and copper-rich precipitates into the sample matrix. The calcium and copper are supersaturated in the system by complete melting, and the fine calcium and copper particles precipitated during subsequent crystallization anneal to obtain the superconducting phases. The intragrain critical current density has been increased from the order of 10.sup.5 A/cm.sup.2 to 10.sup.7 A/cm.sup.2 at 5 T.

  6. New method for fabrication of superconducting pipes in the Bi-Sr-Ca-Cu-O system

    NASA Astrophysics Data System (ADS)

    Abe, Yoshihiro; Hosono, Hideo; Lee, Won-Hyuk; Hosoe, Masahiro; Nakamura, Koichi; Inukai, Eikichi

    1993-01-01

    Pipes or hollow cylinders in the Bi-Sr-Ca-Cu-O system were found to be fabricated easily by inspiring or sucking the low viscosity melt into a cold silica glass tube. The outer part of the cast rod-like melt solidified, and the inner hot low-viscosity part of the rod melt was expired. The precursor pipes were reheated at 800 C for 50 h in air, resulting in the formation of superconducting (Tc = 87 K) pipes which were of smooth surface without machining and high bending strength (100-150 MPa).

  7. The growth and characterization of Pb-doped Bi-Sr-Ca-Cu-O thin films

    SciTech Connect

    Tseng, M.R.; Chu, J.J.; Huang, Y.T.; Wu, P.T. ); Wang, W.N. )

    1990-03-01

    The growth and characterization of Bi-Pb-Sr-Ca-Cu-O films on single-crystal (001)MgO substrates by rf magnetron sputtering with a single target are reported. The comparison of different post-annealing conditions revealed that the film annealed under controlled Pb potential gave best superconducting properties with {ital T}{sub {ital c}0} above 105 K. The proper doping of Pb not only accelerated the formation of the high-{ital T}{sub {ital c}} phase, but also improved the connectivity of high-{ital T}{sub {ital c}} grains.

  8. Photoluminescence in the Ca{sub x}Sr{sub 1-x}WO{sub 4} system at room temperature

    SciTech Connect

    Porto, S.L.; Longo, E.; Simoes, L.G.P.; Lima, S.J.G.; Ferreira, J.M.; Soledade, L.E.B.; Espinoza, J.W.M.; Cassia-Santos, M.R.; Maurera, M.A.M.A.; Paskocimas, C.A.; Santos, I.M.G. Souza, A.G.

    2008-08-15

    In this work, a study was undertaken about the structural and photoluminescent properties, at room temperature, of powder samples from the Ca{sub x}Sr{sub 1-x}WO{sub 4} (x=0-1.0) system, synthesized by a soft chemical method and heat treated between 400 and 700 deg. C. The material was characterized using Infrared, UV-vis and Raman spectroscopy and XRD. The most intense PL emission was obtained for the sample calcined at 600 deg. C, which is neither highly disordered (400-500 deg. C), nor completely ordered (700 deg. C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO{sub 4} or SrWO{sub 4}, but for Ca{sub 0.6}Sr{sub 0.4}WO{sub 4}. The PL emission spectra could be separated into two Gaussian curves. The lower wavelength peak is placed around 530 nm, and the higher wavelength peak at about 690 nm. Similar results were reported in the literature for both CaWO{sub 4} and SrWO{sub 4}. - Graphical abstract: The structural and room temperature photoluminescence of Ca{sub x}Sr{sub 1-x}WO4 synthesized by a soft chemical method was studied. The most intense PL emission was obtained for the sample calcined at 600 deg. C, that is neither highly disordered (400-500 deg. C), nor completely ordered (700 deg. C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO{sub 4} or SrWO{sub 4}, but for Ca{sub 0.6}Sr{sub 0.4}WO{sub 4}.

  9. First-principles study on the structural, electronic, and optical properties of Ca1- x Sr x Se alloys

    NASA Astrophysics Data System (ADS)

    Ahmadian, F.; Salary, A.

    2016-01-01

    The structural, electronic, and optical properties of binary CaSe and SrSe compounds and Ca1- x Sr x Se alloys were studied by using the full potential linearized augmented plane wave (FPLAPW) method within density functional theory (DFT). The band structure calculations showed that the CaSe and the SrSe binary compounds in the rocksalt (RS), zinc-blende (ZB) and wurtzite (WZ) phases were semiconductors while they had a metallic characteristic in the CsCl phase. The lattice constant and bulk modulus values for the Ca1- x Sr x Se alloys in the RS and the ZB phases at different concentrations were calculated and compared with those obtained by using Vegard's law. The energy band gap values in the RS and the ZB phases were estimated for different x values by using both define acronyms the Perdew, Burke, and Ernzerhof (PBE-GGA) and the Engel and Vosko (EV-GGA) schemes, and the results were compared with those obtained by using the empirical electronegativity expression. The band gap bowing parameters were calculated by using quadratic functions and the procedure of Bernard and Zunger to fit the non-linear variation of the band gaps. The static dielectric constant ɛ 1(0) was calculated at different concentrations. The energy loss function L( ω) for the Ca1- x Sr x Se alloys in the RS and the ZB phases has a main peak corresponding to the plasmon frequency. The values of the static refractive index ( n(0)) for the Ca1- x Sr x Se alloys were calculated and compared with the values predicted by using the Moss, Ravindra, and Vandamme models. Finally, the extinction indic incident photon energies. es ( k( ω)) and the reflectivities ( R( ω)) for the Ca1- x Sr x Se alloys were calculated within a wide range of incident photon energies.

  10. Local atomic configuration and Auger Valence Electron Spectra in BiSrCaCuO single crystals

    SciTech Connect

    Fujiwara, Y.; Hirata, S.; Nishikubo, M.; Kobayashi, T. ); Nakayama, H.; Fujita, H. . Faculty of Engineering)

    1991-03-01

    This paper reports on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) and Ca-doped Bi{sub 2}Sr{sub 2}CuO{sub y} (2201) single crystals systematically investigated by Auger Valence Electron Spectroscopy (AVES). In AVES measurements on two kinds of crystals, a drastic difference was observed in the spectral shape of Ca(2p,3p,3p), reflecting a difference in spin-orbit splitting induced by local atomic configuration in the vicinity of Ca atoms. Furthermore, Ca(2p,3p,4s) spectrum appeared in both the crystals, which indicates that the real valency of Ca atoms is deviated from + 2 in the crystals. These results suggest that AVES is a promising probe for characterizing local atomic configuration and valence electron states of the constituent elements.

  11. Coupled magnetic and elastic properties in LaPr(CaSr)MnO manganites

    NASA Astrophysics Data System (ADS)

    Eslava, G. G.; Parisi, F.; Bernardo, P. L.; Quintero, M.; Leyva, G.; Cohen, L. F.; Ghivelder, L.

    2016-09-01

    We investigate a series of manganese oxides, the La0.225Pr0.4(Ca1-xSrx)0.375MnO3 system. The x = 0 sample is a prototype compound for the study of phase separation in manganites, where ferromagnetic and charge ordered antiferromagnetic phases coexist. Replacing Ca2+ by Sr2+ gradually turns the system into a homogeneous ferromagnet. Our results show that the material structure plays a major role in the observed magnetic properties. On cooling, at temperatures below ∼ 100 K, a strong contraction of the lattice is followed by an increase in the magnetization. This is observed both through thermal expansion and magnetostriction measurements, providing distinct evidence of magneto-elastic coupling in these phase separated compounds.

  12. Sr/Ca ratios in cold-water corals - a 'low-resolution' temperature archive?

    NASA Astrophysics Data System (ADS)

    Rüggeberg, Andres; Riethdorf, Jan-Rainer; Raddatz, Jacek; López Correa, Matthias; Montagna, Paolo; Dullo, Wolf-Christian; Freiwald, André

    2010-05-01

    One of the basic data to understand global change and past global changes is the measurement and the reconstruction of temperature of marine water masses. E.g. seawater temperature controls the density of seawater and in combination with salinity is the major driving force for the oceans circulation system. Geochemical investigations on cold-water corals Lophelia pertusa and Desmophyllum cristagalli indicated the potential of these organisms as high-resolution archives of environmental parameters from intermediate and deeper water masses (Adkins and Boyle 1997). Some studies tried to use cold-water corals as a high-resolution archive of temperature and salinity (Smith et al. 2000, 2002; Blamart et al. 2005; Lutringer et al. 2005). However, the fractionation of stable isotopes (delta18O and delta13C) and element ratios (Sr/Ca, Mg/Ca, U/Ca) are strongly influenced by vital effects (Shirai et al. 2005; Cohen et al. 2006), and difficult to interpret. Nevertheless, ongoing studies indicate the potential of a predominant temperature dependent fractionation of distinct isotopes and elements (e.g. Li/Ca, Montagna et al. 2008; U/Ca, Mg/Ca, delta18O, Lòpez Correa et al. 2008; delta88/86Sr, Rüggeberg et al. 2008). Within the frame of DFG-Project TRISTAN and Paläo-TRISTAN (Du 129/37-2 and 37-3) we investigated live-collected specimens of cold-water coral L. pertusa from all along the European continental margin (Northern and mid Norwegian shelves, Skagerrak, Rockall and Porcupine Bank, Galicia Bank, Gulf of Cadiz, Mediterranean Sea). These coral samples grew in waters characterized by temperatures between 6°C and 14°C. Electron Microprobe investigations along the growth direction of individual coral polyps were applied to determine the relationship between the incorporation of distinct elements (Sr, Ca, Mg, S). Cohen et al. (2006) showed for L. pertusa from the Kosterfjord, Skagerrak, that ~25% of the coral's Sr/Ca ratio is related to temperature, while 75% are influenced

  13. A coral Sr/Ca calibration and replication study of two massive corals from the Gulf of Mexico

    USGS Publications Warehouse

    DeLong, Kristine L.; Flannery, Jennifer A.; Maupin, Christopher R.; Poore, Richard Z.; Quinn, Terrence M.

    2011-01-01

    This study examined the variations in the ratio of strontium-to-calcium (Sr/Ca) for two Atlantic corals (Montastraea faveolata and Siderastrea siderea) from the Dry Tortugas National Park (centered on 24.7°N, 82.8°W) in the Gulf of Mexico. Cores from coral colonies in close proximity (10s of meters) and with the same environmental conditions (i.e., depth and water chemistry) were micro-sampled with approximately monthly resolution and the resulting Sr/Ca variations were calibrated with local sea surface temperature (SST) records. Replication tests for coral Sr/Ca variations found high agreement between intra-colony variations and between individual colonies of S. siderea (a single M. faveolata colony was sampled). Regression analysis of monthly variations in coral Sr/Ca and local SST revealed significant correlation on monthly and inter-annual timescales. Verification of the calibration on different timescales found coral Sr/Ca–SST reconstructions in S. siderea were more accurate than those from M. faveolata, especially on inter-annual timescales. Sr/Ca–SST calibration equations for the two species are significantly different (cf., Sr/Ca = -0.042 SST + 10.070, S. siderea; Sr/Ca = -0.027 SST + 9.893, M. faveolata). Mean linear extension for M. faveolata is approximately twice that of S. siderea (4.63, 4.31, and 8.31 mm year−1, A1, F1, and B3, respectively); however, seasonal Sr/Ca variability in M. faveolata is less than S. siderea (0.323, 0.353, and 0.254 mmol mol−1, A1, F1, and B3, respectively). The reduced slope for M. faveolata is attributed to physical sampling issues associated with complex time-skeletal structure of M. faveolata, i.e., a sampling effect, and not a growth effect since the faster growing M. faveolata has the reduced Sr/Ca variability.

  14. Relation Between Simultaneous Ca and Sr Transport Rates in Isolated Segments of Vetch, Barley, and Pine Roots 1

    PubMed Central

    Hutchin, Maxine E.; Vaughan, Burton E.

    1968-01-01

    Root segments of vetch, barley, and pine were exposed to a nutrient solution containing 85Sr and 45Ca tracers. Translocation was measured from solutions containing stable ions at concentrations of 2.5 mm Ca, and at either 0.5 mm or 2.5 mm Sr. Polar transport was established between 12 and 18 hr in barley, and between 16 and 22 hr in vetch. Acropetal transport remained below 5% of basipetal transport of tracer during these intervals. Transport in both vetch and barley usually declined before an elapsed time of 24 hr unlike corn, which maintained its steady state beyond 24 hr. Pine was radically different in that it showed no difference between acropetal and basipetal transport rates and had very low rates. Sr transport in all plants studied to date paralleled that of Ca and the ratio Sr:Ca transported was equal to the ratio Sr:Ca in the nutrient. In vetch, stable Ca transport was reduced to one-fifth when Sr concentration was increased from 0.5 mm to 2.5 mm. Yet stable Sr transport did not change, indicating that the effect on transport was not due to competitive inhibition. A similar effect was less pronounced in barley, but could not be detected in pine. The magnitude of the transport rates varied considerably among the various species, corn having the greatest followed by barley, vetch, and pine in decreasing order. Transport did not correlate with root weight or surface area; it amounted to from 0.03 to 0.60 nanomoles per hr in these experiments as compared to 7 nanomoles per hr previously established in corn (in all cases, 55 mm segments, sectioned 10 mm from apex). Images PMID:5725599

  15. Acropora interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high-resolution paleothermometer

    NASA Astrophysics Data System (ADS)

    Sadler, James; Nguyen, Ai D.; Leonard, Nicole D.; Webb, Gregory E.; Nothdurft, Luke D.

    2016-04-01

    The majority of coral geochemistry-based paleoclimate reconstructions in the Indo-Pacific are conducted on selectively cored colonies of massive Porites. This restriction to a single genus may make it difficult to amass the required paleoclimate data for studies that require deep reef coring techniques. Acropora, however, is a highly abundant coral genus in both modern and fossil reef systems and displays potential as a novel climate archive. Here we present a calibration study for Sr/Ca ratios recovered from interbranch skeleton in corymbose Acropora colonies from Heron Reef, southern Great Barrier Reef. Significant intercolony differences in absolute Sr/Ca ratios were normalized by producing anomaly plots of both coral geochemistry and instrumental water temperature records. Weighted linear regression of these anomalies from the lagoon and fore-reef slope provide a sensitivity of -0.05 mmol/mol °C-1, with a correlation coefficient (r2 = 0.65) comparable to those of genera currently used in paleoclimate reconstructions. Reconstructions of lagoon and reef slope mean seasonality in water temperature accurately identify the greater seasonal amplitude observed in the lagoon of Heron Reef. A longer calibration period is, however, required for reliable reconstructions of annual mean water temperatures.

  16. Influence of cetyltrimethylammonium bromide on the morphology of AWO 4 (A = Ca, Sr) prepared by cyclic microwave irradiation

    NASA Astrophysics Data System (ADS)

    Thongtem, Titipun; Kaowphong, Sulawan; Thongtem, Somchai

    2008-09-01

    AWO 4 (A = Ca, Sr) was prepared from metal salts [Ca(NO 3) 2·4H 2O or Sr(NO 3) 2], Na 2WO 4·2H 2O and different moles of cetyltrimethylammonium bromide (CTAB) in water by cyclic microwave irradiation. The structure of AWO 4 was characterized by X-ray diffraction (XRD) and selected area electron diffraction (SAED). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the presence of nanoparticles in clusters with different morphologies; spheres, peaches with notches, dumb-bells and bundles, influenced by CTAB. Six Raman vibrational peaks of scheelite structure were detected at 908, 835, 793, 399, 332 and 210 cm -1 for CaWO 4 and 917, 833, 795, 372, 336 and 192 cm -1 for SrWO 4, which are assigned as ν1(A g), ν3(B g), ν3(E g), ν4(B g), ν2(A g) and νf.r.(A g), respectively. Fourier transform infrared (FTIR) spectra provided the evidence of W-O stretching vibration in [WO 4] 2- tetrahedrons at 793 cm -1 for CaWO 4 and 807 cm -1 for SrWO 4. The peaks of photoluminescence (PL) spectra were at 428-434 nm for CaWO 4, and 447-451 nm for SrWO 4.

  17. Calcium Sensing Receptor (CaSR) activation elevates proinflammatory factor expression in human adipose cells and adipose tissue

    PubMed Central

    Cifuentes, Mariana; Fuentes, Cecilia; Acevedo, Ingrid; Villalobos, Elisa; Hugo, Eric; Ben Jonathan, Nira; Reyes, Marcela

    2013-01-01

    We have previously established that human adipose cells and the human adipose cell line LS14 express the calcium sensing receptor (CaSR) and that its expression is elevated upon exposure to inflammatory cytokines that are typically elevated in obese humans. Research in recent years has established that an important part of the adverse metabolic and cardiovascular consequences of obesity derive from a dysfunction of the tissue, one of the mechanisms being a disordered secretion pattern leading to an excess of proinflammatory cytokines and chemokines. Given the reported association of the CaSR to inflammatory processes in other tissues, we sought to evaluate its role elevating the adipose expression of inflammatory factors. We exposed adipose tissue and in-vitro cultured LS14 preadipocytes and differentiated adipocytes to the calcimimetic cinacalcet and evaluated the expression or production of the proinflammatory cytokines IL6, IL1β and TNFα as well as the chemoattractant factor CCL2. CaSR activation elicited an elevation in the expression of the inflammatory factors, which was in part reverted by SN50, an inhibitor of the inflammatory mediator NFκB. Our observations suggest that CaSR activation elevates cytokine and chemokine production through a signaling pathway involving activation of NFκB nuclear translocation. These findings confirm the relevance of the CaSR in the pathophysiology of obesity-induced adipose tissue dysfunction, with an interesting potential for pharmacological manipulation in the fight against obesity- associated diseases. PMID:22449852

  18. Sr/Ca ratios in cold-water corals - a 'low-resolution' temperature archive?

    NASA Astrophysics Data System (ADS)

    Rüggeberg, Andres; Riethdorf, Jan-Rainer; Raddatz, Jacek; López Correa, Matthias; Montagna, Paolo; Dullo, Wolf-Christian; Freiwald, André

    2010-05-01

    One of the basic data to understand global change and past global changes is the measurement and the reconstruction of temperature of marine water masses. E.g. seawater temperature controls the density of seawater and in combination with salinity is the major driving force for the oceans circulation system. Geochemical investigations on cold-water corals Lophelia pertusa and Desmophyllum cristagalli indicated the potential of these organisms as high-resolution archives of environmental parameters from intermediate and deeper water masses (Adkins and Boyle 1997). Some studies tried to use cold-water corals as a high-resolution archive of temperature and salinity (Smith et al. 2000, 2002; Blamart et al. 2005; Lutringer et al. 2005). However, the fractionation of stable isotopes (delta18O and delta13C) and element ratios (Sr/Ca, Mg/Ca, U/Ca) are strongly influenced by vital effects (Shirai et al. 2005; Cohen et al. 2006), and difficult to interpret. Nevertheless, ongoing studies indicate the potential of a predominant temperature dependent fractionation of distinct isotopes and elements (e.g. Li/Ca, Montagna et al. 2008; U/Ca, Mg/Ca, delta18O, Lòpez Correa et al. 2008; delta88/86Sr, Rüggeberg et al. 2008). Within the frame of DFG-Project TRISTAN and Paläo-TRISTAN (Du 129/37-2 and 37-3) we investigated live-collected specimens of cold-water coral L. pertusa from all along the European continental margin (Northern and mid Norwegian shelves, Skagerrak, Rockall and Porcupine Bank, Galicia Bank, Gulf of Cadiz, Mediterranean Sea). These coral samples grew in waters characterized by temperatures between 6°C and 14°C. Electron Microprobe investigations along the growth direction of individual coral polyps were applied to determine the relationship between the incorporation of distinct elements (Sr, Ca, Mg, S). Cohen et al. (2006) showed for L. pertusa from the Kosterfjord, Skagerrak, that ~25% of the coral's Sr/Ca ratio is related to temperature, while 75% are influenced

  19. Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy₂Ti₂O₇.

    PubMed

    Anand, V K; Tennant, D A; Lake, B

    2015-11-01

    Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been investigated by ac magnetic susceptibility χ(ac)(T), dc magnetic susceptibility χ(T), isothermal magnetization M(H) and heat capacity C(p)(T) measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a spin-glass type freezing behavior near 16 K. Our frequency dependent χ(ac)(T) data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly influenced by Ca substitution. The effect of partial nonmagnetic Ca(2+) substitution for magnetic Dy(3+) is similar to the previous study on nonmagnetic isovalent Y(3+) substituted Dy(2-x)Y(x) Ti2O7 (for low levels of dilution), however the suppression of spin-freezing behavior is substantially stronger for Ca than Y. The Cole-Cole plot analysis reveals semicircular character and a single relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca(2+) substitution for Dy(3+) ions.

  20. Improved thermoelectric property of cation-substituted CaMnO3

    NASA Astrophysics Data System (ADS)

    Kumar, Pradeep; Kashyap Subhash, C.; Sharma Vijay, Kumar; Gupta, H. C.

    2015-09-01

    Single-phase pristine and cation-substituted calcium manganite (Ca1-xBixMn1-yVyO3-δ) polycrystalline samples were synthesized by the solid state reaction technique. Their thermoelectric properties were measured by a set up that was designed and assembled in the laboratory. The Ca1-xBixMn1-yVyO3-δ sample with x = y = 0.04 has shown a power factor (S2σ) of 176 μW/m/K2 at 423 K, which is nearly two orders of magnitude higher than that of the pristine sample (2.1 μW/m/K2). The power factor of the substituted oxide remains almost temperature independent as the Seebeck coefficient increases monotonically with temperature, along with the simultaneous decrease in electrical resistivity which is attributed to enhanced electron density due to co-doping of bismuth and vanadium and grain boundary scattering. These cation-substituted calcium manganites can be used as a potential candidate for an n-type leg in a thermoelectric generator (module).

  1. CaSR function in the intestine: Hormone secretion, electrolyte absorption and secretion, paracrine non-canonical Wnt signaling and colonic crypt cell proliferation.

    PubMed

    Macleod, R John

    2013-06-01

    Expression and function of the CaSR have been shown in some mammalian taste buds and basal cells of the esophagus. Signaling cascades responsible for CaSR-mediated stimulation of H(+)-K(+)-ATPase on human parietal cells have been defined. Transgenic mice and reductionistic cell culture models have shown that the CaSR promotes gastrin secretion from G cells, cholecystokinin (CCK) secretion from duodenal I cells and BMP-2 secretion from sub-epithelial myofibroblasts. In addition, the CaSR mediates a novel paracrine relationship between myofibroblasts and overlying epithelial cells in the colon. Thus, CaSR activators stimulate secretion of Wnt5a from myofibroblasts and expression of the Wnt5a receptor Ror2 in epithelial cells. CaSR-mediated Wnt5a/Ror2 engagement stimulates epithelial differentiation and reduces expression of the receptor for tumor necrosis factor (TNFR1). CaSR activators also modulate intestinal motility, inhibit Cl(-) secretion and stimulate Na(+) absorption in both the small intestine and colon. Colonic epithelia from conditional and global CaSR knockout mice exhibit increased proliferation with increased Wnt/β-catenin signaling, demonstrating that the CaSR negatively modulates colonic epithelial growth.

  2. Theoretical studies of the osmium based perovskites AOsO3 (A=Ca, Sr and Ba)

    NASA Astrophysics Data System (ADS)

    Ali, Zahid; Sattar, Abdul; Asadabadi, S. Jalali; Ahmad, Iftikhar

    2015-11-01

    Osmium based perovskites AOsO3 (A=Ca, Sr and Ba) have been studied theoretically using density functional theory approach. These studies show that CaOsO3 and SrOsO3 are orthorhombic and BaOsO3 is cubic and are consistent with the experiments. The electronic band structures demonstrate that these compounds are metals. The magnetic studies verify the experimental observations at low temperature, where the spin effects are canceled by the orbitals. The stable magnetic phase optimizations and magnetic susceptibilities calculations by the post-DFT treatment confirm that CaOsO3 and SrOsO3 are weak ferromagnetic whereas BaOsO3 is a paramagnetic material. The directional magnetic study shows that these compounds are magnetically anisotropic, and reveals that the easy magnetization axis is [001] direction.

  3. Structural and magnetic properties of Ca-substituted barium W-type hexagonal hexaferrites

    NASA Astrophysics Data System (ADS)

    Huang, Kai; Liu, Xiansong; Feng, Shuangjiu; Zhang, Zhanjun; Yu, Jiangying; Niu, Xiaofei; Lv, Farui; Huang, Xing

    2015-04-01

    A series of W-type hexagonal ferrites with the composition Ba1-xCaxCo2Fe16O27 (x=0, 0.1, 0.3, 0.4 and 0.5) were synthesized using a sol-gel method. The effects of doping on structural and magnetic properties are studied by X-ray diffraction, thermal analyzer, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer, respectively. The X-ray diffraction analysis shows that the samples belong to the W-type hexagonal ferrite. The lattice constants a and c decreases as Ca contents increases. The grains exhibit well defined hexagonal shape. The saturation magnetization and the intrinsic coercive force increases with the increase of the Ca substitution amount. The real part of complex permittivity (ε‧) and imaginary part (ε″) increase with more addition of Ca2+ amount. The imaginary part of complex permittivity (μ‧) increases and the real part (μ‧‧) goes down after Ca2+ is doped. Furthermore, the Ca2+ ions doped in the ferrite improved microwave absorbency.

  4. Stimulatory effects of the degradation products from Mg-Ca-Sr alloy on the osteogenesis through regulating ERK signaling pathway

    NASA Astrophysics Data System (ADS)

    Li, Mei; He, Peng; Wu, Yuanhao; Zhang, Yu; Xia, Hong; Zheng, Yufeng; Han, Yong

    2016-09-01

    The influence of Mg-1Ca-xwt.% Sr (x = 0.2, 0.5, 1.0, 2.0) alloys on the osteogenic differentiation and mineralization of pre-osteoblast MC3T3-E1 were studied through typical differentiation markers, such as intracellular alkaline phosphatase (ALP) activity, extracellular collagen secretion and calcium nodule formation. It was shown that Mg-1Ca alloys with different content of Sr promoted cell viability and enhanced the differentiation and mineralization levels of osteoblasts, and Mg-1Ca-2.0Sr alloy had the most remarkable and significant effect among all. To further investigate the underlying mechanisms, RT-PCR and Western Blotting assays were taken to analyze the mRNA expression level of osteogenesis-related genes and intracellular signaling pathways involved in osteogenesis, respectively. RT-PCR results showed that Mg-1Ca-2.0Sr alloy significantly up-regulated the expressions of the transcription factors of Runt-related transcription factor 2 (RUNX2) and Osterix (OSX), Integrin subunits, as well as alkaline phosphatase (ALP), Bone sialoprotein (BSP), Collagen I (COL I), Osteocalcin (OCN) and Osteopontin (OPN). Western Blotting results suggested that Mg-1Ca-2.0Sr alloy rapidly induced extracellular signal-regulated kinase (ERK) activation but showed no obvious effects on c-Jun N terminal kinase (JNK) and p38 kinase of MAPK. Taken together, our results demonstrated that Mg-1Ca-2.0Sr alloy had excellent biocompatibility and osteogenesis via the ERK pathway and is expected to be promising as orthopedic implants and bone repair materials.

  5. Stimulatory effects of the degradation products from Mg-Ca-Sr alloy on the osteogenesis through regulating ERK signaling pathway.

    PubMed

    Li, Mei; He, Peng; Wu, Yuanhao; Zhang, Yu; Xia, Hong; Zheng, Yufeng; Han, Yong

    2016-01-01

    The influence of Mg-1Ca-xwt.% Sr (x = 0.2, 0.5, 1.0, 2.0) alloys on the osteogenic differentiation and mineralization of pre-osteoblast MC3T3-E1 were studied through typical differentiation markers, such as intracellular alkaline phosphatase (ALP) activity, extracellular collagen secretion and calcium nodule formation. It was shown that Mg-1Ca alloys with different content of Sr promoted cell viability and enhanced the differentiation and mineralization levels of osteoblasts, and Mg-1Ca-2.0Sr alloy had the most remarkable and significant effect among all. To further investigate the underlying mechanisms, RT-PCR and Western Blotting assays were taken to analyze the mRNA expression level of osteogenesis-related genes and intracellular signaling pathways involved in osteogenesis, respectively. RT-PCR results showed that Mg-1Ca-2.0Sr alloy significantly up-regulated the expressions of the transcription factors of Runt-related transcription factor 2 (RUNX2) and Osterix (OSX), Integrin subunits, as well as alkaline phosphatase (ALP), Bone sialoprotein (BSP), Collagen I (COL I), Osteocalcin (OCN) and Osteopontin (OPN). Western Blotting results suggested that Mg-1Ca-2.0Sr alloy rapidly induced extracellular signal-regulated kinase (ERK) activation but showed no obvious effects on c-Jun N terminal kinase (JNK) and p38 kinase of MAPK. Taken together, our results demonstrated that Mg-1Ca-2.0Sr alloy had excellent biocompatibility and osteogenesis via the ERK pathway and is expected to be promising as orthopedic implants and bone repair materials. PMID:27580744

  6. Stimulatory effects of the degradation products from Mg-Ca-Sr alloy on the osteogenesis through regulating ERK signaling pathway

    PubMed Central

    Li, Mei; He, Peng; Wu, Yuanhao; Zhang, Yu; Xia, Hong; Zheng, Yufeng; Han, Yong

    2016-01-01

    The influence of Mg-1Ca-xwt.% Sr (x = 0.2, 0.5, 1.0, 2.0) alloys on the osteogenic differentiation and mineralization of pre-osteoblast MC3T3-E1 were studied through typical differentiation markers, such as intracellular alkaline phosphatase (ALP) activity, extracellular collagen secretion and calcium nodule formation. It was shown that Mg-1Ca alloys with different content of Sr promoted cell viability and enhanced the differentiation and mineralization levels of osteoblasts, and Mg-1Ca-2.0Sr alloy had the most remarkable and significant effect among all. To further investigate the underlying mechanisms, RT-PCR and Western Blotting assays were taken to analyze the mRNA expression level of osteogenesis-related genes and intracellular signaling pathways involved in osteogenesis, respectively. RT-PCR results showed that Mg-1Ca-2.0Sr alloy significantly up-regulated the expressions of the transcription factors of Runt-related transcription factor 2 (RUNX2) and Osterix (OSX), Integrin subunits, as well as alkaline phosphatase (ALP), Bone sialoprotein (BSP), Collagen I (COL I), Osteocalcin (OCN) and Osteopontin (OPN). Western Blotting results suggested that Mg-1Ca-2.0Sr alloy rapidly induced extracellular signal-regulated kinase (ERK) activation but showed no obvious effects on c-Jun N terminal kinase (JNK) and p38 kinase of MAPK. Taken together, our results demonstrated that Mg-1Ca-2.0Sr alloy had excellent biocompatibility and osteogenesis via the ERK pathway and is expected to be promising as orthopedic implants and bone repair materials. PMID:27580744

  7. Stimulatory effects of the degradation products from Mg-Ca-Sr alloy on the osteogenesis through regulating ERK signaling pathway.

    PubMed

    Li, Mei; He, Peng; Wu, Yuanhao; Zhang, Yu; Xia, Hong; Zheng, Yufeng; Han, Yong

    2016-09-01

    The influence of Mg-1Ca-xwt.% Sr (x = 0.2, 0.5, 1.0, 2.0) alloys on the osteogenic differentiation and mineralization of pre-osteoblast MC3T3-E1 were studied through typical differentiation markers, such as intracellular alkaline phosphatase (ALP) activity, extracellular collagen secretion and calcium nodule formation. It was shown that Mg-1Ca alloys with different content of Sr promoted cell viability and enhanced the differentiation and mineralization levels of osteoblasts, and Mg-1Ca-2.0Sr alloy had the most remarkable and significant effect among all. To further investigate the underlying mechanisms, RT-PCR and Western Blotting assays were taken to analyze the mRNA expression level of osteogenesis-related genes and intracellular signaling pathways involved in osteogenesis, respectively. RT-PCR results showed that Mg-1Ca-2.0Sr alloy significantly up-regulated the expressions of the transcription factors of Runt-related transcription factor 2 (RUNX2) and Osterix (OSX), Integrin subunits, as well as alkaline phosphatase (ALP), Bone sialoprotein (BSP), Collagen I (COL I), Osteocalcin (OCN) and Osteopontin (OPN). Western Blotting results suggested that Mg-1Ca-2.0Sr alloy rapidly induced extracellular signal-regulated kinase (ERK) activation but showed no obvious effects on c-Jun N terminal kinase (JNK) and p38 kinase of MAPK. Taken together, our results demonstrated that Mg-1Ca-2.0Sr alloy had excellent biocompatibility and osteogenesis via the ERK pathway and is expected to be promising as orthopedic implants and bone repair materials.

  8. Influence of calcium content on the preparation of the high Tc (110 K class) Bi-Pb-Sr-Ca-Cu-O thin film

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Keizou; Shimojima, Hiromasa; Yamagishi, Chitake

    1991-03-01

    The Bi-Pb-Sr-Ca-Cu-O thin films with various Ca/Sr ratios were prepared by RF magnetron sputtering using multitargets of Bi(0.5)Pb(0.5)O(x), and SrCu(0.75)O(x). The high-Tc (2223) phase was obtained by firing these films. The film with the highest Ca/Sr ratio (Ca/Sr greater than 1.0) produced the largest amount of 2223 phase on firing at 850 C. The highest Ca/Sr ratio ( = 1.17) film contained 91 percent volume ratio of 2223 phase compared with the low Tc phase (2212 phase) after 15 h firing. However, the 2223 phase decreased with increasing long-term firing (65 h).

  9. Introduction of artificial pinning centres in Bi2Sr2CaCu2O8 ceramics

    NASA Technical Reports Server (NTRS)

    Majewski, P.; Elschner, S.; Bestgen, H.; Aldinger, F.

    1995-01-01

    Considering the phase equilibrium diagram of the system Bi203-SrO-CaO-CuO, single phase 'Bi2Sr2CaCu208' ceramics have been transformed by a simple annealing procedure into multiphase samples. The transformation results in the formation of second phases and in an increase of the intra-grain critical current density at 1 T of five times. This increase is believed to express improved pinning properties of the superconducting crystals. The prepared pinning centers are believed to be e.g. coherent precipitates (Guinier-Preston-zones) within the superconducting crystals.

  10. Average and local structure of the Pb-free ferroelectric perovskites (Sr,Sn)TiO3 and (Ba,Ca,Sn)TiO3

    DOE PAGES

    Laurita, Geneva; Page, Katharine; Suzuki, Shoichiro; Seshadri, Ram

    2015-12-16

    The characteristic structural off -centering of Pb2+ in oxides, associated with its 6s2 lone pair, allows it to play a dominant role in polar materials, and makes it a somewhat ubiquitous component of ferroelectrics. In this work, we examine the compounds Sr0.9Sn0.1TiO3 and Ba0.79Ca0.16Sn0.05TiO3 using neutron total scattering techniques with data acquired at di erent temperatures. In these compounds, previously reported as ferroelectrics, Sn2+ appears to display some of the characteristics of Pb2+. We compare the local and long-range structures of the Sn2+-substituted compositions to the unsubstituted parent compounds SrTiO3 and BaTiO3. Lastly, we find that even at these smallmore » substitution levels, the Sn2+ lone pairs drive the local ordering behavior, with the local structure of both compounds more similar to the structure of PbTiO3 rather than the parent compounds.« less

  11. Ab initio study of the structural phase transitions of the double perovskites Sr2MWO6 (M=Zn, Ca, Mg)

    NASA Astrophysics Data System (ADS)

    Petralanda, U.; Etxebarria, I.

    2014-02-01

    We study the interplay of structural distortions in double perovskites Sr2MWO6 (M = Zn, Ca, Mg) by means of first-principles calculations and group theoretical analysis. Structure relaxations of the cubic, tetragonal, and monoclinic phases show that the ground states of the three compounds are monoclinic, although the energy difference between the monoclinic and tetragonal structures is very small in the case of Sr2MgWO6. The symmetry analysis of the distortions involved in the experimental and calculated low-temperature structures shows that the amplitude of two primary distortions associated to rigid rotations of the MX6 and WO6 octahedra are dominant, although the amplitude of a third mode related to deformations of the MX6 groups can not be neglected. The energy maps of the space spanned by the three relevant modes are calculated, and the couplings among the modes are evaluated, showing that the role of a hard secondary mode (in the Landau sense) coupled trilinearly to the two primary instabilities is crucial to stabilize the monoclinic ground state. Results suggest that the key role of the trilinear coupling among three modes could be rather common. A phenomenological theory including the effects of the chemical pressure is also developed. We find that the evolution of the stiffness constants in terms of the atomic substitution follows an accurate linear dependence and that the influence of quantum saturation of the order parameters could stabilize the tetragonal phase of Sr2MgWO6.

  12. Energy gaps in Bi2Sr2CaCu2O8+δ cuprate superconductors

    PubMed Central

    Ren, J. K.; Zhu, X. B.; Yu, H. F.; Tian, Ye; Yang, H. F.; Gu, C. Z.; Wang, N. L.; Ren, Y. F.; Zhao, S. P.

    2012-01-01

    The relationship between the cuprate pseudogap (Δp) and superconducting gap (Δs) remains an unsolved mystery. Here, we present a temperature- and doping-dependent tunneling study of submicron Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions, which provides a clear evidence that Δs closes at a temperature Tc0 well above the superconducting transition temperature Tc but far below the pseudogap opening temperature T*. We show that the superconducting pairing first occurs predominantly on a limited Fermi surface near the node below Tc0, accompanied by a Fermi arc due to the lifetime effects of quasiparticles and Cooper pairs. The arc length has a linear temperature dependence, and as temperature decreases below Tc it reduces to zero while pairing spreads to the antinodal region of the pseudogap leading to a d-wave superconducting gap on the entire Fermi surface at lower temperatures. PMID:22355760

  13. Vortex matter in Bi2Sr2CaCu2O8 with pointlike disorder

    NASA Astrophysics Data System (ADS)

    Konczykowski, M.; van der Beek, C. J.; Koshelev, A. E.; Mosser, V.; Li, M.; Kes, P. H.

    2009-03-01

    We investigate the effect of point-like disorder, introduced by irradiation with 2.3 MeV electrons, on the mixed state phase diagram of Bi2Sr2CaCu2O8 single crystals. We focus on the higher irradiation doses that produce a significant depression of the critical temperature Tc, to as low as 2/3 of the initial value. Surprisingly, the first order phase transition (FOT) of the vortex ensemble, from a crystal to the pancake vortex liquid, persists in those highly disordered samples. The second peak in the irreversible magnetization, observed at low temperatures, is equally observed after high irradiation doses, but at much lower magnetic fields. A simple scaling of the phase diagram for samples with various degrees of disorder is not possible, indicating that several fundamental parameters of the superconductor are affected. From the analysis of the angular dependence of the FOT, we deduce that the effective anisotropy factor increases after irradiation.

  14. Fabrication and characterization of (Bi,Pb)-Sr-Ca-Cu-O (2223) bars

    SciTech Connect

    Chudzik, M.P.; Polzin, B.J.; Thayer, R.; Picciolo, J.J.; Fisher, B.L.; Lanagan, M.T.

    1996-08-01

    Bulk bars for current lead applications were fabricated from (Bi,Pb)- Sr-Ca-Cu-O (Bi-2223) for low thermal conductivity and high critical current. Bars measuring 17.8 cm in length were made by uniaxially pressing Bi-2223 powder of controlled (1.7/0.34)223 and (1.8/0.4)223 phase composition. The bulk bars were densified by subjecting them to a schedule of alternate liquid-phase sintering and cold isostatic pressing. Liquid phase sintering temperatures were optimized from differential thermal analysis and microstructure morphology. Phase purity and microstructure were evaluated by x-ray diffraction and scanning electron microscopy. Low-resistance silver contacts were applied to the bars by hot-pressing at 820{degrees}C and 3 MPa. Critical current densities {approx} 1000 A/cm{sup 3} (critical currents of 750 A at 77 K in self-field conditions) were achieved.

  15. Microwave Absorption Study on (Bi, Pb)-Sr-Ca-Cu-O Granular Superconductors

    NASA Astrophysics Data System (ADS)

    Jurga, W.; Piekara-Sady, L.; Gazda, M.

    2008-07-01

    (Bi, Pb)-Sr-Ca-Cu-O is considered as a system of 2201, 2212 and 2223 superconductors embedded in the insulating matrix. The size of the grains depends on the time of recrystallization. These types of ceramics exhibit a two-step transition to superconducting state. Because electrical properties depend among other on the Josephson coupling between grains, the magnetically modulated microwave absorption study was undertaken. Magnetically modulated microwave absorption signal was observed to arise just as temperature had been lowered below T1. The shape of this signal was studied to recognize the second temperature T2. Some strong oscillations appear on magnetically modulated microwave absorption at lower temperatures, which might be related to local percolation breakdown in superconducting network.

  16. Superconducting and normal-state properties of APd2As2 (A = Ca, Sr, Ba) single crystals

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Kim, H.; Tanatar, M. A.; Prozorov, R.; Johnston, D. C.

    2013-06-01

    The synthesis and crystallography, magnetic susceptibility χ, magnetization M, specific heat Cp, in-plane electrical resistivity ρ, and in-plane magnetic penetration depth measurements are reported for single crystals of APd2As2 (A = Ca, Sr, Ba) versus temperature T and magnetic field H. The crystals were grown using PdAs self-flux. CaPd2As2 and SrPd2As2 crystallize in a collapsed body-centered tetragonal ThCr2Si2-type structure (I4/mmm), whereas BaPd2As2 crystallizes in the primitive tetragonal CeMg2Si2-type structure (P4/mmm), in agreement with literature data. The ρ(T) data exhibit metallic behavior for all three compounds. Bulk superconductivity is reported for CaPd2As2 and SrPd2As2 below Tc=1.27 and 0.92 K, respectively, whereas only a trace of superconductivity is found in BaPd2As2. No other phase transitions were observed. The χ(T) and M(H) data reveal anisotropic diamagnetism in the normal state, with χc>χab for CaPd2As2 and BaPd2As2, and χc<χab for SrPd2As2. The normal and superconducting state data indicate that CaPd2As2 and SrPd2As2 are conventional type-II nodeless s-wave electron-phonon superconductors. The electronic superconducting state heat capacity data for CaPd2As2, which has an extremely sharp heat capacity jump at Tc, are analyzed using our recent elaboration of the α-model of the BCS theory of superconductivity, which indicates that the s-wave gap in this compound is anisotropic in momentum space.

  17. High temperature phase equilibria studies in the Bi-Sr-Ca-Cu-O-Ag system

    SciTech Connect

    Margulies, Lawrence

    1999-11-08

    A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi-Sr-Ca-Cu-O-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO{sub 2}). A liquid immiscibility region between oxide and Ag liquids in the 8--98 at% range was found above 900 C. Two eutectics were found in the Bi2212-Ag pseudobinary. On the oxide rich side, a eutectic exists at approximately 4 at% Ag. On the Ag rich side, a eutectic exists at approximately 98 at% Ag at a temperature of 15 C below the melting point of pure Ag. Six distinct solid phases were found to be in equilibrium with the partial melt within the Ag content and PO{sub 2} range studied. The stability of these solid phases were found to be highly sensitive to PO{sub 2}, and to a much lesser extent Ag content. High temperature x-ray diffraction (HTXRD) studies of this system are in conflict with these results. It is suggested that these discrepancies are due to experimental artifacts caused by the significant thermal gradients and lack of full bulk sampling which is inherent in conventional HTXRD designs. In part 2, a new furnace design compatible with synchrotron radiation sources is introduced to address these problems. This design allows for full bulk sampling in a low thermal gradient environment using Debye-Scherrer transmission geometry. Sample spinning is also introduced in the design to eliminate preferred orientation and incomplete powder averaging and allow for quantitative phase analysis and structural refinement. Studies on model systems are presented to demonstrate the capabilities for high resolution structural studies (Al{sub 2}O{sub 3}) and time resolved phase transformation studies (SrCO{sub 3}). Finally, the Bi2212 system is examined to confirm the quenching results

  18. Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6}:Eu{sup 3+}, Li{sup +}: An emission tunable phosphor through site symmetry and excitation wavelength

    SciTech Connect

    Xiao, Ning; Shen, Jun; Xiao, Tengjiao; Wu, Bing; Luo, Xiaobing; Li, Li; Wang, Zhongqing; Zhou, Xianju

    2015-10-15

    The emission of Eu{sup 3+} doped Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6} phosphors could be tunable by the site symmetry of the activators and the excitation wavelengths. - Highlights: • The emission of Eu{sup 3+} depends on site symmetry and excitation wavelengths. • The color of the samples was tunable by structure and excitation wavelength. • The effect of W and Eu content on the properties of the samples was investigated. - Abstract: A series of Eu{sup 3+} substituted double-perovskite Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6} phosphors were prepared by solid state reactions. The phase, photoluminescence and energy transfer of the phosphors were investigated by X-ray diffraction (XRD), photoluminescence (PL) and luminescence decay respectively. It is found that the emission of the Eu{sup 3+} substituted double perovskites depends on both the site symmetry of the activators and the excitation wavelengths. Based on the decay analysis of Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6} matrix and Eu{sup 3+} doped samples, the energy transfer efficiencies between the host and activators Eu{sup 3+} were investigated. The results of the emission tunable phosphors indicate their potential applications in LEDs.

  19. Structural Stabilities and Elastic Thermodynamic Properties of SrTe Compound and SrTe1-x Ca x Alloy Under High Pressure

    NASA Astrophysics Data System (ADS)

    Saoud, Fatma Saad; Rabah, Khenata; Bouhemadou, Abdelmadjid; Plenet, Jean Claude; Henini, Mohamed; Djabou, Rihabe El Houda

    2016-09-01

    The effect of pressure on the structural, elastic, and thermodynamic properties of SrTe in both B1 (rocksalt) and B2 (CsCl-type) phases and the SrTe1-x Ca x alloys with Ca dopant concentrations at x = 0.16667, 0.20, 0.33333, 0.42857, 0.44444 and 0.50 have been investigated using the two new gradient-corrected functional developed by Perdew, J.P.; Burke, K.; Ernzerhof named Density-Gradient Expansion for Exchange in Solids (PBEsol) and generalized Wu-Cohen (WC), in a significant range of pressure from 0 GPa to 30 GPa. The structure parameters, elastic stiffness constants c ij , the bulk modulus (B), Kleinman parameter ( &xi), shear anisotropies A shear are also determined. Furthermore, as reported in this study, the aggregate elastic modulus (B, G, E), Poisson's ratio (ν) and the Lame's coefficients (λ) are estimated. On the other hand, the ductility, brittleness, longitudinal, transverse sound velocities and the Debye temperature ΘD(T) are also obtained. Importantly, our results are in reasonable agreement with the available theoretical and experimental data. To the best of our knowledge, this is the first study of the effect of the composition on the properties of the SrTe1-x Ca x alloys which may encourage other works for the confirmation of the reported results.

  20. Electrical conductivity and superconductivity in (Bi-Pb)-Sr-Ca-Cu-O glass ceramics during the first minutes of crystallization

    NASA Astrophysics Data System (ADS)

    Gazda, M.; Kusz, B.; Chudinov, S.; Stizza, S.; Natali, R.

    2003-05-01

    (Bi 0.8Pb 0.2) 4Sr 3Ca 3Cu 4O x glass ceramic samples were obtained by annealing at temperatures between 700 and 870 °C for a short time. The measurements of the temperature dependence of resistivity in annealed samples were carried out with the conventional four-terminal method in a temperature range from 3 to 300 K. The dynamic changes of resistivity during the process of annealing were also monitored in some of the studied annealing temperatures. Low temperature resistivity measurements show that during the growth of crystalline phases a gradual change of conduction mechanism occurs. Some samples were superconducting with transition temperatures characteristic for (Bi 0.8Pb 0.2) 2Sr 2CuO x and (Bi 0.8Pb 0.2) 2Sr 2CaCu 2O x materials.

  1. Hole doping by pressure on the 1111 pnictides CaFeAsF and SrFeAsF.

    PubMed

    Freitas, Daniele C; Garbarino, Gastón; Weht, Ruben; Sow, Amadou; Zhu, Xiyu; Han, Fei; Cheng, Peng; Ju, Jing; Wen, Hai Hu; Núñez-Regueiro, Manuel

    2014-04-16

    We determine the pressure phase diagram of the 1111 compounds CaFeAsF and SrFeAsF, up to 20 GPa and down to 4 K by electrical resistivity measurements and the change of structure up to 40 GPa at room temperature. The antiferromagnetic transition temperature, as determined by the derivative peak, shows a minimum at ~5 GPa (10 GPa) for the Ca (Sr) compound. For CaFeAsF, superconductivity appears at this minimum, coincident with the development of a previously reported monoclinic phase. For SrFeAsF, where the orthorhombic and the monoclinic phase were reported to coexist, superconductivity exists above P≥1 GPa. Both phase diagrams can be scaled by a shift of ~10 GPa pressure at which the volume of SrFeAsF and that of CaFeAsF at ambient pressure coincide. The difference of our phase diagram with that of electron-doped 1111 samples is accounted for by hole doping under pressure, which we verified through electron band structure calculations. PMID:24675791

  2. Pb solubility of the high-temperature superconducting phase Bi2Sr2Ca2Cu3O(10+d)

    NASA Technical Reports Server (NTRS)

    Kaesche, Stefanie; Majewski, Peter; Aldinger, Fritz

    1995-01-01

    For the nominal composition of Bi(2.27-x)Pb(x)Sr2 Ca2 Cu3 O(10+d) lead content was varied from x = 0.05 to 0.45. The compositions were examined between 830 and 890 C which is supposed to be the temperature range over which the so-called 2223 phase (Bi2Sr2Ca2Cu3O(10+d)) is stable. Only compositions between x = 0.18 to 0.36 could be synthesized in a single phase state. For x is greater than 0.36 a lead containing phase with a stoichiometry of Pb4(Sr,Ca)5CuO(d) is formed, for x is less than 0.18 mainly Bi2Sr2CaCu2O(10+d) and cuprates are the equilibrium phases. The temperature range for the 2223 phase was found to be 830 to 890 C but the 2223 phase has extremely varying cation ratios over this temperature range. Former single phase 2223 samples turn to multi phase samples when annealed at slightly higher or lower temperatures. A decrease in the Pb solubility with increasing temperature was found for the 2223 phase.

  3. Sea Surface Temperature Records Using Sr/Ca Ratios in a Siderastrea siderea Coral from SE Cuba

    NASA Astrophysics Data System (ADS)

    Fargher, H. A.; Hughen, K. A.; Ossolinski, J. E.; Bretos, F.; Siciliano, D.; Gonzalez, P.

    2015-12-01

    Sea surface temperature (SST) variability from Cuba remains relatively unknown compared to the rest of the Caribbean. Cuba sits near an inflection point in the spatial pattern of SST from the North Atlantic Oscillation (NAO), and long SST records from the region could reveal changes in the influence of this climate system through time. A Siderastrea siderea coral from the Jardínes de la Reina in southern Cuba was drilled to obtain a 220 year long archive of environmental change. The genus Siderastrea has not been extensively studied as an SST archive, yet Sr/Ca ratios in the Cuban core show a clear seasonal signal and strong correlation to instrumental SST data (r2 = 0.86 and 0.36 for monthly and interannual (winter season) timescales, respectively). Annual growth rates (linear extension) of the coral are observed to have a minor influence on Sr/Ca variability, but do not show a direct correlation to SST on timescales from annual to multidecadal. Sr/Ca measurements from the Cuban coral are used to reconstruct monthly and seasonal (winter, summer) SST extending back more than two centuries. Wintertime SST in southern Cuba is compared to other coral Sr/Ca records of winter-season SST from locations sensitive to the NAO in order to investigate the stationarity of the NAO SST 'fingerprint' through time.

  4. STM Studies of Near-Optimal Doped Bi_2Sr_2CaCu_2O_8 delta

    SciTech Connect

    Kapitulnik, Aharon

    2010-04-05

    In this paper we summarize our STM studies of the density of electronic states in nearly optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8 + {delta}} in zero field. We report on the inhomogeneity of the gap structure, density of states modulations with four-lattice constant period, and coherence peak modulation.

  5. Structural and intrinsic Josephson properties of Bi2Sr2Ca1-yYyCu2O8+δ single crystal

    NASA Astrophysics Data System (ADS)

    Yamaki, K.; Murata, K.; Irie, A.

    2016-10-01

    In this study, Bi2Sr2Ca1-yYyCu2O8+δ (BSCYCO) single crystals with yttrium doping content of y = 0-0.30 were synthesized by a self-flux method. The critical temperature and c-axis lattice constant of BSCYCO were controlled by the substitution of yttrium at the calcium site. A 290 × 90 × 0.4 μm3 mesa structure was fabricated using photolithography and argon-ion milling. A multibranch structure in current-voltage characteristics was successfully observed for mesas of BSCYCO (y = 0-0.10). The critical current of intrinsic Josephson junctions (IJJs) in BSCYCO mesas was systematically investigated.

  6. Dopant-Induced Nanoscale Electronic Inhomogeneities in Ca2-xSrxRuO4

    SciTech Connect

    Zhang, Jiandi; Ismail, #; Moore, R. G.; Wang, S. -C.; Ding, H.; Jin, Rongying; Mandrus, David; Plummer, E Ward

    2006-01-01

    Ca{sub 2-x}Sr{sub x}RuO{sub 4} single crystals with 0.1 {le} x {le} 2.0 have been studied systematically using scanning tunneling microscopy (STM) and spectroscopy, low-energy electron diffraction, and angle resolved photoelectron spectroscopy (ARPES). In contrast with the well-ordered lattice structure, the local density of states at the surface clearly shows a strong doping dependent nanoscale electronic inhomogeneity, regardless of the fact of isovalent substitution. Remarkably, the surface electronic roughness measured by STM and the inverse spectral weight of quasiparticle states determined by ARPES are found to vary with x in the same manner as the bulk in-plane residual resistivity, following the Nordheim rule. For the first time, the surface measurements - especially those with STM - are shown to be in good agreement with the bulk transport results, all clearly indicating a doping-induced electronic disorder in the system.

  7. Structure of molten CaSiO3: neutron diffraction isotope substitution with aerodynamic levitation and molecular dynamics study.

    PubMed

    Skinner, L B; Benmore, C J; Weber, J K R; Tumber, S; Lazareva, L; Neuefeind, J; Santodonato, L; Du, J; Parise, J B

    2012-11-15

    We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO(3), to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the first Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a redistribution of Ca-O bond lengths, especially toward longer distances in the liquid. The first order neutron difference function provides a test of recent molecular dynamics simulations and supports the MD model which contains short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO(3). PMID:23106223

  8. The structure of molten CaSiO3: A neutron diffraction isotope substitution and aerodynamic levitation study.

    SciTech Connect

    Skinner, Lawrie; Benmore, Chris J; Weber, Richard; Santodonato, Louis J; Tumber, Sonia; Neuefeind, Joerg C; Lazareva, Lena; Du, Jincheng; Parise, John B

    2012-01-01

    We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO3, to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a re-distribution of Ca-O bond lengths, especially towards longer distances in the liquid. The first order neutron difference function provides a rigorous test of recent molecular dynamics simulations and supports the model of the presence of short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO3.

  9. Antiferromagnetism in CaAl2Si2-type CaMn2As2 and SrMn2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; Johnston, D. C.

    Magnetic susceptibility versus temperature χ (T) measurements of CaMn2As2 and SrMn2As2 crystals show clear antiferromagnetic (AFM) transitions at TN ~ 65 K and 120 K,1 respectively. The anisotropic behaviors in χ (T <=TN) suggest that both compounds are noncollinear antiferromagnets which may result either from an intrinsic noncollinear structure or from multiple collinear AFM domains that are not aligned collinearly.2 The χ (T) data at T >TN reveal that both compounds exhibit strong short-range AFM ordering, evidently associated with quasi-two-dimensional spin lattices. The electrical resistivities show insulating ground states with activation energies of ~ 63 meV in CaMn2As2 and 44 meV in SrMn2As2 . The experimental results thus reveal that both (Ca , Sr) Mn2As2 materials are AFM insulators at low temperatures and in analogy with the high Tc cuprates, may be potential parent compounds for CaAl2Si2-type superconductors. Work was supported by the USDOE under Contract No. DE-AC02-07CH11358.

  10. Synthesis and luminescence characterization of Sr(0.5)Ca(0.5)TiO3:Sm(3+) phosphor.

    PubMed

    Vidyadharan, Viji; Remya, Mohan P; Gopi, Subhash; Thomas, Sunil; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2015-11-01

    The spectroscopic properties of trivalent samarium doped Sr0.5Ca0.5TiO3 perovskite phosphor material (Sr0.5Ca0.5TiO3:xSm(3+), x=0.05, 0.1, 0.5, 1, 1.5) synthesized by the solid state method have been studied. The X-Ray Diffraction profile confirms the orthorhombic perovskite Sr0.5Ca0.5TiO3 structure of the prepared samples. The SEM study reveals the surface morphology. The Judd-Ofelt intensity parameters were calculated for 0.5 wt% Sm(3+) doped Sr0.5Ca0.5TiO3. Transition probabilities, branching ratios and radiative lifetime were evaluated by using Judd-Ofelt analysis. The emission spectra under 405 nm excitation shows five emission peaks at 564 nm, 599 nm, 645 nm, 707 nm and 776 nm corresponding to the transitions (4)G5/2→(6)Hj (j=5/2, 7/2, 9/2, 11/2 and 13/2) respectively. The higher values of branching ratio and stimulated emission cross-section for (4)G5/2→(6)H7/2 transition of Sr0.5Ca0.5TiO3:0.5 wt% Sm(3+) shows its suitability in the field of visible lasers and optical fiber amplifiers. The experimental lifetimes of Sm(3+) doped samples were estimated using the decay curves corresponding to (4)G5/2→(6)H7/2 transition upon 405 nm excitation. Concentration dependence on emission intensity and experimental lifetime were also studied. From the CIE diagram we can see that as the concentration of Sm(3+) ions increases from 0.05 wt% to 1.5 wt% the CIE color co-ordinates changes from greenish yellow to yellowish orange.

  11. Dependence of superconducting transition temperature on doping and structural distortion of the CuO{sub 2} planes in La{sub 2-x}M{sub x}CuO{sub 4} (M=Nd, Ca, Sr).

    SciTech Connect

    Dabrowski, B.; Rogacki, K.; Jorgensen, J. D.; Hinks, D. G.; Materials Science Division; Northern Illinois Univ.

    1996-01-01

    We have separated the structural and doping effects on the superconducting transition temperature in La2-xMxCuO4 (M=Nd, Ca, Sr). At a fixed doping level, the highest Tc is found for flat and square CuO2 planes in the tetragonal structure. Tc is reduced proportionally to the structural distortions of the CuO2 planes in the orthorhombic structure. The local minimum of Tc vs. doping is observed for both orthorhombic Ca- and Sr-substituted materials around x{approx}0.12. This minimum may be related to the intrinsic dependence of the electronic density of states at EF due to a weakly split singularity of DOS.

  12. Effects of K doping on structural and superconducting properties of Bi{sub 1.5}Pb{sub 0.5}Sr{sub 1.8}CaCu{sub 2}O{sub 8+δ} compounds

    SciTech Connect

    Belala, K; Mosbah, M. F.

    2013-12-16

    Two kinds of potassium doped Bi(Pb)2212 samples are used to investigate the effect of doping the Bi(Pb)2212 ((Bi,Pb){sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}) phase by potassium (K): In the first one K is substituted on the Sr site; In the second one K is added. Using the solid state method reaction samples of Bi{sub 1.5}Pb{sub 0.5}(Sr{sub 1.8−x}K{sub x})CaCu{sub 2}O{sub 8+d} and Bi{sub 1.5}Pb{sub 0.5}Sr{sub 1.8}CaCu{sub 2}O{sub 8+d}K{sub x} (0 ≤ x≤ 0.05) have been prepared from powders of carbonates and primary oxides having purity over 99%. The samples have been characterized by X ray diffraction (XRD), scanning electron microscopy (SEM) and resistivity versus temperature measurements. Results show how the kind and the rate of doping by potassium affects the structural and transport properties of Bi(Pb)2212 phase.

  13. Accurate climate reconstruction from coral aragonite: The impact of seawater pH on skeletal Sr/Ca

    NASA Astrophysics Data System (ADS)

    Cole, C. S.; Allison, N.; Hintz, C.; Finch, A.

    2014-12-01

    The geochemistry of skeletal aragonite deposited by massive tropical corals preserves a valuable record of past climate. In particular, coral skeletal Sr/Ca records sea surface temperature (SST) at the time of deposition and is a widely used palaeothermometer. However, SSTs estimated from many fossil corals are significantly cooler than those predicted from other proxies and climate models. Accurately interpreting the SST records encoded in coral aragonite requires a greater understanding of the controls on skeletal Sr/Ca, including the effect of variations in seawater pH. We have developed an aquarium system to culture corals over a range of pCO2 scenarios that range from the last glacial maximum (180 ppm) to levels projected by the end of this century (750 ppm). We acclimated heads of massive Porites corals, the coral genus most commonly used in palaeoenvironmental studies, to four pCO2 scenarios over a period of > 6 months. Using SIMS we are measuring the Sr/Ca of the aragonite deposited over a five-week experimental period, following this long acclimation, at a 1-2 day resolution. We explore the relationship between seawater pH and skeletal Sr/Ca, and we investigate how skeletal Sr/Ca varies between fast- and slow-growing axes within the same coral, and between different genotypes within the same treatment. We have quantified net photosynthesis, respiration and calcification rates in each coral head throughout the experimental period, and we observe that calcification in the light is significantly reduced at a pCO2 of 750 ppm compared to 180 ppm (0.94 ± 0.17 and 0.45 ± 0.23 μmol CaCO3 cm-2 hr-1, respectively; p < 0.01). We investigate whether these differences influence skeletal geochemistry within our controlled culture conditions. Understanding the effect of changes in seawater pH, metabolic and calcification rates on the Sr/Ca of coral skeletons will significantly advance the application of this proxy in past climate reconstruction.

  14. Judd-Ofelt analysis of Pr3+ ions in Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices

    NASA Astrophysics Data System (ADS)

    Vidyadharan, Viji; Gopi, Subash; Remya, Mohan P.; Thomas, Vinoy; Joseph, Cyriac; Unnikrishnan, N. V.; Biju, P. R.

    2016-01-01

    The spectroscopic properties of Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices have been investigated using optical absorption and emission spectra. The oscillator strengths of observed bands of Pr3+ ions and Judd-Ofelt intensity parameters were calculated by including and excluding the hypersensitive 3H4 → 3P2 transition using standard and modified Judd-Ofelt (JO) theory. In both the host matrices the JO parameters follow the same trend as Ω6 > Ω2 > Ω4. The JO intensity parameters obtained by using the Modified JO theory was used to compute the radiative properties such as radiative transition probability (AR), branching ratio (βR) and radiative lifetime (τR) for the observed fluorescence bands. The photoluminescence spectrum of Pr3+ doped Sr1.5Ca0.5SiO4 upon 444 nm excitation shows three emission peaks at 489, 608 and 733 nm corresponding to the transitions 3P0 → 3H4, 3H6 and 3F4 respectively. But in the case of Sr0.5Ca0.5TiO3 host matrix we observed an emission peak at 611 nm corresponding to the 1D2 → 3H4 transition at λex = 336 nm. The experimental branching ratio (βexp) obtained from the fluorescence spectra was compared with the calculated values. The non radiative relaxation rate was calculated from the experimental (τexp) and predicted (τR) lifetimes. Stimulated emission cross section (σe), gain bandwidth (σe × Δλeff) and optical gain (σe × τR) for 0.5 wt% Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 phosphor samples were also calculated and their high value suggests its candidature as a good optical material.

  15. Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O{sub 3-y} perovskites - perspective cathode materials for IT-SOFC

    SciTech Connect

    Napolsky, Ph.S.; Drozhzhin, O.A.; Istomin, S.Ya.; Kazakov, S.M.; Antipov, E.V.; Galeeva, A.V.; Gippius, A.A.; Svensson, G.; Abakumov, A.M.; Van Tendeloo, G.

    2012-08-15

    .75}O{sub 3-y}, 0.1{<=}y{<=}0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the {sigma} value from {approx}1 to {approx}50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E{sub p}) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6. - Graphical abstract: The substitution of cobalt in the 314-phase Sr{sub 0.75}Y{sub 0.25}CoO{sub 2.62} by manganese leads to the formation of oxygen deficient compounds Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, with the cubic and orthorhombic perovskite structures. The conductivity of the x=0.5 sample (110 S/cm) at 1173 K is substantially higher in comparison with x=0.75 (44 S/cm). Together with comparable TEC values for x=0.5 (15.5 ppm K{sup -1}) and 0.75 (15.1 ppm K{sup -1}) samples this makes the former one a promising cathode material for IT-SOFC. Partial replacement of Sr by Ca in Sr{sub 0.75}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} leads to the formation of the solid solution with the orthorhombic perovskite structure, Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6. Along with Sr{sub 0.75}Y{sub 0.25}Co{sub 0.5}Mn{sub 0.5}O{sub 3-y}, novel perovskite Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} represent promising cathode material for IT-SOFC due to low TEC value (13.8 ppm K{sup -1}) and high conductivity of 135 S/cm at 1173 K. Highlights: Black-Right-Pointing-Pointer Mn-doped 314-phases Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 were synthesized. Black-Right-Pointing-Pointer Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, x=0.1--0.6, Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} were made. Black-Right-Pointing-Pointer High

  16. Structural studies of the rhombohedral and orthorhombic monouranates: CaUO4, α-SrUO4, β-SrUO4 and BaUO4

    NASA Astrophysics Data System (ADS)

    Murphy, Gabriel; Kennedy, Brendan J.; Johannessen, Bernt; Kimpton, Justin A.; Avdeev, Maxim; Griffith, Christopher S.; Thorogood, Gordon J.; Zhang, Zhaoming

    2016-05-01

    The structures of some AUO4 (A=Ca, Sr, or Ba) oxides have been determined using a combination of neutron and synchrotron X-ray diffraction, supported by X-ray absorption spectroscopic measurements at the U L3-edge. The smaller Ca cation favours a rhombohedral AUO4 structure with 8-coordinate UO8 moieties whilst an orthorhombic structure based on UO6 groups is found for BaUO4. Both the rhombohedral and orthorhombic structures can be stabilised for SrUO4. The structural studies suggest that the bonding requirements of the A site cation play a significant role in determining which structure is favoured. In the rhombohedral structure, Bond Valence Sums demonstrate the A site is invariably overbonded, which, in the case of rhombohedral α-SrUO4, is compensated for by the formation of vacancies in the oxygen sub-lattice. The uranium cation, with its flexible oxidation state, is able to accommodate this by inducing vacancies along its equatorial coordination site as demonstrated by neutron powder diffraction.

  17. Synthesis, characterization and biological evaluation of strontium/magnesium-co-substituted hydroxyapatite.

    PubMed

    Geng, Zhen; Wang, Renfeng; Li, Zhaoyang; Cui, Zhenduo; Zhu, Shengli; Liang, Yanqin; Liu, Yunde; Huijing, Bao; Li, Xue; Huo, Qianyu; Liu, Zhili; Yang, Xianjin

    2016-07-01

    The present study aims to investigate the contribution of two biologically important cations, Mg(2+) and Sr(2+), when co-substituted into the structure of hydroxyapatite (Ca10(PO4)6(OH)2, HA). The substituted samples were synthesized by a hydrothermal method that involved the addition of Mg(2+) and Sr(2+) containing precursors to partially replace Ca(2+) in the apatite structure. Four co-substituted HA samples with different concentrations of Mg(2+) and Sr(2+) ((Mg + Sr)/(Mg + Sr + Ca) = 30%) were investigated, and they were compared with pure HA. Experimental results showed that only a limited amount of Mg (Mg/(Mg + Ca + Sr) < 14%) could successfully substitute for Ca in HA. In addition, Mg substitution resulted in reduced crystallinity, thermal stability and lattice parameters of HA. In contrast, Sr could fully substitute for Ca. Furthermore, the addition of Sr increased the lattice parameters of HA. Here, we obtained the cation leach liquor by immersing the prepared samples in a culture medium for cell experiments. The in vitro study showed that 10Mg20Sr promoted better MG63 cell attachment, proliferation and differentiation than HA. Thus, the presence of an appropriate proportion of Mg and Sr could play a significant role in the increased biocompatibility of HA. PMID:26916949

  18. Optically pumped cerium-doped LiSrAlF.sub.6 and LiCaAlF.sub.6

    DOEpatents

    Marshall, Christopher D.; Payne, Stephen A.; Krupke, William F.

    1996-01-01

    Ce.sup.3+ -doped LiSrAlF.sub.6 crystals are pumped by ultraviolet light which is polarized along the c axis of the crystals to effectively energize the laser system. In one embodiment, the polarized fourth harmonic light output from a conventional Nd:YAG laser operating at 266 nm is arranged to pump Ce:LiSrAlF.sub.6 with the pump light polarized along the c axis of the crystal. The Ce:LiSrAlF.sub.6 crystal may be placed in a laser cavity for generating tunable coherent ultraviolet radiation in the range of 280-320 nm. Additionally, Ce-doped crystals possessing the LiSrAlF.sub.6 type of chemical formula, e.g. Ce-doped LiCaAlF.sub.6 and LiSrGaF.sub.6, can be used. Alternative pump sources include an ultraviolet-capable krypton or argon laser, or ultraviolet emitting flashlamps. The polarization of the pump light will impact operation. The laser system will operate efficiently when light in the 280-320 nm gain region is injected or recirculated in the system such that the beam is also polarized along the c axis of the crystal. The Ce:LiSrAlF.sub.6 laser system can be configured to generate ultrashort pulses, and it may be used to pump other devices, such as an optical parametric oscillator.

  19. Optically pumped cerium-doped LiSrAlF{sub 6} and LiCaAlF{sub 6}

    DOEpatents

    Marshall, C.D.; Payne, S.A.; Krupke, W.F.

    1996-05-14

    Ce{sup 3+}-doped LiSrAlF{sub 6} crystals are pumped by ultraviolet light which is polarized along the c axis of the crystals to effectively energize the laser system. In one embodiment, the polarized fourth harmonic light output from a conventional Nd:YAG laser operating at 266 nm is arranged to pump Ce:LiSrAlF{sub 6} with the pump light polarized along the c axis of the crystal. The Ce:LiSrAlF{sub 6} crystal may be placed in a laser cavity for generating tunable coherent ultraviolet radiation in the range of 280-320 nm. Additionally, Ce-doped crystals possessing the LiSrAlF{sub 6} type of chemical formula, e.g. Ce-doped LiCaAlF{sub 6} and LiSrGaF{sub 6}, can be used. Alternative pump sources include an ultraviolet-capable krypton or argon laser, or ultraviolet emitting flashlamps. The polarization of the pump light will impact operation. The laser system will operate efficiently when light in the 280-320 nm gain region is injected or recirculated in the system such that the beam is also polarized along the c axis of the crystal. The Ce:LiSrAlF{sub 6} laser system can be configured to generate ultrashort pulses, and it may be used to pump other devices, such as an optical parametric oscillator. 10 figs.

  20. Systematic Study of Compositional and Synthetic Control of Vacancy and Magnetic Ordering in Oxygen-Deficient Perovskites Ca2Fe2 xMnxO5+yand CaSrFe2 xMnxO5+y (x = 1/2, 2/3, and 1; y = 0 1/2)

    SciTech Connect

    Ramezanipour, Farshid; Greedan, John E; Cranswick, Lachlan M.D.; Donaberger, R. L.; Garlea, Vasile O; Siewenie, Joan

    2012-01-01

    Ten compounds belonging to the series of oxygen-deficient perovskite oxides Ca2Fe2 xMnxO5 and CaSrFe2 xMnxO5+y, where x = 1/2, 2/3, and 1 and y 0 0.5, were synthesized and investigated with respect to the ordering of oxygen vacancies on both local and long-range length scales and the effect on crystal structure and magnetic properties. For the set with y 0 the oxygen vacancies always order in the long-range sense to form the brownmillerite structure containing alternating layers of octahedrally and tetrahedrally coordinated cations. However, there is a change in symmetry from Pnma to Icmm upon substitution of Sr for one Ca for all x, indicating local Td chain (vacancy) disorder. In the special case of CaSrFeMnO5 the neutron diffraction peaks broaden, indicating only short-range structural order on a length scale of 160 . This reveals a systematic progression from Ca2FeMnO5 (Pnma, well-ordered tetrahedral chains) to CaSrFeMnO5 (Icmm, disordered tetrahedral chains, overall short-range order) to Sr2FeMnO5 (Pm3m, destruction of tetrahedral chains in a long-range sense). Systematic changes occur in the magnetic properties as well. While long-range antiferromagnetic order is preserved, the magnetic transition temperature, Tc, decreases for the same x when Sr substitutes for one Ca. A review of the changes in Tc for the series Ca2Fe2 xMxO5, taking into account the tetrahedral/octahedral site preferences for the various M3+ ions, leads to a partial understanding of the origin of magnetic order in these materials in terms of a layered antiferromagnetic model. While in all cases the preferred magnetic moment direction is (010) at low temperatures, there is a cross over for x = 0.5 to (100) with increasing temperature for both the Ca2Fe2 xMnxO5 and the CaSrFe2 xMnxO5 series. For the y > 0 phases, while a brownmillerite ordering of oxygen vacancies is preserved for the Ca2 phases, a disordered Pm3m cubic perovskite structure is always found when Sr is substituted for one Ca

  1. Phonons and stability of infinite-layer iron oxides SrFeO2 and CaFeO2

    NASA Astrophysics Data System (ADS)

    Gupta, M. K.; Mittal, R.; Chaplot, S. L.; Tassel, Cédric; Kageyama, Hiroshi; Tomiyasu, K.; Taylor, Jon

    2016-09-01

    We present detailed ab-initio lattice dynamical analysis of the Fe-O infinite-layer compounds CaFeO2 and SrFeO2 in various magnetic configurations. These indicate strong spin-phonon coupling in SrFeO2 in contrast to that in case of CaFeO2. From our ab-initio calculations in SrFeO2 as a function of volume, we suggest that the distortion in SrFeO2 above 300 K is similar to that in CaFeO2 at ambient conditions. The distortion of the planer structure of CaFeO2 involves doubling of the planer unit cell that may be usually expected to be due to a soft phonon mode at the M-point (1/2 1/2 0). However, our ab-initio calculations show quite unusually that all the M-point (1/2 1/2 0) phonons are stable, but two stable M3+ and M2- modes anharmonically couple with an unstable Bu mode at the zone center and lead to the cell doubling and the distorted structure. Magnetic exchange interactions in both the compounds have been computed on the basis of the ideal planar structure (P4/mmm space group) and with increasing amplitude of the Bu phonon mode. These reveal that the magnetic exchange interactions reduce significantly with increasing distortion. We have extended the ab-initio phonon calculation to high pressures, which reveal that, above 20 GPa of pressure, the undistorted planer CaFeO2 becomes dynamically stable. We also report computed phonon spectra in SrFeO3 that has a cubic structure, which is useful to understand the role of the difference in geometry of oxygen atoms around the Fe atom with respect to planer SrFeO2. Finally, powder neutron inelastic scattering experiments on SrFeO2 have also been performed at temperatures from 5 K to 353 K in the antiferromagnetic phase. The 5-K data are compared to the ab-initio calculations.

  2. X-ray absorption investigation of the valence state and electronic structure of La 1- xCa xCoO 3- δ in comparison with La 1- xSr xCoO 3- δ and La 1- xSr xFeO 3- δ

    NASA Astrophysics Data System (ADS)

    Haas, O.; Ludwig, Chr.; Bergmann, U.; Singh, R. N.; Braun, A.; Graule, T.

    2011-12-01

    3 d metal K-shell X-ray absorption spectra of perovskites with the composition La 1- xCa xCoO 3- δ ( x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La 1- xSr xCoO 3- δ ( x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La 1- xSr xFeO 3- δ ( x=0, 0.2, 0.4, 0.5, 0.6, 0.8) are compared on the basis of pre-edges, white line features and extended fine structures. The measurements were performed at 300 K and for La 1- xCa xCoO 3- δ also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t2g* and a decrease in eg* orbital occupancy, which is most accentuated in the LaCoO 3 sample. Virtually no Co K-edge shift was observed for the La 1- xCa xCoO 3- δ and La 1- xSr xCoO 3- δ compounds and the Co-O distances are also not significantly reduced when La 3+ is partially substituted by Ca 2+ or Sr 2+. From the pre-edge features of these perovskites we are tended to conclude that the t2g* orbitals are less, and the eg* orbitals are more occupied with increasing x in the Ca and Sr substituted compounds, whereas the total d-electron density is not changing. These results indicate that cobalt prefers a valence state of 3 + in these Co perovskites. This could also be confirmed with iodometric titrations. The Fe perovskites behave differently. In contrast to the Co perovskites, for La 1- xSr xFeO 3- δ perovskites the Fe K-edge is shifted, the pre-edge features intensity is increasing and the Fe-O bond length is decreasing with increasing x. The valence states of the iron in the La 1- xSr xFeO 3- δ perovskites in fact increase as much as x increases.

  3. Tracing Environmental Variation Over The Past 130 Years In The Barents Sea: Mineral Ratio (Mg/Ca, Sr/Ca, Ba/Ca, And Mn/Ca) Evidence In Shells Of The Circumpolar Greenland Cockle, Serripes groenlandicus

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Ambrose, W. G.; Johnson, B. J.; Carroll, M. L.; McMahon, K. W.; Denisenko, S. G.; Thorrold, S. R.

    2007-12-01

    In order to quantify the impacts of human induced climate change on Arctic marine ecosystems it is crucial to establish high-resolution proxies to record regional environmental variability. The Barents Sea region is highly influenced by the annual recession and precession of Arctic sea ice and, as an ecosystem is extremely sensitive to seasonal to decadal climatic changes. Long-lived, sessile, marine bivalves have the potential to provide detailed oceanographic and biological proxy information from the Barents Sea in locations where historic, long- term data logging does not exist. Here, we present preliminary mineral ratio evidence (Mg, Sr, Ba, Mn) for Barents Sea environmental variation from shells of the circumpolar Greenland cockle, Serripes groenlandicus, over the past 130 years from 4 different locations in Norwegian and Russian waters. For all mineral ratios there are clear seasonal trends corresponding with dark winter growth checks on the external surface of each individual. The seasonal patterns of Mg and Sr show progressive change. On average for 9 individuals, Mg/Ca was 10.6 percent greater and Sr/Ca was 5.5 percent lower on the winter checks compared to other values, while Ba/Ca and Mn/Ca ratios show peaks during the middle of the summer growth period. Mineral patterns from the Pechora Sea region are particularly pronounced, which may be related to the influence freshwater from summer river discharge. While the mineral data are initially compelling enough to demonstrate clear seasonal periodicity and inter-annual variation, we believe that a multi-proxy approach to interpreting the information obtained from these bivalves is critical. Therefore, parallel to this study, we are examining external, incremental growth and organic carbon isotopes of shell material from the same collection of bivalves.

  4. Pharmacological evidence that potentiation of plasmalemmal Ca(2+)-extrusion is functionally coupled to inhibition of SR Ca(2+)-ATPases in vascular smooth muscle cells.

    PubMed

    Zhang, Wen-Bo; Kwan, Chiu-Yin

    2016-04-01

    Cyclopiazonic acid (CPA), a specific inhibitor of sarcoplasmic reticulum (SR) Ca(2+)-ATPases, causes slowly developing and subsequently diminishing characteristic contractions in vascular smooth muscle, and the second application of CPA has incompletely repeatable effects, depending on the vessel type. The objective of the present study was to examine the mechanisms underlying the significant decrease of CPA-induced contractions upon the second application. A pharmacological intervention of Ca(2+) extrusion process as a strategy was performed to modulate vasoconstrictor effects of CPA in rat aortic ring preparations. CPA-induced contractions, expressed as percentages of the contractions induced by KCl (80 mM), were significantly decreased from 44.1 ± 5.7 to 7.6 ± 1.8 % (P < 0.001) upon the second application. The contractions, however, were completely repeatable in the presence of vanadate, an inhibitor of ATPases, but not of ouabain, an inhibitor of Na(+)-pumps. Strikingly, CPA-induced contractions were sustained and completely repeatable in Na(+)-free and low Na(+) medium. Furthermore, we found that the contractions were completely repeatable in the presence of 2',4'-dichlorobenzamil, an inhibitor of the forward mode of Na(+)/Ca(2+) exchangers, but not of KBR7943, an inhibitor of the reverse mode of Na(+)/Ca(2+) exchangers. Our findings indicate that CPA by inducing a transient rise in cytosolic Ca(2+) level causes a long-lasting upregulation of plasma membrane (PM) Ca(2+) extruders and thus leads to a diminished contraction upon its second application in blood vessels. This suggests that there is a functional coupling between PM Ca(2+) extruders and SR Ca(2+)-ATPases in rat aortic smooth muscle cells. PMID:26842648

  5. Multiferroicity in Mn-deficient Ca3CoMnO6: The consequence of Fe substitution

    NASA Astrophysics Data System (ADS)

    Lin, L.; Xie, Y. L.; Liu, M. F.; Guo, Y. J.; Yan, Z. B.; Liu, J.-M.

    2013-07-01

    We present careful experiments on the multiferroicity in Ca3CoMn0.92O6 by Fe substitution of Mn. It is revealed that a proper Fe substitution modulates the Co/Mn spin order, favoring the ferroelectricity. The multifold interactions between the intra-chain spins and inter-chain spins are analyzed. It is suggested that the Mn deficiency and Fe substitution can break the inter-chain interactions to some extent, resulting in the delicate competition between these mutual interactions. The modulation of the ionic (charge) disorder and spin frustration order is the core physics for improving the ferroelectric performance.

  6. In vitro and in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass.

    PubMed

    Li, H F; Xie, X H; Zhao, K; Wang, Y B; Zheng, Y F; Wang, W H; Qin, L

    2013-11-01

    In order to enhance the corrosion resistance of the Ca65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass because of the unique properties of high-entropy alloys. Our results showed that the mechanical properties and corrosion behavior were enhanced. The in vitro tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass did not show any obvious degradation after 4 weeks of implantation, and they can promote osteogenesis and new bone formation after 2 weeks of implantation. The improved mechanical properties and corrosion behavior can be attributed to the different chemical composition as well as the formation of a unique high-entropy atomic structure with a maximum degree of disorder.

  7. Critical currents and magnetization in c -axis textured Bi-Pb-Sr-Ca-Cu-O superconductors

    SciTech Connect

    Jin, S.; van Dover, R.B.; Tiefel, T.H.; Graebner, J.E. ); Spencer, N.D. )

    1991-02-25

    Transport critical currents and magnetization behavior in {ital c}-axis textured Bi-Pb-Sr-Ca-Cu-O superconductor ribbons have been studied. The highly oriented layer structure was achieved by a combination processing of spray coating on silver foil, cold rolling, and partial melting. Transport {ital J}{sub {ital c}} values as high as 2.3{times}10{sup 5} A/cm{sup 2} at 4.2 K, {ital H}=8 T ({ital H}{perpendicular}{ital ab}) have been obtained. The high {ital J}{sub {ital c}} at {ital H}{ge}5 T is maintained to temperatures near 20 K but it vanishes completely at or above {similar to}30 K, thus showing the limitation in useful, high-field operating temperatures for the Bi-system superconductors. A comparison of {ital J}{sub {ital c}} (transport) and {ital J}{sub {ital c}} (magnetization) indicates that the size scale of the circulating supercurrent loop in the Bean model nearly corresponds to the whole sample dimension rather than the orders-of-magnitude-smaller grain size. This demonstrates that the {ital a}-{ital b} grain boundaries in the melt-processed ribbons are not weakly coupled. The time decay of magnetization has also been studied.

  8. Synthesis and characterization of 110 K superconducting phase in Bi(Pb)-Sr-Ca-Cu-oxide

    NASA Astrophysics Data System (ADS)

    Chen, Y. L.; Stevens, R.; Lo, W.; Zhen, Y. S.

    1990-12-01

    The temperatures and sequence of formation of superconducting phases within the composition Bi(1.6)Pb(0.4)Sr2Ca2Cu4O(x) were determined using simultaneous DTA and TGA, XRD, and SEM. A single phase high-Tc ceramic was obtained by a solid state reaction using predetermined firing conditions, although a TEM study showed a small amount of glass phase in the grain boundary tripoint regions. The unit cell of the high-Tc phase was refined as a = 0.5413 nm, b = 0.5414 nm, c = 3.715 nm. The melting temperature of the high-Tc phase is in the region of 852-862 C. The effect of lead was believed to lower the temperature of formation of the high-Tc phase. Lead was also found to evaporate from the matrix during and after high-Tc phase formation, whereas bismuth was found to be stable in both the low-Tc phase and high-Tc phase compounds.

  9. Preparation of 110K (Bi, Pb)-Sr-Ca-Cu-O superconductor from glass precursor

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1990-01-01

    The Bi1.5Pb0.5Sr2Ca2Cu3O(x) glass, prepared by rapid quenching of the melt, showed T(sub g) of 383 C, crystallization temperature of approx. 446 C, melting temperature of approx. 855 C, and bulk density of 5.69 g/cu. cm. in air. The as-quenched glass was oxygen deficient. On heating in O2, it showed a slow, irreversible, and continuous weight gain starting at approx. 530 C. The influence of annealing conditions on the formation of various phases was investigated by XRD and electrical resistivity measurements. The 110K-T(sub c) phase did not form below 840 C. The amount of this phase increased with the sintering time at 840 C. A sample annealed at 840 C for 243 h in air and furnace cooled showed the highest T(sub c) (R=0) of 107.2 K and transition width delta T(sub c) (10 to 90 percent) of approx. 2 K.

  10. Preparation of 110K (Bi, Pb)-Sr-Ca-Cu-O superconductor from glass precursor

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1989-01-01

    The Bi1.5Pb0.5Sr2Ca2Cu3O(x) glass, prepared by rapid quenching of the melt, showed T(sub g) of 383 C, crystallization temperature of approx. 446 C, melting temperature of approx. 855 C, and bulk density of 5.69 g/cu. cm. in air. The as-quenched glass was oxygen deficient. On heating in O2, it showed a slow, irreversible, and continuous weight gain starting at approx. 530 C. The influence of annealing conditions on the formation of various phases was investigated by XRD and electrical resistivity measurements. The 110K-T(sub c) phase did not form below 840 C. The amount of this phase increased with the sintering time at 840 C. A sample annealed at 840 C for 243 h in air and furnace cooled showed the highest T(sub c)(R=0) of 107.2K and transition width delta T(sub c)(10 to 90 percent) of approx. 2 K.

  11. Ca, Sr, O and D isotope approach to defining the chemical evolution of hydrothermal fluids: example from Long Valley, CA, USA

    USGS Publications Warehouse

    Brown, Shaun T.; Kennedy, B. Mack; DePaolo, Donald J.; Hurwitz, Shaul; Evans, William C.

    2013-01-01

    We present chemical and isotopic data for fluids, minerals and rocks from the Long Valley meteoric-hydrothermal system. The samples encompass the presumed hydrothermal upwelling zone in the west moat of the caldera, the Casa Diablo geothermal field, and a series of wells defining a nearly linear, ∼16 km long, west-to-east trend along the likely fluid flow path. Fluid samples were analyzed for the isotopes of water, Sr, and Ca, the concentrations of major cations and anions, alkalinity, and total CO2. Water isotope data conform to trends documented in earlier studies, interpreted as indicating a single hydrothermal fluid mixing with local groundwater. Sr isotopes show subtle changes along the flow path, which requires rapid fluid flow and minimal reaction between the channelized fluids and the wallrocks. Sr and O isotopes are used to calculate fracture spacing using a dual porosity model. Calculated fracture spacing and temperature data for hydrothermal fluids indicate the system is (approximately) at steady-state. Correlated variations among total CO2, and the concentration and isotopic composition of Ca suggest progressive fluid degassing (loss of CO2), which drives calcite precipitation as the fluid flows west-to-east and cools. The shifts in Ca isotopes require that calcite precipitated at temperatures of 150–180 °C is fractionated by ca. −0.3‰ to −0.5‰ relative to aqueous species. Our data are the first evidence that Ca isotopes undergo kinetic fractionation at high temperatures (>100 °C) and can be used to trace calcite precipitation along hydrothermal fluid flow paths.

  12. Exploring the impact of temperature and fluid chemistry on Ca and Sr isotope composition of Arctica islandica shells via experimental alteration

    NASA Astrophysics Data System (ADS)

    Goos, Manuela; Eisenhauer, Anton; Liebetrau, Volker; Böhm, Florian; Fietzke, Jan; Nehrke, Gernot; Buhl, Dieter; Mavromatis, Vasileios; Dietzel, Martin

    2016-04-01

    Carbonate shells of marine organisms record by their chemical and isotopic composition environmental conditions like temperature, salinity and pH during their formation. However, primary signals can be overprinted by diagenesis, which has to be considered for the interpretation of environmental proxy data and on the other side may provide additional information about distinct reaction pathways throughout diagenesis (e.g. Allison et al, 2007). Aragonitic Arctica islandica shells widely used as proxy archives (e.g. Schöne et al, 2005) were chosen for hydrothermal alteration experiments in order to get a more detailed insight into diagenetic effects. Here we present results of experiments in which Arctica islandica shell fragments were exposed to North Sea seawater at temperatures of 100r{ }C and 175r{ }C at distinct reaction times. Strontium isotope composition of the experimental medium was adjusted from an original composition of δ 88/86SrSRM987= 0.391(1)‰ and 87Sr/86Sr= 0.70921(1) to δ 88/86SrSRM987= 0.179(1)‰ and 87Sr/86Sr= 0.70789(1) by sulfate extraction and Sr replacement procedures. The artificially altered shell material (six sub-samples of six shell fragments) and the corresponding solutions were prepared and analyzed. Results show that at 100r{ }C aragonite is still the predominant phase, but show lower peak intensities with Raman and XRD near the surface of the shell fragments. At 175r{ }C the aragonitic shell material recrystallized almost completely to calcite. In addition a rim of weakly ordered dolomite (10μ m) was found around these samples. Analysis of element concentrations of initial and final solutions show that at 175r{ }C Sr and Ca concentrations increase (Sr: 79 to 183 μ mol/l; Ca: 8 to 30 mmol/l), while Mg concentration decreases (Mg: 42 to 22 mmol/l). A corresponding Sr and Ca depletion along with an increase of Mg occurred in the samples, especially in the dolomite rim. At 100r{ }C only minor increase of Sr, Ca and Mg

  13. Synthesis and magnetic properties of La-substituted M-type Sr hexaferrites

    NASA Astrophysics Data System (ADS)

    Seifert, D.; Töpfer, J.; Langenhorst, F.; Le Breton, J.-M.; Chiron, H.; Lechevallier, L.

    2009-12-01

    Single-phase M-type hexagonal ferrites Sr 1-xLa xFe 12O 19 (0≤ x≤1) were prepared by a ceramic route. The stability limits of the ferrite phases were determined with a combination of various microscopy techniques, electron-probe micro-analysis, powder X-ray diffraction and thermal analysis. SrFe 12O 19 ( x=0) is stable up to 1420 °C, whereas LaFe 12O 19 ( x=1) exists between 1360 and 1400 °C only. The lattice parameters of Sr 1-xLa xFe 12O 19 exhibit a linear variation with x, i.e. a0 slightly increases and c0 decreases with x, leading to a decrease of the unit cell volume with x. The saturation magnetization at T=5 K decreases with increasing La concentration. Room temperature Mössbauer analysis shows that the Fe 3+/Fe 2+ valence change occurs in the 2a sites for the whole composition range.

  14. Sr/Ca proxy sea-surface temperature reconstructions from modern and holocene Montastraea faveolata specimens from the Dry Tortugas National Park

    USGS Publications Warehouse

    Flannery, Jennifer A.; Poore, Richard Z.

    2013-01-01

    Sr/Ca ratios from skeletal samples from two Montastraea faveolata corals (one modern, one Holocene, ~6 Ka) from the Dry Tortugas National Park were measured as a proxy for sea-surface temperature (SST). We sampled coral specimens with a computer-driven triaxial micromilling machine, which yielded an average of 15 homogenous samples per annual growth increment. We regressed Sr/Ca values from resulting powdered samples against a local SST record to obtain a calibration equation of Sr/Ca = -0.0392 SST + 10.205, R = -0.97. The resulting calibration was used to generate a 47-year modern (1961-2008) and a 7-year Holocene (~6 Ka) Sr/Ca subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual Sr/Ca cycles ranging in amplitude from ~0.3 and 0.5 mmol/mol. The amplitude of ~0.3 to 0.5 mmol/mol equates to a 10-15°C seasonal SST amplitude, which is consistent with available local instrumental records. Summer maxima proxy SSTs calculated from the modern coral Sr/ Ca tend to be fairly stable: most SST maxima from 1961–2008 are 29°C ± 1°C. In contrast, winter minimum SST calculated in the 47-year modern time-series are highly variable, with a cool interval in the early to mid-1970s. The Holocene (~6 Ka) Montastraea faveolata coral also yields distinct annual Sr/Ca cycles with amplitudes ranging from ~0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and thus resulting SST estimates over the ~7-year long record are similar to those from the modern coral. We conclude that Sr/Ca from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.

  15. The effect of skeletal mass accumulation in Porites on coral Sr/Ca and δ18O paleothermometry

    NASA Astrophysics Data System (ADS)

    Gagan, Michael K.; Dunbar, Gavin B.; Suzuki, Atsushi

    2012-03-01

    Paleotemperature estimates based on coral Sr/Ca have not been widely accepted because the reconstructed glacial-Holocene shift in tropical sea-surface temperature (˜4-6°C) is larger than that indicated by foraminiferal Mg/Ca (˜2-4°C). We show that corals over-estimate changes in sea-surface temperature (SST) because their records are attenuated during skeletogenesis within the living tissue layer. To quantify this process, we microprofiled skeletal mass accumulation within the tissue layer of Porites from Australasian coral reefs and laboratory culturing experiments. The results show that the sensitivity of the Sr/Ca and δ18O thermometers in Porites will be suppressed, variable, and dependent on the relationship between skeletal growth rate and mass accumulation within the tissue layer. Our findings help explain why δ18O-SST sensitivities for Porites range from -0.08‰/°C to -0.22‰/°C and are always less than the value of -0.23‰/°C established for biogenic aragonite. Based on this observation, we recalibrated the coral Sr/Ca thermometer to determine a revised sensitivity of -0.084 mmol/mol/°C. After rescaling, most of the published Sr/Ca-SST estimates for the Indo-Pacific region for the last ˜14,000 years (-7°C to +2°C relative to modern) fall within the 95% confidence envelope of the foraminiferal Mg/Ca-SST records. We conclude that two types of calibration scales are required for coral paleothermometry; an attenuated Porites-specific thermometer sensitivity for studies of seasonal to interannual change in SST and, importantly, the rescaled -0.084 mmol/mol/°C Sr/Ca sensitivity for studies of 20th-century trends and millennial-scale changes in mean SST. The calibration-scaling concept will apply to the development of transfer functions for all geochemical tracers in corals.

  16. Structural and dielectric behavior of pulsed laser ablated Sr 0.6Ca 0.4TiO 3 thin film and asymmetric multilayer of SrTiO 3 and CaTiO 3

    NASA Astrophysics Data System (ADS)

    Chakraborty, Pradip; Choudhury, Palash Roy; Krupanidhi, S. B.

    2011-12-01

    Homogeneous thin films of Sr 0.6Ca 0.4TiO 3 (SCT40) and asymmetric multilayer of SrTiO 3 (STO) and CaTiO 3 (CTO) were fabricated on Pt/Ti/SiO 2/Si substrates by using pulsed laser deposition technique. The electrical behavior of films was observed within a temperature range of 153 K-373 K. A feeble dielectric peak of SCT40 thin film at 273 K is justified as paraelectric to antiferroelectric phase transition. Moreover, the Curie-Weiss temperature, determined from the ɛ'( T) data above the transition temperature is found to be negative. Using Landau theory, the negative Curie-Weiss temperature is interpreted in terms of an antiferroelectric transition. The asymmetric multilayer exhibits a broad dielectric peak at 273 K, and is attributed to interdiffusion at several interfaces of multilayer. The average dielectric constants for homogeneous Sr 0.6Ca 0.4TiO 3 films (˜650) and asymmetric multilayered films (˜350) at room temperature are recognized as a consequence of grain size effect. Small frequency dispersion in the real part of the dielectric constants and relatively low dielectric losses for both cases ensure high quality of the films applicable for next generation integrated devices.

  17. Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr3Ru2O7

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Bohnenbuck, B.; Chuang, Y.-D.; Geck, J.; Tokura, Y.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Sawatzky, G. A.; Damascelli, A.

    2010-03-01

    We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr3(Ru1-xMnx)2O7, performed at both Ru and Mn L-edges. Resonant magnetic superstructure reflections, which indicate an incipient instability of the parent compound, are detected below the transition. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x˜0.05 Mn substitution. In collaboration with A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley Lab), I. Zegkinoglou, M.W. Haverkort (MPI, Stuttgart), I.S. Elfimov, D.G. Hawthorn (UBC), R. Mathieu, S. Satow, H. Takagi (Tokyo), H.-H. Wu and C. Sch"ußler-Langeheine (Cologne).

  18. 40K-40Ca and 87Rb-86Sr Dating by SIMS: The Double-Plus Advantage

    NASA Astrophysics Data System (ADS)

    Harrison, T. M.; McKeegan, K. D.; Schmitt, A. K.

    2009-12-01

    retentivity of 40Ca* relative to 40Ar* in white micas. This approach offers the potential to develop a branched-decay thermochronometer (K-Ca-Ar) permitting simultaneous solution of temperature-time history from μm-scale isotopic variations. A further advantage is that even low resolution SIMS instruments (e.g., ims7f) can utilize the double-plus method. Initial investigations using the same double-plus approach for Rb-Sr dating show promise. While resolving 87Rb+ from 87Sr+ requires an MRP of ~290k, unattainable using any current SIMS instrument, 87Rb++ is so strongly suppressed that determination of 87Sr++ is possible with minor peak stripping. 87Rb/86Sr can be determined either from 85Rb+/88Sr+ at MRP≈ 8k or by the use of energy filtering. In addition to micas, these approaches may be applicable to any mineral systems enriched in alkali metals relative to alkaline earths, such as alkali feldspars, feldspathoids, and alkaline halides.

  19. The incongruent melting and melt textured solidification process of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}

    SciTech Connect

    Polonka, J.

    1993-09-01

    The melting and solidification was studied using in-situ high temperature XRD from melting point to 900{degree}C in 0.2, 0.1, 0.02 atm O{sub 2} and pure N{sub 2}. The incongruent melting point of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} was lowered by decreasing the partial O{sub 2} pressure from 870C (in .2 atm O{sub 2}) to 830C (in pure N{sub 2} atmosphere). As temperature was increased the incongruent melting of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} followed a phase sequence in which (Ca, Sr)CuO{sub 2} {r_arrow} (Ca, Sr)CuO{sub 2} {r_arrow} (Ca,Sr)O occur in presence of Bi-rich liquid. At 900C, the only crystalline phase present in the melt was (Ca,Sr)O. This phase sequence remained the same for all four different partial O{sub 2} pressures. During the solidification of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}, from 10C below the melting point to 760C, the major phases that form depend on the partial O{sub 2} pressure. As partial O{sub 2} pressures was lowered from 0.2 to 0 atm, the major second phase formation out of the melt follows the sequence of (Ca, Sr)CuO{sub 2} {r_arrow} (Ca, Sr)CuO{sub 2} {r_arrow} (Ca,Sr)O respectively. At 0.1 Atm partial O{sub 2} pressure and below, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} solidified out of the melt; at 0.2 atm of O{sub 2} Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 6} forms instead.

  20. Evaluation of Sr/Ca-based paleoclimate reconstructions in modern and Medieval Diploria strigosa corals in the northeastern Caribbean

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Pearson, S. P.; Kilbourne, K.

    2013-12-01

    Tropical sea surface temperature (SST) has been implicated as a driver of climate changes during the Medieval Climate Anomaly (MCA, 950-1300 A.D.) but little data exists from the tropical oceans during this time period. We collected three modern and seven sub-fossil Diploria strigosa coral colonies from an overwash deposit on Anegada, British Virgin Islands (18.73 °N, 63.33 °W) in order to reconstruct climate in the northeastern Caribbean and Tropical North Atlantic during the MCA. The first step in our reconstruction was to verify the climate signal from this species at this site. We sub-sampled the modern corals along thecal walls with an average sampling resolution of 11-13 samples per year. Sr/Ca ratios measured in the sub-samples were calibrated to temperature using three different calibration techniques (ordinary least squares, reduced major axis, and weighted least squares (WLS)) on the monthly data that includes the seasonal cycles and on the monthly anomaly data. WLS regression accounts for unequal errors in the x and y terms, so we consider it the most robust technique. The WLS regression slope between gridded SST and coral Sr/Ca is similar to the previous two calibrations of this species. Mean Sr/Ca for each of the three modern corals is 8.993 × 0.004 mmol/mol, 9.127 × 0.003 mmol/mol, and 8.960 × 0.007 mmol/mol. These straddle the mean Diploria strigosa Sr/Ca found by Giry et al., (2010), 9.080 mmol/mol, at a site with nearly the same mean SST as Anegada (27.4 °C vs. 27.5 °C). The climatological seasonal cycles for SST derived from the modern corals are statistically indistinguishable from the seasonal cycles in the instrumental SST data. The coral-based seasonal cycles have ranges of 2.70 × 0.31 °C, 2.65 × 0.08 °C and 2.71 × 0.53 °C. These results indicate that this calibration can be applied to our sub-fossil coral data. We applied the WLS calibration to monthly-resolution Sr/Ca data from multiple sub-fossil corals dating to the medieval

  1. Strain-induced topological transition in SrRu2O6 and CaOs2O6

    NASA Astrophysics Data System (ADS)

    Ochi, Masayuki; Arita, Ryotaro; Trivedi, Nandini; Okamoto, Satoshi

    2016-05-01

    The topological property of SrRu2O6 and isostructural CaOs2O6 under various strain conditions is investigated using density functional theory. Based on an analysis of parity eigenvalues, we anticipate that a three-dimensional strong topological insulating state should be realized when band inversion is induced at the A point in the hexagonal Brillouin zone. For SrRu2O6 , such a transition requires rather unrealistic tuning, where only the c axis is reduced while other structural parameters are unchanged. However, given the larger spin-orbit coupling and smaller lattice constants in CaOs2O6 , the desired topological transition does occur under uniform compressive strain. Our study paves a way to realize a topological insulating state in a complex oxide, which has not been experimentally demonstrated so far.

  2. Characterization of Bi sbnd Pb sbnd Sb sbnd Ca sbnd Sr sbnd Cu sbnd O superconductor sintered in controlled atmosphere

    NASA Astrophysics Data System (ADS)

    Wang, W. N.; Koo, H. S.; Liu, R. S.; Wu, P. T.

    1989-12-01

    (Bi 1.6Pb 0.4-xSb xCa 2Sr 2Cu 3 superconductors were prepared by sintering under the reduced oxygen partial pressure. Tc,zero above 105 K can be achieved bu much shorter heat treatment compared with the conventional preparation under ambient atmosphere. DTA study indicated that a significant decrease of reation temperature in forming the superconducting phase was observed under reduced oxygen partial pressure. A densor material with better superconducting properties was obtained due to this effect. Tc,zero of 108 K in (Bi 1.6Pb 0.4-xSb x)Ca 2Sr 2Cu 3O y superconductors with x ≤ 0.1 can be prepared by sinterting for 24 hours under 1/13 O 2 and 12/13 Ar.

  3. Strain-induced topological transition in SrRu2O6 and CaOs2O6

    DOE PAGES

    Ochi, Masayuki; Arita, Ryotaro; Trivedi, Nandini; Okamoto, Satoshi

    2016-05-24

    The topological property of SrRu$_2$O$_6$ and isostructural CaOs$_2$O$_6$ under various strain conditions is investigated using density functional theory. Based on an analysis of parity eigenvalues, we anticipate that a three-dimensional strong topological insulating state should be realized when band inversion is induced at the A point in the hexagonal Brillouin zone. For SrRu$_2$O$_6$, such a transition requires rather unrealistic tuning, where only the $c$ axis is reduced while other structural parameters are unchanged. However, given the larger spin-orbit coupling and smaller lattice constants in CaOs$_2$O$_6$, the desired topological transition does occur under uniform compressive strain. Our study paves a waymore » to realize a topological insulating state in a complex oxide, which has not been experimentally demonstrated so far.« less

  4. Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr3 Ru 2 O 7

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Zhu, Z. H.; Bohnenbuck, B.; Chuang, Y.-D.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Elfimov, I. S.; Sawatzky, G. A.; Damascelli, A.

    2011-03-01

    We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr 3 (Ru 1-x Mn x)2 O7 , performed at both Ru and Mn L -edges. Resonant magnetic superstructure reflections together with ab-initio density functional theory calculations identify the ground state as a spin checkerboard with blocks of 4 spins up and 4 spins down. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x ~ 0.05 Mn substitution. Perhaps more important, our results suggest that the same checkerboard instability might be present already in the parent compound Sr 3 Ru 2 O7 . In collaboration with: A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley) I. Zegkinoglou, M.W. Haverkort (MPI) J. Geck, D.G. Hawthorn (UBC) R. Mathieu, Y. Tokura, S. Satow, H. Takagi (Tokyo) H.-H. Wu and C. Schussler-Langeheine (Cologne).

  5. Cluster Chemistry in Electron-Poor Ae-Pt-Cd Systems (Ae=Ca, Sr, Ba): (Sr,Ba)Pt2Cd4, Ca6Pt8Cd16, and Its Known Antitype Er6Pd16Sb8

    SciTech Connect

    Samal, Saroj L.; Gulo, Fakhili; Corbett, John D.

    2013-02-18

    Three new ternary polar intermetallic compounds, cubic Ca6Pt8Cd16, and tetragonal (Sr, Ba)Pt2Cd4 have been discovered during explorations of the Ae–Pt–Cd systems. Cubic Ca6Pt8Cd16 (Fm-3m, Z = 4, a = 13.513(1) Å) contains a 3D array of separate Cd8 tetrahedral stars (TS) that are both face capped along the axes and diagonally bridged by Pt atoms to generate the 3D anionic network Cd8[Pt(1)]6/2[Pt(2)]4/8. The complementary cationic surface of the cell consists of a face-centered cube of Pt(3)@Ca6 octahedra. This structure is an ordered ternary variant of Sc11Ir4 (Sc6Ir8Sc16), a stuffed version of the close relative Na6Au7Cd16, and a network inverse of the recent Er6Sb8Pd16 (compare Ca6Pt8Cd16). The three groups of elements each occur in only one structural version. The new AePt2Cd4, Ae = Sr, Ba, are tetragonal (P42/mnm,Z = 2, a ≈ 8.30 Å, c ≈ 4.47 Å) and contain chains of edge-sharing Cd4 tetrahedra along c that are bridged by four-bonded Ba/Sr. LMTO-ASA and ICOHP calculation results and comparisons show that the major bonding (Hamilton) populations in Ca6Pt8Cd16 and Er6Sb8Pd16 come from polar Pt–Cd and Pd–Sb interactions, that Pt exhibits larger relativistic contributions than Pd, that characteristic size and orbital differences are most evident for Sb 5s, Pt8, and Pd16, and that some terms remain incomparable, Ca–Cd versus Er–Pd.

  6. Thermoelectromotive force in Bi2Sr2Ca2Cu4O11 bismuth-based high-temperature superconductor

    NASA Astrophysics Data System (ADS)

    Ragimov, S. S.; Askerzade, I. N.

    2010-10-01

    The temperature dependence of the thermoemf in Bi2Sr2Ca2Cu4O11 bismuth-based high-temperature superconductors is studied. The thermoemf is positive at high temperatures ( T > 300 K) and negative at low temperatures. As the temperature decreases, the thermoemf reaches a maximum slightly above T c and then sharply drops to zero. The results can be explained in the framework of the two-band theory with a linear temperature term.

  7. Incommensurate fluctuations in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}

    SciTech Connect

    Mook, H.A.; Chakoumakos, B.C.

    1996-12-31

    A special neutron scattering technique has been used to discover an incommensurate fluctuation in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} that appears below {Tc}. The fluctuation is identified as a dynamic charge density wave since its scattering intensity appears to increase with increasing momentum transfer. The fluctuation is found at a wavevector near 2k{sub F} and could be associated with a dynamic stripe phase.

  8. Temperature-dependent photoemission features for overdoped Bi2Sr2CaCu2O8 + x cuprates

    NASA Astrophysics Data System (ADS)

    Rast, S.; Frazer, B. H.; Onellion, M.; Schmauder, T.; Abrecht, M.; Touzelet, O.; Berger, H.; Margaritondo, G.; Pavuna, D.

    2000-07-01

    We report temperature-dependent angle-resolved photoemission spectra for overdoped Bi2Sr2CaCu2O8 + x single-crystal samples. The data indicate that there is a special temperature (T+) where the spectral function changes intensity, and where the energy difference between the peak and dip features changes. The data also demonstrate that immediately above the superconducting transition temperature, the system exhibits a non-Lorentzian lineshape. We discuss implications of the data.

  9. Temperature and wavevector dependence of overdoped Bi_2Sr_2CaCu_2O_8+x single crystal samples

    NASA Astrophysics Data System (ADS)

    Rast, S.; Klohs, A.; Frazer, B. H.; Hirai, Y.; Schmauder, T.; Gatt, R.; Abrecht, M.; Pavuna, D.; Margaritondo, G.; Onellion, M.

    2000-03-01

    We report on measuring the temperature and wavevector change of angle-resolved photoemission spectra for overdoped Bi_2Sr_2CaCu_2O_8+x single crystal samples. Spectra taken from close to <0, π > to close to <π , π > were analyzed. The changes of spectral lineshape with temperature and wave vector indicate qualitatively different behavior in different parts of the Brillouin zone and will be analyzed and presented.

  10. Adsorption of bivalent ions (Ca(II), Sr(II) and Co(II)) onto FEBEX bentonite

    NASA Astrophysics Data System (ADS)

    Missana, T.; García-Gutiérrez, M.

    The sorption of the bivalent ions Ca, Sr and Co onto the Spanish “ FEBEX” bentonite, converted to its Na-form was analysed. Several batch experiments were carried out to study, the effects of pH, ionic strength and radionuclide concentration on the uptake of these bivalent elements, independently. Results showed that the sorption behaviour of Ca and Sr is very similar both from a qualitative and quantitative point of view. The main sorption mechanism for Ca and Sr on the Na-montmorillonite is the ionic exchange and sorption is linear in the whole range of concentrations investigated. The mean logarithm of selectivity coefficient, with respect to Na, obtained from the above-mentioned sorption studies, considering trace concentrations of these elements, is 0.65 ± 0.11 and 0.66 ± 0.06 for Ca and Sr, respectively. However, a small contribution due to surface complexation at the clay edge sites (SOH) had to be considered to fit adequately the sorption results obtained at pH higher than 8 and higher ionic strengths. The sorption behaviour of Co is quite different from that observed for the previous elements. The pH-dependence of Co sorption on the clay is significantly more noticeable, indicating a major contribution of surface complexation at the edge sites. Sorption due to ionic exchange becomes more evident when the ionic strength decreases. The value of the logarithm of the selectivity coefficient, with respect to Na, used in the simulations was 0.62 ± 0.13. The sorption isotherms with Co indicated the existence of two different complexation sites (weak and strong) that were accounted for in the final modelling.

  11. Effect of neutron irradiation on Tc of Pb-doped BiSrCaCuO superconductor

    NASA Astrophysics Data System (ADS)

    Herr, Young-Hoi; Lee, Kwang-Hee; Kim, Chan-Joong; Lee, Hee-Gyoun; Kim, Chun-Taik

    1989-09-01

    A Pb-doped BiSrCaCuO superconductor was irradiated in a TRIGA MARK III reactor up to a neutron fluence of 7.6 x 10 to the 17th n/sq cm. The measured superconducting transition temperature (Tc) after irradiation was decreased to 92.5 K from nonirradiated data of 102 K. The fractional decrease of the Tc was compared with results for other superconducting materials. Some recovery of irradiation-induced Tc decrease was observed.

  12. Effect of Sr-substitution on the restitution of superconductivity in Pr-substituted at rare earth and Ba-site in EuBa 2Cu 3O z

    NASA Astrophysics Data System (ADS)

    Thampi, R. S.; Rayaprol, S.; Mavani, Krushna; Kuberkar, D. G.; Gonal, M. R.; Prasad, R.; Kulkarni, R. G.

    2001-06-01

    We report the effect of Sr-substitution in restoring the superconductivity of Pr-doped (Eu 1- xPr x)Ba 2Cu 3O z [A] and Eu(Ba 2- xPr x)Cu 3O z [B] samples. The structural and superconducting properties of these A and B samples have been investigated using X-ray diffraction, a.c. susceptibility, electrical resistivity, d.c. magnetization and iodometric measurements. It is observed that the superconductivity gets suppressed at the rate of 1.6 K per at.% of Pr substitution at Eu-site due to the localization of mobile holes, while the sample with 15% Pr at Ba-site [B(0.3)] becomes non-superconducting mainly due to the hole filling and localization of holes. However, the increasing substitution of Sr at Ba-site in both A(0.4) and B(0.3) samples upto 25% resulted in the restoration of superconductivity (T c∼33 K) due to the delocalization of holes. Interestingly, the increasing substitution of Sr at Eu-site in the non-superconducting B(0.4) sample upto 30%, increases Tc from 0 to 52 K mainly due to the hole doping mechanism which is much faster and larger restoration of superconductivity than the Ba-site doping of Sr in the same sample.

  13. Persistent Fe moments in the normal-state collapsed-tetragonal phase of the pressure-induced superconductor Ca0.67Sr0.33Fe2As2

    NASA Astrophysics Data System (ADS)

    Jeffries, J. R.; Butch, N. P.; Lipp, M. J.; Bradley, J. A.; Kirshenbaum, K.; Saha, S. R.; Paglione, J.; Kenney-Benson, C.; Xiao, Y.; Chow, P.; Evans, W. J.

    2014-10-01

    Using nonresonant Fe Kβ x-ray emission spectroscopy, we reveal that Sr substitution into CaFe2As2 decouples the Fe moment from the volume collapse transition, yielding a collapsed-tetragonal, paramagnetic normal state out of which superconductivity develops. X-ray diffraction measurements implicate the c-axis lattice parameter as the controlling criterion for the Fe moment, promoting a generic description for the appearance of pressure-induced superconductivity in the alkaline-earth-based 122 ferropnictides (AFe2As2). The evolution of Tc with pressure lends support to theories for superconductivity involving unconventional pairing mediated by magnetic fluctuations.

  14. Sintering and hot isostatic pressing of Bi2Sr2CaCu2O(x)

    NASA Astrophysics Data System (ADS)

    Nash, A. S.; Nash, P.; Poeppel, R. B.; Goretta, K. C.

    1991-01-01

    The Bi2Sr2CaCu2O(x) phase was synthesized by solid-state reaction of oxides and carbonates. Initial compositions of Bi:Sr:Ca:Cu were 4:3:3:6 and 2:1.7:1:2. Pellets of the pure powder and powder containing 2.5, 5, or 15 wt percent Ag were cold-pressed and either sintered or hot isostatically pressed (HIPped). For HIPping, the pellets were encased in thin Ag sheets, canned in steel, and pressed at 105 MPa in argon at 800 or 850 C. HIPping produced dense specimens, but sintering did not. HIPping induced very little decomposition of the Bi2Sr2CaCu2O(x), but a post-HIP anneal was needed to raise the transition temperature above 80 K. The Ag additions appeared to minimize microcracking during HIPping at 800 C. Little microcracking was evident in any of the specimens HIPped at 850 C.

  15. ^99,101Ru NMR Study of Sr_1-xCa_xRuO3 single crytals.

    NASA Astrophysics Data System (ADS)

    Daniel, M.; Budnick, J. I.; Hines, W. A.; Cao, G.

    2000-03-01

    A zero-field spin-echo NMR study of ^99,101Ru has been carried out on 60 mg samples of Sr_1-xCa_xRuO3 (x=0, 0.25, and 0.50) single crystals[1]. The NMR spectrum of SrRuO3 consists of two peaks at 64.4 and 72.2 MHz, corresponding to the ^99Ru and ^101Ru isotopes, respectively, and a hyperfine field of 328 kOe. A clear modulation of the spin-echo amplitude, with a period of τ m = 25 μ s, was observed for the ^99Ru isotope. Measurements of the magnetization indicate that the easy axis lies in the plane perpendicular to the c-axis[1]. Using this result, the electric quadrupole frequency is calculated to be 80 kHz, much less than the centeral peak linewidth which is principally magnetic in orign. With the replacement of Sr by Ca, there is essentially no change in the peak frequencies; however, both peaks show a significant reduction in height with intensity being shifted into the broad wings. The effect of Ca doping on the electric field is observed through the variation of ν _Q. These results will be discussed in terms of structural variation and ferromagnetic exchange coupling. [1] G. Cao, S. McCall, M. Shepard, J. E. Crow, and R. P. Guertin, Phys. Rev. B56, 321(1997).

  16. Chronology of lunar granite 12033,576: Resetting of Rb-Sr and K-Ca isochrons

    NASA Technical Reports Server (NTRS)

    Shih, C.-Y.; Wiesmann, H.; Garrison, D. H.; Nyquist, L. E.; Bogard, D. D.

    1993-01-01

    Lunar granite 12033,576 is a subsample of the 'large' (approximately 1 g) felsite 12033,507 which was identified from a collection of 4-10 mm particles from the 12033 soil sampled from the north rim of Head Crater in the eastern part of Oceanus Procellarum. Discordant ages of approximately 3.6, approximately 0.8, approximately 3.9, and approximately 2.2 Ga for this lunar granite were obtained, respectively, by the K-Ca, Ar-39/Ar-40, and U-Pb zircon methods in previous studies and by the Rb-Sr method is this study. Assuming the granite crystallized approximately 3.9 Ga ago (zircon age) and was shocked by meteoritic impacts at 0.8 Ga ago (Ar-39-Ar-40 age), the intermediate apparent ages by the Rb-Sr and K-Ca methods can be interpreted as reset by diffusion of the parent and daughter nuclides. The Rb-Sr age is less resistant to resetting than the K-Ca age, but more resistant that the Ar-39/Ar-40 age.

  17. Ultracold magnetically tunable interactions without radiative-charge-transfer losses between Ca+, Sr+, Ba+, and Yb+ ions and Cr atoms

    NASA Astrophysics Data System (ADS)

    Tomza, Michał

    2015-12-01

    The Ca+, Sr+, Ba+, and Yb+ ions immersed in an ultracold gas of the Cr atoms are proposed as experimentally feasible heteronuclear systems in which ion-atom interactions at ultralow temperatures can be controlled with magnetically tunable Feshbach resonances without charge transfer and radiative losses. Ab initio techniques are applied to investigate electronic-ground-state properties of the (CaCr)+, (SrCr)+, (BaCr)+, and (YbCr)+ molecular ions. The potential energy curves, permanent electric dipole moments, and static electric dipole polarizabilities are computed. The spin-restricted open-shell coupled-cluster method restricted to single, double, and noniterative triple excitations and the multireference configuration-interaction method restricted to single and double excitations are employed. The scalar relativistic effects are included within the small-core energy-consistent pseudopotentials. The leading long-range induction and dispersion interaction coefficients are also reported. Finally, magnetic Feshbach resonances between the Ca+, Sr+, Ba+, and Yb+ ions interacting with the Cr atoms are analyzed. The present proposal opens the way towards robust quantum simulations and computations with ultracold ion-atom systems free of radiative charge-transfer losses.

  18. Manufacture of (Bi,Pb)2Sr2Ca2Cu3O10-based tapes with a composite sheath

    NASA Astrophysics Data System (ADS)

    Grivel, J.-C.; Abrahamsen, A. B.; Andersen, N. H.; Saksl, K.

    2008-02-01

    (Bi,Pb)2Sr2Ca2Cu3O10-based single-filament tapes were prepared using a pure Ag protective sheath in contact with the ceramic core and an external sheath consisting of Ni. The influence of the composite sheath geometry on the (Bi,Pb)2Sr2Ca2Cu3O10 phase formation kinetics was studied by in-situ synchrotron x-ray diffraction in a 8.5% O2 - 91.5% N2 gas mixture and was found to depend strongly on the sheath architecture as a consequence of differences in the oxygen supply between the ceramic core and the outer atmosphere. Owing to the efficient protection of the pure Ag layer against Ni diffusion, the critical temperature of the (Bi,Pb)2Sr2Ca2Cu3O10 phase is unaffected. Critical current densities as high as 35 kA/cm2 (77K, self field) were obtained in a single heat treatment when a slow cooling rate was used. The ceramic density was significantly improved in comparison with that of tapes prepared using only pure Ag as sheath material and heat treated once. This effect can be attributed to the higher mechanical strength of the composite sheath at elevated temperatures, which prevents the development of an otherwise significant porosity during the growth of the superconducting crystallites.

  19. Interaction between endoplasmic/sarcoplasmic reticulum stress (ER/SR stress), mitochondrial signaling and Ca(2+) regulation in airway smooth muscle (ASM).

    PubMed

    Delmotte, Philippe; Sieck, Gary C

    2015-02-01

    Airway inflammation is a key aspect of diseases such as asthma. Several inflammatory cytokines (e.g., TNFα and IL-13) increase cytosolic Ca(2+) ([Ca(2+)]cyt) responses to agonist stimulation and Ca(2+) sensitivity of force generation, thereby enhancing airway smooth muscle (ASM) contractility (hyper-reactive state). Inflammation also induces ASM proliferation and remodeling (synthetic state). In normal ASM, the transient elevation of [Ca(2+)]cyt induced by agonists leads to a transient increase in mitochondrial Ca(2+) ([Ca(2+)]mito) that may be important in matching ATP production with ATP consumption. In human ASM (hASM) exposed to TNFα and IL-13, the transient increase in [Ca(2+)]mito is blunted despite enhanced [Ca(2+)]cyt responses. We also found that TNFα and IL-13 induce reactive oxidant species (ROS) formation and endoplasmic/sarcoplasmic reticulum (ER/SR) stress (unfolded protein response) in hASM. ER/SR stress in hASM is associated with disruption of mitochondrial coupling with the ER/SR membrane, which relates to reduced mitofusin 2 (Mfn2) expression. Thus, in hASM it appears that TNFα and IL-13 result in ROS formation leading to ER/SR stress, reduced Mfn2 expression, disruption of mitochondrion-ER/SR coupling, decreased mitochondrial Ca(2+) buffering, mitochondrial fragmentation, and increased cell proliferation.

  20. Mg/Ca, Sr/Ca, and stable isotopes in modern and Holocene Protothaca staminea shells from a northern California coastal upwelling region

    USGS Publications Warehouse

    Takesue, R.K.; VanGeen, A.

    2004-01-01

    This study explores the potential of intertidal Protothaca staminea shells as high-resolution geochemical archives of environmental change in a coastal upwelling region. Mg/Ca and Sr/Ca ratios were analyzed by excimer laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) at sub-weekly temporal resolution in shells growing ???1 mm per month. Growth patterns of a modern P. staminea shell from Humboldt Bay, California, collected in December 1999 made it possible to infer a lifespan from 1993 to 1998. Growth hiatuses in the shell may have excluded records of extreme events. Mg/Ca ratios appeared to be partly controlled by water temperature; the correlation coefficient between temperature and Mg/Ca was r = 0.71 in one of four growth increments. Significant year-to-year differences in the sensitivity of Mg/Ca to temperature in P. staminea could not be explained, however. Sr/Ca ratios appeared to be more closely related to shell growth rate. Oxygen isotopes, measured at 2-week temporal resolution in the same shell, did not show a clear relation to local temperature in summer, possibly because temperatures were higher and less variable at the King Salmon mudflat, where the shell was collected, than in the main channel of Humboldt Bay, where water properties were monitored. Negative shell ??13C values (<-0.5???) marked spring and summer coastal upwelling events. The Mg contents of P. staminea midden shells dated to ???3 ka and ???9 ka were significantly lower than in the modern shell. This may have resulted from degradation of a Mg-rich shell organic matrix and precluded quantitative interpretation of the older high-resolution records. Elevated ??13C values in the ???3 ka shell suggested that the individual grew in highly productive or stratified environment, such as a shallow coastal embayment or lagoon. Copyright ?? 2004 Elsevier Ltd.

  1. Photoluminescence performance of thulium doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} under irradiation of ultraviolet and vacuum ultraviolet lights

    SciTech Connect

    Wang, Zhaofeng; Li, Yezhou; Liu, Xiong; Wei, Xingmin; Chen, Yueling; Zhou, Fei; Wang, Yuhua

    2014-11-15

    Highlights: • A novel blue-emitting phosphor Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} was reported. • Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} exhibited excellent thermal and irradiation stability. • Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} was found to possess high color purity. - Abstract: In this work, we synthesized Tm{sup 3+} doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors and investigated their photoluminescence properties under the excitation of ultraviolet and vacuum ultraviolet lights. The crystal structure analysis and variation of cell parameters confirm that Tm{sup 3+} ions have been successfully doped in the structure of Li{sub 4}SrCa(SiO{sub 4}){sub 2} host by occupying the sites of Ca{sup 2+} with the coordination number of 6. The luminescence results suggest that Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} is a good blue-emitting phosphor when excited by ultraviolet and vacuum ultraviolet irradiations. In addition, it is observed that there is nearly no degradation for Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} after undergoing thermal and irradiation treatments. Possible mechanisms for the luminescence processes are proposed on the basis of the discussion of excitation and emission spectra. In particular, the emission color of Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} by excitation of 147 and 172 nm irradiations is very close to the standard blue color, suggesting that it could be potentially applied in plasma display panels and mercury-free fluorescence lamps.

  2. Calcilytic Ameliorates Abnormalities of Mutant Calcium-Sensing Receptor (CaSR) Knock-In Mice Mimicking Autosomal Dominant Hypocalcemia (ADH).

    PubMed

    Dong, Bingzi; Endo, Itsuro; Ohnishi, Yukiyo; Kondo, Takeshi; Hasegawa, Tomoka; Amizuka, Norio; Kiyonari, Hiroshi; Shioi, Go; Abe, Masahiro; Fukumoto, Seiji; Matsumoto, Toshio

    2015-11-01

    Activating mutations of calcium-sensing receptor (CaSR) cause autosomal dominant hypocalcemia (ADH). ADH patients develop hypocalcemia, hyperphosphatemia, and hypercalciuria, similar to the clinical features of hypoparathyroidism. The current treatment of ADH is similar to the other forms of hypoparathyroidism, using active vitamin D3 or parathyroid hormone (PTH). However, these treatments aggravate hypercalciuria and renal calcification. Thus, new therapeutic strategies for ADH are needed. Calcilytics are allosteric antagonists of CaSR, and may be effective for the treatment of ADH caused by activating mutations of CaSR. In order to examine the effect of calcilytic JTT-305/MK-5442 on CaSR harboring activating mutations in the extracellular and transmembrane domains in vitro, we first transfected a mutated CaSR gene into HEK cells. JTT-305/MK-5442 suppressed the hypersensitivity to extracellular Ca(2+) of HEK cells transfected with the CaSR gene with activating mutations in the extracellular and transmembrane domains. We then selected two activating mutations locating in the extracellular (C129S) and transmembrane (A843E) domains, and generated two strains of CaSR knock-in mice to build an ADH mouse model. Both mutant mice mimicked almost all the clinical features of human ADH. JTT-305/MK-5442 treatment in vivo increased urinary cAMP excretion, improved serum and urinary calcium and phosphate levels by stimulating endogenous PTH secretion, and prevented renal calcification. In contrast, PTH(1-34) treatment normalized serum calcium and phosphate but could not reduce hypercalciuria or renal calcification. CaSR knock-in mice exhibited low bone turnover due to the deficiency of PTH, and JTT-305/MK-5442 as well as PTH(1-34) increased bone turnover and bone mineral density (BMD) in these mice. These results demonstrate that calcilytics can reverse almost all the phenotypes of ADH including hypercalciuria and renal calcification, and suggest that calcilytics can become a

  3. Luminescence and energy transfer in Eu2+, Mn2+ co-doped Ca2SrNaLa(PO4)3F

    NASA Astrophysics Data System (ADS)

    Shanshan, Hu; Wanjun, Tang

    2013-12-01

    A new compound Ca2SrNaLa(PO4)3F, isotypic with hexagonal Ca(Sr,Na,Ca)(Ca,Sr,Ce)3(PO4)3F, is reported. Its cell parameters have been determined from X-ray powder diffraction data. Crystallization occurs in the hexagonal space group P63 (No. 173) with a = 9.515(1) Å, c = 7.028(1) Å, and Z = 2. Eu2+ and Mn2+ activated Ca2SrNaLa(PO4)3F phosphors have been prepared. The energy transfer of Eu2+ → Mn2+ has been investigated. The resonant type energy transfer from Eu2+ to Mn2+ has been demonstrated, and the energy transfer efficiency has also been calculated according to their PL decay curves. A color-tunable emission in Ca2SrNaLa(PO4)3F phosphors can be realized by Eu2+ → Mn2+ energy transfer. White light can be achieved in a single-phased Ca2SrNaLa(PO4)3F host by co-doping Eu2+ and Mn2+ with CIE (0.32, 0.31). Our results demonstrate that the potential application of these phosphors in solid-state lighting and (or) other areas.

  4. X-ray absorption investigation of the valence state and electronic structure of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} in comparison with La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}

    SciTech Connect

    Haas, O.; Ludwig, Chr.; Bergmann, U.; Singh, R.N.; Braun, A.; Graule, T.

    2011-12-15

    3d metal K-shell X-ray absorption spectra of perovskites with the composition La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8) are compared on the basis of pre-edges, white line features and extended fine structures. The measurements were performed at 300 K and for La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t{sub 2g}{sup Low-Asterisk} and a decrease in e{sub g}{sup Low-Asterisk} orbital occupancy, which is most accentuated in the LaCoO{sub 3} sample. Virtually no Co K-edge shift was observed for the La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} compounds and the Co-O distances are also not significantly reduced when La{sup 3+} is partially substituted by Ca{sup 2+} or Sr{sup 2+}. From the pre-edge features of these perovskites we are tended to conclude that the t{sub 2g}{sup Low-Asterisk} orbitals are less, and the e{sub g}{sup Low-Asterisk} orbitals are more occupied with increasing x in the Ca and Sr substituted compounds, whereas the total d-electron density is not changing. These results indicate that cobalt prefers a valence state of 3{sup +} in these Co perovskites. This could also be confirmed with iodometric titrations. The Fe perovskites behave differently. In contrast to the Co perovskites, for La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites the Fe K-edge is shifted, the pre-edge features intensity is increasing and the Fe-O bond length is decreasing with increasing x. The valence states of the iron in the La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites in fact increase as much as x increases. - Graphical abstract: Co K and Fe K pre-edge of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites one of the

  5. Effects of sex hormones on genioglossal muscle contractility and SR Ca2+-ATPase activity in aged rat.

    PubMed

    Liu, Yue-Hua; Qi, Juan; Hou, Yu-Xia; Wang, Fei

    2008-04-01

    This investigation was designed to examine whether short-term administration of sex hormones could produce changes in contractile properties and the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) function in genioglossal muscle (GG) of aged male rats. Twenty-four aged male rats were randomly divided into three groups to receive an intramuscular injection of either 0.1mg/kg oestrogen (group A), 2.5 mg/kg testosterone (group B), or 0.2 ml sterile peanut oil (group C, control), twice a week, during 4 weeks. After hormone treatment, in vivo isometric contractile properties were determined using surgically prepared GG muscles with platinum electrodes for stimulation of the medial branch of the hypoglossus nerve. Sarcoplasmic reticulum Ca(2+)-ATPase activity was measured in muscle homogenates by detecting the amount of inorganic phosphorus ion released in a standard coupled enzyme assay. SERCA1 mRNA level was observed using a real-time quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR). It was found that, compared with group C, testosterone treatment decreased the fatigue resistance in GG muscles (p<.05), whereas no change was observed in the isometric twitch (P(t)) and tetanic tension (P(0)) (p>.05). By contrast, in oestrogen treated GG muscles, no significant modification was found either in the contractile or in endurance properties (p>.05). The change in GG fatigue resistance of group B was associated with a marked decrease in SR Ca(2+)-ATPase activity when compared with that of the control group (p<.01). Furthermore, SERCA1 mRNA level was also down regulated in group B (p<.05). No prominent differences in SR Ca(2+)-ATPase activity and SERCA1 mRNA expression existed between group A and group C (p>.05). The present results show that exogenous testosterone produces more pronounced changes in GG muscle fatigue resistance than oestrogen does by acting at SR Ca(2+)-ATPase activity and SERCA gene expression.

  6. Tunneling spectroscopy of heavily underdoped crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}

    SciTech Connect

    Ozyuzer, L.; Zasadzinski, J. F.; Miyakawa, N.; Kendziora, C.; Jian, S.; Hinks, D. G.; Gray, K. E.

    2000-02-17

    Crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} with optimal {Tc} = 95 K have been underdoped using two different methods and the superconducting gaps have been obtained by tunneling. In some cases, three different tunneling geometries have been utilized: point contact, STM and break junctions. The first doping method involves control of the oxygen content by annealing in various partial pressures of oxygen. These crystals exhibit a narrow spread of gap values over a wide doping range from overdoped ({Tc} = 56 K) to underdoped with {Tc} = 70 K. However, for underdoped crystals with {Tc} midpoints in the range 25 K--63 K, there is a dramatic increase in the spread of gap values which may signal the development of static phase separation of either chemical or electronic origin. To avoid possible chemical phase separation, the authors have explored another doping procedure which incorporates Dy substitution on the Ca site. These crystals exhibit a relatively narrow superconducting transition width and some preliminary tunneling spectra will be presented.

  7. Thermodynamic properties of Sr-doped LaMnO{sub 3} perovskite in the La-Sr-Mn-O system

    SciTech Connect

    Zheng, F.; Pederson, L.R.

    1999-08-01

    Thermodynamic properties of Sr-doped perovskite-type lanthanum manganites (LSM) were generated by measuring the electromotive force (EMF) of test materials, using the solid galvanic cell technique. The cell consisted of an anode (SrO/SrF{sub 2}), an electrolyte (CaF{sub 2} or SrF{sub 2}) and a cathode (LSM/SrF{sub 2}). Two types of cells were tested in which type 1 used a CaF{sub 2} electrolyte and type 2 used a SrF{sub 2} electrolyte. The activity of SrO substituting into various LSM compositions was calculated using the measured EMF. The Sr content was varied from 0.16 to 0.6 mol, and the temperature of interest varied from 700 to 1000 C. It was found that the SrO activity decreased with increasing temperature (at fixed composition) and increased with increasing Sr content (at fixed temperature).

  8. Cardiac microvascular endothelial cells express a functional Ca+ -sensing receptor.

    PubMed

    Berra Romani, Roberto; Raqeeb, Abdul; Laforenza, Umberto; Scaffino, Manuela Federica; Moccia, Francesco; Avelino-Cruz, Josè Everardo; Oldani, Amanda; Coltrini, Daniela; Milesi, Veronica; Taglietti, Vanni; Tanzi, Franco

    2009-01-01

    The mechanism whereby extracellular Ca(2+) exerts the endothelium-dependent control of vascular tone is still unclear. In this study, we assessed whether cardiac microvascular endothelial cells (CMEC) express a functional extracellular Ca(2+)-sensing receptor (CaSR) using a variety of techniques. CaSR mRNA was detected using RT-PCR, and CaSR protein was identified by immunocytochemical analysis. In order to assess the functionality of the receptor, CMEC were loaded with the Ca(2+)-sensitive fluorochrome, Fura-2/AM. A number of CaSR agonists, such as spermine, Gd(3+), La(3+) and neomycin, elicited a heterogeneous intracellular Ca(2+) signal, which was abolished by disruption of inositol 1,4,5-trisphosphate (InsP(3)) signaling and by depletion of intracellular stores with cyclopiazonic acid. The inhibition of the Na(+)/Ca(2+) exchanger upon substitution of extracellular Na(+) unmasked the Ca(2+) signal triggered by an increase in extracellular Ca(2+) levels. Finally, aromatic amino acids, which function as allosteric activators of CaSR, potentiated the Ca(2+) response to the CaSR agonist La(3+). These data provide evidence that CMEC express CaSR, which is able to respond to physiological agonists by mobilizing Ca(2+) from intracellular InsP(3)-sensitive stores.

  9. Effects of Mn Substitution on the Thermoelectric Properties and Thermal Excitations of the Electron-doped Perovskite Sr1-xLaxTiO3

    NASA Astrophysics Data System (ADS)

    Okuda, Tetsuji; Hata, Hiroto; Eto, Takahiro; Sobaru, Shogo; Oda, Ryosuke; Kaji, Hiroki; Nishina, Kousuke; Kuwahara, Hideki; Nakamura, Mitsutaka; Kajimoto, Ryoichi

    2016-09-01

    We studied how Mn substitution affects the thermoelectric properties and thermal excitations of the electron-doped perovskite Sr1-xLaxTiO3 by measuring its electrical and thermal transport properties, magnetization, specific heat, and inelastic neutron scattering. Slight Mn substitution with the lattice defects enhanced the Seebeck coefficient, perhaps because of coupling between itinerant electrons and localized spins or between itinerant electrons and local lattice distortion around Mn3+ ions, while it enhanced anharmonic lattice vibrations, which effectively suppressed thermal conductivity in a state of high electrical conductivity. Consequently, slight Mn substitution increased the dimensionless thermoelectric figure of merit for Sr1-xLaxTiO3 near room temperature.

  10. Magnetic and dielectric properties of Bi3+ substituted SrFe12O19 hexaferrite

    NASA Astrophysics Data System (ADS)

    Auwal, I. A.; Erdemi, H.; Sözeri, H.; Güngüneş, H.; Baykal, A.

    2016-08-01

    In the present study, SrBixFe12-xO19 (0.0≤x≤1.0) nanomaterials were successfully synthesized by using chemical co-precipitation method. Products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating sample magnetometer (VSM), Mössbauer spectroscopy, AC conductivity and dielectric measurements. The crystal structural information studied by X-ray diffraction (XRD) indicated the formation of single phase pure hexagonal structure, while electron-dispersive X-ray spectroscopy (EDX) revealed the stoichiometric ratio among Bi, Sr, Fe elements. The crystallite sizes of the products were in the range of 65-82 nm. VSM analysis showed a tendency in saturation magnetization as Bi2O3 concentration raises, which can be ascribed to preferential site occupied by Bi3+ ions. The frequency-dependent ac conductivity plots exhibited similar trends for all samples. A significant temperature-dependent behavior was only observed at low and medium frequencies. The replacement of non-magnetic Bi3+ ions by Fe3+ ones having magnetic moment of 5 μB decrease the magnetic moment of 4f1 site. The AC conductivity increases with frequency as hopping of the charge carriers increases between Fe2+and Fe3+. The DC conductivity exhibited an improvement with increasing temperature and Bi content, and the highest conductivity was measured as 2.84×10-9 S cm-1 for x=0.8 at 120 °C. The variation of dielectric constant, dielectric loss and tangent loss was observed with the frequency and temperature due to change of electrical conductivity as x changes.

  11. An apparent “vital effect” of calcification rate on the Sr/Ca temperature proxy in the reef coral Montipora capitata

    NASA Astrophysics Data System (ADS)

    Kuffner, Ilsa B.; Jokiel, Paul L.; Rodgers, Ku'ulei S.; Andersson, Andreas J.; MacKenzie, Fred T.

    2012-08-01

    Measuring the strontium to calcium ratio in coral skeletons reveals information on seawater temperatures during skeletal deposition, but studies have shown additional variables may affect the ratio. Here we measured Sr/Ca in the reef coral Montipora capitata grown in six mesocosms continuously supplied with seawater from the adjacent reef flat. Three mesocosms were ambient controls, and three had seawater chemistry simulating "ocean acidification" (OA). We found that Sr/Ca was not affected by the OA treatment and neither was coral calcification for these small colonies (larger colonies did show an OA effect). The lack of OA effects allowed us to test the hypothesis that coral growth rate can affect Sr/Ca using the natural range in calcification rates of the corals grown at the same temperature. We found that Sr/Ca was inversely related to calcification rate (Sr/Ca = 9.385 - 0.0040 (calcification rate)). Using a previously published calibration curve for this species, a 22 mg d-1 colony-1increase in calcification rate introduced a 1°C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9°C, with mean 26.6 ± 0.9°C standard deviation. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

  12. Single crystal growth and structural characterization of four complex uranium oxides: CaUO4, β-Ca3UO6, K4CaU3O12, and K4SrU3O12

    NASA Astrophysics Data System (ADS)

    Read, Cory M.; Bugaris, Daniel E.; zur Loye, Hans-Conrad

    2013-03-01

    Single crystals of complex uranium oxides, CaUO4, β-Ca3UO6, K4CaU3O12 and K4SrU3O12 were grown from carbonate melts. The crystal structures of the four uranates were determined by single crystal X-ray diffraction. CaUO4 crystallizes in the hexagonal space group R-3m, with lattice parameters a = 6.2570(7) Å and α = 36.04(2)°. The U6+ atom in CaUO4 is 8-coordinate and exhibits hexagonal bipyramidal geometry with six long and two short U-O bonds, typical of a uranyl species. β-Ca3UO6 forms in the monoclinic space group P21/n, with lattice parameters a = 5.728(1) Å, b = 5.956(1) Å, c = 8.298(2) Å, and β = 90.55(3)°, and adopts a distorted double perovskite structure. K4CaU3O12 and K4SrU3O12 crystallize in the cubic space group Im-3m with lattice parameters a = 8.483(1) Å and a = 8.582(1) Å, respectively. In all three perovskite-type oxides, the U(VI) cation is located in an octahedral coordination environment and exhibits typical uranyl geometry with four long and two short U-O bonds.

  13. Determining Solute Sources and Water Flowpaths in a Forested Headwater Catchment: Advances With the Ca-Sr-Ba Multi-tracer

    NASA Astrophysics Data System (ADS)

    Bullen, T. D.; Bailey, S. W.; McGuire, K. J.; Zimmer, M. A.; Ross, D. S.

    2011-12-01

    Determining solute sources and water flowpaths in catchments is of critical importance to development of models that effectively describe catchment function. For solutes in soil water and stream water, simple mass balance models that compare precipitation input to catchment outlet compositions can predict average mineral weathering contributions for the catchment as a whole, but fail to provide information about either variability of contributions from different portions of the catchment and different soil depths or processes such as ion exchange and biological cycling. In order to better understand how forested headwater catchments function, we are interpreting concentration and isotope ratios of the alkaline earth elements Ca, Sr and Ba in streamwater, groundwater, the soil ion exchange pool and plants in a hydropedologic context at the 41 hectare hydrologic reference catchment (Watershed 3) at the Hubbard Brook Experimental Forest, New Hampshire, USA. This forested headwater catchment consists of a beech-birch-maple-spruce forest growing on vertically- and laterally-developed Spodosols and Inceptisols formed on granitoid glacial till that mantles Paleozoic metamorphic bedrock. Across the watershed in terms of the soil ion exchange pool, the forest floor has high Sr/Ba and Ca/Sr ratios, mineral soils have intermediate Sr/Ba and low Ca/Sr, and relatively unweathered till in the C horizon has low Sr/Ba and high Ca/Sr. Waters moving through these various compartments will obtain Sr/Ba and Ca/Sr ratios reflecting these characteristics, and thus variations of Sr/Ba and Ca/Sr of streamwater provide evidence of the depth of water flowpaths feeding the streams. 87Sr/86Sr of exchangeable Sr spans a broad range from 0.715 to 0.725, with highest values along the mid-to upper flanks of the catchment and lowest values in a broad zone along the central axis of the catchment associated with numerous groundwater seeps. Thus, variations of 87Sr/86Sr in streamwater provide

  14. Molecular layer-by-layer engineering of superconducting and superionic materials in the (AgI)Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} system

    SciTech Connect

    Choy, J.H.; Park, N.G.; Kim, Y.I.; Hwang, S.H.; Lee, J.S.; Yoo, H.I.

    1995-05-18

    We have developed a new interstratified system consisting of a superconducting layer alternating with a superionic conducting one, which is the AgI intercalated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} with well-defined 2-dimensional heterostructure. Before and after the intercalation of AgI, the superconducting properties remained unchanged with the T{sub c}`s of 76 K for the pristine and 63 K for the intercalate. From the extended X-ray absorption fine structure spectroscopic analysis, it is found that the intercalated AgI is formed as the {beta}-like intracrystalline structure in the 2-dimensional interlayer space of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y}. According to the ac impedance and dc relaxation measurements, the ionic transference number (t{sub i} = {sigma}{sub i}/{sigma}{sub r}) has been estimated to be 0.27 (at 167{degree}C), indicating that the substantial ionic conductivity ({sigma}{sub 1}) contributes to the total electrical one ({sigma}{sub T}). In comparison of the ionic conductivity for (AgI)Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} ({sigma}{sub i} = 10{sup -3}-10{sup -23} {Omega}{sup -1} cm{sup -1}) with those for the well-known superionic conductors of cation-substituted {beta}-aluminas, the ionic transport in (AgI)Bi{sub 2}Sr{sub 2}-CaCu{sub 2}O{sub y} turned out to be significant, even comparable with the superionic conductors. 15 refs., 4 figs., 1 tab.

  15. Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals

    NASA Astrophysics Data System (ADS)

    Cole, Catherine; Finch, Adrian; Hintz, Christopher; Hintz, Kenneth; Allison, Nicola

    2016-05-01

    Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2–4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to ‑5 °C.

  16. Obesity-associated proinflammatory cytokines increase calcium sensing receptor (CaSR) protein expression in primary human adipocytes and LS14 human adipose cell line.

    PubMed

    Cifuentes, Mariana; Fuentes, Cecilia; Mattar, Pamela; Tobar, Nicolas; Hugo, Eric; Ben-Jonathan, Nira; Rojas, Cecilia; Martínez, Jorge

    2010-08-15

    Obesity-associated health complications are thought to be in part due to the low-grade proinflammatory state that characterizes this disease. The calcium sensing receptor (CaSR), which is expressed in human adipose cells, plays an important role in diseases involving inflammation. To assess the relevance of this protein in adipose pathophysiology, we evaluated its expression in adipocytes under obesity-related proinflammatory conditions. As in primary adipose cells, we established that LS14, a recently described human adipose cell line, expresses the CaSR. Differentiated LS14 and primary adipose cells were exposed overnight to cytokines typically involved in obesity-related inflammation (interleukin (IL)1beta, IL6 and tumor necrosis factor (TNF)alpha). The cytokines increased CaSR abundance in differentiated adipocytes. We incubated LS14 cells with medium previously conditioned (CM) by adipose tissue from subjects with a wide range of body mass index (BMI). Cells exposed to CM from subjects of higher BMI underwent a greater increase in CaSR protein, likely resulting from the greater proinflammatory cytokines secreted from obese tissue. Our observations that proinflammatory factors increase CaSR levels in adipocytes, and the reported ability of CaSR to elevate cytokine levels, open new aspects in the study of obesity inflammatory state pathophysiology, providing a potential novel therapeutic prevention and treatment target.

  17. Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals

    PubMed Central

    Cole, Catherine; Finch, Adrian; Hintz, Christopher; Hintz, Kenneth; Allison, Nicola

    2016-01-01

    Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2–4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to −5 °C. PMID:27241795

  18. The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+ partitioning

    SciTech Connect

    Tsigabu Gebrehiwet; Mikala S. Beig; George Redden; Yoshiko Fujita; Robert W. Smith

    2012-01-01

    Engineering the precipitation of calcium carbonate, which can co-precipitate trace metal contaminants, is a proposed strategy for remediating toxic or radioactive metals in subsurface environments. Engineering precipitation of multi-component minerals will involve injection of chemical amendments that must be mixed at a molecular level to supersaturated conditions that are sufficient to promote rapid mineral precipitation relative to natural systems. In subsurface systems this often means reactant mixing zones will be formed that are characterized by gradients in solute concentrations, saturation state, and solute activity ratios. To better understand the effect of ion activity ratios on CaCO{sub 3} precipitation kinetics and Sr{sup 2+} co-precipitation we experiments were conducted under constant composition conditions where the supersaturation state ({Omega}) with respect to calcite was held constant at 9.4, but the ion activity ratio (r = a{sub co{sub 3}{sup 2-}}/a{sub Ca{sup 2+}}) ranged from 0.003 to 4.15. Results: Under the chosen experimental conditions the CaCO{sub 3} phase formed was calcite and initial precipitation rates varied from a maximum rate of 84.7 {mu}mol/ m{sup 2}/min for a carbonate to calcium activity ratio of (0.21). However, precipitation rates were found to vary with time which could be indicative of variations in precipitation mechanisms that are related to the ion activity ratio. The observed trends in the distribution coefficients for co-precipitated Sr2+ (D{sup P}{sub Sr}{sup 2+}) relative to the calcite precipitation rate (i.e. a positive correlation) indicate that increasing calcite precipitation rates increase the incorporation of Sr{sup 2+}. Conclusion: The observed variation between the rate maxima and minima based on the ion activity ratio could have great deal of implication for sequestering radionuclides (e.g. {sup 90}Sr) and other toxic metals in engineered systems at contaminated sites. Extending our data plot range allowed us

  19. Spin-on Bi4Sr3Ca3Cu4O(16+x) superconducting thin films from citrate precursors

    NASA Astrophysics Data System (ADS)

    Furcone, S. L.; Chiang, Y.-M.

    1988-06-01

    Thin films in the Bi-Sr-Ca-Cu-O system have been synthesized from homogeneous liquid citrate precursors by a spin-coating and pyrolysis method. Films prepared on SrTiO3 substrates of 100-line orientation show strongly textured orientations with the c axis of the predominant Bi4Sr3Ca3Cu(4)O(16+x) phase normal to the film plane. In a single coating and firing, crack-free films of 0.2-0.5 thickness are obtained. For films fired to peak temperatures of 850-875 C, linearly decreasing resistance with temperature is observed. Clear onsets of superconductivity are observed at 90-100 K, with occasional films showing smaller resistant drops at 110-120 K. For all films, T(c) (R = 0) occurs in the range 70-75 K. High critical current densities at 4.2 K of 500,000-800,000 A/sq cm are measured by direct transport.

  20. Performance of thin CaSO4:Dy pellets for calibration of a Sr90+Y90 source

    NASA Astrophysics Data System (ADS)

    Oliveira, M. L.; Caldas, L. V. E.

    2007-09-01

    Because of the radionuclide long half-life, Sr90+Y90, plane or concave sources, utilized in brachytherapy, have to be calibrated initially by the manufacturer and then routinely while they are utilized. Plane applicators can be calibrated against a conventional extrapolation chamber, but concave sources, because of their geometry, should be calibrated using relative dosimeters, as thermoluminescent (TL) materials. Thin CaSO4:Dy pellets are produced at IPEN specially for beta radiation detection. Previous works showed the feasibility of this material in the dosimetry of Sr90+Y90 sources in a wide range of absorbed dose in air. The aim of this work was to study the usefulness of these pellets for the calibration of a Sr90+Y90 concave applicator. To reach this objective, a special phantom was designed and manufactured in PTFE with semi spherical geometry. Because of the dependence of the TL response on the mass of the pellet, the response of each pellet was normalized by its mass in order to reduce the dispersion on TL response. Important characteristics of this material were obtained in reference of a standard Sr90+Y90 source, and the pellets were calibrated against a plane applicator; then they were utilized to calibrate the concave applicator.

  1. High-Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides

    DOE PAGES

    Di Castro, D.; Cantoni, C.; Ridolfi, F.; Aruta, C.; Tebano, A.; Yang, N.; Balestrino, G.

    2015-09-28

    At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case can oxygen ions be incorporated in themore » interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. In addition, a detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1–2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explaining the dependence of Tc on the number of CuO2 planes in these systems.« less

  2. Influence of chemical substitution on the photoluminescence of Sr{sub (1−x)}Pb{sub x}WO{sub 4} solid solution

    SciTech Connect

    Hallaoui, A.; Taoufyq, A.; Arab, M.; Bakiz, B.; Benlhachemi, A.; Bazzi, L.; Villain, S.; Valmalette, J-C.; Guinneton, F.; Gavarri, J-R.

    2015-07-15

    The solid solution Sr{sub 1−x}Pb{sub x}WO{sub 4} based on luminescent tungstates SrWO{sub 4} and PbWO{sub 4} has been synthesized by solid-state reaction for all compositions 0≤x≤1. Using Rietveld method, the structural data of all polycrystalline samples have been refined and crystal cell parameters exhibited a linear behavior as a function of x. All substituted structures are of scheelite type. Scanning electron microscopy showed that a high level of crystallization characterized the samples, with modifications in sizes and shapes depending on composition x. Infrared and Raman spectroscopy have been performed to characterize the evolution of vibrational modes with substitution rate. Finally, a systematic study of luminescence under X-ray excitation has been performed: in the composition range x=0.2 to 0.4, intensities of emission exhibited increased values. The luminescence profiles have been interpreted in terms of four Gaussian components, two of them depending on substitution rate. - Graphical abstract: Photoluminescence under X-ray excitation of Sr{sub 1−x}Pb{sub x}WO{sub 4} solid solution: (left) decomposition of emission large band into four components for composition x=0.3; (right) variation of total emission intensity with composition x. - Highlights: • Structural study of solid solution Sr{sub 1−x}Pb{sub x} WO{sub 4} using Rietveld analyses. • Variation of Debye–Waller factor with composition x, disorder parameter. • Existence of four components of luminescence under X-ray excitation. • Effect of substitution of Sr by Pb on two components, due to Pb–O–W interactions. • Enhancement of luminescence intensity in a specific composition range.

  3. Characterization of hot isostatically pressed Bi-Sr-Ca-Cu-O as a function of consolidation variables

    SciTech Connect

    Goretta, K.C.; Miller, D.J.; Poeppel, R.B. ); Nash, A.S. )

    1991-11-01

    Fully dense, bulk Bi{sub 2}Sr{sub 1.7}CaCu{sub 2}O{sub x} (2212) superconductor pellets were made by hot isostatic pressing in an inert atmosphere. Electron microscopy revealed that rotation and bending of the platelike 2212 grains were responsible for much of the densification. Under processing conditions of 825{degrees}C and 105 MPa, dense pellets were obtained in 15 min. Many dislocations, planar faults, and, perhaps, intergrowths of the Bi{sub 2}Sr{sub 2}CuO{sub x} phase were produced during pressing. The dislocations were largely present in subgrain boundaries when the pressing times were increased to 45--120 min.

  4. Store-operated Ca²⁺ entry and depolarization explain the anomalous behaviour of myometrial SR: effects of SERCA inhibition on electrical activity, Ca²⁺ and force.

    PubMed

    Noble, Debbie; Borysova, Lyudmyla; Wray, Susan; Burdyga, Theodor

    2014-09-01

    In the myometrium SR Ca(2+) depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca(2+) sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca(2+)-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca(2+) transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 μM), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca(2+)]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca(2+) spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca(2+) and depolarization continued a point was reached when electrical and Ca(2+) spikes and phasic contractions ceased, and a maintained, tonic force and Ca(2+) was produced. Lanthanum, a non-selective blocker of store-operated Ca(2+) entry, but not the L-type Ca(2+) channel blocker nifedipine (1-10 μM), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca(2+) depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca(2+) release is coupled to marked Ca(2+) entry, via store operated Ca(2+) channels, leading to depolarization and enhanced electrical and mechanical activity. PMID:25084623

  5. Texture analysis of monofilamentary, Ag-sheathed (Pb,Bi) 2Sr 2Ca 2Cu 3O x tapes by electron backscatter diffraction (EBSD)

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Qu, T.; Han, Z.; Mücklich, F.

    2008-02-01

    Using automated orientation imaging, the grain orientations and texture of monofilamentary, Ag-sheathed (Pb,Bi) 2Sr 2Ca 2Cu 3O x (Bi-2223) tape is analysed in detail by means of electron backscatter diffraction (EBSD). The achieved high image quality of the Kikuchi patterns enables multi-phase scans including Bi-2223, Bi 2Sr 2CaCu 2O x, Bi 2Sr 2CuO x, (Sr,Ca) 14Cu 24O 41 and Ag to be performed. Two areas are selected for the EBSD analysis, one close to the silver sheath, the other located in the center of the sample. The grain orientation maps are presented for each phase separately allowing a new insight into the microtexture of Ag-sheathed Bi-2223 tapes. Furthermore, the EBSD analysis provides the possibility for a misorientation angle analysis within each individual phase.

  6. Structural and Magnetic Phase Coexistence in Oxygen Deficient Perovskites (Sr,Ca)FeO 2 . 5 + δ

    NASA Astrophysics Data System (ADS)

    Carlo, J. P.; Evans, M. E.; Anczarski, J. A.; Ock, J.; Boyd, K.; Pollichemi, J. R.; Leahy, I. A.; Vogel, W.; Viescas, A. J.; Papaefthymiou, G. C.

    A variety of compounds crystallize into perovskite and similar structures, making them versatile laboratories for many phenomena and applications, including multiferroicity, superconductivity, and photovoltaics. Oxygen-deficient perovskites ABOx have attracted interest for use in fuel cells and related applications due to high oxygen mobility and the possibility of charge disproportionation. Vast chemical flexibility is obtained through reductions in lattice symmetry and rotation/distortion of the BO6 octahedra, as well as ordering of oxygen vacancies. We have synthesized and studied the structural and magnetic properties of oxygen-deficient perovskites (Sr,Ca)FeO2 . 5 + δ using x-ray diffraction and Mossbauer spectroscopy. While the ideal perovskite has δ = 0.5, this requires Fe4+, and hence strongly oxidizing environments. When grown in air, Fe3+ is favored, yielding δ ~ 0. SrFeO2 . 5 + δ exhibits cubic symmetry and paramagnetism at 300K, but CaFeO2 . 5 + δ crystallizes into the orthorhombic brownmillerite structure, and is magnetically ordered at 300K. In the doped intermediaries we find coexistence of cubic/paramagnetic and orthorhombic/magnetic phases over a wide range of Ca content. Financial support from the Villanova Undergraduate Research Fellowship program and the Research Corporation for Science Advancement.

  7. Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x

    NASA Astrophysics Data System (ADS)

    Hamidian, M. H.; Edkins, S. D.; Joo, Sang Hyun; Kostin, A.; Eisaki, H.; Uchida, S.; Lawler, M. J.; Kim, E.-A.; MacKenzie, A. P.; Fujita, K.; Lee, Jinho; Davis, J. C. Séamus

    2016-04-01

    The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density. Such a state has been created in ultracold 6Li gas but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase of the copper oxide superconductors contains such a ‘pair density wave’ state. Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms and at the Bi2Sr2CaCu2O8+x crystal supermodulation. Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors QP ≈ (0.25, 0)2π/a0 and (0, 0.25)2π/a0 in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s‧ symmetry. This phenomenology is consistent with Ginzburg-Landau theory when a charge density wave with d-symmetry form factor and wavevector QC = QP coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase.

  8. Microstructure and magnetic properties of electrospun one-dimensional Al{sup 3+}-substituted SrFe{sub 12}O{sub 19} nanofibers

    SciTech Connect

    Liu, Mingquan; Shen, Xiangqian; Song, Fuzhan; Xiang, Jun; Meng, Xianfeng

    2011-04-15

    SrAl{sub x}Fe{sub 12-x}O{sub 19} (x=0-3.0) nanofibers with diameters about 100 nm have been prepared by electrospinning and subsequent heat treatment. With Al{sup 3+} ion content ranging from 0 to 3.0, the lattice parameters decrease due to Fe{sup 3+} ions substituted by smaller Al{sup 3+} ions and the average grain size calculated by the Scherrer's equation reduces from 65 to 37 nm. The magnetization shows a continuous reduction with the Al content and its value measured at 77 K is higher than at room temperature, which can be explained by Bloch's law. For the coercivity, its value initially increases, reaching a maximum value of 617 (298 K) and 547 kA m{sup -1} (77 K) at x=2.0, and then reduces with the Al content further increase largely arising from the substituted Al{sup 3+} ion arrangement in different interstitial sites of the strontium ferrite unit cell. -- Graphical abstract: Al{sup 3+} ions substituted strontium ferrite nanofibers have been prepared by the electrospinning with a diameter of about 100 nm and the Al{sup 3+} ion substitution has a great effect on the microstructure and magnetic property of SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers. Display Omitted Research highlights: {yields} SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers have been fabricated by the electrospinning. {yields} There is a relation between the Al{sup 3+} ions substitution and microstructure. {yields} The magnetic property can be tuned effectively by Al{sup 3+} ion substitution. {yields} The magnetic property is influenced by measurement temperature.

  9. The deposition of strontium-substituted hydroxyapatite coatings.

    PubMed

    Boyd, Adrian R; Rutledge, L; Randolph, L D; Mutreja, I; Meenan, B J

    2015-02-01

    Strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interest recently as strontium (Sr) has been shown to have the dual benefit of promoting bone formation and reducing bone resorption, in vivo. In this work, SrHA coatings were deposited onto polycrystalline titanium surfaces using radio frequency (RF) magnetron co-sputtering and compared to those deposited from HA alone. In particular, the influence of different levels of Sr-substitution of the sputtering targets (5 and 13% Sr-substituted HA targets) on the properties of the deposited coatings produced at a low discharge power level (150 W) were investigated using FTIR, XPS, XRD, ToFSIMS and AFM techniques (both before and after annealing at 500 °C). The results show that Sr could be successfully incorporated into the HA lattice to form SrHA coatings and that they contained no other impurities. However, the coating produced from the 13% Sr-substituted target had a higher Ca+Sr/P ratio (1.95±0.14) and Sr content when compared to the coating produced from the 5% Sr-substituted target (1.58±0.20). The deposition rate also decreased with increasing Sr content of the sputtering targets. Furthermore, as the Sr content of the coatings increased, so did the preferred 002 orientation of the coating along with increased surface roughness and heterogeneity of the surface features. Therefore, this study has shown that RF magnetron sputtering offers a means to control attendant properties of Sr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surface topography.

  10. The deposition of strontium-substituted hydroxyapatite coatings.

    PubMed

    Boyd, Adrian R; Rutledge, L; Randolph, L D; Mutreja, I; Meenan, B J

    2015-02-01

    Strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interest recently as strontium (Sr) has been shown to have the dual benefit of promoting bone formation and reducing bone resorption, in vivo. In this work, SrHA coatings were deposited onto polycrystalline titanium surfaces using radio frequency (RF) magnetron co-sputtering and compared to those deposited from HA alone. In particular, the influence of different levels of Sr-substitution of the sputtering targets (5 and 13% Sr-substituted HA targets) on the properties of the deposited coatings produced at a low discharge power level (150 W) were investigated using FTIR, XPS, XRD, ToFSIMS and AFM techniques (both before and after annealing at 500 °C). The results show that Sr could be successfully incorporated into the HA lattice to form SrHA coatings and that they contained no other impurities. However, the coating produced from the 13% Sr-substituted target had a higher Ca+Sr/P ratio (1.95±0.14) and Sr content when compared to the coating produced from the 5% Sr-substituted target (1.58±0.20). The deposition rate also decreased with increasing Sr content of the sputtering targets. Furthermore, as the Sr content of the coatings increased, so did the preferred 002 orientation of the coating along with increased surface roughness and heterogeneity of the surface features. Therefore, this study has shown that RF magnetron sputtering offers a means to control attendant properties of Sr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surface topography. PMID:25631262

  11. Thermodynamic investigation of the magnetic phase transitions of CaMnO3 and SrRuO3

    NASA Astrophysics Data System (ADS)

    Neumeier, J. J.; Cornelius, A. L.; Andres, K.

    2001-11-01

    Measurements of the linear thermal expansion Δl/l and molar heat capacity CP at constant pressure are presented on antiferromagnetic CaMnO3 and ferromagnetic SrRuO3 in the neighborhood of their magnetic phase transitions. The jumps in the linear thermal-expansion coefficient α and CP are used to calculate the influence of pressure on the magnetic ordering temperatures Tc through the Ehrenfest relation. Good agreement is obtained with measured values of dTc/dP.

  12. Properties of Bi(Pb)-Sr-Ca-Cu-O superconducting tapes prepared by the doctor-blade process

    SciTech Connect

    Yanagisawa, E.; Morimoto, T.; Dietderich, D. R.; Kumakura, H.; Togano, K.; Maeda, H.

    1989-06-19

    Improved superconducting and mechanical properties were obtained forBi(Pb)-Sr-Ca-Cu-O tapes, prepared by the combined process of doctor-bladecasting, cold rolling, and sintering. The tape has an oriented microstructurewith the high /ital T//sub /ital c// plate-like grains having their /ital c/ axesperpendicular to the rolling surface. The tape is flexible and can be bentwithout any degradation of /ital J//sub /ital c// to just before fracture (strainlarger than /similar to/0.12%).

  13. Spectroscopic Signatures of Defect-Induced Pair Breaking in Bi2Sr2CaCu2O8+x

    NASA Astrophysics Data System (ADS)

    Vobornik, I.; Berger, H.; Pavuna, D.; Onellion, M.; Margaritondo, G.; Rullier-Albenque, F.; Forró, L.; Grioni, M.

    1999-04-01

    We investigated the effect of disorder on the spectral properties of the high temperature superconductor Bi2Sr2CaCu2O8+x. We find that small defect densities, in the low 10-3 range, already suppress the characteristic spectral signature of the superconducting state, while new excitations appear within the gap. We conclude that, due to defect-induced pair breaking, superconducting pairs and normal carriers coexist below Tc. At higher levels of disorder the normal state is also strongly affected, and the quasiparticle features progressively smeared out.

  14. Formation of the 110-K superconducting phase in Pb-doped Bi-Sr-Ca-Cu-O thin films

    SciTech Connect

    Kula, W.; Sobolewski, R.; Gorecka, J.; Lewandowski, S.J. )

    1991-09-15

    Investigation of the 110-K Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {ital x}} phase formation in superconducting thin films of Bi-based cuprates is reported. The films were dc magnetron sputtered from single Bi(Pb)-Sr-Ca-Cu-O targets of various stoichiometries, and subsequently annealed in air at high temperatures. The influence of the initial Pb content, annealing conditions, as well as the substrate material on the growth of the 110-K phase was investigated. We found that the films, fully superconducting above 100 K could be reproducibly fabricated on various dielectric substrates from Pb-rich targets by optimizing annealing conditions for each initial Pb/Bi ratio. Heavy Pb doping considerably accelerated formation of the 110-K phase, reducing the film annealing time to less than 1 h. Films containing, according to the x-ray measurement, more than 90% of the 110-K phase were obtained on MgO substrates, after sputtering from the Bi{sub 2}Pb{sub 2.5}Sr{sub 2}Ca{sub 2.15}Cu{sub 3.3}O{sub {ital x}} target and annealing in air for 1 h at 870 {degree}C. The films were {ital c}-axis oriented, with 4.5-K-wide superconducting transition, and zero resistivity at 106 K. Their critical current density was 2 {times} 10{sup 2} A/cm{sup 2} at 90 K, and above 10{sup 4} A/cm{sup 2} below 60 K. The growth of the 110-K phase on epitaxial substrates, such as CaNdAlO{sub 4} and SrTiO{sub 3}, was considerably deteriorated, and the presence of the 80- and 10-K phases was detected. Nevertheless, the best films deposited on these substrates were fully superconducting at 104 K and exhibited critical current densities above 2 {times} 10{sup 5} A/cm{sup 2} below 60 K{minus}one order of magnitude greater than the films deposited on MgO.

  15. New vortex-matter size effect observed in Bi(2)Sr(2)CaCu(2)O(8 + delta).

    PubMed

    Wang, Y M; Fuhrer, M S; Zettl, A; Ooi, S; Tamegai, T

    2001-04-16

    The vortex-matter 3D to 2D phase transition is studied in micron-sized Bi(2)Sr(2)CaCu(2)O(8 + delta) single crystals using local Hall magnetization measurements. At a given temperature, the second magnetization peak, the signature of a possible 3D--2D vortex phase transition, disappears for samples smaller than a critical length. We suggest that this critical length should be equated with the 2D vortex lattice ab-plane correlation length R(2D)(c). The magnitude and temperature dependence of R(2D)(c) agree well with Larkin-Ovchinnikov collective pinning theory.

  16. Crystallography, chemistry and structural disorder in the new high-Tc Bi-Ca-Sr-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Veblen, D. R.; Heaney, P. J.; Angel, R. J.; Finger, L. W.; Hazen, R. M.

    1988-01-01

    Diffraction experiments are reported which indicate that the new Bi-Ca-Sr-Cu-O layer-structure superconductor possesses a primitive orthorhombic unit cell with probable space group Pnnn. The material exhibits severe structural disorder which is primarily related to stacking within the layers. The apparent orthorhombic structure is an average resulting from orthorhombic material mixed with monoclinic domains in two twinned orientations. Two distinct types of structural disorder that are common in materials synthesized to date are also described. This disorder complicates the crystallographic analysis and suggests that X-ray and neutron diffraction methods may yield only an average structure.

  17. Replicating and calibrating Haitian microatoll coral Sr/Ca variations to build confidence in sea surface temperature reconstructions

    NASA Astrophysics Data System (ADS)

    Ouellette, G., Jr.; DeLong, K. L.; Kilbourne, K. H.; Taylor, F. W.; Mann, P.; Jean, P.

    2014-12-01

    Paleoclimatologists reconstruct sea surface temperature (SST) from corals by sampling boulder-shaped massive corals along the vertical growth direction or the assumed maximum growth axis to avoid kinetic effects related to variations in growth rate. Microatolls are a morphological variation of long-lived massive coral colonies that grow laterally just beneath the ocean surface. Cross-sections from five Siderastrea siderea microatolls, 35 km west of Port-au-Prince Haiti (18.479070°N, 72.668659°W), were recovered following the 2010 earthquake. Two colonies (10BELOC4 and 10LEO1), ~5.5 km apart, were sampled along paths oriented at 25° and 91° from the vertical growth direction; respectively, to determine differences in path orientation and between colonies. We find mean linear extension rates are similar (4.2 ±1.2 mm/year-1, 1σ for 10LEO1; and 4.3 ±1.3 mm/year-1, 1σ for 10BELOC4) with no significant correlation between intercolony linear extension rates (r=0.52, p=0.18, n=8) or between linear extension rates and SST (r=-0.20, p=0.31, n=29 for 10LEO1). We find similar intercolony seasonal variability in coral Sr/Ca (1.35 ±0.04 mmol/mol, 1σ for 10LEO1; and 1.41 ±0.05 mmol/mol, 1σ for 10BELOC4) and no significant difference (p<0.001) in mean coral Sr/Ca (8.90 ±0.05 mmol/mol, 1σ for 10LEO1; and 8.83 ±0.06 mmol/mol, 1σ for 10BELOC4; n=100). Calibration of coral Sr/Ca to OISST for the 1º grid including our study site results in a slope similar to previous studies using boulder-shaped S. siderea colonies (Sr/Ca=7.91-0.04(SST), r2=0.96, n=57). These results suggest that reliable SST reconstructions that span many centuries can be derived from large S. siderea microatolls.

  18. Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba)

    SciTech Connect

    Josse, M.; El-Ghozzi, M.; Avignant, D.; Andre, G.; Bouree, F.; Isnard, O.

    2012-01-15

    Neutron powder diffraction has been performed on the MTbF{sub 6} fluorides (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba). Four of these fluorides (Cd, Ca, Sr, {beta}-Ba) are built of a (pseudo-) tetragonal packing of [TbF{sub 6}]{sup 2-} chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb{sup 4+}-Tb{sup 4+} magnetic interactions. All the compounds displayed antiferromagnetic order (T{sub N}=2.70 K (Cd), 2.15 K (Ca), 2.60 K (Sr), 2.10 K ({beta}-Ba)), except for the {alpha} form of BaTbF{sub 6}. The crystal structure of this latter fluoroterbate has also been investigated by means of high-resolution neutron powder diffraction. From Neutron Powder Diffraction data, CdTbF{sub 6} and {beta}-BaTbF{sub 6} magnetic structures were determined, together with the metamagnetic behaviour of {beta}-BaTbF{sub 6} as a function of an external magnetic field. A tentative phase diagram is then given for {beta}-BaTbF{sub 6}. Advantage was taken of the polymorphism of the BaTbF{sub 6} fluoroterbate to analyse, on the basis of topological parameters such as bond distances and angles, the magnetic behaviour of its {alpha} and {beta} forms. It was shown that superexchange interactions are present in {beta}-BaTbF{sub 6}, and that these interactions may also rule the magnetic behaviour of the other MTbF{sub 6} (M=Ca, Sr, Cd) tetravalent terbium fluorides. - Graphical abstract: Powder neutron diffraction revealed magnetic order in four of the five investigated fluoroterbates, while crystal chemical analyses of {alpha} and {beta} forms of BaTbF{sub 6} evidenced the existence of superexchange interactions. Highlights: Black-Right-Pointing-Pointer Five fluoroterbates are investigated by Powder Neutron Diffraction (PND). Black-Right-Pointing-Pointer Four of them are antiferromagnetically ordered at 1.4 K. Black-Right-Pointing-Pointer Magnetic structures of {beta}-BaTbF{sub 6} and CdTbF{sub 6} are determined. Black

  19. Juxtaglomerular cell CaSR stimulation decreases renin release via activation of the PLC/IP(3) pathway and the ryanodine receptor.

    PubMed

    Ortiz-Capisano, M Cecilia; Reddy, Mahendranath; Mendez, Mariela; Garvin, Jeffrey L; Beierwaltes, William H

    2013-02-01

    The calcium-sensing receptor (CaSR) is a G-coupled protein expressed in renal juxtaglomerular (JG) cells. Its activation stimulates calcium-mediated decreases in cAMP content and inhibits renin release. The postreceptor pathway for the CaSR in JG cells is unknown. In parathyroids, CaSR acts through G(q) and/or G(i). Activation of G(q) stimulates phospholipase C (PLC), and inositol 1,4,5-trisphosphate (IP(3)), releasing calcium from intracellular stores. G(i) stimulation inhibits cAMP formation. In afferent arterioles, the ryanodine receptor (RyR) enhances release of stored calcium. We hypothesized JG cell CaSR activation inhibits renin via the PLC/IP(3) and also RyR activation, increasing intracellular calcium, suppressing cAMP formation, and inhibiting renin release. Renin release from primary cultures of isolated mouse JG cells (n = 10) was measured. The CaSR agonist cinacalcet decreased renin release 56 ± 7% of control (P < 0.001), while the PLC inhibitor U73122 reversed cinacalcet inhibition of renin (104 ± 11% of control). The IP(3) inhibitor 2-APB also reversed inhibition of renin from 56 ± 6 to 104 ± 11% of control (P < 0.001). JG cells were positively labeled for RyR, and blocking RyR reversed CaSR-mediated inhibition of renin from 61 ± 8 to 118 ± 22% of control (P < 0.01). Combining inhibition of IP(3) and RyR was not additive. G(i) inhibition with pertussis toxin plus cinacalcet did not reverse renin inhibition (65 ± 12 to 41 ± 8% of control, P < 0.001). We conclude stimulating JG cell CaSR activates G(q), initiating the PLC/IP(3) pathway, activating RyR, increasing intracellular calcium, and resulting in calcium-mediated renin inhibition.

  20. Multi-species Coral Sr/Ca-Based Sea-Surface Temperature Reconstruction Using Orbicella faveolata and Siderastrea siderea from Dry Tortugas National Park, FL

    NASA Astrophysics Data System (ADS)

    Flannery, J. A.; Richey, J. N.; Thirumalai, K.; Poore, R. Z.

    2015-12-01

    Massive coral skeletons provide an important geologic archive of climate information over the past several centuries, due to their annual banding patterns and longevity. The ratio of strontium to calcium (Sr/Ca) in coral skeletons is dependent on the temperature of the seawater at the time of growth and, therefore, provides a powerful proxy of historic sea-surface temperature (SST). This study used cores from two modern coral colonies—Orbicella faveolata (formerly Montastraea faveolata) and Siderastrea siderea—collected from the Dry Tortugas National Park, Florida (DRTO), located in the southern Gulf of Mexico. The corals were subsampled at monthly resolution and Sr/Ca determinations were made using ICP-OES. Sr/Ca was calibrated to SST using previously-published calibration equations specific to each species. Both the O. faveolata (1893-2008) and S. siderea (1837-2012) records have well-defined annual cycles of Sr/Ca, which suggest a seasonal SST range of ~10-15°C: a range consistent with in situ instrumental SST records from DRTO. Our reconstructions of mean annual Sr/Ca-based SST and Sr/Ca variability from the two coral species show similar multi-decadal trends and strong coherency through overlapping time intervals. We investigated the intervals of divergence among the three independent DRTO records (two different species), and found that sudden drops in linear extension in S. siderea likely skewed the mean annual temperature record. This result underscores the importance of using multiple-coral geochemical records when reconstructing regional climate. A stacked record of SST derived from the three different coral colonies growing at DRTO from 1837-2008 showed a distinct trend toward cooler mean annual Sr/Ca-based SST from the late 1950s to the late 1960s, which coincides with a cooling trend found in several other Northern Hemisphere temperature reconstructions, and is likely linked to variability of the Atlantic Multi-decadal Oscillation.

  1. Fermi-surface measurements on the low-carrier density ferromagnet Ca1-xLaxB6 and SrB6

    NASA Astrophysics Data System (ADS)

    Hall, Donavan; Young, D. P.; Fisk, Z.; Murphy, T. P.; Palm, E. C.; Teklu, A.; Goodrich, R. G.

    2001-12-01

    Recently it has been discovered that weak ferromagnetism of a dilute three-dimensional electron gas develops on the energy scale of the Fermi temperature in some of the hexaborides; that is, the Curie temperature approximately equals the Fermi temperature. We report the results of de Haas-van Alphen experiments on two concentrations of La-doped CaB6 as well as Ca-deficient Ca1-δB6 and Sr-deficient Sr1-δB6. The results show that a Fermi surface exists in each case and that there are significant electron-electron interactions in the low-density electron gas.

  2. The Ca element effect on the enhancement performance of Sr2Fe1.5Mo0.5O6-δ perovskite as cathode for intermediate-temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Qiao, Jinshuo; Chen, Wenjun; Wang, Wenyi; Wang, Zhenhua; Sun, Wang; Zhang, Jing; Sun, Kening

    2016-11-01

    In this paper, the partial substitution of atomic elements from the A site of a perovskite is investigated in order to develop cathode materials for solid oxide fuel cell (SOFC) applications. Herein, Sr2-xCaxFe1.5Mo0.5O6-δ (SCFM), compounds were investigated by characterizing structural properties, chemical compatibility, electrical properties, electrochemical performance and stability. Thermal expansion coefficients were found to decrease when increasing the Ca content. X-ray photoelectron spectroscopy analysis suggests that Ca doping significantly affects the Fe2+/Fe3+ and Mo6+/Mo5+ ratios. For a doping level of x = 0.4, the sample showed the lowest interface polarization (Rp), the highest conductivity and a maximum power density of 1.26 W cm-2 at 800 °C. These results suggest that SCFM cathode materials are excellent candidates for intermediate temperature solid oxide fuel cells applications.

  3. Spectroscopic properties of UV active medium Ce3+:LiSr0.8Ca0.2AlF6

    NASA Astrophysics Data System (ADS)

    Nizamutdinov, A. S.; Shavelev, A. A.; Marisov, M. A.; Semashko, V. V.

    2016-02-01

    The aim of this work is phase composition and near UV spectroscopic studies of UV active media in fluoride crystals with colquiriite structure, such as Ce3+:LiSr0.8Ca0.2AlF6. Colquiriite structure mixed crystals show higher segregation coefficient of Ce3+ activator ions than common LiCaAlF6 hosts. An important result is based on the fact that this enhancement was achieved for two types of Ce3+ centers in a multisite Ce:LiSr0.8Ca0.2AlF6 system. Thus, it provides a higher gain coefficient for the 5d-4f transitions of Ce3+ ions and it spans a wider continuous wavelength tuning range between 280 and 320 nm for tunable Ce:LiSr0.8Ca0.2AlF6 laser systems.

  4. Combustion Synthesis of CaAl2Si2O8:Eu2+, Dy3+ And CaSrAl2SiO7:Eu2+ Long After Glow Phosphors

    NASA Astrophysics Data System (ADS)

    Talwar, Gurjeet; Joshi, C. P.; Moharil, S. V.; Kondawar, V. K.

    2011-10-01

    CaSrAl2SiO7:Eu2+ and CaAl2Si2O8:Eu2+, Dy3+ are prepared through modified combustion technique. The photoluminescence and long after glow decay characteristics are studied. PL emission spectra of both the phosphors are obtained in blue region.

  5. Enhancement of redox- and phase-stability of thermoelectric CaMnO{sub 3−δ} by substitution

    SciTech Connect

    Thiel, Philipp; Populoh, Sascha; Yoon, Songhak; Weidenkaff, Anke

    2015-09-15

    Redox Reactivity and structural phase transitions have a major impact on transport and me-chemical properties of thermoelectric CaMnO{sub 3−δ}. In this study series of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} (0≤x,y≤0.8) compounds, each with A-site (Dy{sup 3+}, Yb{sup 3+}) or B-site (Nb{sup 5+}, Ta{sup 5+} and Mo{sup 6+}, W{sup 6+}) substitution, were synthesized and crystallographically analyzed. It was found that the high-temperature oxygen content is widely independent from the substituent. Subsequently, with increasing temperature the differences in the Seebeck coefficient vanish above 1200 K. With increasing substitution the orthorhombic distortion of the perovskite-like phase increases. The orthorhombic distortion and the upper temperature limit of the stability of the orthorhombic crystal structure show an almost linear dependency. Accordingly, the mechanical stability of all-oxides thermoelectric converters at temperatures exceeding 1000 K will be increased employing materials with high substitution level and substituents inducing a high orthorhombic distortion. - Graphical abstract: Thermoelectric n-type CaMn{sub 0.98}W{sub 0.02}O{sub 3−δ}—Transport properties and expansion coefficient of: Oxygen loss (green region) and upper stability limit of the orthorhombic phase (yellow region) strongly affect the transport properties. Both features also cause lattice expansion, which leads to cracking of thermoelectric all-oxide converters. We report how the upper limit for application can be shifted to even higher temperatures. - Highlights: • Level of Mn{sup 3+} at RT determines reduction behavior of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} at HT. • Differences in Seebeck coefficient vanish at T>1200 K independent from substitution. • Substitution increases orthorhombicity of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ}. • Linear dependence of orthorhombicity and phase stability. • Design guidelines for

  6. The series Bi2Sr2Ca(n-1) Cu(n)O(2n+4) (1 less than or equal to n less than or equal to 5): Phase stability and superconducting properties

    NASA Technical Reports Server (NTRS)

    Deguire, Mark R.; Bansal, Narottam P.; Farrell, David E.; Finan, Valerie; Kim, Cheol J.; Hills, Bethanie J.; Allen, Christopher J.

    1989-01-01

    Phase relations at 850 and 870 C, melting transitions in air, oxygen, and helium were studied for Bi(2.1)Sr(1.9) CuO6 and for the Bi2Sr2Ca(n-1) Cu(n)O(2n+4) for n = 1, 2, 3, 4, 5, and infinity (CaCuO2). Up to 870 C, the n = 2 composition resides in the compatibility tetrahedron bounded by Bi(2+x)(Sr,Ca)(3-y) Cu2O8, (Sr,Ca)14 Cu24O41, Ca2CuO3, and a Bi-Sr-Ca-O phase. The n is greater than or equal to 3 compositions reside in the compatibility tetrahedron Bi(2+x)(Sr,Ca)(3-y) Cu2O8 - (Sr,Ca)14 Cu24O41 - Ca2CuO3 - CuO up to 850 C. However, Bi(2+x)Sr(4-y) Cu3O10 forms for n is greater than or equal to 3 after extended heating at 870 C. Bi(2+x)Sr(2-y) CuO6 and Bi(2+x)(Sr,Ca)(3-y) Cu2O8 melt in air at 914 C and 895 C respectively. During melting, all of the compositions studied lose 1 to 2 percent by weight of oxygen from the reduction of copper. Bi(2+x)Sr(2-y) CuO6, Bi(2+n)(Sr,Ca)(3-y) Cu2O8, and Bi(2+x)(Sr,Ca)(4-y) Cu3O10 exhibit crystallographic alignment in a magnetic field, with the c-axes orienting parallel to the field.

  7. Effects of compositional phase transitions on luminescence of Sr 1- xCa xTiO 3:Pr 3+

    NASA Astrophysics Data System (ADS)

    Jia, Weiyi; Xu, Wuliang; Rivera, Iris; Pérez, Angélica; Fernández, Félix

    2003-04-01

    The mixed-compound of Sr 1- xCa xTiO 3 has shown several compositional phase transformations. Photoluminescence and excitation spectra of the samples with different x and doped with 0.2% Pr 3+ were investigated. Changes in the emission spectra were observed in different phases. The blue emission at 491 nm from 3P 0 state was found quite strong in the tetragonal phase, and was thermally quenched in the orthorhombic phases. The intensity of the red luminescence from 1D 2 increases with increasing content of calcium. The strongest red emission is obtained from CaTiO 3:Pr 3+. The results are discussed based on the configuration coordinate model and interaction of Pr with the charge transfer exciton state of the Ti complex.

  8. Endohedral metallofullerenes, M@C60 (M = Ca, Na, Sr): selective adsorption and sensing of open-shell NOx gases.

    PubMed

    Tawfik, Sherif Abdulkader; Cui, X Y; Ringer, S P; Stampfl, C

    2016-08-21

    Based on density-functional theory and non-equilibrium Green's function calculations, we demonstrate that endohedral metallofullerenes (EMFs) are reactive to open-shell gases, and therefore have the potential application as selective open-shell gas sensors. The adsorption of eight gas species (CO, H2O, H2S, NO2, NO, SO2, O2 and NH3) on three EMFs (M@C60, M = Ca, Na and Sr) shows that the adsorption energies of the EMFs towards NO2 and NO are significantly higher than the closed-shell species. Moreover, the high selectivity appears relatively insensitive to the inserted metal atoms. The calculated current-voltage characteristics of gold-M@C60-gold structures (M = Ca, Na) show that the adsorption of NO2 leads to significant change in conductivity, suggesting a potential application as an EMF gas resistive sensing device. PMID:27426253

  9. Endohedral metallofullerenes, M@C60 (M = Ca, Na, Sr): selective adsorption and sensing of open-shell NOx gases.

    PubMed

    Tawfik, Sherif Abdulkader; Cui, X Y; Ringer, S P; Stampfl, C

    2016-08-21

    Based on density-functional theory and non-equilibrium Green's function calculations, we demonstrate that endohedral metallofullerenes (EMFs) are reactive to open-shell gases, and therefore have the potential application as selective open-shell gas sensors. The adsorption of eight gas species (CO, H2O, H2S, NO2, NO, SO2, O2 and NH3) on three EMFs (M@C60, M = Ca, Na and Sr) shows that the adsorption energies of the EMFs towards NO2 and NO are significantly higher than the closed-shell species. Moreover, the high selectivity appears relatively insensitive to the inserted metal atoms. The calculated current-voltage characteristics of gold-M@C60-gold structures (M = Ca, Na) show that the adsorption of NO2 leads to significant change in conductivity, suggesting a potential application as an EMF gas resistive sensing device.

  10. Tropical Atlantic SSTS at the Last Glacial Maximum derived from Sr/Ca ratios of fossil coral

    NASA Astrophysics Data System (ADS)

    Cohen, A. L.; Saenger, C. P.

    2006-12-01

    The sensitivity of the tropics to climate change is a particularly controversial issue in paleoclimatology. At the heart of this controversy are disagreements amongst different proxy datasets regarding the amplitude of glacial-interglacial changes in temperature, particularly at the sea surface. Data obtained from the aragonitic skeletons of massive reef corals have contributed in no small measure to the debate, yielding LGM and deglacial SSTs 5-6°C cooler than today (Guilderson et al., 1994; McCulloch et al., 1999; Correge et al., 2004), that imply a high sensitivity of Earth's climate to changes in boundary conditions (Crowley, 2000). We used SIMS ion microprobe to analyze Sr/Ca ratios of small pieces of Montastrea coral retrieved from a Barbados drillcore (Guilderson et al., 2001). U/Th dates place the samples between 22 and 24 kyr BP. Localized areas of dissolution and re-growth of secondary (diagenetic) aragonite crystals were identified at centers of septa. Sr/Ca ratios of these crystals were higher than Sr/Ca ratios of original coral crystals preserved in adjacent fasciculi and yielded relatively cooler derived SSTs. The original coral crystals, recognized by their size and orientation, were selectively targeted for analysis using a 20 micron-diameter sample spot. Our calibration study using modern corals from Bermuda, St Croix (USVI) and Barbados indicates that Montastrea Sr/Ca is strongly correlated with SST and with annual extension (growth) rate (Saenger et al., 2006). Growth rate of the fossil corals was determined from measurement of daily growth bands identified in petrographic thin-sections. Application of a growth-dependent Sr/Ca-T calibration yielded Barbados SSTs that were, on average, 2.5°C cooler than today during the LGM and ~1°C cooler than today during Heinrich Event 2. Our LGM SSTs are consistent with the original CLIMAP estimates (CLIMAP, 1976) and with more recent Mg/Ca-based SSTs derived from calcitic foraminifera in the Caribbean

  11. Oxygen partial pressure dependence of magnetic, optical and magneto-optical properties of epitaxial cobalt-substituted SrTiO₃ films.

    PubMed

    Onbaşlı, Mehmet C; Goto, Taichi; Tang, Astera; Pan, Annia; Battal, Enes; Okyay, Ali K; Dionne, Gerald F; Ross, C A

    2015-05-18

    Cobalt-substituted SrTiO3 films (SrTi0.70Co0.30O(3-δ)) were grown on SrTiO3 substrates using pulsed laser deposition under oxygen pressures ranging from 1 μTorr to 20 mTorr. The effect of oxygen pressure on structural, magnetic, optical, and magneto-optical properties of the films was investigated. The film grown at 3 μTorr has the highest Faraday rotation (FR) and magnetic saturation moment (M(s)). Increasing oxygen pressure during growth reduced M(s), FR and optical absorption in the near-infrared. This trend is attributed to decreasing Co2+ ion concentration and oxygen vacancy concentration with higher oxygen partial pressure during growth. PMID:26074589

  12. Assessing the impact of diagenesis on δ11B, δ13C, δ18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite

    NASA Astrophysics Data System (ADS)

    Edgar, Kirsty M.; Anagnostou, Eleni; Pearson, Paul N.; Foster, Gavin L.

    2015-10-01

    The geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo-climatic, -oceanographic and -ecological changes. However, dissolution of biogenic calcite and precipitation of inorganic calcite (overgrowth and recrystallization) at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test, biasing any resulting paleoenvironmental reconstruction. The δ11B of planktic foraminiferal calcite is a promising ocean pH-proxy but the effect of diagenesis is still poorly known. Here we present new δ11B, δ13C, δ18O, Sr/Ca and B/Ca data from multiple species of planktic foraminifera from time-equivalent samples for two low latitude sites: clay-rich Tanzanian Drilling Project (TDP) Site 18 from the Indian Ocean containing well-preserved ('glassy') foraminifera and carbonate-rich Ocean Drilling Program (ODP) Site 865 from the central Pacific Ocean hosting recrystallized ('frosty') foraminifera. Our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis. Planktic foraminiferal δ18O and δ13C records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration. Sr/Ca and B/Ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa. In contrast, δ11B values indicate no large differences between well-preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the δ11B of biogenic calcite appears robust, potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing CaCO3. Our finding may remove one potential source of uncertainty in δ11B based p

  13. Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF2 and SrF2 crystals.

    PubMed

    Barandiarán, Zoila; Seijo, Luis

    2015-10-14

    Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF2 and Yb/Sr pairs in SrF2 crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4f(N-1)5d excited states of Y b(2+): these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b(2+) + Ca(2+) (Sr(2+)) → Y b(3+) + Ca(+) (Sr(+)) electron phototransfer. This mechanism applies to all the observed Y b(2+) 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF2:Y b(2+) because the Y b(3+)-Ca(+) states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF2:Y b(2+) at the wavelengths of the first 4f-5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b(2+) active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF2 host, associated with the lowest 4f-5d band. PMID:26472390

  14. Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF{sub 2} and SrF{sub 2} crystals

    SciTech Connect

    Barandiarán, Zoila Seijo, Luis

    2015-10-14

    Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF{sub 2} and Yb/Sr pairs in SrF{sub 2} crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4f{sup N−1}5d excited states of Y b{sup 2+}: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b{sup 2+} + Ca{sup 2+} (Sr{sup 2+}) → Y b{sup 3+} + Ca{sup +} (Sr{sup +}) electron phototransfer. This mechanism applies to all the observed Y b{sup 2+} 4f–5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF{sub 2}:Y b{sup 2+} because the Y b{sup 3+}–Ca{sup +} states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF{sub 2}:Y b{sup 2+} at the wavelengths of the first 4f–5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b{sup 2+} active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF{sub 2} host, associated with the lowest 4f–5d band.

  15. Electrochemical insertion of lithium into the Bi2Sr2CaCu2O8+ y high- Tc superconductor

    NASA Astrophysics Data System (ADS)

    Fleischer, Niles A.; Manassen, Joost; Coppens, Philip; Lee, Peter; Gao, Yan; Greenbaum, Steven G.

    1992-01-01

    The insertion compound LixBi2Sr2CaCu2O8+ y (for lithium contents up to the studied level of x=2) was prepared by electro-chemical insertion of lithium into Bi2Sr2CaCu2O8+ y pellets at room temperature in galvanic cells using 1.4 M LiAsF 6 in 2Me-THF as electrolyte. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists but the superconducting fraction appears to be lower in the reacted samples. XRD data show that insertion of Li ions is accompanied by interlayer expansion between BiO planes and a small increase in the a and b cell lattice parameters. 7Li NMR measurements indicate a substantial donation of electrons to the 2212 host lattice. The changes in the a and b lattice parameters and the effect on superconductivity is consistent with some of the donated electrons entering the CuO planes and reducing holes in these layers.

  16. The k-space origins of scattering in Bi2Sr2CaCu2O8+x.

    PubMed

    Alldredge, Jacob W; Calleja, Eduardo M; Dai, Jixia; Eisaki, H; Uchida, S; McElroy, Kyle

    2013-08-21

    We demonstrate a general, computer automated procedure that inverts the reciprocal space scattering data (q-space) that are measured by spectroscopic imaging scanning tunnelling microscopy (SI-STM) in order to determine the momentum space (k-space) scattering structure. This allows a detailed examination of the k-space origins of the quasiparticle interference (QPI) pattern in Bi2Sr2CaCu2O8+x within the theoretical constraints of the joint density of states (JDOS). Our new method allows measurement of the differences between the positive and negative energy dispersions, the gap structure and an energy dependent scattering length scale. Furthermore, it resolves the transition between the dispersive QPI and the checkerboard ([Formula: see text] excitation). We have measured the k-space scattering structure over a wide range of doping (p ∼ 0.22-0.08), including regions where the octet model is not applicable. Our technique allows the complete mapping of the k-space scattering origins of the spatial excitations in Bi2Sr2CaCu2O8+x, which allows for better comparisons between SI-STM and other experimental probes of the band structure. By applying our new technique to such a heavily studied compound, we can validate our new general approach for determining the k-space scattering origins from SI-STM data.

  17. A Robust and Fully-Automated Chromatographic Method for the Quantitative Purification of Ca and Sr for Isotopic Analysis

    NASA Astrophysics Data System (ADS)

    Smith, H. B.; Kim, H.; Romaniello, S. J.; Field, P.; Anbar, A. D.

    2014-12-01

    High throughput methods for sample purification are required to effectively exploit new opportunities in the study of non-traditional stable isotopes. Many geochemical isotopic studies would benefit from larger data sets, but these are often impractical with manual drip chromatography techniques, which can be time-consuming and demand the attention of skilled laboratory staff. Here we present a new, fully-automated single-column method suitable for the purification of both Ca and Sr for stable and radiogenic isotopic analysis. The method can accommodate a wide variety of sample types, including carbonates, bones, and teeth; silicate rocks and sediments; fresh and marine waters; and biological samples such as blood and urine. Protocols for these isotopic analyses are being developed for use on the new prepFAST-MCTM system from Elemental Scientific (ESI). The system is highly adaptable and processes up to 24-60 samples per day by reusing a single chromatographic column. Efficient column cleaning between samples and an all Teflon flow path ensures that sample carryover is maintained at the level of background laboratory blanks typical for manual drip chromatography. This method is part of a family of new fully-automated chromatographic methods being developed to address many different isotopic systems including B, Ca, Fe, Cu, Zn, Sr, Cd, Pb, and U. These methods are designed to be rugged and transferrable, and to allow the preparation of large, diverse sample sets via a highly repeatable process with minimal effort.

  18. Microstructure and electrical properties of pure 110K phase in the BiPbSrCaCuO system

    NASA Astrophysics Data System (ADS)

    Holguin, E.; Berger, H.; Lévy, F.; Dwir, B.; Pavuna, D.; Burri, G.

    1991-01-01

    The temperature dependence of the d.c. resistivity and a.c. magnetic susceptibility was investigated in bulk ceramics of the BiPbSrCaCuO system with 2212 - free (2223) phase. The temperature domain needed to synthesize this phase was small and, according to the actual temperature used, the superconducting properties of the samples were strongly modified. The corresponding X-ray diffraction lines of the 110K phase can be indexed in the pseudo-orthorhombic unit cell with parameters 5.40x5.41x37Å 3. SEM microprobe study revealed the presence of several non-superconducting phases and a composition 2.1:0.1:2:2:3 for the cation ratio Bi:Pb:Sr:Ca:Cu of the 110K phase. Electrical measurements (d.c. resistivity and a.c. susceptibility) confirmed the existence of a 2212 - free (2223) phase. A low temperature "tail" in the d.c. electrical resistivity marks the low value of critical current in the samples.

  19. Laser performance of diode-pumped Nd, Y-codoped CaF 2-SrF 2 mixed crystal

    NASA Astrophysics Data System (ADS)

    Liu, J.; Fan, M. W.; Su, L. B.; Jiang, D. P.; Ma, F. K.; Zhang, Q.; Xu, J.

    2014-03-01

    A disordered Nd, Y-codoped CaF2-SrF2 mixed crystal was obtained by the temperature gradient technique (TGT). The absorption and fluorescence spectra of the crystal were measured at room temperature. Diode-pumped continuous-wave (CW) and Q-switched laser operations were demonstrated at 1056 nm with a 0.65 at.% Nd, 10 at.% Y-codoped crystal, for the first time to our knowledge. The CW output power of 724 mW was obtained in a compact linear cavity. Also the Q-switched pulse characteristics of Nd, Y:CaF2-SrF2 laser crystal were reported based on Cr4+:YAG saturable absorbers in a folded cavity. The shortest pulse width of 110 ns and the highest peak power of 383 W were obtained when the initial transmission of the Cr4+:YAG crystals was 90%. The dependence of the operational parameters on the pump power was also investigated experimentally.

  20. Linear optical and electronic properties of the polar metallic ruthenate (Sr,Ca)Ru2O6.

    PubMed

    Puggioni, Danilo; Rondinelli, James M

    2014-07-01

    Using first-principles calculations, we compute the linear optical properties for cation ordered (Sr,Ca)Ru2O6. Our calculations show that this polar ferromagnetic metallic oxide exhibits optical anisotropy along the principal directions of the optical indicatrix owing to the absence of inversion symmetry in the crystal structure. The calculated reflectivity is used to locate the onset of the inter-band transitions at an energy of 1.3 eV. Comparing the optical conductivity with the electronic band structure, we identify the possible optical transitions. Finally, we apply the generalized Drude model to deduce an enhancement of the effective mass, m(*) ∼ 4.9m(e), in ordered (Sr,Ca)Ru2O6. Moreover, we show that removal of the polar distortions decrease the effective mass to m(*) ∼ 4.4m(e), suggesting that control over the amplitude of the polar displacements could be used to tune the degree of electronic correlation in oxide conductors without inversion symmetry.

  1. Solvothermal synthesis of well-dispersed MF(2) (M = Ca,Sr,Ba) nanocrystals and their optical properties.

    PubMed

    Zhang, Xiaoming; Quan, Zewei; Yang, Jun; Yang, Piaoping; Lian, Hongzhou; Lin, Jun

    2008-02-20

    MF(2) (M = Ca,Sr,Ba) nanocrystals (NCs) were synthesized via a solvothermal process in the presence of oleic acid and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, UV/vis absorption spectra, photoluminescence (PL) excitation and emission spectra, and lifetimes, respectively. In the synthetic process, oleic acid as a surfactant played a crucial role in confining the growth and solubility of the MF(2) NCs. The as-prepared CaF(2), SrF(2) and BaF(2) NCs present morphologies of truncated octahedron, cube and sheet in a narrow distribution, respectively. Possible growth mechanisms were proposed to explain these results. The as-prepared NCs are highly crystalline and can be well dispersed in cyclohexane to form stable and clear colloidal solutions, which demonstrate strong emission bands centred at 400 nm in photoluminescence (PL) spectra compared with the cyclohexane solvent. The PL properties of the colloidal solutions of the as-prepared NCs can be ascribed to the trap states of surface defects.

  2. Atomic layer-by-layer growth of superconducting Bi Sr Ca Cu O thin films by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bove, P.; Rogers, D. J.; Hosseini Teherani, F.

    2000-11-01

    In situ reflection high-energy electron diffraction (RHEED) is employed to investigate the growth kinetics, and monitor the crystal surface evolution, during plasma-assisted molecular beam epitaxy growth of Bi 2Sr 2Ca n-1 Cu nO (BSCCO) compounds. By varying the growth parameters such as operating pressure, substrate temperature, cation flux and shutter opening pulse duration, it is found that the crystal growth front exhibits surface reconstructions with (1×1), (2×2), c(2×2) and (3×1) symmetries for the Sr, Ca and Cu species, and a RHEED pattern characteristic of twinning for Bi. Through manipulation of these surface reconstructions, and use of an adapted growth mode, it was possible to achieve a monolayer coverage for each species supplied. For the n=1, 2 and 3 compounds the resulting films exhibit a crystal quality characterised by an X-ray diffraction rocking curve width of 0.03° and an atomic force microscope mean surface roughness of 0.9 nm [over 10×10 μm] for 40 nm thick films.

  3. SrZn2Sn2 and Ca2Zn3Sn6 — two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    NASA Astrophysics Data System (ADS)

    Stegmaier, Saskia; Fässler, Thomas F.

    2012-08-01

    SrZn2Sn2 and Ca2Zn3Sn6, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn2Sn2 comprises (anti-)PbO-like {ZnSn4/4} and {SnZn4/4} layers. Ca2Zn3Sn6 shows similar {ZnSn4/4} layers and {Sn4Zn} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn2Sn2 adopts the SrPd2Bi2 structure type, and Ca2Zn3Sn6 is isotypic to the R2Zn3Ge6 compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn2Sn2 and Ca2Zn3Sn6 are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {Sn4Zn} layers of Ca2Zn3Sn6.

  4. The effect of chemical pressure on the structure and properties of A2CrOsO6 (A=Sr, Ca) ferrimagnetic double perovskite

    NASA Astrophysics Data System (ADS)

    Morrow, Ryan; Soliz, Jennifer R.; Hauser, Adam J.; Gallagher, James C.; Susner, Michael A.; Sumption, Michael D.; Aczel, Adam A.; Yan, Jiaqiang; Yang, Fengyuan; Woodward, Patrick M.

    2016-06-01

    The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. As reported previously Sr2CrOsO6 crystallizes with R 3 bar symmetry due to a-a-a- octahedral tilting. A decrease in the tolerance factor leads to a-a-b+ octahedral tilting and P21/n space group symmetry for Ca2CrOsO6. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 μB. Sr2CrOsO6 orders at 660 K while Ca2CrOsO6 orders at 490 K. Variable temperature magnetization measurements suggest that the magnetization of the Cr3+ and Os3+ sublattices have different temperature dependences in Sr2CrOsO6. This leads to a non-monotonic temperature evolution of the magnetic moment. Similar behavior is not seen in Ca2CrOsO6. Both compounds have similar levels of Os/Cr antisite disorder, with order parameters of η=80.2(4)% for Sr2CrOsO6 and η=76.2(5)% for Ca2CrOsO6, where η=2θ-1 and θ is the occupancy of the osmium ion on the osmium-rich Wyckoff site.

  5. Effects of antimony substitution on bismuth based superconductors

    NASA Technical Reports Server (NTRS)

    Barrientos, Alfonso

    1990-01-01

    The effect of Sb substitution and simultaneous substitution of Pb and Sb on the superconducting transition temperatures in the BiSrCaCuO system is investigated. The 2:2:2:3 phase is of particular interest since any small increase in the transition temperature could be of great interest. More that 90 different samples were prepared based on 2:2:2:3 stoichiometry in the BiSrCaCuO system. After this preliminary attempt, four different families of samples were investigated. In the first family of samples, Bi was substituted by Sb to form Bi(1.9)Sb(0.1)Sr2Ca2Cu3O(y). The second group of samples were prepared by simultaneous addition of Pb and Sb with nominal composition Bi(1.8)Pb(0.1)Sb(0.1)Sr2Ca2Cu3O(y). The third and fourth groups were prepared to determine the effect created when the Pb concentration is increased with the nominal compositions being Bi(1.7)Pb(0.1)Sr2Ca2Cu3O(y) and Bi(1.6)Sb(0.1)Sr2Ca2Cu3O(y). The results of these investigations are presented with a discussion.

  6. The North Atlantic Oscillation Reconstructed at Bermuda for 220 Years Using Sr/Ca Ratios in Diploria labyrinthiformis (brain coral)

    NASA Astrophysics Data System (ADS)

    Goodkin, N. F.; Hughen, K. A.; Cohen, A. L.; Curry, W. B.; Doney, S. C.

    2006-12-01

    The North Atlantic Oscillation (NAO) is a meridional oscillation in atmospheric mass measured by pressure anomalies between Iceland (65°N, 23°W) and the Azores (38°N, 26°W) (Hurrell, 1995). Changes between the positive and negative phase of the NAO strongly influence weather patterns across the US, Europe and the Middle East. A shift in recent decades toward a sustained positive NAO has raised questions about the influence of greenhouse gas emissions on this system. Unfortunately, instrumental records are too short to identify the natural baseline variability of the NAO, and NAO reconstructions generally encompass only land-based proxies, excluding ocean processes. Winter-time sea surface temperatures (SST) in the Sargasso Sea have previously been shown to correlate to the NAO (Visbeck et al., 2001), and thus a long winter SST record based on proxy data could be used to reconstruct NAO variability back in time. Here we present an annually resolved winter-time strontium to calcium ratio (Sr/Ca) record from a 220-year old brain coral (Diploria labyrinthiformis) collected from the south shore of Bermuda. Brain coral is prevalent in Bermuda and shows distinct annual banding in its skeleton providing precise age models. Winter-time coral Sr/Ca has previously been shown to accurately record winter SST free from growth rate influences (Goodkin et al., 2005), and that relationship is confirmed here. Cross-spectral analysis between winter-time coral Sr/Ca and four instrumental and proxy records of the NAO (Hurrell, 1995, Jones et al., 1997, Luterbacher et al., 2001, Cook et al., 2002) show two frequencies of coherence with >95% confidence. At periods greater than 20 years and between 3 and 5 years, the coral Sr/Ca effectively captures the NAO variability. Filtering the coral record to these frequencies and comparing to the instrumental and proxy records, including another marine-based NAO reconstruction from the North and Norwegian Seas (Schoene et al., 2003), show

  7. Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Tennant, D. A.; Lake, B.

    2015-11-01

    Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been investigated by ac magnetic susceptibility {χ\\text{ac}}(T) , dc magnetic susceptibility χ (T) , isothermal magnetization M(H) and heat capacity {{C}\\text{p}}(T) measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a spin-glass type freezing behavior near 16 K. Our frequency dependent {χ\\text{ac}}(T) data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly influenced by Ca substitution. The effect of partial nonmagnetic Ca2+ substitution for magnetic Dy3+ is similar to the previous study on nonmagnetic isovalent Y3+ substituted Dy2-x Y x Ti2O7 (for low levels of dilution), however the suppression of spin-freezing behavior is substantially stronger for Ca than Y. The Cole-Cole plot analysis reveals semicircular character and a single relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca2+ substitution for Dy3+ ions.

  8. Ca, Sr, Mo and U isotopes evidence ocean acidification and deoxygenation during the Late Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Silva-Tamayo, Juan Carlos; Payne, Jon; Wignall, Paul; Newton, Rob; Eisenhauer, Anton; Weyer, Stenfan; Neubert, Nadja; Lau, Kim; Maher, Kate; Paytan, Adina; Lehrmann, Dan; Altiner, Demir; Yu, Meiyi

    2014-05-01

    The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained. Here we use multiple isotope systems - Ca, Sr, Mo and U - measured from well dated Upper Permian- Lower Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry and the effects of ocean acidification and de-oxygenation through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing δ44/40Ca compositions, from ~-1.4‰ to -2.0‰ in the interval preceding the main extinction. These values remain low during most of the Griesbachian, to finally return to -1.4‰ in the middle Dienerian. The limestone succession from southern Turkey also displays a major decrease in the δ88/86Sr values from 0.45‰ to 0.3‰ before the extinction. These values remain low during the Griesbachian and finally increase to 0.55‰ by the middle Dienerian. The paired negative anomalies on the carbonate δ44/40Ca and δ88/86Sr suggest a decrease in the carbonate precipitation and thus an episode of ocean acidification coincident with the major biotic crisis. The Mo and U isotope records also exhibit significant rapid negative anomalies at the onset of the main extinction interval, suggesting rapid expansion of anoxic and euxinic marine bottom waters during the extinction interval. The rapidity of the isotope excursions in Mo and U suggests substantially reduced residence times of these elements in seawater relative to the modern, consistent with expectations for a time of widespread anoxia. The large C-isotope variability within Lower Triassic rocks, which is similar to that of the Lower-Middle Cambrian, may reflect biologically controlled perturbations of the oceanic carbon cycle

  9. Competitive inhibition and selectivity enhancement by Ca in the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, Hf) by carrot (Daucus carota cv. U.S. harumakigosun).

    PubMed

    Ozaki, Takuo; Ambe, Shizuko; Abe, Tomoko; Francis, Arokiasamy J

    2005-01-01

    We investigated the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, and Hf) and the effect of Ca on their uptake in carrots (Daucus carota cv. U.S. harumakigosun) by the radioactive multitracer technique. The experimental results suggested that Na, Mg, K, and Rb competed for the functional groups outside the cells in roots with Ca but not for the transporter-binding sites on the plasma membrane of the root cortex cells. In contrast, Y, Ce, Pm, and Gd competed with Ca for the transporters on the plasma membrane. The selectivity, which was defined as the value obtained by dividing the concentration ratio of an elemental pair, K/Na, Rb/Na, Be/Sr, and Mg/Sr, in the presence of 0.2 and 2 ppm Ca by that of the corresponding elemental pair in the absence of Ca in the solution was estimated. The selectivity of K and Rb in roots was increased in the presence of Ca. The selectivity of Be in roots was not affected, whereas the selectivity of Mg was increased by Ca. These observations suggest that the presence of Ca in the uptake solution enhances the selectivity in the uptake of metabolically important elements against unwanted elements. PMID:15695849

  10. Synthesis, structure and chemical bonding of CaFe{sub 2−x}Rh{sub x}Si{sub 2} (x=0, 1.32, and 2) and SrCo{sub 2}Si{sub 2}

    SciTech Connect

    Hlukhyy, Viktor Hoffmann, Andrea V.; Fässler, Thomas F.

    2013-07-15

    The finding of superconductivity in Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2} put the attention on the investigation of compounds that crystallize with ThCr{sub 2}Si{sub 2} structure type such as AT{sub 2}X{sub 2} (A=alkali/alkaline earth/rare earth element; T=transition metal and X=element of the 13–15th group). In this context the silicides CaFe{sub 2}Si{sub 2}, CaFe{sub 0.68(6)}Rh{sub 1.32(6)}Si{sub 2}, CaRh{sub 2}Si{sub 2} and SrCo{sub 2}Si{sub 2} have been synthesized by reaction of the elements under an argon atmosphere. Single crystals were obtained by special heat treatment in welded niobium/tantalum ampoules. The compounds were investigated by means of powder and single crystal X-ray diffraction. All compounds crystallize in the ThCr{sub 2}Si{sub 2}-type structure with space group I4/mmm (No. 139): a=3.939(1) Å, c=10.185(1) Å, R{sub 1}=0.045, 85 F{sup 2} values, 8 variable parameters for CaFe{sub 2}Si{sub 2}; a=4.0590(2) Å, c=9.9390(8) Å, R{sub 1}=0.030, 90 F{sup 2} values, 10 variable parameters for CaFe{sub 0.68(6)}Rh{sub 1.32(6)}Si{sub 2}; a=4.0695(1) Å, c=9.9841(3) Å, R{sub 1}=0.031, 114 F{sup 2} values, 9 variable parameters for CaRh{sub 2}Si{sub 2}; and a=3.974(1) Å, c=10.395(1) Å, R{sub 1}=0.036, 95 F{sup 2} values, 8 variable parameters for SrCo{sub 2}Si{sub 2}. The structure of SrCo{sub 2}Si{sub 2} contains isolated [Co{sub 2}Si{sub 2}]{sup 2−} 2D-layers in the ab-plane whereas in CaFe{sub 2−x}Rh{sub x}Si{sub 2} the [T{sub 2}Si{sub 2}] layers (T=Fe and Rh) are interconnected along the c-axis via Si3Si bonds resulting in a three-dimentional (3D) [T{sub 2}Si{sub 2}]{sup 2−} polyanions and therefore belong to the so-called collapsed form of the ThCr{sub 2}Si{sub 2}-type structure. The SrCo{sub 2}Si{sub 2} and CaRh{sub 2}Si{sub 2} are isoelectronic to the parent 122 iron–pnictide superconductors AeFe{sub 2}As{sub 2} (Ae=alkaline earth elements), whereas CaFe{sub 2}Si{sub 2} is a full substituted variant (As/Si) of CaFe{sub 2}As{sub 2

  11. Variations in the Sr/Ca, δ44Ca and δ18O composition of calcite as a function of solution chemistry and crystal growth rate

    NASA Astrophysics Data System (ADS)

    Watkins, J. M.; DePaolo, D. J.; Ryerson, F. J.

    2012-12-01

    The trace element and isotopic composition of calcite can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The accuracy with which these effects can be interpreted is limited by our ability to distinguish signatures arising from equilibrium partitioning versus kinetic or mass transport effects. Our focus in this work is on mass transport effects in aqueous environments, and specifically, the growth rate-dependence of trace element and isotopic incorporation into calcite. This requires experiments in which the degree of supersaturation, or the solution chemistry, is held constant and the rate of crystal growth can be determined. In our experiments, N2+CO2 gas mixture is bubbled through a beaker containing 1300 mL of solution (30 mM CaCl2 + 5 mM NH4Cl + 0.1 mM SrCl2). The degree of supersaturation with respect to calcite is controlled by the pCO2 of the gas mixture, which is constantly replenished from a gas source. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls and the pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. During an experiment we control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate. At the same time we monitor the total alkalinity, the pCO2 of the gas outflow, the gas outflow rate, and the amount of NaOH added. The rate of calcite precipitation can be determined in three ways: (1) the change in total alkalinity due to Ca2+ removal, mass balance of C in the system, and (3) post-run measurement of [Ca2+] in aliquots of solution taken during an experiment. We present results from experiments where growth rates are estimated to range from 0.5 to 16 mmol/m2/hr. Our experiments thus far have yielded calcite crystals that are out of calcium and oxygen isotopic equilibrium with the parent solution. Crystals are enriched in the light isotope of Ca by 0.4 to 1.8‰. The light isotope

  12. Surface modification of MAl2O4:Eu2+,Dy3+ (M = Sr, Ca, Ba) phosphors to enhance water resistance by combustion method

    NASA Astrophysics Data System (ADS)

    Deng, Suqing; Xue, Zhiping; Yang, Qu; Liu, Yingliang; Lei, Bingfu; Xiao, Yong; Zheng, Mingtao

    2013-10-01

    A facile combustion method was introduced into surface modification of MAl2O4:Eu2+,Dy3+ (M = Sr, Ca, Ba) phosphors to improve their water resistance. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), pH measurements and photoluminescence (PL) spectrophotometry were used to characterize the phosphors before and after modification, respectively. Experimental results showed that compact layer of MAl2B2O7 (M = Sr, Ca, Ba) substance was formed on the surface of aluminate phosphors by direct chemical reaction between aluminate and boracic acid. MAl2B2O7 (M = Sr, Ca, Ba) substance is chemically stable in water and could improve water resistance of aluminate phosphors effectively with little influence of luminescence property. It was considered that the versatility of combustion method for surface modification of aluminate phosphors has been confirmed.

  13. Synthesis of high-T(c) superconducting Bi-Pb-Sr-Ca-Cu-O ceramics prepared by an ultrastructure processing via the oxalate route

    NASA Astrophysics Data System (ADS)

    Chen, F. H.; Tseng, T. Y.; Koo, H. S.

    1990-07-01

    Fourier-transform IR (FTIR) spectroscopy has been used to monitor sol-gel reaction mechanisms involved in the generation of the high-T(c) superconductor in the Pb-doped Bi-Sr-Ca-Cu-O system during the 840 C pyrolyzation and oxidation of an oxalate precursor. XRD and FTIR were then used to analyze the specimens after firing, in order to identify their various phases. The results obtained imply a Bi2Sr2CaCu2O(8+delta), or phase 2212, formation mechanism via the Bi2Sr2CuO(6+delta)-Ca2CuO3-CuO reaction at 800 C.

  14. Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO{sub 3}

    SciTech Connect

    Tsekouras, George Boudoire, Florent; Braun, Artur; Pal, Banabir; Sarma, D. D.; Vondráček, Martin; Prince, Kevin C.

    2015-09-21

    The electronic structure of the (La{sub 0.8}Sr{sub 0.2}){sub 0.98}Mn{sub 1−x}Cr{sub x}O{sub 3} model series (x = 0, 0.05, or 0.1) was measured using soft X-ray synchrotron radiation at room and elevated temperature. O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra showed that low-level chromium substitution of (La,Sr)MnO{sub 3} resulted in lowered hybridisation between O 2p orbitals and M 3d and M 4sp valance orbitals. Mn L{sub 3}-edge resonant photoemission spectroscopy measurements indicated lowered Mn 3d–O 2p hybridisation with chromium substitution. Deconvolution of O K-edge NEXAFS spectra took into account the effects of exchange and crystal field splitting and included a novel approach whereby the pre-peak region was described using the nominally filled t{sub 2g}↑ state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t{sub 2g}↑ state, which appears to provide an explanation for the 0.15 eV rise in activation energy for the oxygen reduction reaction, while decreased overlap between hybrid O 2p–Mn 3d states was in qualitative agreement with lowered electronic conductivity. An orbital-level understanding of the thermodynamically predicted solid oxide fuel cell cathode poisoning mechanism involving low-level chromium substitution on the B-site of (La,Sr)MnO{sub 3} is presented.

  15. Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO3

    NASA Astrophysics Data System (ADS)

    Tsekouras, George; Boudoire, Florent; Pal, Banabir; Vondráček, Martin; Prince, Kevin C.; Sarma, D. D.; Braun, Artur

    2015-09-01

    The electronic structure of the (La0.8Sr0.2)0.98Mn1-xCrxO3 model series (x = 0, 0.05, or 0.1) was measured using soft X-ray synchrotron radiation at room and elevated temperature. O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra showed that low-level chromium substitution of (La,Sr)MnO3 resulted in lowered hybridisation between O 2p orbitals and M 3d and M 4sp valance orbitals. Mn L3-edge resonant photoemission spectroscopy measurements indicated lowered Mn 3d-O 2p hybridisation with chromium substitution. Deconvolution of O K-edge NEXAFS spectra took into account the effects of exchange and crystal field splitting and included a novel approach whereby the pre-peak region was described using the nominally filled t2g↑ state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t2g↑ state, which appears to provide an explanation for the 0.15 eV rise in activation energy for the oxygen reduction reaction, while decreased overlap between hybrid O 2p-Mn 3d states was in qualitative agreement with lowered electronic conductivity. An orbital-level understanding of the thermodynamically predicted solid oxide fuel cell cathode poisoning mechanism involving low-level chromium substitution on the B-site of (La,Sr)MnO3 is presented.

  16. A high-resolution Sr/Ca and [delta][sup 18]O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Nino

    SciTech Connect

    McCulloch, M.T.; Gagan, M.K.; Mortimer, G.E.; Chivas, A.R. ); Isdale, P.J. )

    1994-06-01

    A high-resolution (near weekly) Sr/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period of 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the [delta][sup 18]O value of seawater. Using the Sr/Ca temperature calibration of De Villiers et al., the Sr/Ca records exhibit seasonally controlled cyclical SST (sea surface temperature) variations of from [approximately] 21 to [approximately] 28[degrees]C. During the very strong El Nino of 1982-1983, the Sr/CA systematics indicate a sharp drop in the winter SST to [approximately] 18.5[degrees]C. This represents a temperature anomaly of -3[degrees]C which is approximately twice that given by the [delta][sup 18]O variations, suggesting an [approximately] x2 amplification of the anomaly by the Sr/Ca system, possibly due to the increasing dominance of inorganically controlled aragonite-seawater fractionation. The oxygen isotope systematics show the combined effects of both temperature and changing seawater [delta][sup 18]O values, the latter reflecting the influx of [sup 18]O-depleted runoff during periods of high rainfall. Due to the extremely low ([approximately] 10[sup [minus]3]) Sr and Ca contents of river runoff relative to seawater, it is possible to use the Sr/Ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the [delta][sup 18]O value of seawater. Using this approach it is possible to quantitatively reproduce the volume of runoff from the Burdekin River during the periods of major flooding that occurred in early 1979 and 1981. The results of this study demonstrate that the combined use of high-resolution Sr/Ca and [delta][sup 18]O systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate.

  17. Effect of temperature and oxygen pressure on preparation of Bi2Sr2CaCu2O(x) thin films by metalorganic deposition

    NASA Astrophysics Data System (ADS)

    Yaegashi, Seiji; Murakami, Hirohiko; Nishino, Junya; Shiohara, Yuh; Tanaka, Shoji

    1991-03-01

    Bi2Sr2CaCu2O(x) superconducting thin films have been prepared by metalorganic deposition (MOD) under various oxygen pressures. The pressure-temperature (P-T) phase diagram of Bi2Sr2CaCu2O(x) was determined under oxygen pressures from 0.02 to 0.2 atm. A film which was fired at 785 C in 0.06 atm oxygen with the thickness of about 0.1 micron showed a critical current density of 20,000 A/sq cm at 30 K. The relationship between the critical current density and firing conditions is discussed.

  18. Spectroscopic study and laser operation of Cr 4+-doped (Sr,Ca)Gd 4(SiO 4) 3O single crystals

    NASA Astrophysics Data System (ADS)

    Moncorgé, R.; Manaa, H.; Deghoul, F.; Borel, C.; Wyon, Ch.

    1995-02-01

    Cr-doped oxyapatite single crystals with formula AGd 4(SiO 4) 3O and A = Sr or Ca were grown and studied. The shape and the intensity of their optical absorption and fluorescence bands as well as the values and the temperature variations of the fluorescence lifetimes are characteristic of those of tetrahedrally coordinated Cr 4+ ions. Gain measurements show their potential wavelength tunability between about 1.2 and 1.5 μm. Room temperature laser action is demonstrated at 1.37 and 1.44 μm in the Ca- and Sr-compounds, respectively.

  19. Significantly enhanced ferroelectricity and magnetic properties in (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3}-modified BiFeO{sub 3} ceramics

    SciTech Connect

    Liu, Juan; Liu, Xiao Qiang E-mail: xmchen59@zju.edu.cn; Chen, Xiang Ming E-mail: xmchen59@zju.edu.cn

    2015-05-07

    BiFeO{sub 3} multiferroic ceramics were modified by introducing (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} to form solid solutions. The single phase structure was easy to be obtained in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the present solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with M{sub r} = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe{sup 3+} by Ti{sup 4+}, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.

  20. Hydrothermal preparation and characterization of ultralong strontium-substituted hydroxyapatite whiskers using acetamide as homogeneous precipitation reagent.

    PubMed

    Xu, Jianqiang; Yang, Yaoqi; Wan, Rong; Shen, Yuhui; Zhang, Weibin

    2014-01-01

    The ultralong strontium- (Sr-) substituted hydroxyapatite (SrHAp) whiskers were successfully prepared using acetamide as homogeneous precipitation reagent. The effect of the Sr substitution amount on the lattice constants and proliferation of human osteoblast cells (MG-63) was further investigated. The results showed that the SrHAp whiskers with diameter of 0.2-12 μm and ultralong length up to 200 μm were obtained and the Sr substitution level could be facilely tailored by regulating the initial molar ratio of Sr/(Sr + Ca) in raw materials. The Sr(2+) replaced part of Ca(2+) and the lattice constants increased apparently with the increase of the Sr substitution amount. Compared with the pure HAp whiskers, the Sr substitution apparently stimulated the proliferation of MG-63 at certain extracted concentrations. Our study suggested that the obtained SrHAp whiskers might be used as bioactive and mechanical reinforcement materials for hard tissue regeneration applications. PMID:24592192

  1. Theoretical survey on M@C80 (M = Ca, Sr, and Ba): Behavior of different alkaline earth metal impacting the chemical stability and electronic properties

    NASA Astrophysics Data System (ADS)

    Cui, Jin-Bo; Guo, Yi-Jun; Li, Qiao-Zhi; Zhao, Pei; Zhao, Xiang

    2016-08-01

    Structures of mono-metallofullerenes M@C80 (M = Ca, Sr, and Ba) that separated in early experiment are determined owning the C2v(31920)-C80 cage. The change rule of properties for M@C80 (M = Ca, Sr, and Ba) influenced by different inner metal are discussed. As the trapped metal changes from calcium to barium, performance of thermodynamic stabilities for M@C2v(31920)-C80, M@C2v(31922)-C80, and M@D5h(31923)-C80 are significantly different. Orbital analysis suggests that the lowest unoccupied molecular orbitals (LUMOs) of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 are mostly located on the trapped metal, whereas reduction reactions of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 occur on the fullerene cage. Natural electron configuration analyses demonstrates that the decentralized electron back-donation of Ba@C2v(31920)-C80 would take responsible for the instability of itself. Electronic properties such as electron affinities and ionization potentials are significantly affected by encapsulated metal are also found. Computational UV-visible-NIR spectra for M@C2v(31920)-C80 (M = Ca, Sr, Ba) are in perfect accord with the spectra obtained experimentally.

  2. Microwave property improvement of Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ perovskite by A-site substitution

    NASA Astrophysics Data System (ADS)

    Hu, Mingzhe; Xiong, Gang; Ding, Zhao

    2016-04-01

    The crystal structure and microwave dielectric properties of Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramic (CLNZ) are tuned by A-site substitution of Sr2+ and Ba2+ ions in the present paper. The tuning effect on the crystal structure is investigated by the X-ray diffraction (XRD) pattern and it illustrates that single phase of orthorhombic perovskite structure is formed, however, minor amount of BaNb2O6-type second phase is also detected in (Ca1-xBax)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramics (CBLNZ) in the range of x ≥ 0.025, while pure perovskite phase is obtained in (Ca1-xSrx)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramics (CSLNZ) in the whole investigation range of 0 ≤ x ≤ 0.2. With the increase of x value, the unit cell volumes of both CBLNZ and CSLNZ perovskites gradually expand, which results in the degradation of the vibration bond strength between the B-site ions and oxygen in the perovskites. The microscopic structure related thermal parameters in CSLNZ and CBLNZ perovskites are analyzed in terms of Clausius-Mossotti equation to reveal the original contributors in the temperature coefficients. The results show that both Sr2+ and Ba2+ substitution can effectively improve the permittivity and Qf value, especially, improve the temperature coefficient of CLNZ ceramic in a certain range.

  3. Structural, electrical, dielectric and magnetic properties of Gd-Sn substituted Sr-hexaferrite synthesized by sol-gel combustion method

    NASA Astrophysics Data System (ADS)

    Ashiq, Muhammad Naeem; Shakoor, Sajeela; Najam-ul-Haq, Muhammad; Warsi, Muhammad Farooq; Ali, Irshad; Shakir, Imran

    2015-01-01

    The effect of Gd-Sn substitution on the structural, electrical and magnetic properties of Sr1-xGdx Fe12-ySny O19 (where x=0.00, 0.025, 0.05, 0.075, 0.1) and (y=0.00, 0.25, 0.5, 0.75, 1) prepared by the sol-gel combustion method has been investigated. The XRD analysis shows the presence of Fe2O3 phase at higher substitution. The average crystallite size obtained lies between 19-42 nm which is beneficial in obtaining suitable signal-to-noise ratio in high density recording media. The FTIR spectra of annealed samples of SrFe12O19, Sr0.95Gd0.05 Fe11.5Sn0.5O19 show that strontium hexaferrite nanoparticles have been synthesized successfully. DC electrical resistivity shows metal-to-semiconductor transition with temperature. The value of transition temperature increases with dopant content. Room temperature dc resistivity and energy of activation decreases while drift mobility increases on increasing the dopant concentration. The magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) decreases with increasing the dopant concentration.

  4. Overcoming phase instability of RBaCo2O5+ (R = Y and Ho) by Sr substitution for application as cathodes in solid oxide fuel cells

    SciTech Connect

    Kim, Jung-Hyun; Young Nam, Kim; Bi, Zhonghe; Manthiram, Arumugam; Paranthaman, Mariappan Parans; Huq, Ashfia

    2013-01-01

    Phase instabilities of the RBaCo2O5+ (R = Y and Ho) layered-perovskites and their decompositions into RCoO3 and BaCoO3-z at 800 oC in air were investigated. This will restrict their high temperature applications such as cathodes in solid oxide fuel cell (SOFC). However, appropriate amount of Sr substitution ( 60 % for R = Y and 70 % for R = Ho) for Ba successfully stabilized the R(Ba1-xSrx)Co2O5+ phase at elevated temperatures. This can be explained by decreasing oxygen vacancies at R-O layer, decreasing R-O bonding length, and consequent improvement of structural integrity. In addition, the Sr substitution (x = 0.6 - 1.0) for Ba provided added benefit with respect to the chemical stability against Ce0.8Gd0.2O1.9 (GDC) electrolyte, which is a critical requirement for the cathodes in SOFC. Among the various compositions investigated, the Y(Ba0.3Sr0.7)Co2O5+ + GDC composite cathode delivered the optimum electrochemical performances with a stable phase demonstrating the potential as a cathode in SOFC.

  5. Periodic c-axis modulation and crystallographic Fourier analysis of Bi 2Sr 2Ca nCu n+1O 6+2n+x ( n=0,1) single crystals with excess Bi

    NASA Astrophysics Data System (ADS)

    Ariosa, D.; Berger, H.; Schmauder, T.; Pavuna, D.; Margaritondo, G.; Christensen, S.; Kelley, R. J.; Onellion, M.

    2001-04-01

    We report on a distortion of Bi 2Sr 2Ca nCu n+1O 6+2n+x ( n=0,1) single crystals, perpendicular to the CuO 2 planes (the c-axis), for non-stoichiometric samples containing an excess of Bi. The distortion involves two parts: (a) symmetric displacements in the SrO and CuO 2 planes along the c-axis, and (b) an antisymmetric longitudinal compressive wave. The latter is revealed by observing odd harmonics in the X-ray diffraction (XRD) data. Such odd harmonics are typically extinguished for the I4/mmm space group of the exact stoichiometric phase. The antisymmetric compressive wave is reported for both BSCCO-2201 and BSCCO-2212 Bi excess samples, as well as for La-doped BSCCO-2201 samples. We have performed XRD model calculations for all samples studied, combined with Fourier analysis of the periodic c-axis modulation. The antisymmetric compressive wave was proven by reconstructing the atomic position profile from the intensity of odd XRD peaks caused by this commensurate modulation. Our results indicate preferential ordered substitution of Bi ions on nominally Sr ion positions. We also discuss implications for oxygen mobility, reversible sample doping, and electronic properties.

  6. Electronic structure of the ingredient planes of the cuprate superconductor Bi2Sr2CuO6+δ: A comparison study with Bi2Sr2CaCu2O8+δ

    DOE PAGES

    Yan -Feng Lv; Gu, G. D.; Wang, Wen -Lin; Ding, Hao; Wang, Yang; Ding, Ying; Zhong, Ruidan; Schneeloch, John; Wang, Lili; He, Ke; et al

    2016-04-15

    By means of low-temperature scanning tunneling microscopy, we report on the electronic structures of the BiO and SrO planes of the Bi2Sr2CuO6+δ (Bi-2201) superconductor prepared by argon-ion bombardment and annealing. Depending on post annealing conditions, the BiO planes exhibit either a pseudogap (PG) with sharp coherence peaks and an anomalously large gap magnitude of 49 meV or van Hove singularity (vHS) near the Fermi level, while the SrO is always characteristic of a PG-like feature. This contrasts with the Bi2Sr2CaCu2O8+δ (Bi-2212) superconductor where vHS occurs solely on the SrO plane. We disclose the interstitial oxygen dopants (δ in the formulas)more » as a primary cause for the occurrence of vHS, which are located dominantly around the BiO and SrO planes, respectively, in Bi-2201 and Bi-2212. This is supported by the contrasting structural buckling amplitude of the BiO and SrO planes in the two superconductors. Furthermore, our findings provide solid evidence for the irrelevance of PG to the superconductivity in the two superconductors, as well as insights into why Bi-2212 can achieve a higher superconducting transition temperature than Bi-2201, and by implication, the mechanism of cuprate superconductivity.« less

  7. Terahertz electromagnetic radiation from Bi2Sr2CaCu2Oy intrinsic Josephson junction stack

    NASA Astrophysics Data System (ADS)

    Oikawa, Dai; Irie, Akinobu; Yamaki, Kazuhiro; Oya, Gin-ichiro

    We have observed terahertz (THz) electromagnetic wave radiation from Bi2Sr2CaCu2Oy intrinsic Josephson junction (IJJ) stacks using high sensitive detector made of a small IJJ mesa. In this study, we focused on the THz radiation from a few hundred IJJs. We fabricated the IJJ oscillator and detector. The oscillators consist of 55 ∼ 300 IJJs with the lateral dimensions of 290 ¥ 50 μm2. The current-voltage characteristics of the IJJ oscillators showed a negative resistance accompanied with large hysteresis. The THz radiation was observed for several samples when the oscillator was biased at some current in the negative resistance region. We attribute the observed radiation to synchronized emission from many IJJs in the stack and find the emission frequency corresponds to the in-phase cavity resonance frequency.

  8. Fabrication of Ultrasmall High-Quality Bi2Sr2CaCu2O8+δ Intrinsic Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Matsumoto, Tetsuro; Kashiwaya, Hiromi; Shibata, Hajime; Eisaki, Hiroshi; Yoshida, Yoshiyuki; Kashiwaya, Satoshi

    2008-10-01

    The fabrication of ultrasmall high-quality intrinsic Josephson junctions (IJJs) using a cuprate superconductor is critical for the realization of a qubit. We investigated the mechanism of damage induced by a Ga+ beam in a Bi2Sr2CaCu2O8+δ IJJ during focused ion beam (FIB) processing. On the basis of the results, we developed a process that allowed the successful fabrication of an ultrasmall and high-quality IJJ. The damage induced by the FIB is reduced by restricting the direction of the Ga+ beam so that the junction area is not directly irradiated by the ion beam. The fabricated ultrasmall IJJ device has a junction area of 0.3 µm2 and shows excellent current-voltage characteristics.

  9. Macroscopic Quantum Tunneling in a Bi2Sr2CaCu2O8+δ Single Crystalline Whisker

    NASA Astrophysics Data System (ADS)

    Kubo, Yuimaru; Takahide, Yamaguchi; Ueda, Shinya; Takano, Yoshihiko; Ootuka, Youiti

    2010-06-01

    Macroscopic quantum tunneling (MQT) has been observed in an intrinsic Josephson junction (IJJ) stack of a Bi2Sr2CaCu2O8+δ (BSCCO) single crystalline whisker with high precision using a home made setup. The cross-over temperature between thermal activation and MQT was about 260 mK, and the Josephson plasma frequency was estimated to be 86 GHz. Both the thermal escape theory and the MQT theory are consistent with the experiments. These facts strongly suggest that single crystalline BSCCO whiskers are high enough quality to be used as intrinsic Josephson quantum devices such as intrinsic Josephson phase qubits. This is the first demonstration of MQT in BSCCO single crystalline whiskers.

  10. Reconstructed Fermi surface of underdoped Bi2Sr2CaCu2O(8+δ) cuprate superconductors.

    PubMed

    Yang, H-B; Rameau, J D; Pan, Z-H; Gu, G D; Johnson, P D; Claus, H; Hinks, D G; Kidd, T E

    2011-07-22

    The Fermi surface topologies of underdoped samples of the high-T(c) superconductor Bi2Sr2CaCu2O(8+δ) have been measured with angle resolved photoemission. By examining thermally excited states above the Fermi level, we show that the observed Fermi surfaces in the pseudogap phase are actually components of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the magnetic zone boundary, creating the illusion of Fermi "arcs." The area of the pockets as measured in this study is consistent with the doping level, and hence carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by phenomenological models of the pseudogap phase as a spin liquid. PMID:21867032

  11. Reconstructed Fermi Surface of Underdoped Bi2Sr2CaCu2O8 Cuprate Superconductors

    SciTech Connect

    H Yang; J Rameau; Z Pan; G Gu; P Johnson; H Claus; D Hinks; T Kidd

    2011-12-31

    The Fermi surface topologies of underdoped samples of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} have been measured with angle resolved photoemission. By examining thermally excited states above the Fermi level, we show that the observed Fermi surfaces in the pseudogap phase are actually components of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the magnetic zone boundary, creating the illusion of Fermi 'arcs.' The area of the pockets as measured in this study is consistent with the doping level, and hence carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by phenomenological models of the pseudogap phase as a spin liquid.

  12. Correlation of Tunneling Spectra in Bi{sub 2} Sr{sub 2} CaCu{sub 2} O

    SciTech Connect

    Zasadzinski, J. F.; Ozyuzer, L.; Miyakawa, N.; Gray, K. E.; Hinks, D. G.; Kendziora, C.

    2001-08-06

    New break-junction tunneling data are reported in Bi{sub 2}Sr {sub 2}CaCu{sub 2}O{sub 8+{delta}} over a wide range of hole concentration from underdoped (T{sub c}=74 K) to optimal doped (T{sub c}=95 K) to overdoped (T{sub c}=48 K) . The conductances exhibit sharp dips at a voltage, {Omega}/e , measured with respect to the superconducting gap. Clear trends are found such that the dip strength is maximum at optimal doping and that {Omega} scales as 4.9kT{sub c} over the entire doping range. These features link the dip to the resonance spin excitation and suggest quasiparticle interactions with this mode are important for superconductivity.

  13. Structural and Optoelectronic Properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds

    NASA Astrophysics Data System (ADS)

    Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.

    2016-06-01

    We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) anti-perovskite compounds using an all-electron full-potential linearized augmented plane-wave method. Optimized structural parameters are found to be in good agreement with the available experimental measurements. The electronic band structure is calculated using different exchange-correlation potentials which reveal that the investigated compounds are narrow direct band gap semiconductors. A direct narrow band gap at the center of the Brillouin zone emphasises the optical activity of these compounds. Prediction of the optical properties, such as the real and imaginary parts of the dielectric function and refractive index along with reflectivity and optical conductivity, reveals the importance of these compounds in the visible and near UV optoelectronic devices industry.

  14. Unadulterated spectral function of low-energy quasiparticles in Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Evtushinsky, D. V.; Kordyuk, A. A.; Borisenko, S. V.; Zabolotnyy, V. B.; Knupfer, M.; Fink, J.; Büchner, B.; Pan, A. V.; Erb, A.; Lin, C. T.; Berger, H.

    2006-11-01

    Fitting the momentum distribution photoemission spectra to the Voigt profile appears to be a robust procedure to purify the interaction effects from the experimental resolution. In application to Bi2Sr2CaCu2O8+δ high- Tc cuprates, the procedure reveals the true scattering rate at low binding energies and temperatures, and consequently, the true value of the elastic scattering. Reaching the minimal value ˜16meV , the elastic scattering does not reveal a systematic dependence on doping level, but is rather sensitive to impurity concentration and can be explained by the forward scattering on out-of-plane impurities. The inelastic scattering is found to form well-defined quasiparticles with the scattering rate ˜ω2 and ˜ω3 , above and below Tc , respectively.

  15. Ultraviolet to near-infrared downconversion in Yb3+-Na+ codoped Sr2CaWO6

    NASA Astrophysics Data System (ADS)

    Li, Yong; Li, XuZhi; Wei, XianTao; Li, ZhongYuan; Chen, Hongmei; Wang, WenMing; Zhao, Wei; Ji, Yuexia

    2016-07-01

    This study investigated photoluminescent properties of Sr2CaWO6:Yb3+, Na+ phosphor. The samples were successfully synthesized via a solid-state reaction method with various doping concentrations. The phosphor can efficiently absorb ultraviolet photons of 250-350 nm and transfer its absorbed photon energy to Yb3+ ions. Then subsequent quantum cutting between WO6 groups and Yb3+ ions takes place, down-converting an absorbed ultraviolet photon into two photons of 1007 nm radiations. Analyses of decay curves of different samples reveal an efficient energy transfer from WO6 groups to Yb3+ ions. Cooperative energy transfer from host to Yb3+ ions is responsible for downconversion via lifetime analysis. Quantum efficiencies were calculated, and estimated maximum efficiency reached 190%. These phosphors combine wide wavelength absorption in the ultraviolet range with high quantum efficiency, enabling potential application of efficiency enhancement of Si solar cell.

  16. Relaxor behavior of ferroelectric Ca0.22Sr0.12Ba0.66Nb2O6

    NASA Astrophysics Data System (ADS)

    Shekhar Pandey, Chandra; Schreuer, Jürgen; Burianek, Manfred; Mühlberg, Manfred

    2013-01-01

    The relaxor behavior of tetragonal tungsten bronze uniaxial relaxor ferroelectric calcium strontium barium niobate (Ca0.22Sr0.12Ba0.66Nb2O6 or CSBN-22) single crystal was studied by measuring elastic constants and thermal expansion with the aid of resonant ultrasound spectroscopy and dilatometry, respectively, in the temperature range 300 K-1503 K. Thermal expansion yields evidence of the Burns temperature TB and the intermediate characteristic temperature T*, which was also supported by the temperature evolutions of the elastic constants cij. CSBN-22 was found to be ˜2%-3% elastically stiffer than CBN-28. The presented results open the perspective to understand the relaxor behavior of CSBN.

  17. Geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro basin, Texas

    SciTech Connect

    Langmuir, D.; Melchior, D.

    1985-11-01

    The geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro Basin of north Texas, was studied to define geochemical controls on radionuclides such as /sup 90/Sr and /sup 226/Ra. Published solubility data for gypsum, anhydrite, celestite, barite and RaSO/sub 4/ were first reevaluated, in most cases using the ion interaction approach of Pitzer, to determine solubility products of the sulfates as a function of temperature and pressure. Ionic strengths of the brines were from 2.9 to 4.8 m, their temperatures and pressures up to 40/sup 0/C and 130 bars. Saturation indices of the sulfates were computed with the ion-interaction approach in one brine from the arkosic granite wash facies and four from the carbonate Wolfcamp Formation. All five brines are saturated with respect to gypsum, anhydrite and celestite, and three of the five with respect to barite. All are undersaturated by from 5 to 6 orders of magnitude with respect to pure RaSO/sub 4/. /sup 226/Ra concentrations in the brines, which ranged from 10/sup -11.3/ to 10/sup -12.7/ m, are not controlled by RaSO/sub 4/ solubility or adsorption, but possibly by the solubility of trace Ra solid solutions in sulfates including celestite and barite.

  18. The geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro Basin, Texas

    NASA Astrophysics Data System (ADS)

    Langmuir, Donald; Melchior, Daniel

    1985-11-01

    The geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro Basin of north Texas, was studied to define geochemical controls on radionuclides such as 90Sr and 226Ra. Published solubility data for gypsum, anhydrite, celestite, barite and RaSO 4 were first reevaluated, in most cases using the ion interaction approach of Pitzer, to determine solubility products of the sulfates as a function of temperature and pressure. Ionic strengths of the brines were from 2.9 to 4.8 m, their temperatures and pressures up to 40°C and 130 bars. Saturation indices of the sulfates were computed with the ion-interaction approach in one brine from the arkosic granite wash fades and four from the carbonate Wolfcamp Formation. All five brines are saturated with respect to gypsum, anhydrite and celestite, and three of the five with respect to barite. All are undersaturated by from 5 to 6 orders of magnitude with respect to pure RaSO 4. 226Ra concentrations in the brines, which ranged from 10 -11.3 to 10 -12.7 m, are not controlled by RaSO 4 solubility or adsorption, but possibly by the solubility of trace Ra solid solutions in sulfates including celestite and barite.

  19. CaMKIIδ mediates β-adrenergic effects on RyR2 phosphorylation and SR Ca2+ leak and the pathophysiological response to chronic β-adrenergic stimulation

    PubMed Central

    Grimm, Michael; Ling, Haiyun; Pereira, Laetitia; Willeford, Andrew; Gray, Charles B. B.; Erickson, Jeffrey R.; Sarma, Satyam; Respress, Jonathan L.; Wehrens, Xander H.T.; Bers, Donald M.; Brown, Joan Heller

    2015-01-01

    Chronic activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the deleterious effects of β-adrenergic receptor (β-AR) signaling on the heart, in part by enhancing RyR2-mediated sarcoplasmic reticulum (SR) Ca2+ leak. We used CaMKIIδ knockout (CaMKIIδ-KO) mice, and knock-in mice with an inactivated CaMKII site S2814 on the ryanodine receptor type-2 (S2814A), to interrogate the involvement of these processes in β-AR signaling and cardiac remodeling. Langendorff-perfused hearts from CaMKIIδ-KO mice showed inotropic and chronotropic responses to isoproterenol (ISO) that were similar to those of wild type (WT) mice, however in CaMKIIδ-KO mice CaMKII phosphorylation of phospholamban and RyR2 was decreased and isolated myocytes from CaMKIIδ-KO mice had reduced SR Ca2+ leak in response to isoproterenol (ISO). Chronic catecholamine stress with ISO induced comparable increases in relative heart weight and other measures of hypertrophy from day 9 through week 4 in WT and CaMKIIδ-KO mice, but development of cardiac fibrosis was prevented in CaMKIIδ-KO animals. A 4-week challenge with ISO resulted in reduced cardiac function and pulmonary congestion in WT, but not in CaMKIIδ-KO or S2814A mice, implicating CaMKIIδ-dependent phosphorylation of RyR2-S2814 in the cardiomyopathy, independent of hypertrophy, induced by prolonged β-AR stimulation. PMID:26080362

  20. Composite superconducting wires obtained by high-rate tinning in molten Bi-Pb-Sr-Ca-Cu-O system

    NASA Technical Reports Server (NTRS)

    Grozav, A. D.; Konopko, L. A.; Leporda, N. I.

    1990-01-01

    The preparation of high-T(sub c) superconducting long composite wires by short-time tinning of the metal wires in a molten Bi-Pb-Sr-Ca-Cu-O compound is discussed. The application of this method to the high-T(sub c) materials is tested, possibly for the first time. The initial materials used for this experiment were ceramic samples with nominal composition Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) and T(sub c) = 80 K prepared by the ordinary solid-state reaction, and industrial copper wires from 100 to 400 microns in diameter and from 0.5 to 1 m long. The continuously moving wires were let through a small molten zone (approximately 100 cubic mm). The Bi-based high-T(sub c) ceramics in a molten state is a viscous liquid and it has a strongly pronounced ability to spread on metal wire surfaces. The maximum draw rate of the Cu-wire, at which a dense covering is still possible, corresponds to the time of direct contact of wire surfaces and liquid ceramics for less than 0.1 s. A high-rate draw of the wire permits a decrease in the reaction of the oxide melt and Cu-wire. This method of manufacture led to the fabrication of wire with a copper core in a dense covering with uniform thickness of about h approximately equal to 5 to 50 microns. Composite wires with h approximately equal to 10 microns (h/d approximately equal to 0.1) sustained bending on a 15 mm radius frame without cracking during flexing.

  1. Comparative study of the ab initio potential curves for Be2+, Mg2+, Ca2+ and Sr2+ molecular ions

    NASA Astrophysics Data System (ADS)

    Banerjee, Sandipan; Montgomery, John; Côté, Robin

    2013-05-01

    We perform a comparative study of the X 2Σu+, A 2Πu and B 2Σg+ states in the homonuclear alkaline-earth family of molecular ions -- Be2+, Mg2+, Ca2+ and Sr2++. A qualitative comparison of the ``double-well'' in the B 2Σg+ state and interaction with the excited 2 2Σg+ state is made for all the molecular ions. Multireference configuration interaction (MRCI) calculations are performed with a complete active space (CAS) wavefunction as reference. Spectroscopic constants, bound vibrational levels, transition moments and radiative lifetimes are calculated. The static dipole and quadrupole polarizabilities, and the leading order van der Waals coefficients are also reported. We also show preliminary results for corrections to the Born-Oppenheimer Hamiltonian -- non-adiabatic couplings and and hyperfine structure due to nuclear spins and electric quadrupoles. We perform a comparative study of the X 2Σu+ , A 2Πu and B 2Σg+ states in the homonuclear alkaline-earth family of molecular ions -- Be2+, Mg2+, Ca2+ and Sr2+. A qualitative comparison of the ``double-well'' in the B 2Σg+ state and interaction with the excited 2 2Σg+ state is made for all the molecular ions. Multireference configuration interaction (MRCI) calculations are performed with a complete active space (CAS) wavefunction as reference. Spectroscopic constants, bound vibrational levels, transition moments and radiative lifetimes are calculated. The static dipole and quadrupole polarizabilities, and the leading order van der Waals coefficients are also reported. We also show preliminary results for corrections to the Born-Oppenheimer Hamiltonian -- non-adiabatic couplings and and hyperfine structure due to nuclear spins and electric quadrupoles. This work was funded in part by the Air Force Office for Scientific Research MURI and the Department of Energy Office of Basic Sciences.

  2. San Francisco Estuary Striped Bass Migration History Determined by Electron-microprobe Analysis of Otolith Sr/Ca Ratio

    SciTech Connect

    Ostrach, D J; Phillis, C C; Weber, P K; Ingram, B L; Zinkl, J G

    2004-09-17

    Habitat use has been shown to be an important factor in the bioaccumulation of contaminants in striped bass. This study examines migration in striped bass as part of a larger study investigating bioaccumulation and maternal transfer of xenobiotics to progeny in the San Francisco Estuary system. Habitat use, residence time and spawning migration over the life of females (n = 23) was studied. Female striped bass were collected between Knights Landing and Colusa on the Sacramento River during the spawning runs of 1999 and 2001. Otoliths were removed, processed and aged via otolith microstructure. Subsequently, otoliths were analyzed for strontium/calcium (Sr/Ca) ratio using an electron-microprobe to measure salinity exposure and to distinguish freshwater, estuary, and marine habitat use. Salinity exposure during the last year before capture was examined more closely for comparison of habitat use by the maternal parent to contaminant burden transferred to progeny. Results were selectively confirmed by ion microprobe analyses for habitat use. The Sr/Ca data demonstrate a wide range of migratory patterns. Age of initial ocean entry differs among individuals before returning to freshwater, presumably to spawn. Some fish reside in freshwater year-round, while others return to more saline habitats and make periodic migrations to freshwater. Frequency of habitat shifts and residence times differs among fish, as well as over the lifetime of individual fish. While at least one fish spent its final year in freshwater, the majority of spawning fish spent their final year in elevated salinity. However, not all fish migrated to freshwater to spawn in the previous year. Results from this investigation concerning migration history in striped bass can be combined with contaminant and histological developmental analyses to better understand the bioaccumulation of contaminants and the subsequent effects they and habitat use have on fish populations in the San Francisco Estuary system.

  3. The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+ partitioning

    PubMed Central

    2012-01-01

    Background A proposed strategy for immobilizing trace metals in the subsurface is to stimulate calcium carbonate precipitation and incorporate contaminants by co-precipitation. Such an approach will require injecting chemical amendments into the subsurface to generate supersaturated conditions that promote mineral precipitation. However, the formation of reactant mixing zones will create gradients in both the saturation state and ion activity ratios (i.e., aCO32-/aCa2+). To better understand the effect of ion activity ratios on CaCO3 precipitation kinetics and Sr2+ co-precipitation, experiments were conducted under constant composition conditions where the supersaturation state (Ω) for calcite was held constant at 9.4, but the ion activity ratio (r=aCO32-/aCa2+) was varied between 0.0032 and 4.15. Results Calcite was the only phase observed, by XRD, at the end of the experiments. Precipitation rates increased from 41.3 ± 3.4 μmol m-2 min-1 at r = 0.0315 to a maximum rate of 74.5 ± 4.8 μmol m-2 min-1 at r = 0.306 followed by a decrease to 46.3 ± 9.6 μmol m-2 min-1 at r = 1.822. The trend was simulated using a simple mass transfer model for solute uptake at the calcite surface. However, precipitation rates at fixed saturation states also evolved with time. Precipitation rates accelerated for low r values but slowed for high r values. These trends may be related to changes in effective reactive surface area. The aCO32-/aCa2+ ratios did not affect the distribution coefficient for Sr in calcite (DPSr2+), apart from the indirect effect associated with the established positive correlation between DPSr2+ and calcite precipitation rate. Conclusion At a constant supersaturation state (Ω = 9.4), varying the ion activity ratio affects the calcite precipitation rate. This behavior is not predicted by affinity-based rate models. Furthermore, at the highest ion ratio tested, no precipitation was observed, while at the lowest ion ratio precipitation occurred immediately

  4. Concentrations and ratios of Sr, Ba and Ca along an estuarine river to the Gulf of Mexico - implication for sea level rise effects on trace metal distribution

    NASA Astrophysics Data System (ADS)

    He, S.; Xu, Y. J.

    2015-11-01

    Strontium and barium to calcium ratios are often used as proxies for tracking animal movement across salinity gradients. As sea level rise continues, many estuarine rivers in the world face saltwater intrusion, which may cause changes in mobility and distribution of these metals upstream. Despite intensive research on metal adsorption and desorption in marine systems, knowledge of the spatiotemporal distribution of these elements along estuarine rivers is still limited. In this study, we conducted an intensive monitoring of Sr and Ba dynamics along an 88 km long estuary, the Calcasieu River in South Louisiana, USA, which has been strongly affected by saltwater intrusion. Over the period from May 2013 to August 2015, we collected monthly water samples and performed in-situ water quality measurements at six sites from the upstream to the river mouth, with a salinity range from 0.02 to 29.50 ppt. Water samples were analyzed for Sr, Ba, and Ca concentrations. In-situ measurements were made on salinity, pH, water temperature, dissolved oxygen concentration, and specific conductance. We found that the Sr and Ca concentrations and the Sr / Ca ratio all increased significantly with increasing salinity. The average Sr concentration at the site closest to the Gulf of Mexico (site 6) was 46.21 μmol L-1, which was about 130 times higher than that of the site furthest upstream (site 1, 0.35 μmol L-1). The average Ca concentration at site 6 was 8.19 mmol L-1, which was about 60 times higher than that of site 1 (0.13 mmol L-1). The average Sr / Ca ratio at site 6 (8.41 mmol mol-1) was about 3 times the average Sr / Ca ratio at site 1 (2.89 mmol mol-1). However, the spatial variation in Ba concentration was marginal, varying from 0.36 μmol L-1 at site 6 to 0.47 at site 5. The average Ba / Ca ratio at site 1 (4.82 mmol mol-1) was about 54 times the average Ba / Ca ratio at site 6 (0.09 mmol mol-1), showing a clear negative relation between the Ba / Ca ratio and increasing

  5. Improved structure stability, optical and magnetic properties of Ca and Ti co-substituted BiFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kumar, Vijay; Singh, Satyendra

    2016-11-01

    We report the optical and magnetic properties of single-crystalline Ca and Ti co-substituted bismuth ferrite, Bi1-xCaxFe1-xTixO3, nanoparticles, synthesized by a facile sol-gel methodology in the compositional range wherein 0 ≤ x ≤ 0.25. X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations show that all samples possess a rhombohedrally distorted perovskite structure with space group R3c. Ca and Ti co-substitution controls the formation of secondary phases and improved the stability of perovskite phase of BiFeO3. The average particle size was estimated by Williamson Hall plot, confirmed by TEM, and found to be about 59, 50, 46, 41, 40 and 38 nm of Bi1-xCaxFe1-xTixO3 for x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25, respectively. The UV-vis absorption study reveal the strong absorption of visible light with a small optical band gap (1.77-2.25 eV) for 0 ≤ x ≤ 0.25 indicates a possibility of utilizing for photocatalytic activities. The magnetic study at room-temperature displays the improved magnetization and coercive field in Bi1-xCaxFe1-xTixO3 nanoparticles due to the release of the latent magnetization locked within the toroidal spin structure of BiFeO3.

  6. Influence of Cu-site substitution on La2Ca1Ba2Cu5Oz superconducting system

    NASA Astrophysics Data System (ADS)

    Bhalodia, J. A.; Mankadia, S. R.; Dalsaniya, S. M.; Gonal, M. R.

    2012-07-01

    We have prepared a series of La2CaBa2Cu5-xCoxOz; x = 0.0, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 (La-2125) compounds by the standard solid state reaction method and characterized for their structural, superconducting, magnetic properties and oxygen content through X-ray diffraction, scanning electron microscopy, d. c. resistivity, magnetic susceptibility and iodometric titration respectively. All the compounds crystallize with the tetragonal LaBa2Cu3Oz type structure, space group P4/mmm. Here the effect of higher Co substitution for Cu in the La2CaBa2Cu5-xCoxOz system has been studied. It is observed that only 2 at. % Co substitution for Cu destroys the superconductivity of the sample. For heavily doped samples (with x >= 0.1) are found non-superconducting presumably because of magnetic pair- breaking effect. These samples do not show superconductivity but are of interest for understanding the interplay between superconductivity and magnetism. Possible reasons for destruction of superconductivity are discussed in this communication.

  7. Crystal structure and magnetic properties of Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy

    SciTech Connect

    Rangi, Manisha; Agarwal, Ashish Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.

    2014-08-15

    Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A{sup 2+} results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe{sup 4+} ruled out by Mössbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi{sub 0.8}Ba{sub 0.2}FeO{sub 3} sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

  8. Influence of strontium for calcium substitution in bioactive glasses on degradation, ion release and apatite formation.

    PubMed

    Fredholm, Yann C; Karpukhina, Natalia; Brauer, Delia S; Jones, Julian R; Law, Robert V; Hill, Robert G

    2012-05-01

    Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO(2)-P(2)O(5)-CaO-Na(2)O) with 0-100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition-structure-property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions. PMID:21993007

  9. Influence of strontium for calcium substitution in bioactive glasses on degradation, ion release and apatite formation

    PubMed Central

    Fredholm, Yann C.; Karpukhina, Natalia; Brauer, Delia S.; Jones, Julian R.; Law, Robert V.; Hill, Robert G.

    2012-01-01

    Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO2–P2O5–CaO–Na2O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions. PMID:21993007

  10. Creep of polycrystalline (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}

    SciTech Connect

    Martinez-Fernandez, J.; Dominguez-Rodriguez, A.; Routbort, J.L.; Goretta, K.C.

    2000-04-14

    Plastic deformation has proved to be essential to the manufacture of bulk (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) superconductors. Compressive creep of dense, forged Bi-2223, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi-2212), and Bi{sub 2}Sr{sub 2}CuO{sub x} (Bi-2201) superconductors has been studied. These previous studies left unanswered questions about the large variation in Q among the Bi-superconductors and the rate-controlling deformation mechanism. The goals of this work were to test high-quality bulk Bi-2223 to determine whether steady state can be established, and if so, to determine the dominant creep mechanism and the values of n and Q.

  11. Intracavity dye laser spectroscopy studies of the Ba + N(2)O, Ca + N(2)O + CO, and Sr + N(2)O + CO reactions.

    PubMed

    Eckstrom, D J; Barker, J R; Hawley, J G; Reilly, J P

    1977-08-01

    A search for gain or absorption on several candidate visible chemical laser transitions has been carried out using the intracavity dye laser probe technique. Absorption was found on the following v'' ? v' bands of the BaO(A(1)Sigma ? X(1)Sigma) bands in the Ba + N(2)O reaction: 0 ? 1; 0 ? 4; 1 ? 1; 1 ? 2, and 5 ? 1. No gain or absorption could be detected on the 7 ? 1, 6 ? 0, and 4 ? 0 bands (sensitivity ~10(-4)/cm). In Ca, Sr + N(2)O + CO flames, absorption was found in the green arc bands of CaO and the red arc bands of SrO. Several new bandhead wavelengths are reported. Our results support assignment of the arc bands to the diatomic metal oxides. Absorptions and enhancements were found on various Sr, Ba, and Ba(+) transitions. PMID:20168881

  12. Red/blue-shift dual-directional regulation of α-(Ca, Sr)2SiO4:Eu(2+) phosphors resulting from the incorporation content of Eu(2+)/Sr(2+) ions.

    PubMed

    Lu, Zhijuan; Mao, Zhiyong; Chen, Jingjing; Wang, Dajian

    2015-09-21

    In this work, tunable emission from green to red and the inverse tuning from red to green in α-(Ca, Sr)2SiO4:Eu(2+) phosphors were demonstrated magically by varying the incorporation content of Eu(2+) and Sr(2+) ions, respectively. The tunable emission properties and the tuning mechanism of red-shift resulting from the Eu(2+) content as well as that of blue-shift induced by the Sr(2+) content were investigated in detail. As a result of fine-controlling the incorporation content of Eu(2+), the emission peak red-shifts from 541 nm to 640 nm. On the other hand, the emission peak inversely blue-shifts from 640 nm to 546 nm through fine-adjusting the incorporation content of Sr(2+). The excellent tuning characteristics for α-(Ca, Sr)2SiO4:Eu(2+) phosphors presented in this work exhibited their various application prospects in solid-state lighting combining with a blue chip or a near-UV chip.

  13. In vitro synthesis of amorphous Mg-, Ca-, Sr- and Ba-carbonates: What do we learn about intracellular calcification by cyanobacteria?

    NASA Astrophysics Data System (ADS)

    Cam, N.; Georgelin, T.; Jaber, M.; Lambert, J.-F.; Benzerara, K.

    2015-07-01

    Some cyanobacteria, including Candidatus Gloeomargarita lithophora, which was isolated from Lake Alchichica (Mexico), can form intracellular carbonates. This contradicts the common paradigm that cyanobacterial calcification is always extracellular and suggests that calcification might be controlled by these cyanobacterial species. Intracellular carbonates have several peculiar characteristics: they are relatively small (between 60 and 500 nm), they are poorly crystalline, and they have Sr/Ca and Ba/Ca ratios much higher than the solution in which the cells grow. It is therefore crucial to understand whether these unique features may indicate the involvement of specific biological processes. Here, in vitro abiotic syntheses were performed to synthesize Mg-, Ca-, Sr- and Ba-containing carbonates with compositions, crystallinities and sizes close to those observed in intracellularly calcifying cyanobacteria. Precipitates were characterized by scanning and transmission electron microscopies coupled with energy dispersive X-ray spectroscopy, thermogravimetric analysis and X-ray diffraction. The size and the poor crystallinity of cyanobacterial intracellular carbonates could be mimicked under these abiotic conditions. It was shown that similarly to Mg, elements such as Sr and Ba can favor stabilization of poorly crystalline carbonates. In contrast, the differential partitioning of Sr, Ba and Ca between the solution and the solids as observed in cyanobacteria could not be mimicked in vitro. This provides keys to a better understanding of biological processes involved in the formation of intracellular carbonates by some cyanobacteria, including the involvement of membrane transporters.

  14. Effects of Ca and Sr chemical doping on the average superconducting kinetic energy of YBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Vieira, V. N.; Mendonça, A. P. A.; Dias, F. T.; Hneda, M. L.; Pureur, P.; Schaf, J.; Mesquita, F.

    2015-03-01

    In this brief communication we applied the MZFC(T) and MFCC(T) reversible dc magnetizations to get the average superconducting kinetic energy density, kS(T,B) of YBa2Cu3O7-δ, Y0.95Ca0.05Ba2Cu3O7-δ and YBa1.75Sr0.25Cu3O7-δ ceramic samples with the aim of study the effects of Ca and Sr doping on the kS(T,B). The MZFC(T) and MFCC(T) measurements were performed with a SQUID magnetometer from quantum design to dc magnetic fields up to 50kOe. The determination of the kS(T,B) from reversible dc magnetization is supported by virial theorem of superconductivity [kS(T,B) = - MB]. The kS(T,B) results show an common temperature profile for all the samples which is smoothly affected by the magnetic field. On the other hand the kS(T,B) results to T > Tc could not be associated to the pseudogap phenomenon. The Ca doping affects more effectively the kS(T,B) behaviour then Sr doping. A possible explanation to this feature could be associated to the fact that the hole doping promoted by Ca doping depress more considerably the superconducting state and enhances the granular character of the YBa2Cu3O7-δ superconductor than the chemical pressure effect promoted by Sr doping.

  15. Specific heat and thermodynamic characteristics of the system Bi-Sr-Ca-Mg-Cu-O in the temperature range 4.2 300 K

    NASA Astrophysics Data System (ADS)

    Gololobov, E. M.; Novysh, B. V.; Prytkova, N. A.; Tomilo, Zh. M.; Shimanskaya, N. M.; Abeliov, Ya. A.; Maiornikova, G. V.; Yagina, A. B.

    1991-06-01

    Results are presented from an experimental study of specific heat of the superconductive metal oxide system Bi -Sr-Ca-Mg-Cu-O over the temperature range 4.2 300 K. Temperature-dependent components of entropy and enthalpy are calculated. A correlation is made between Tc and standard entropy and enthalpy values for high temperature superconductors of various classes.

  16. Vortex-lattice melting in Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+[delta

    SciTech Connect

    Balestrino, G.; Livanov, D.V.; Milani, E. ); Camarota, B.; Fiorani, D.; Testa, A.M. )

    1994-08-01

    We have studied the effects of the oxygen stoichiometry on the magnetic irreversibility line and on the decay of the zero-field-cooled (ZFC) magnetization in Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+[delta

  17. Spectroscopic and photoluminescence characterization of Dy(3+) in Sr0.5Ca0.5TiO3 phosphor.

    PubMed

    Vidyadharan, Viji; Sreeja, E; Jose, Saritha K; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2016-02-01

    The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex. PMID:26032295

  18. Coral Sr/Ca-based sea surface temperature and air temperature variability from the inshore and offshore corals in the Seribu Islands, Indonesia.

    PubMed

    Cahyarini, Sri Yudawati; Zinke, Jens; Troelstra, Simon; Suharsono; Aldrian, Edvin; Hoeksema, B W

    2016-09-30

    The ability of massive Porites corals to faithfully record temperature is assessed. Porites corals from Kepulauan Seribu were sampled from one inshore and one offshore site and analyzed for their Sr/Ca variation. The results show that Sr/Ca of the offshore coral tracked SST, while Sr/Ca variation of the inshore coral tracked ambient air temperature. In particular, the inshore SST variation is related to air temperature anomalies of the urban center of Jakarta. The latter we relate to air-sea interactions modifying inshore SST associated with the land-sea breeze mechanism and/or monsoonal circulation. The correlation pattern of monthly coral Sr/Ca with the Niño3.4 index and SEIO-SST reveals that corals in the Seribu islands region respond differently to remote forcing. An opposite response is observed for inshore and offshore corals in response to El Niño onset, yet similar to El Niño mature phase (December to February). SEIO SSTs co-vary strongly with SST and air temperature variability across the Seribu island reef complex. The results of this study clearly indicate that locations of coral proxy record in Indonesia need to be chosen carefully in order to identify the seasonal climate response to local and remote climate and anthropogenic forcing.

  19. Aurivillius-Popper mixed superconductors in BiO--CuO--(Sr/sub 0. 5/, Ca/sub 0. 5/)O system

    SciTech Connect

    Fukuhara, M.; Bhalla, A.S.; Mulay, L.N.; Newnham, R.E.

    1989-03-01

    We report the effect of inhomogeneities on the electric resistivity and ac magnetic susceptibility in Aurivillius-like bismuth mixed phase oxides of the BiO--Cuo--(Sr/sub 0.5/, Ca/sub 0.5/)O system and propose a crystal structure of the major phase having highest T/sub c/. Nominal Aurivillius compositions with molar ratios of BiO/(Sr/sub 0.5/, Ca/sub 0.5/)O = 1/2 are superconductors with T/sub c/ ranging from 83 to 107 K, and are accompanied by a large expansion during sintering due to the formation of Kirkendall voids. T/sub c/ increases with decreasing of the c lattice parameter. An oxide BiSrCaCu/sub 2/O/sub x/ (n = 2) shows a maximum T/sub c/ value of 107 K and an onset of superconductivity at a much higher temperature. It seems that the structure of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ consists of an Aurivillius-like phase having two perovskite layers and a Popper mixed phase. The ac magnetic susceptibility showed an overall decrease in susceptibility with time up to 220 days. This appears to be related to the relief of intralattice strain.

  20. Dipole polarizability of alkali-metal (Na, K, Rb)–alkaline-earth-metal (Ca, Sr) polar molecules: Prospects for alignment

    SciTech Connect

    Gopakumar, Geetha Abe, Minori; Hada, Masahiko; Kajita, Masatoshi

    2014-06-14

    Electronic open-shell ground-state properties of selected alkali-metal–alkaline-earth-metal polar molecules are investigated. We determine potential energy curves of the {sup 2}Σ{sup +} ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes ({sup 23}Na, {sup 39}K, {sup 85}Rb)–({sup 40}Ca, {sup 88}Sr) are compared with available theoretical and experimental results. The variation of the permanent dipole moment (PDM), average dipole polarizability, and polarizability anisotropy with internuclear distance is determined using finite-field perturbation theory at the CCSD(T) level. Owing to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u., RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for alignment and orientation in combined intense laser and external static electric fields.

  1. Comment on ``Electrical and dielectric propertiesof the Bi4Sr3Ca3Cu4Ox (4:3:3:4) glassy semiconductor''

    NASA Astrophysics Data System (ADS)

    Ghosh, A.

    1997-01-01

    A recent paper from Som and Chaudhuri [Phys. Rev. B 41, 1581 (1990)], regarding the electrical and dielectric properties of Bi4Sr3Ca3Cu4Ox glass is reanalyzed. It is shown that the theoretical analysis for the ac conductivity and its frequency exponent performed by the authors is incorrect.

  2. Spectroscopic and photoluminescence characterization of Dy(3+) in Sr0.5Ca0.5TiO3 phosphor.

    PubMed

    Vidyadharan, Viji; Sreeja, E; Jose, Saritha K; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2016-02-01

    The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex.

  3. Coral Sr/Ca-based sea surface temperature and air temperature variability from the inshore and offshore corals in the Seribu Islands, Indonesia.

    PubMed

    Cahyarini, Sri Yudawati; Zinke, Jens; Troelstra, Simon; Suharsono; Aldrian, Edvin; Hoeksema, B W

    2016-09-30

    The ability of massive Porites corals to faithfully record temperature is assessed. Porites corals from Kepulauan Seribu were sampled from one inshore and one offshore site and analyzed for their Sr/Ca variation. The results show that Sr/Ca of the offshore coral tracked SST, while Sr/Ca variation of the inshore coral tracked ambient air temperature. In particular, the inshore SST variation is related to air temperature anomalies of the urban center of Jakarta. The latter we relate to air-sea interactions modifying inshore SST associated with the land-sea breeze mechanism and/or monsoonal circulation. The correlation pattern of monthly coral Sr/Ca with the Niño3.4 index and SEIO-SST reveals that corals in the Seribu islands region respond differently to remote forcing. An opposite response is observed for inshore and offshore corals in response to El Niño onset, yet similar to El Niño mature phase (December to February). SEIO SSTs co-vary strongly with SST and air temperature variability across the Seribu island reef complex. The results of this study clearly indicate that locations of coral proxy record in Indonesia need to be chosen carefully in order to identify the seasonal climate response to local and remote climate and anthropogenic forcing. PMID:27181035

  4. Effects of the annealing conditions on the structural and superconducting properties of Bi2- xPbxSr2Y0.2Ca0.8Cu2Oz

    NASA Astrophysics Data System (ADS)

    Calestani, G.; Salsi, G.; Francesconi, M. G.; Masini, R.; Dimesso, L.; Migliori, A.; Zhang, X. F.; van Tendeloo, G.

    1993-02-01

    The effects produced by the annealing in nitrogen atmosphere at relatively low temperatures (400-500°C) on the structural and superconducting properties of Bi2- xPbxSr2Y0.2Ca0.8Cu2Oz have been investigated. The electrical propertie s of the examined samples (0.0≤ x≤0.4), which are comparable when prepared in air, vary remarkably for similar nitrogen annealing, depending on the lead content of the phase. The disappearance of the superconducting transition (reversible for retreatments in air) was found for x=0 whereas no appreciable variation of Tc was evidenced for x=0.4, at least for the applied treatments; an intermediate behavior was observed for the x=0.2 sample. The structural changes and the local modulated structure were observed by high-resolution electron microscopy. The effect of lead substitution in stabilizing Tc is discussed.

  5. Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO3)2-Ca (HCO3)2-CO2-H2O solutions

    USGS Publications Warehouse

    Plummer, L.N.; Busenberg, E.; Glynn, P.D.; Blum, A.E.

    1992-01-01

    Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated non-stoichiometric solutions of Sr(HCO3)2 and Ca(HCO3)2 at 25??C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO3)2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HCO3)2 solutions and 0-4 layers thick in Ca(HCO3)2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO3)2 and Ca(HCO3)2 solutions, respectively. In Sr(HCO3)2 solutions, the XPS signal from the outer ~ 60 A?? on aragonite indicates a composition of 16 mol% SrCO3 after only 2 min of contact, and 14-18 mol% SrCO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO3 after 2 min of contact with Ca(HCO3)2 solution, and is 34-39 mol% CaCO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer ~25

  6. Synthesis, structure, and properties of four ternary compounds: CaSrTt, Tt=Si, Ge, Sn, Pb

    SciTech Connect

    Liu Shengfeng; Corbett, John D. . E-mail: jcorbett@iastate.edu

    2006-03-15

    The title compounds were synthesized and characterized by structural measurements and electronic structure calculations. Single-crystal X-ray diffraction analyses established that they all have the orthorhombic inverse-PbCl{sub 2}-type structure (Pnma, Z=4, a=8.108(2), 8.124(2), 8.421(2), 8.509(2)A; b=4.944(1), 4.949(1), 5.168(1), 5.189(1)A; c=9.170(2), 9.184(2), 9.685(2), 9.740(2)A, respectively). The tetrel (Tt) atoms are situated in tricapped trigonal prisms of ordered Sr and Ca atoms in which the smaller Ca atoms play a distinctive role. The structure is distinguishable from the Co{sub 2}Si type by its more nearly ideal 6+3 (TCTP) environment about Tt rather than a higher coordination by cations. Other representations of the two structural types are also considered. Electronic band structure calculations suggest that the compounds are semiconductors, in agreement with literature data on their Ae{sub 2}Tt analogues.

  7. Effect of cryogenic temperature on spectroscopic and laser properties of Er,La:SrF2-CaF2 crystal

    NASA Astrophysics Data System (ADS)

    Švejkar, Richard; Šulc, Jan; Němec, Michal; Jelínková, Helena; Doroshenko, Maxim E.; Nakladov, Andrei N.; Osiko, Vjatcheslav V.

    2016-03-01

    The laser and spectroscopic properties of crystal Er,La:SrF2-CaF2 at temperature range 80 - 300 K, which is appropriate for generation of radiation around 2.7 um is presented. The sample of Er,La:SrF2-CaF2 (concentration Er(0.04), La(0.12):Ca(0.77)Sr(0.07)) had plan-parallel face-polished faces without anti-reflection coatings (thickness 8.2 mm). During spectroscopy and laser experiments the Er,La:SrF2-CaF2 was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra of Er,La:SrF2-CaF2 together with the fluorescence decay time were measured in dependence on temperature. The excitation of Er,La:SrF2-CaF2 was carried out by a laser diode radiation (pulse duration 5 ms, repetition rate 20 Hz, pump wavelength 973 nm). Laser resonator was hemispherical, 140 mm in length with at pumping mirror (HR @ 2.7 µm) and spherical output coupler (r = 150 mm, R = 95 % @ 2.5 - 2.8 µm). Tunability of laser at 80 K in range 2690 - 2765 nm was obtained using MgF2 birefringent filter. With decreasing temperature of sample the fluorescence lifetime of manifold 4I11/2 (upper laser level) became shorter and intensity of up-conversion radiation was increasing. The highest slope efficiency with respect to absorbed power was 2.3 % at 80 K. The maximum output of peak amplitude power was 0.3 W at 80 K, i.e. 1.5 times higher than measured this value at 300 K. The wavelength generated by Er,La:SrF2-CaF2 laser (2.7 µm) is relatively close to absorption peak of water (3 µm) and so, one of the possible usage should be in medicine and spectroscopy.

  8. A Modern Sr/Ca-δ18O-Sea Surface Temperature Calibration for Isopora Corals in the Great Barrier Reef

    NASA Astrophysics Data System (ADS)

    Brenner, L. D.; Linsley, B. K.; Potts, D. C.

    2014-12-01

    Most coral-based paleoceanographic studies have used massive colonies of Porites or Faviidae, due to their long, continuously accreted skeletal records and sub-annual resolution, but other sub-massive corals provide an untapped resource. The genus Isopora is a dominant reef builder in some high-energy environments in the tropical western Pacific, and was a major component of cores recovered on IODP Leg 325 off the Great Barrier Reef (GBR). Despite its abundance, Isopora remains largely unexplored and hence underutilized in paleoceanographic studies. We present a modern Sr/Ca-δ18O-Sea Surface Temperature (SST) calibration of modern Isopora corals (n=3) collected from inner and outer reef locations ranging from 1-13m depth by Heron Island in the southern GBR in 2012. Pairing the Isopora Sr/Ca record with monthly SST yielded an average relationship of SST=-11.48×(Sr/Ca)+131.1 (r2 = 0.42-0.78). The Sr/Ca sensitivity of -0.087 mmol/mol/°C is similar to the sensitivity for Porites that was corrected for tissue layer smoothing effects determined by Gagan et al. (2012). The similarity between our Sr/Ca-SST sensitivity and the corrected sensitivity for Porites suggests tissue layer effects are minimal in Isopora. The mean annual SST amplitude recorded by the corals from 2008-2011 (full annual cycles) was 5.3°C and the average δ18O annual cycle of 1.1‰ approximates that expected if salinity had little effect on coral δ18O, assuming a previously established conversion of -0.23‰ (δ18O)/°C for biogenic aragonite. The average annual salinity amplitude of 0.3 in gridded data from around Heron Island supports our conclusion that δ18O variability is forced almost completely by SST. This modern Sr/Ca-SST calibration will expand the paleoceanographic utility of Isopora and, by assisting interpretation of Sr/Ca data from fossil corals collected during IODP 325, will better constrain the timing and magnitude of sea level changes and surface conditions since the Last

  9. Methods for estimating a critical value for determining the freshwater/estuarine habitat residence of American eels from otolith Sr:Ca data

    NASA Astrophysics Data System (ADS)

    Jessop, B. M.; Shiao, J. C.; Iizuka, Y.

    2013-11-01

    Linear discriminant analysis (LDA) and habitat discrimination critical value (HDCV) methods are alternatives for evaluating the migratory history, such as the proportion of residence in freshwater (%fwr) and estuarine/marine habitats, of individual American eels (Anguilla rostrata) via the analysis of otolith Sr:Ca data. The LDA process requires Sr:Ca data from both freshwater and estuarine/marine groups while the mean + cSD method requires only a freshwater standard. For the two group (freshwater, estuarine/marine), single predictor variable (Sr:Ca) case, the LDA process defaults to Fisher's linear discriminant where the HDCV equals the average of the group mean Sr:Ca values. The difference between freshwater and estuarine resident eel mean otolith Sr:Ca values, based on 13 published studies and the current study (n = 14), decreased with increasing freshwater group otolith mean (r = 0.80, p < 0.001), reflecting a relatively constant estuarine group mean (r = 0.38, p = 0.17). A process is proposed for estimating a HDCV from freshwater group otolith Sr:Ca mean and SD values based on empirical linear relations between the LDA, HDCV and freshwater mean (n = 14, r = 0.90, p < 0.0001) and c and SD (n = 14, r = -0.89, p < 0.0001) from the equation HDCV = mean + cSD. Variation in the sample sizes of otolith Sr:Ca values used in the discriminant process of estimating a HDCV, while statistically significant, had trivial effect sizes that were likely of little biological consequence. However, larger sample sizes are preferred over smaller sample sizes. Estimates of %fwr increased with increases in the HDCV. Differences in %fwr estimates over a range of HDCVs were highly statistically significant and effect sizes increased with increased HDCV difference. As HDCV levels increased, growth rate estimates increased for a given %fwr value. A HDCV difference of ≤0.5 × 10-3 produced a small effect size. Accurate estimation of a HDCV is fundamental to the assessment of the habitat

  10. Effect of Cd substitution on the optical and transport properties of CaCu_3Ti_4O_12 boldmath

    NASA Astrophysics Data System (ADS)

    Homes, C. C.; Vogt, T.; Subramanian, M. A.; Ramirez, A. P.

    2003-03-01

    The effect of Cd doping on the transport and optical properties of CaCu_3Ti_4O_12 has been studied. At room temperature, CaCu_3Ti_4O_12 has a very high dielectric constant, \\varepsilon_0 ˜ 10^4. However, substituting Cd for Ca reduces \\varepsilon0 by nearly two orders of magnitude. Cd has a strong effect on the low frequency infrared active modes, and in addition a new mode is activated. A normal coordinate analysis has been performed to determine the nature of the vibrational modes, in particular the activated mode as well as the low frequency vibration, where an anomalous increase in the oscillator strength has been observed.(C.C. Homes et al.), Science 293, 673 (2001). It has been suggested that the large values of \\varepsilon0 may be due to a internal barrier layer capacitance effect due to twinning. The lower value for \\varepsilon0 in the Cd material may have implications for the degree of twinning and the associated changes in vibrational structure. This work was supported by the Department of Energy under contract number DE-AC02-98CH10886.

  11. Phase relations in the composition(Pb 1- yCu y)Sr 2(Ln 1- xCa x)Cu 2O 7 and the crystal structure of La 8- xSr xCu 8- yO 20

    NASA Astrophysics Data System (ADS)

    Lee, J. Y.; Kim, J. S.; Swinnea, J. S.; Steinfink, H.

    1990-02-01

    The compound (Pb 0.71Cu 0.29)Sr 2(Ln 1-xCa x)Cu 2O 7 (1212) has been synthesized as single phase material for La, Pr, Nd, Gd, Er, and Y from the proper starting compositions fired above 950°C. Calcium can be substituted up to x = 0.5. When this limit is exceeded the 1212 phase, SrCuO 2, and a hexagonal phase are formed. When x = 1 only SrCuO 2 and the hexagonal phase are formed. The hexagonal phase has the general composition Sr 5- xPb 3+ xCu yO 11+ z. When a mixture corresponding to PbSr 2Co 0.5Cu 0.5O z is fired above 960°C a tetragonal phase isostructural with TlSr 2CuO 5 (121) forms, but below 960°C the hexagonal phase is formed. A nominal mixture of PbSr 2CaCu 2 (1212) fired at 930°C and quenched forms primarily the SrCuO 2 phase and some of the hexagonal compound, but slow cooling in the furnace produces a nearly single phase hexagonal product. The crystal structure of a crystal found in a reaction product from a nominal mixture PbSr 2LaCu 2 (1212) fired at 1050°C was determined from three-dimensional X-ray diffraction data. Its composition is (La 6.16Sr 1.84)Cu 7.66O 20, M r = 1823.6 , tetragonal, P4/mbm, a = 10.7468(8)Å, c = 3.8633(3)Å, V = 446.2(1)Å 3, Z = 1, D x = 6.79g cm -3, λ = 0.71069Å, μ = 288.0 cm -1, R = 0.032, wR = 0.034 for 385 observed reflections. The structure is formed by the articulation of Cu octahedra, square pyramids, and square coplanar nets into a three-dimensional framework. LaSr are in 10-fold coordination to oxygen atoms that are in a perovskite-like arrangement. The octahedral Cul site contains 17% vacancies on the basis of the least-squares refinement of the site occupancy. The two apical Cul sbnd O bond lengths are 1.9317(1)Å, and the four equatorial lengths are 1.978(7)Å. The square Cu2 sbnd O bond lengths are 1.9317(1) and 1.869(6)Å, respectively. The square pyramidal Cu3 sbnd O bond lengths are 2.364(6)Åto the apex and 1.9322(2) and 1.878(7)Å, respectively, to pairs of the four equatorial oxygen ions. Valence

  12. Dilution of two-dimensional antiferromagnetism by Mn site substitution in La1Sr2Mn2-xAlxO7

    NASA Astrophysics Data System (ADS)

    Nair, Sunil; Banerjee, A.

    2004-09-01

    We report the effect of Al substitution on the Mn site of the bilayered half doped manganite La1Sr2Mn2O7 . This substitution dilutes the magnetically active Mn-O-Mn network without introducing an appreciable distortion in the lattice, and ionic considerations lead to a predominant reduction of Mn4+ with increasing Al. The rate of fall of the long-range antiferromagnetic transition temperature as a function of substitution is seen to match well with established quasi-two-dimensional (quasi-2D) Heisenberg systems indicating that the nature of magnetic interactions in this quasi-2D system is of the short-range Heisenberg type. The magnetic contribution of the specific heat estimated using Fisher’s relation could be fitted with a function incorporating the presence of a gapped Fermi surface appropriate for this type of system. The resistivity is seen to increase as a function of substitution due to the weakening of the double exchange within the ferromagnetic layers of this A -type of antiferromagnets and justifiably, in the paramagnetic region the data could be fitted to Mott’s equation for the variable range hopping of polarons in two dimensions.

  13. Sr-containing hydroxyapatite: morphologies of HA crystals and bioactivity on osteoblast cells.

    PubMed

    Aina, Valentina; Bergandi, Loredana; Lusvardi, Gigliola; Malavasi, Gianluca; Imrie, Flora E; Gibson, Iain R; Cerrato, Giuseppina; Ghigo, Dario

    2013-04-01

    A series of Sr-substituted hydroxyapatites (HA), of general formula Ca(10-x)Srx(PO4)6(OH)2, where x=2 and 4, were synthesized by solid state methods and characterized extensively. The reactivity of these materials in cell culture medium was evaluated, and the behavior towards MG-63 osteoblast cells (in terms of cytotoxicity and proliferation assays) was studied. Future in vivo studies will give further insights into the behavior of the materials. A paper by Lagergren et al. (1975), concerning Sr-substituted HA prepared by a solid state method, reports that the presence of Sr in the apatite composition strongly influences the apatite diffraction patterns. Zeglinsky et al. (2012) investigated Sr-substituted HA by ab initio methods and Rietveld analyses and reported changes in the HA unit cell volume and shape due to the Sr addition. To further clarify the role played by the addition of Sr on the physico-chemical properties of these materials we prepared Sr-substituted HA compositions by a solid state method, using different reagents, thermal treatments and a multi-technique approach. Our results indicated that the introduction of Sr at the levels considered here does influence the structure of HA. There is also evidence of a decrease in the crystallinity degree of the materials upon Sr addition. The introduction of increasing amounts of Sr into the HA composition causes a decrease in the specific surface area and an enrichment of Sr-apatite phase at the surface of the samples. Bioactivity tests show that the presence of Sr causes changes in particle size and/or morphology during soaking in MEM solution; on the contrary the morphology of pure HA does not change after 14 days of reaction. The presence of Sr, as Sr-substituted HA and SrCl2, in cultures of human MG-63 osteoblasts did not produce any cytotoxic effect. In fact, Sr-substituted HA increased the proliferation of osteoblast cells and enhanced cell differentiation: Sr in HA has a positive effect on MG-63 cells

  14. The suitability of annual tree growth rings as environmental archives: Evidence from Sr, Nd, Pb and Ca isotopes in spruce growth rings from the Strengbach watershed

    NASA Astrophysics Data System (ADS)

    Stille, Peter; Schmitt, Anne-Désirée; Labolle, François; Pierret, Marie-Claire; Gangloff, Sophie; Cobert, Florian; Lucot, Eric; Guéguen, Florence; Brioschi, Laure; Steinmann, Marc; Chabaux, François

    2012-05-01

    The combination of the Sr, Nd and Pb isotope systems, recognized as tracers of sources, with the Ca isotope system, known to reveal biology-related fractionations, allowed us to test the reliability of spruce (Picea abies) growth rings as environmental archives through time (from 1916 to 1983) in a forest ecosystem affected by acid atmospheric deposition. Sr and Pb isotopes have already been applied in former tree-ring studies, whereas the suitability of Nd and Ca isotope systems is checked in the present article. Our Sr and Nd isotope data indicate an evolution in the cation origin with a geogenic origin for the oldest rings and an atmospheric origin for the youngest rings. Ca isotopes show, for their part, an isotopic homogeneity which could be linked to the very low weathering flux of Ca. Since this flux is weak the spruces' root systems have pumped the Ca mainly from the organic matter-rich top-soil over the past century. In contrast, the annual growth rings studied are not reliable and suitable archives of past Pb pollution.

  15. Effect of Mn and Ti substitution on the reflection loss characteristic of Ba0.6Sr0.4Fe11-zMnTizO19 (z = 0, 1, 2 and 3)

    NASA Astrophysics Data System (ADS)

    Gunanto, Y. E.; Cahyadi, L.; Adi, W. Ari

    2016-04-01

    The synthesis and characterization of composition Ba0.6Sr0.4Fe11-zMnTizO19 (z = 0; 1; 2 and 3) compound by solid state reaction using mechanical milling have been performed. The raw materials were BaCO3, SrCO3, Fe2O3, MnCO3, and TiO2. The mixed powder was compacted and sintered at 1000°C for 5 hours. X-ray diffraction studies indicate expansion of hexagonal unit cell and compression of atomic density with substitution of Mn2+ and Ti4+ ions. Effect of substitution upon magnetic properties revealed that total magnetization, remanence, and coercivity changed with substitution due to preferential site occupancy of substituted Mn2+ and Ti4+ ions. Since the coercivity and total magnetization may be controlled by substitution while maintaining resistive properties, this material is useful for microwave absorber.

  16. Human Pavlovian HR decelerative conditioning with negative tilt as US: a review of some S-R, stimulus-substitution evidence.

    PubMed

    Furedy, J J; Shulhan, D; Randall, D C

    1989-03-01

    Interest in human Pavlovian heart rate (HR) conditioning with conventional shock and loud noise unconditional stimuli has declined, as measured by reports in the literature. Accompanying this decline have been the following views: (a) that HR should be abandoned as a psychophysiological index of the psychological (learning) process of Pavlovian conditioning; (b) that, following psychology's shift to a more cognitive emphasis, the self-regulation (S-R), stimulus-substitution view of pavlovian conditioning is wrong, because there is no equivalence in direction between shock- and loud noise-induced HR-accelerative unconditional response and the conditional response. This paper reviews recent reports of human Pavlovian conditioning of HR deceleration with negative tilt as the unconditional stimulus. The results support an S-R, stimulus-substitution interpretation of conditioning. In addition, these studies have potential therapeutic application in the teaching of (medically desirable) HR deceleration, especially when Pavlovian procedures are combined with instrumental (biofeedback) ones. However, such physiological aspects of the decelerative unconditioned response as the degree of vagal involvement are difficult to investigate in the human preparation.

  17. New photocathode materials for hydrogen evolution: CaFe/sub 2/O/sub 4/ and Sr/sub 7/Fe/sub 10/O/sub 22/

    SciTech Connect

    Matsumoto, Y.; Omae, M.; Sugiyama, K.; Sato, E.

    1987-01-29

    The photoelectrochemical properties of p-type CaFe/sub 2/O/sub 4/ and Sr/sub 7/Fe/sub 10/O/sub 22/ are studied in N/sub 2/-saturated 0.25 M K/sub 2/SO/sub 4/ (pH 6.0). The differences between the Fermi level and the top of the valence band are determined to be 0.14 and 0.4 eV for Sr/sub 7/Fe/sub 10/O/sub 22/ and CaFe/sub 2/O/sub 4/, respectively, from the activation energies of the conductivities and the Seebeck coefficients. The cathodic photocurrents of the hydrogen evolution are observed in the potential region more positive than RHE by 0.7-0.8 V. The band gaps are 1.8 and 1.9 eV for Sr/sub 7/Fe/sub 10/O/sub 22/ and CaFe/sub 2/O/sub 4/, respectively. The flatband potential of Sr/sub 7/Fe/sub 10/O/sub 22/ is 0.1 V vs. SCE, but that of CaFe/sub 2/O/sub 4/ cannot be determined because of the Fermi level pinning. Pt deposited on the surfaces of both electrodes accelerates the electrochemical process of the hydrogen evolution reaction. CaFe/sub 2/O/sub 4/ is more stable than Sr/sub 7/Fe/sub 10/O/sub 22/ in the long-term test. The short circuit photocurrent of 0.3-0.4 ..mu..A/cm is observed in a Pt-deposited CaFe/sub 2/O/sub 4/(p type)/Zn/sub 1.2/Fe/sub 1.8/O/sub 4/ (n type) assembly under a xenon lamp illumination. The band structures of Sr/sub 7/Fe/sub 10/O/sub 22/ and CaFe/sub 2/O/sub 4/ and their photoelectrochemical processes are also discussed.

  18. Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices—A designed playground for honeycomb physics

    NASA Astrophysics Data System (ADS)

    Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

    2015-04-01

    We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

  19. Study of grain boundary properties in Ag-clad Bi2Sr2Ca2Cu3Ox tapes by multi-phase electron backscatter diffraction analysis

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.

    2008-01-01

    The properties of grain boundaries within Ag-clad (Pb,Bi)2Sr2Ca2Cu3Ox (Bi-2223) tapes are studied by means of electron backscatter diffraction (EBSD). The achieved high image quality of the Kikuchi patterns enables multi-phase EBSD scans including Bi-2223, Bi2Sr2CaCu2Ox (Bi-2212), Bi2Sr2CuOx (Bi-2201), (Sr,Ca)14Cu24O41 and Ag to be performed. For the EBSD scans a maximum spatial resolution of 30 nm was reached enabling a detailed orientation analysis. The nature of the grain boundaries is discussed on the base of the EBSD data. While the main orientation of the tape is in [0 0 1] direction, a large number of misorientations is detected. These misorientations are visualized using crystal direction (CD) maps. Furthermore, EBSD enables the spatially resolved mapping of the misorientation angles within each phase separately. The influence of these grain boundaries on the current transport properties is discussed.

  20. Superconducting ceramics in the Bi1.5SrCaCu2O sub x system by melt quenching technique

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Deguire, Mark R.

    1989-01-01

    Bi sub 1.5 SrCaCu sub 2 O sub x has been prepared in the glassy state by rapid quenching of the melt. The kinetics of crystallization of various phases in the glass have been evaluated by a variable heating rate differential scanning calorimetry method. The formation various phases on thermal treatments of the glass has been investigated by powder X-ray diffraction and electrical resistivity measurements. Heating at 450 C formed Bi sub 2 Sr sub 2 CuO sub 6, which disappeared on further heating at 765 C, where Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 formed. Prolonged heating at 845 C resulted in the formation of a small amount of a phase with T sub c onset of approx. 108 K, believed to be Bi sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub 10. This specimen showed zero resistivity at 54 K. The glass ceramic approach could offer several advantages in the fabrication of the high-T sub c superconductors in desired practical shapes such as continuous fibers, wires, tapes, etc.

  1. Effects of Cl(-) substitution on electrophysiological properties, Ca(2+) influx and prolactin secretion of rat lactotropes in vitro.

    PubMed

    Garcia, L; Couderc, B; Odessa, M F; Dufy-Barbe, L; Sartor, P

    1999-11-01

    In this study, we compared the effects of different chloride (Cl(-)) substitutes - methane sulfonate (CH(3)SO(-)(3)), bromide (Br(-)), nitrate (NO(-)(3)), thiocyanate (SCN(-)) and perchlorate (ClO(-)(4)) - on the secretory activity and calcium current activation of rat lactotropes in primary culture. We observed that CH(3)SO(-)(3) decreased basal prolactin (PRL) secretion. Br(-) had no effect, whereas the more lyotropic anions, such as NO(-3), SCN(-) and C1O(-4), increased basal PRL secretion. The latter three substitutes induced a significant shift in the voltage dependence of T-type calcium channel activation towards hyperpolarized values. However, this shift alone cannot explain the increase in secretion. Anion permeability studies also demonstrated that the organic anion CH(3)SO(-3) was less permeant than Cl(-), whereas monovalent inorganic anions were more permeant, with the following anion permeability sequence: SCN(-) > ClO(-4) > NO(-3) > Br(-). In conclusion, deprivation of Cl(-) ions has converse consequences on basal and induced secretion; permeating anions result in a transient increase in intracellular Ca(2+) ions. This process involves voltage-dependent Ca(2+) channels. We propose that an alteration in intracellular anion concentrations may influence the activation of internal effectors such as G proteins or channel proteins and, therefore, interfere with exocytosis. These effects are correlated with an external action of lyotropic anions, particularly NO(-3), ClO(-4) and SCN(-), on the gating properties of T-type calcium channels, probably through changes in cell surface charges. The results demonstrate the modulatory effect of anions on the secretory activity of rat lactotropes and underline the specific role played by chloride in stimulus-secretion coupling. PMID:10567859

  2. Nanostructured silicate substituted calcium phosphate (NanoSiCaPs) nanoparticles - Efficient calcium phosphate based non-viral gene delivery systems.

    PubMed

    Shekhar, Sudhanshu; Roy, Abhijit; Hong, Daeho; Kumta, Prashant N

    2016-12-01

    Nanostructured ceramic particles, particularly, nanoparticles of calcium phosphate (CaP) remain an attractive option among the various types of non-viral gene delivery vectors studied because of their safety, biocompatibility, biodegradability, and ease of handling as well as their adsorptive capacity for DNA. We have accordingly developed an enhanced version of nanostructured calcium phosphates (NanoCaPs), by substituting known amounts of silicate for phosphate in the hydroxyapatite (HA) lattice (NanoSiCaPs). Results indicate that in addition to the excellent transfection levels exhibited by un-substituted NanoCaPs alone in vitro, an additional 20-50% increase in transfection is observed for NanoCaPs containing 8.3-50mol% silicate aptly called NanoSiCaPs, owing to its rapid dissolution properties enabling nanoparticles escaping the lysosomal degradation. However, high silicate substitution (>50mol%) resulted in a drastic decline in transfection as the synthesized NanoCaPs deviated far from the characteristic hydroxyapatite phase formed as evidenced by the materials characterization results. PMID:27612739

  3. Effects of Cr/Zn Substitutions on Dielectric Properties of CaCu{sub 3}Ti{sub 4}O{sub 12}(CCTO) Ceramics

    SciTech Connect

    Rajmi, R.; Yahya, A. K.; Deni, M. S. M.

    2010-07-07

    Effects of Zn and Cr substitutions on dielectric properties of CaCu{sub 3-x}Zn{sub x}Ti{sub 4-y}Cr{sub y}O{sub 12} ceramics are reported. Dielectric measurements at room temperature for un-substituted CaCu{sub 3-x}Zn{sub x}Ti{sub 4-y}Cr{sub y}O{sub 12}(x = 0, y = 0) between 10{sup 2}-10{sup 6} Hz showed dielectric constant of 2.7x10{sup 4} at 10{sup 2} Hz. Substitution of Zn for Cu in CaCu{sub 3-x}Zn{sub xTi{sub 4{sub -{sub yCr{sub yO{sub 1{sub 2}}}}}}}(y = 0, x = 0.10, 0.50)caused dielectric constant to drop with increasing x. Cr substitution at Ti-site in CaCu{sub 3-x}Zn{sub xTi{sub 4{sub -{sub yCr{sub yO{sub 1{sub 2}}}}}}}(x = 0, x = 0,) also caused decrease in dielectric constant. However, at x = 0.50, the dielectric constant at low frequency was enhanced compared to the un-substituted sample. Our results indicate that Cu and Ti sites play an important role in the formation of Internal Barrier Layer Capacitance (IBLC) in CCTO.

  4. Melt processing of the Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] superconductor in oxygen and argon atmospheres

    SciTech Connect

    Holesinger, T.G.; Miller, D.J. ); Chumbley, L.S. )

    1992-08-01

    Solidification and subsequent annealing of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O[sub 2] and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi[sub 2]Sr[sub 3-x]Ca[sub x]O[sub y] and Cu[sub 2]O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi[sub 2.15]Sr[sub 2]Ca[sub 0.85]Cu[sub 2]O[sub y].

  5. Melt processing of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} superconductor in oxygen and argon atmospheres

    SciTech Connect

    Holesinger, T.G.; Miller, D.J.; Chumbley, L.S.

    1992-08-01

    Solidification and subsequent annealing of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O{sub 2} and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi{sub 2}Sr{sub 3-x}Ca{sub x}O{sub y} and Cu{sub 2}O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi{sub 2.15}Sr{sub 2}Ca{sub 0.85}Cu{sub 2}O{sub y}.

  6. Electron-spectroscopy investigation of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{ital y}} single-crystal cleaved surfaces

    SciTech Connect

    Ori, D.M.; Goldoni, A. |; del Pennino, U.

    1995-08-01

    This paper presents spectroscopic investigations of the normal-state properties of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{ital y}} single crystals. Ultraviolet photoemission and electron energy loss data are consistent with the filling in of the charge transfer gap upon doping due to spectral weight transfer mechanisms. The modifications occurring in the surface electronic properties after exposure to pure O{sub 2} and after the deposition of one monolayer of bismuth are studied and discussed.

  7. Effect of electron correlation in Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3}: Density functional calculation

    SciTech Connect

    Hadipour, H.; Akhavan, M.

    2010-07-15

    We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr{sup 4+}-Ru{sup 4+} hybridization is responsible for the high Curie temperature T{sub C} in SrRu{sub 1-x}Cr{sub x}O{sub 3}, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu{sub 1-x}Cr{sub x}O{sub 3} clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted Ca-based compounds as compared to the Sr-based systems shows that the hybridization mechanism is not relevant for these compounds. The bigger exchange splitting of Ru 4d and Cr 3d at the Fermi level with Ru{sup 4+,5+} and Cr{sup 3+,4+} orbital occupancies of CaRu{sub 0.75}Cr{sub 0.25}O{sub 3} in the LSDA+U calculation, compared with that of the LSDA calculation, shows that repulsion between electrons tend to keep the localized spins from overlapping. The low screening of the Ru t{sub 2g} electrons increases T{sub C} in the Ca-based systems, which is consistent with the both high Ru exchange splitting and magnetic moment. The insulating behavior of the high Cr-doped systems can be explained by considering the Ru{sup 4+}+Cr{sup 4+{yields}}Ru{sup 5+}+Cr{sup 3+} charge transfer. - Graphical Abstract: We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using different ab-initio calculation such as LSDA and LSDA+U approximation. The antiferromagnetic hybridization of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The LSDA+U calculation for the more distorted Cr impurity doped Ca

  8. Monoclinic distortion and magnetic coupling in the double perovskite Sr{sub 2−x}Ca{sub x}YRuO{sub 6}

    SciTech Connect

    Bernardo, P.L.; Ghivelder, L.; Eslava, G.G.; Amorim, H.S.; Felner, I.; Garcia, S.

    2014-12-15

    Abstracts: This work investigates in the insulating double perovskites Sr{sub 2−x}Ca{sub x}YRuO{sub 6}. We address the angular dependence of the strength of the magnetic coupling due to the deviation from planarity of the basal layers of the monoclinic structure, characterized by the in-plane angle α<180°, in order to probe the impact of the structural distortions in the magnetic properties of the compounds. High resolution x-ray powder diffraction, susceptibility, and specific heat measurements were performed. The deviation from planarity significantly increases (α=144° for x=1) while the bond distances vary in a complex way as a consequence of the strong monoclinic distortion. We found that the magnetic transition temperature, T{sub M}, shows a linear dependence on cos [(π−α)/2]. This result is discussed in terms of t{sub 2g}(π)–e{sub g}(σ) mixing of the magnetic orbitals of the Ru{sup 5+} ions and unbalanced competitive super-exchange interactions. The deleterious effect of Ca doping for the magnetic coupling is confirmed by the reduction in the short-range antiferromagnetic correlations characteristic of the parent compound at T>>T{sub M} and the enhancement of magnetic frustration for TSr{sub 2−x}Ca{sub x}YRuO{sub 6} due to strong monoclinic distortions. - Highlights: • Neel temperatures in SrCaYRuO were correlated quantitatively with lattice distortions. • Bending of Ru–O–Y planes plays a major role in the magnetic properties of SrCaYRuO. • The structural–magnetic correlation is due to π–σ mixing of the magnetic orbitals.

  9. Combined effects of transition metal (Ni and Rh) substitution and annealing/quenching on the physical properties of CaFe2As2

    SciTech Connect

    Ran, S; Bud'ko, S L; Straszheim, W E; Canfield, P C

    2014-08-01

    We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T=Ni, Rh substitution (x) on the physical properties of Ca(Fe1-xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co substitution. Ni substitution, which brings one more extra electron per substituted atom and suppresses the c-lattice parameter at roughly the same rate as Co substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as that found for Co substitution, but the parameter range for superconductivity has been shrunk (roughly by a factor of 2). This result is similar to what is found when Co- and Ni-substituted BaFe2As2 are compared. On the other hand, Rh substitution, which brings the same amount of extra electrons as does Co substitution, but suppresses the c-lattice parameter more rapidly, has a different phase diagram. The collapsed tetragonal phase exists much more pervasively, to the exclusion of the normal, paramagnetic, tetragonal phase. The range of antiferromagnetic/orthorhombic phase space is noticeably reduced, and the superconducting region is substantially suppressed, essentially truncated by the collapsed tetragonal phase. In addition, we found that whereas for Co substitution there was no difference between phase diagrams for samples annealed for 1 or 7 days, for Ni and Rh substitutions a second, reversible effect of annealing was revealed by 7-day anneals.

  10. Suppression of structural phase transition by Sr substitution in the improper ferroelectric BaAl2O4

    NASA Astrophysics Data System (ADS)

    Mori, Shigeo; Ishii, Yui; Tanaka, Eri; Tsukasaki, Hirofumi; Kawaguchi, Shogo

    2015-10-01

    To clarify lattice fluctuations and precursor phenomena accompanied by structural phase transition in stuffed tridymite compounds, changes in diffuse scattering as a function of temperature in Ba0.6Sr0.4Al2O4 have been carefully investigated by powder X-ray diffraction using synchrotron radiation, electron diffraction and transmission electron microscopy (TEM) experiments. In situ electron diffraction experiments revealed that Ba0.6Sr0.4Al2O4 exhibits lattice fluctuation manifested as a unique honeycomb-shaped diffuse scattering in the wide temperature range between 298 and 100 K. Unlike in the case of BaAl2O4, Ba0.6Sr0.4Al2O4 shows no structural phase transition to the ferroelectric structure with the hexagonal P63 space group in the temperature range. In contrast, it is revealed that the electron beam irradiation to the Ba0.6Sr0.4Al2O4 sample inside the transmission electron microscope induced structural change from the hexagonal P6322 structure to the modulated structure with double periodicity in the three equivalent <110> directions in the low-temperature region. This implies that the total energy difference between these two structures is small. The hexagonal P6322 structure transforms into the modulated one with short correlation length owing to some small external perturbations.

  11. Bipartite electronic superstructures in the vortex core of Bi2Sr2CaCu2O8+δ

    PubMed Central

    Machida, T.; Kohsaka, Y.; Matsuoka, K.; Iwaya, K.; Hanaguri, T.; Tamegai, T.

    2016-01-01

    The central issue in the physics of cuprate superconductivity is the mutual relationship among superconductivity, pseudogap and broken-spatial-symmetry states. A magnetic field B suppresses superconductivity, providing an opportunity to investigate the competition among these states. Although various B-induced electronic superstructures have been reported, their energy, spatial and momentum-space structures are unclear. Here, we show using spectroscopic-imaging scanning tunnelling microscopy on Bi2Sr2CaCu2O8+δ that there are two distinct B-induced electronic superstructures, both being localized in the vortex core but appearing at different energies. In the low-energy range where the nodal Bogoliubov quasiparticles are well-defined, we observe the so-called vortex checkerboard that we identify as the B-enhanced quasiparticle interference pattern. By contrast, in the high-energy region where the pseudogap develops, the broken-spatial-symmetry patterns that pre-exist at B=0 T is locally enhanced in the vortex core. This evidences the competition between superconductivity and the broken-spatial-symmetry state that is associated with the pseudogap. PMID:27230420

  12. Composite superconducting wires obtained by high-rate tinning in molten Bi-Pb-Sr-Ca-Cu-O system

    NASA Technical Reports Server (NTRS)

    Grosav, A. D.; Konopko, L. A.; Leporda, N. I.

    1991-01-01

    Long lengths of metal superconductor composites were prepared by passing a copper wire through the bismuth based molten oxide system at a constant speed. The key to successful composite preparation is the high pulling speed involved, which permits minimization of the severe interaction between the unbuffered metal surface and the oxide melt. Depending on the temperature of the melt and the pulling speed, a coating with different thickness and microstructure appeared. The nonannealed thick coatings contained a Bi2(Sr,Ca)2Cu1O6 phase as a major component. After relatively short time annealing at 800 C, both resistivity and initial magnetization versus temperature measurements show superconducting transitions beginning in the 110 to 115 K region. The effects of annealing and composition on obtained results are discussed. This method of manufacture led to the fabrication of wire with a copper core in a dense covering with uniform thickness of about h approximately equal to 5 to 50 microns. Composite wires with h approximately equal to 10 microns (h/d approximately equal to 0.1) sustained bending on a 15 mm radius frame without cracking during flexing.

  13. A momentum-dependent perspective on quasiparticleinterference in Bi2Sr2CaCu2O_8+delta

    SciTech Connect

    Vishik, I. M.

    2010-04-29

    Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space electronic structure of materials, and provides invaluable information about the high-temperature superconducting cuprates. Likewise, cuprates real-space, inhomogeneous electronic structure is elucidated by Scanning Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle interference (QPI) - wave-like electrons scattering off impurities to produce periodic interference patterns - to infer properties of the QP in momentum-space. Surprisingly, some interference peaks in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212) are absent beyond the antiferromagnetic (AF) zone boundary, implying the dominance of particular scattering process. Here, we show that ARPES sees no evidence of quasiparticle (QP) extinction: QP-like peaks are measured everywhere on the Fermi surface, evolving smoothly across the AF zone boundary. This apparent contradiction stems from different natures of single-particle (ARPES) and two-particle (STS) processes underlying these probes. Using a simple model, we demonstrate extinction of QPI without implying the loss of QP beyond the AF zone boundary.

  14. Characterization of the macrocyclic carbon suboxide factors as potent Na,K-ATPase and SR Ca-ATPase inhibitors.

    PubMed

    Kerek, Franz; Stimac, Robert; Apell, Hans-Jürgen; Freudenmann, Frank; Moroder, Luis

    2002-12-23

    Recently discovered macrocyclic carbon suboxide (MCS) factors with the general formula (C(3)O(2))(n) were found to strongly inhibit rabbit and rat Na,K-ATPase as well as SR Ca-ATPase. Highly active MCS factors were obtained by a base/acid treatment of their lipophilic precursor isolated from plants. In the ESI-MS spectra, the dominant molar mass ion of 431 Da corresponds to a 1:1 complex of the carbon suboxide hexamer (n=6; M(r)=408 Da) with a Na(+) ion. Additional mass ions identified in positive and negative ion mode were assigned as complexes of the MCS hexamer (n=6) and octamer (n=8) with Na(+) or with TFA(-) in various ratios. The dominant mass ion values of these active MCS factors from plants are also found in mass spectra of previously described endogenous digitalis-like factors (EDLF) from animals. This would suggest that ubiquitously distributed MCS factors may function as putative endogenous regulatory substances of Na,K-ATPase and possibly of other ATPases. With the symmetric display of several equivalent carbonyl or hydroxy groups, the structure of MCS factors is particularly suited for interactions with proteins and other bio-molecules. This could explain the high biological activity and the unusual properties of the MCS factors. PMID:12488055

  15. Artificially induced hotspots in Bi2Sr2CaCu2O8 mesa terahertz sources

    NASA Astrophysics Data System (ADS)

    Hao, Yang; Welp, Ulrich; Koshelev, Alexei; Vlasko-Vlasov, Vitalii; Kwok, Wai-Kwong; Kadowaki, Kazuo; Benseman, Timothy

    Mesa-shaped devices comprising stacked Intrinsic Josephson Junctions (IJJs) in the high-temperature superconductor Bi2Sr2CaCu2O8 can be used as compact sources of coherent terahertz radiation. Achieving high emission levels of THz emission power from these devices depends on efficient synchronization of the approximately 600 IJJs in the stack. Theoretical simulations of stacked IJJs, as well as some empirical results, suggest that thermal inhomogeneity of the stack may enhance THz emission power. There are a number of possible mechanisms by which this might occur, including a hotspot acting as a local resistive shunt for the IJJs (thus altering the spread of bias voltages in the stack and the junction damping dynamics) or by local self-heating reducing the phase-stiffness of the superconducting condensate in critical locations. Here we report results of artificially inducing local heating in these devices with thin film micro-heaters patterned on their surfaces, in order to determine which mechanism(s) could be responsible for self-heating-induced THz emission enhancement. Sample patterning was performed at the Center for Nanoscale Materials, an Office of Science user facility, supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  16. Flux creep in Bi2Sr2CaCu2O8(sub +x) single crystals

    NASA Technical Reports Server (NTRS)

    Agostinelli, E.; Balestrino, G.; Fiorani, D.; Muzi, R.; Paroli, P.; Tejada, J.; Testa, A. M.

    1990-01-01

    The results of a magnetic study on a Bi2Sr2CaCu2O(8+x) single crystal are reported. Low field susceptibility (dc and ac), magnetization cycles and time dependent measurements were performed. With increasing the temperature the irreversible regime of the magnetization cycles is rapidly restricted to low fields, showing that the critical current J(sub c) becomes strongly field dependent well below T(sub c). At 2.4 K the critical current in zero field, determined from the remanent magnetization by using the Bean formula for the critical state, is J(sub c) = 2 10(exp 5) A/sq cm. The temperature dependence of J(sub c) is satisfactorily described by the phenomenological law J(sub c) = J(sub c) (0) (1 - T/T(sub c) (sup n), with n = 8. The time decay of the zero field cooled magnetization and of the remanent magnetization was studied at different temperatures for different magnetic fields. The time decay was found to be logarithmic in both cases, at least at low temperatures. At T = 4.2 K for a field of 10 kOe applied parallel to the c axis, the average pinning energy, determined by using the flux creep model, is U(sub o) = 0.010 eV.

  17. Geometry-dependent penetration fields in superconducting Bi2Sr2CaCu2O8+δ platelets

    SciTech Connect

    By: Curran, P. J.; Clem, J. R.; Bending, S. J.; Tsuchiya, Y.; Tamegai, T.

    2010-10-01

    Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation does not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in H{sub p}. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.

  18. Geometry-dependent penetration fields of superconducting Bi2Sr2CaCu2O8+δ platelets

    SciTech Connect

    Curran, P. J.; Clem, J. R.; Bending, S. J.; Tsuchiya, Y.; Tamegai, T.

    2010-10-01

    Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation does not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in Hp. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.

  19. Quench Behavior and Degradation Limit of Ag-sheathed Bi 2Sr2CaCu2Ox Round Wires

    NASA Astrophysics Data System (ADS)

    Ye, Liyang

    High field superconducting magnets are important for scientific research in a variety of disciplines. With nearly field-independent critical current density over a wide range of magnetic field at 4.2 K up to 50 T, Ag-sheathed Bi2Sr2CaCu2Ox (Bi-2212) round wires offer the possibility to generate magnetic fields of 30 T and above. One of the key issues in high field Bi-2212 magnet development is the quench detection and protection. A quench occurs when a part of a superconducting winding, after receiving a small disturbance, enters into the normal (resistive) state, and the event follows with significant temperature rise due to joule heating. An unprotected quench may degrade or even destruct an entire superconducting magnet system. This thesis focuses on experimentally investigating the quench behavior and degradation limit of the state-of-the-art multifilamentary Ag/Bi-2212 round wires to guide the development of Bi-2212 high field magnet, especially the quench detection and protection system. (Abstract shortened by ProQuest.).

  20. Regional variation in otolith Sr:Ca ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes.

    PubMed

    Lin, Y-J; Jessop, B M; Weyl, O L F; Iizuka, Y; Lin, S-H; Tzeng, W-N; Sun, C-L

    2012-07-01

    Otolith Sr:Ca ratios of the African longfinned eel Anguilla mossambica and giant mottled eel Anguilla marmorata from nine freshwater sites in four rivers of South Africa were analysed to reconstruct their migratory life histories between freshwater and saltwater habitats. For A. mossambica, the Sr:Ca ratios in the otolith edge differed significantly among rivers and had large effect sizes, but did not differ among sites within a river. Otolith Sr:Ca ratios did not differ among rivers for A. marmorata. When rivers were pooled, the edge Sr:Ca ratios of A. mossambica were not significantly different from those of A. marmorata. According to the river-specific critical Sr:Ca ratio distinguishing freshwater from saltwater residence, most A. mossambica and A. marmorata had saltwater habitat experience after settlement in fresh water. This was primarily during their elver stage or early in the yellow eel stage. During the middle and late yellow eel stage, freshwater residency was preferred and only sporadic visits were made to saltwater habitats. The data also suggest that regional variations in otolith Sr:Ca ratios affect the critical Sr:Ca value and are a challenge for the reconstruction of migratory life histories that should be explicitly considered to avoid bias and uncertainty.

  1. Ternary CaCu{sub 4}P{sub 2}-type pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb)

    SciTech Connect

    Stoyko, Stanislav S.; Khatun, Mansura; Scott Mullen, C.; Mar, Arthur

    2012-08-15

    Four ternary pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb) were prepared by reactions of the elements at 850 Degree-Sign C and their crystal structures were determined from single-crystal X-ray diffraction studies. These silver-containing pnictides AAg{sub 4}Pn{sub 2} adopt the trigonal CaCu{sub 4}P{sub 2}-type structure (Pearson symbol hR21, space group R3-bar m, Z=3; a=4.5555(6) A, c=24.041(3) A for SrAg{sub 4}As{sub 2}; a=4.5352(2) A, c=23.7221(11) A for EuAg{sub 4}As{sub 2}; a=4.7404(4) A, c=25.029(2) A for SrAg{sub 4}Sb{sub 2}; a=4.7239(3) A, c=24.689(2) A for EuAg{sub 4}Sb{sub 2}), which can be derived from the trigonal CaAl{sub 2}Si{sub 2}-type structure of the isoelectronic zinc-containing pnictides AZn{sub 2}Pn{sub 2} by insertion of additional Ag atoms into trigonal planar sites within [M{sub 2}Pn{sub 2}]{sup 2-} slabs built up of edge-sharing tetrahedra. Band structure calculations on SrAg{sub 4}As{sub 2} and SrAg{sub 4}Sb{sub 2} revealed that these charge-balanced Zintl phases actually exhibit no gap at the Fermi level and are predicted to be semimetals. - Graphical abstract: SrAg{sub 4}As{sub 2} and related pnictides adopt a CaCu{sub 4}P{sub 2}-type structure in which additional Ag atoms enter trigonal planar sites within slabs built from edge-sharing tetrahedra. Highlights: Black-Right-Pointing-Pointer AAg{sub 4}Pn{sub 2} are the first Ag-containing members of the CaCu{sub 4}P{sub 2}-type structure. Black-Right-Pointing-Pointer Ag atoms are stuffed in trigonal planar sites within CaAl{sub 2}Si{sub 2}-type slabs. Black-Right-Pointing-Pointer Ag-Ag bonding develops through attractive d{sup 10}-d{sup 10} interactions.

  2. Elucidating the driving force of superconductivity increase in compressed optimally doped Bi2Sr2CaCu2O8+x

    NASA Astrophysics Data System (ADS)

    Chen, Xiao-Jia; Struzhkin, Viktor; Zhang, Jian-Bo; Gavriliuk, Alexander; Goncharov, Alexander; Mao, Ho-Kwang; Lin, Hai-Qing; Gu, Genda

    An optimally doped cuprate Bi2Sr2CaCu2O8+x is as a perfect model system to explore the mechanism of superconductivity by applying pressure as one can avoid complicated competing orders in the underdoped regime and explore pure intrinsic effects rather than secondary effects related to change in the carrier concentration. Here, by carefully examining the collected high-pressure Raman spectra at low temperatures, we have observed an enhanced two-magnon mode and connected this to the observed 10 K increase in Tc (reaching more than 100 K for the first time) in the optimally doped Bi2Sr2CaCu2O8+x upon compression clearly delineating the effect of pressure-induced charge transfer that must suppress Tc for this optimally doped sample. Our finely designed experiments offer the direct and convincing evidence for identifying the magnetic fluctuations as the pairing interaction in cuprate superconductors.

  3. Synthesis and multiferroic properties of Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A=Ca,Sr,Pb) ceramics

    SciTech Connect

    Khomchenko, V. A.; Kiselev, D. A.; Vieira, J. M.; Kholkin, A. L.; Sa, M. A.; Pogorelov, Y. G.

    2007-06-11

    Bi{sub 1-x}A{sub x}FeO{sub 3} ceramics (A=Ca,Sr,Pb) were sintered by conventional mixed oxide route. The crystallographic structure of all samples is characterized by the rhombohedral symmetry (space group R3c). The existence of switchable ferroelectric polarization is verified by piezoresponse force microscopy that is proven to be a useful technique in semi-insulating ferroelectrics. Magnetic properties of Ca and Sr-doped ceramics are found to reproduce the antiferromagnetic behavior of undoped BiFeO{sub 3} without any enhancement of the magnetization. On the contrary, Pb-doped compound demonstrates appearance of a weak ferromagnetism. It is thus shown that Pb doping of BiFeO{sub 3} is a promising way for preparing multiferroic materials.

  4. Structural changes upon electrochemical insertion of lithium into the Bi2Sr2CaCuO8+y high Tc superconductor

    NASA Astrophysics Data System (ADS)

    Fleischer, Niles A.; Manassen, Joost; Coppens, Philip; Lee, Peter; Gao, Yan

    1992-04-01

    The insertion compound LixBi2Sr2CaCu2O8+y (x≤2) was prepared by electrochemical insertion of lithium into Bi2Sr2CaCu2O8+y pellets at room temperature in galvanic cells. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists, but the superconducting fraction appears to be lower in the reacted samples. The lithiated product was analyzed by crystallographic and chemical measurements. The results show that insertion of Li ions is accompanied by an expansion of the interlayer spacing between Bi-O planes and a small increase in the a- and b-cell parameters. This change is consistent with some, but not all, of the donated electrons entering the Cu-O planes, with a corresponding reduction in hole concentration. At higher levels of Li content, a substantial breakdown of the lattice is observed.

  5. Developments in heterobimetallic s-block systems: synthesis and structural survey of molecular M/Ae (M=Li, Na, K, Cs; Ae=Ca, Sr) aryloxo complexes.

    PubMed

    Zuniga, Maria Felisa; Deacon, Glen B; Ruhlandt-Senge, Karin

    2008-06-01

    A series of novel heterobimetallic group 1/strontium and group 1/calcium aryloxo complexes having the composition [MAe(Odpp)3] [Ae=Sr and M=Na (1), K (2, 3), Cs (4); Ae=Ca and M=Na (5), K (6), Cs (7)] or [M2Ae(Odpp)4] [M=Li and Ae=Sr (9), Ca (10)] have been prepared using 2,6-diphenylphenol (HOdpp) as the ligand. Through the use of solid-state direct metalation, these compounds were obtained either directly from the reaction vessel or after workup in toluene. The Lewis base adduct [KCa(Odpp)3(thf)] (8) was obtained by treatment of [KCa(Odpp)3] (6) with tetrahydrofuran (thf). All of the compounds displayed extensive metal-pi-arene interactions, which provide significant stabilization in these reactive species. The thermal stabilities and volatilities of representative heterobimetallic strontium and calcium complexes were investigated using thermogravimetric analysis.

  6. Luminescence Properties of Self-Activated Mm(VO4)2 (M = Mg, Ca, Sr, and Ba) Phosphors Synthesized by Solid-State Reaction Method.

    PubMed

    Min, Xin; Huang, Zhaohui; Fang, Minghao; Liu, Yan'gai; Tang, Chao; Wu, Xiaowen

    2016-04-01

    In this paper, M3(VO4)2 (M = Mg, Ca, Sr, and Ba) self-activated phosphors were prepared by a solid-state reaction method at 1,000 °C for 5 h. The phase formation and micrographs were analyzed by X-ray diffraction and scanning electron microscopy. The Ca3(VO4)2 phosphor does not show any emission peaks under excitation with ultraviolet (UV) light. However, the M3(VO4)2 (M = Mg, Sr, and Ba) samples are effectively excited by UV light chips ranging from 200 nm to 400 nm and exhibit broad emission bands due to the charge transfer from the oxygen 2p orbital to the vacant 3d orbital of the vanadium in the VO4. The color of these phosphors changes from yellow to light blue via blue-green with increasing ionic radius from Mg to Sr to Ba. The luminescence lifetimes and quantum yield decrease with the increasing unit cell volume and V-V distance, in the order of Mg3(VO4)2 to Sr3(VO4)2 to Ba3(VO4)2. The emission intensity decreases with the increase of temperatures, but presents no color shift. This confirms that these self-activated M3(VO4)2 phosphors can be suggested as candidates of the single-phase phosphors for light using UV light emitting diodes (LEDs). PMID:27451689

  7. Combined effects of post-growth thermal treatment and chemical substitution on physical properties of CaFe2As2

    SciTech Connect

    Ran, Sheng

    2014-12-01

    This thesis summarizes experimental work using process of postgrowth thermal treatment and chemical substitution as tuning parameters in the study of physical properties of CaFe2As2. Details of sample preparation and characterization are given as well as various phase diagrams.

  8. Weak links within a Bi2Sr2Ca1Cu2O(x) single crystal by magnetization and direct optical observations

    NASA Astrophysics Data System (ADS)

    Willis, J. O.; Nakamura, N.; Gotoh, S.; Takamuku, K.; Koshizuka, N.; Tanaka, S.

    1991-06-01

    We have performed magnetic susceptibility and direct optical High Contrast Magnetic Flux (HICOM) observations on a single crystal of Bi2Sr2CaCu2O(x). Low temperature pinning and high temperature flux creep have been observed by HICOM. The results suggest that the breakdown of flux pinning may occur gradually with temperature and may exhibit spatial variation related to sample inhomogeneities.

  9. Weak links within a Bi 2Sr 2Ca 1Cu 2O x single crystal by magnetization and direct optical observations

    NASA Astrophysics Data System (ADS)

    Willis, J. O.; Nakamura, N.; Gotoh, S.; Takamuku, K.; Koshizuka, N.; Tanaka, S.

    1991-12-01

    We have performed magnetic susceptibility and direct optical High Contrast Magnetic Flux (HICOM) observations on a single crystal of Bi 2Sr 2Ca 1Cu 2O x. Low temperature pinning and high temperature flux creep have been observed by HICOM. The results suggest that the breakdown of flux pinning may occur gradually with temperature and may exhibit spatial variation related to sample inhomogeneities.

  10. Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral Sr/Ca records

    NASA Astrophysics Data System (ADS)

    von Reumont, J.; Hetzinger, S.; Garbe-Schönberg, D.; Manfrino, C.; Dullo, W.-Chr.

    2016-03-01

    The rising temperature of the world's oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970-2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (>33°C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6 year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs.

  11. Preparation of Bi-Pb-Sr-Ca-Cu-O oxide superconductors by coprecipitation of nanosize oxalate precursor powders in the aqueous core of water-in-oil microemulsions

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Pillai, V.; Shah, D. O.

    1993-02-01

    We describe a new technique for the synthesis of ultrahomogeneous nanoparticles of precursor oxalate powder by coprecipitation in the aqueous core of a water-in-oil microemulsion for the preparation of Bi-Pb-Sr-Ca-Cu-O (2223) oxide superconductor. This process ensures a uniform mixing of metal cations down to a scale of at least 10 nm. This finely dispersed precursor powder results in phase pure (2223) oxide superconductor after proper heat treatment.

  12. Metal-semiconductor-transition observed in Bi{sub 2}Ca(Sr, Ba){sub 2}Co{sub 2}O{sub 8+δ} single crystals

    SciTech Connect

    Dong, Song-Tao; Zhang, Bin-Bin; Zhang, Lun-Yong; Yao, Shu-Hua E-mail: shyao@nju.edu.cn; Zhou, Jian; Zhang, Shan-Tao; Gu, Zheng-Bin; Chen, Yan-Feng; Chen, Y. B. E-mail: shyao@nju.edu.cn

    2014-07-28

    Electrical property evolution of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} demonstrates semiconductor-like properties. But Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} to semiconductor-like Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} can be attributed to Anderson localization. However the semiconductor behaviour of Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} is related to electronic correlations effect that is inferred by large negative magnetoresistance (∼70%). The theoretical electronic structures and valence X-ray photoemission spectroscopy substantiate that there is a relative large density of state around Fermi level in Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} compared with other two compounds. It suggests that Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} is more apt to be metal in this material system.

  13. Superconductivity up to 114 K in the Bi-Al-Ca-Sr-Cu-O compound system without rare-earth elements

    NASA Technical Reports Server (NTRS)

    Chu, C. W.; Bechtold, J.; Gao, L.; Hor, P. H.; Huang, Z. J.

    1988-01-01

    Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements. Pressure has only a slight positive effect on T(c). These observations provide an extra material base for the study of the mechanism of high-temperature superconductivity and also the prospect of reduced material cost for future applications of superconductivity.

  14. Structural and photoluminescence properties of Dy3+ co-doped and Eu2+ activated MAl2O4 (M = Ba, Ca, Sr) nanophosphors

    NASA Astrophysics Data System (ADS)

    Dejene, F. B.; Kebede, M. A.; Redi-Abshiro, M.; Kgarebe, B. V.

    2013-09-01

    Long afterglow alkaline earth aluminates MAl2O4:Eu, Dy (M: Ca, Sr, Ba) phosphors are generally synthesized by the solid-state process which is more feasible than other conventional processes in terms of operation and large-scale production. However, the constituents of phosphors synthesized using this process are usually not mixed well, the particles agglomerates and very high temperature requirement to synthesize the final powder make it undesirable. In order to circumvent these problems, MAl2O4:Eu, Dy (Ca, Ba, Sr) phosphors were prepared at low temperatures (500 °C) by the solution-combustion of corresponding metal nitrate-urea solution mixtures, over a time of 5-10 min. In order to elucidate the relationship between the constituent, structure and PL properties product's particle size, morphological and structural properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), while the characteristic luminescence properties were investigated using emission spectra. The low temperature monoclinic structure for both CaAl2O4 and SrAl2O4 and the hexagonal structure of BaAl2O4 were observed. The emission spectra of these phosphors indicated that all of them are broad band, and the only emission peaks around 448, 490 and 515 nm of CaAl2O4:Eu, Dy, BaAl2O4:Eu, Dy and SrAl2O4:Eu, Dy, respectively, are due to 5d → 4f transition of Eu2+. The decay curves implied that these phosphors contain fast, medium and slow-decay process. The Dy3+ trap levels may be considered to be responsible for the long afterglow phosphorescence at room temperature.

  15. Strong magnetic correlations to 900 K in single crystals of the trigonal antiferromagnetic insulators SrMn2As2 and CaMn2As2

    DOE PAGES

    Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; Johnston, D. C.

    2016-09-15

    Crystallographic, electronic transport, thermal, and magnetic properties are reported for SrMn2As2 and CaMn2As2 single crystals grown using Sn flux. Rietveld refinements of powder x-ray diffraction data show that the two compounds are isostructural and crystallize in the trigonal CaAl2Si2-type structure (space groupmore » $$P\\bar{3}$$ m1), in agreement with the literature. Electrical resistivity ρ versus temperature T measurements demonstrate insulating ground states for both compounds with activation energies of 85 meV for SrMn2As2 and 61 meV for CaMn2As2. In a local-moment picture, the Mn+2 3d5 ions are expected to have high-spin S=5/2 with spectroscopic splitting factor g≈2. Magnetic susceptibility χ and heat capacity Cp measurements versus T reveal antiferromagnetic (AFM) transitions at TN=120(2) K and 62(3) K for SrMn2As2 and CaMn2As2, respectively. The anisotropic χ(T≤TN) data indicate that the hexagonal c axis is the hard axis and hence that the ordered Mn moments are aligned in the ab plane. Finally, the χ(T) data for both compounds and the Cp(T) for SrMn2As2 show strong dynamic short-range AFM correlations from TN up to at least 900 K, likely associated with quasi-two-dimensional connectivity of strong AFM exchange interactions between the Mn spins within the corrugated honeycomb Mn layers parallel to the ab plane.« less

  16. Formation of superconducting Bi sub 2-y Pb sub y Sr sub 2 Ca sub 2 Cu sub 3 O sub x from coprecipitated oxalates

    SciTech Connect

    Bernhard, K.; Gritzner, G.; Wang, Xianzhong; Baeuerle, D. )

    1990-06-01

    The conditions for the coprecipitation of Bi{sup 3+}, Pb{sup 2+}, Ca{sup 2+} as oxalates are reported. These oxalates were used as precursors for the formation of Bi{sub 2-y}Pb{sub y}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconducting ceramics. The behavior of the oxalates upon heat treatment was studied by thermogravimetry. Both the oxalates and the superconducting oxides were analyzed and characterized by atomic absorption spectroscopy and by X-ray diffraction.

  17. Wideband and Narrowband Microwave Characteristics of Co/Ti-Substituted M-Type Ca-Hexagonal Ferrite

    NASA Astrophysics Data System (ADS)

    Singh, Charanjeet; Bindra Narang, S.

    2016-10-01

    Polycrystalline M-type CaCo x Ti x Fe(12-2x)O19 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) hexagonal ferrite compositions, with substitution of Co2+ and Ti4+ ions, have been synthesized by a two-route ceramic method. Vector network analysis was used to measure various microwave and electromagnetic parameters from 8.2 GHz to 12.4 GHz. The microwave shielding effectiveness (SE) due to absorption (SEA) and reflection (SER) was investigated based on S-parameters for the near field, and intrinsic parameters, accompanied by AC conductivity and skin depth, for the far field. The shielding effectiveness was primarily governed by absorption (SEA), and substitution of Co2+ and Ti4+ ions resulted in near- and far-field SEA of 54.85 dB at 10.49 GHz and 63.43 dB at 1.15 (Ω m)-0.5, respectively, for the composition with x = 0.6. The AC conductivity exhibited a monotonic increase with frequency, whereas the skin depth decreased with frequency for all the compositions. The composition with x = 0.6 exhibited a 20-dB wide absorption bandwidth (WAB) of 3.67 GHz and 3.66 GHz for near and far field, respectively. The composition with x = 0.3 showed a 10-dB narrow absorption bandwidth (NAB) of 80 MHz for the far field.

  18. Growth of superconducting Bi 2Sr 2CaCu 2O 8+ δ(Bi-2212) single crystal whiskers and the characteristics

    NASA Astrophysics Data System (ADS)

    Oh, S.-Y.; Kim, S.-J.; Kim, G.-S.; Nagao, M.; Hatano, T.

    2006-10-01

    We have succeeded in the growth of superconducting Bi2Sr2CaCu2O8+δ(Bi-2212) single crystal whiskers with a Te-doped method. We use a Te-doped precursor with the mixed pure powders Bi2O3, SrCO3, CaCO3, CuO and TeO2 into the ratios of Bi2Sr2Ca2Cu2.5Te0.5Ox. Bi-2212 single crystal whiskers have grown through the pellet surface 2-4 mm in length and 20-100 μm in width. Characteristics of whiskers were investigated by the resistance-temperature (R-T), X-ray diffraction (XRD) and current-voltage (I-V) measurements. The R-T characteristics in ab-plane of the whiskers showed that their Tc,on and Tc,end were about 106 K and 75 K, respectively and confirmed that the whiskers had Bi-2212 single crystal phase by XRD pattern. The I-V curves showed multi-branch structures of intrinsic Josephson junctions (IJJ) as evidence of c-axis transport characteristics.

  19. Synthesis and Microwave Dielectric Properties of A16V18O61 (A = Ba, Sr and Ca) Ceramics for LTCC Applications

    NASA Astrophysics Data System (ADS)

    Suresh, E. K.; Prasad, K.; Arun, N. S.; Ratheesh, R.

    2016-06-01

    Low-temperature co-firable A16V18O61 (A = Ba, Sr, Ca) ceramics have been prepared through the solid state ceramic route. The structural features of these ceramics have been studied using the x-ray diffraction (XRD) technique. The existence of the A16V18O61 (A = Ba, Sr, Ca) ceramic phase was confirmed through laser Raman spectroscopic studies. Scanning electron microscopy analysis revealed a dense microstructure for the ceramics with closely packed polygonal grains. Among the samples studied, Ba16V18O61 ceramic was prepared in the ultralow sintering temperature of 620°C for 1 h, which can be co-firable with an aluminium electrode. XRD and electron dispersive spectroscopy analyses showed that the samples under study have excellent compatibility with metal electrodes. The microwave dielectric properties measured using a vector network analyzer revealed that A16V18O61 (A = Ba, Sr, Ca) ceramics have excellent unloaded quality factors.

  20. Polymorphisms in CaSR and CLDN14 Genes Associated with Increased Risk of Kidney Stone Disease in Patients from the Eastern Part of India.

    PubMed

    Guha, Manalee; Bankura, Biswabandhu; Ghosh, Sudakshina; Pattanayak, Arup Kumar; Ghosh, Saurabh; Pal, Dilip Kumar; Puri, Anurag; Kundu, Anup Kumar; Das, Madhusudan

    2015-01-01

    Kidney stone disease (KSD) is a major clinical problem imposing a large burden for both healthcare and economy globally. In India, the prevalence of kidney stone disease is rapidly increasing. This study aimed to evaluate the association between genetic defects in vitamin D receptor (VDR), calcium sensing receptor (CaSR) and claudin 14 (CLDN14) genes and kidney stone disease in patients from eastern India. We enrolled 200 consecutive kidney stone patients (age 18-60 years) (cases) and their corresponding sex and age matched 200 normal individuals (controls). To identify genetic variants responsible for KSD, we performed sequence analysis of VDR, CaSR and CLDN14 genes. Four non-synonymous (rs1801725, rs1042636, rs1801726 and rs2228570), one synonymous (rs219780) and three intronic single nucleotide polymorphisms (SNPs) (rs731236, rs219777 and rs219778) were identified. Genotype and allele frequency analysis of these SNPs revealed that, rs1801725 (Ala986Ser), rs1042636 (Arg990Gly) of CaSR gene and rs219778, rs219780 (Thr229Thr) of CLDN14 gene were significantly associated with KSD. Serum calcium levels were significantly higher in subjects carrying 986Ser allele and calcium excretion was higher in subjects bearing 990Gly allele. In conclusion, rs1801725, rs1042636, rs219778 and rs219780 SNPs were associated with kidney stone risk in patients from the eastern part of India.

  1. Primary Phase Field of the Pb-Doped 2223 High-Tc Superconductor in the (Bi, Pb)-Sr-Ca-Cu-O System

    PubMed Central

    Wong-Ng, W.; Cook, L. P.; Kearsley, A.; Greenwood, W.

    1999-01-01

    Both liquidus and subsolidus phase equilibrium data are of central importance for applications of high temperature superconductors in the (Bi, Pb)-Sr-Ca-Cu-O system, including material synthesis, melt processing and single crystal growth. The subsolidus equilibria of the 110 K high-Tc Pb-doped 2223 ([Bi, Pb], Sr, Ca, Cu) phase and the location of the primary phase field (crystallization field) have been determined in this study. For the quantitative determination of liquidus data, a wicking technique was developed to capture the melt for quantitative microchemical analysis. A total of 29 five-phase volumes that include the 2223 phase as a component was obtained. The initial melt compositions of these volumes range from a mole fraction of 7.3 % to 28.0 % for Bi, 11.3 % to 27.8 % for Sr, 1.2 % to 19.4 % for Pb, 9.8 % to 30.8 % for Ca, and 17.1 % to 47.0 % for Cu. Based on these data, the crystallization field for the 2223 phase was constructed using the convex hull technique. A section of this “volume” was obtained by holding two components of the composition at the median value, allowing projection on the other three axes to show the extent of the field.

  2. Color tunable and thermally stable luminescence of Tb{sup 3+} doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors

    SciTech Connect

    Zhang, Xinmin; Seo, Hyo Jin

    2012-08-15

    Highlights: ► Lowest spin-allowed and spin-forbidden f–d transitions locate at 250 and 280 nm. ► Cross relaxation shortens lifetime of {sup 5}D{sub 3} level, while that of {sup 5}D{sub 4} are unaffected. ► Cross-relaxation can explain concentration quenching of the {sup 5}D{sub 3} emission. ► Dipole–quadrupole interaction is responsible for the non-radiative relaxation. ► Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tb{sup 3+} is thermally stable and color tunable phosphor. -- Abstract: Tb{sup 3+} ions activated Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors were synthesized using a solid state reaction method. The phase impurity was checked by XRD. The photoluminescence (PL) excitation spectrum, emission spectra at room and high temperature, decay curves of samples with different Tb{sup 3+} ions concentration were studied in detail. Cross-relaxation and the Inokuti–Hirayama model were used to analyze the experimental results. Li{sub 4}SrCa(SiO{sub 4}){sub 2}:xTb{sup 3+} are thermally stable and color tunable phosphors.

  3. Suppression of magnetism and development of superconductivity within the collapsed tetragonal phase of Ca0.67Sr0.33Fe2As2 under pressure

    NASA Astrophysics Data System (ADS)

    Jeffries, J. R.; Butch, N. P.; Kirshenbaum, K.; Saha, S. R.; Samudrala, G.; Weir, S. T.; Vohra, Y. K.; Paglione, J.

    2012-05-01

    Structural and electronic characterizations of (Ca0.67Sr0.33)Fe2As2 have been performed as a function of pressure up to 12 GPa using conventional and designer diamond anvil cells. The compound (Ca0.67Sr0.33)Fe2As2 behaves intermediately between its end members, displaying a suppression of magnetism and the onset of superconductivity. Like other members of the AFe2As2 family, (Ca0.67Sr0.33)Fe2As2 undergoes a pressure-induced isostructural volume collapse, which we associate with the development of As-As bonding across the mirror plane of the structure. This collapsed tetragonal phase abruptly cuts off the magnetic state and supports superconductivity with a maximum Tc=22.2K. The maximum Tc of the superconducting phase is not strongly correlated with any structural parameter, but its proximity to the abrupt suppression of magnetism as well as the volume-collapse transition suggests that magnetic interactions and structural inhomogeneity may play a role in its development.

  4. Charge-compensation effect of Al on luminescence properties of M2(Si, Al)5N8:Ce3+ (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Kuramoto, Daiki; Horikawa, Takashi; Hanzawa, Hiromasa; Machida, Ken-ichi

    2013-09-01

    The charge-compensated materials, M2AlxSi5-xN8:Ce3+ (M = Ca, Sr, Ba), were synthesized from appropriate mixtures of MSi, MAlSi, (MSiHy, MAlSiHy), Si3N4 and CeF3 by a direct nitriding process in a N2 gas and the luminescence properties were characterized. The resultant phosphors showed green emission suitable for LED illumination by optimizing the mixing ratio of metal elements. These phosphors were effectively excited by violet or blue light (400-430 nm) and the emission bands were observed at various wavelength regions for Ca: 489-528 nm, Sr: 511-520 nm, and Ba: 508-514 nm. Although the emission intensity of Ca2(Si, Al)5N8:Ce3+ was decreased with increasing amount of Al, those of Sr- and Ba-analogues were maximized at x = 0.5 of Al content in M2Si5-xAlxN8:Ce3+.

  5. Micro-oxidation treatment to improve bonding strength of Sr and Na co-substituted hydroxyapatite coatings for carbon/carbon composites

    NASA Astrophysics Data System (ADS)

    Zhang, Leilei; Li, Hejun; Li, Kezhi; Zhang, Yulei; Liu, Shoujie; Guo, Qian; Li, Shaoxian

    2016-08-01

    To improve the bonding strength of Sr and Na co-substituted hydroxyapatite (SNH) coatings for carbon/carbon composites, carbon/carbon composites are surface modified by micro-oxidation treatment. The micro-oxidation treatment could generate large number of pores containing oxygenic functional groups on the surface of carbon/carbon composites. SNH is nucleated on the inwall of the pores and form a flaky shape coating with 10-50 nm in thickness and 200-900 nm in width. The bonding strength between SNH coating and carbon/carbon composites increases from 4.27 ± 0.26 MPa to 10.57 ± 0.38 MPa after the micro-oxidation treatment. The promotion of bonding strength is mainly attributed to the pinning effect caused by the pores and chemical bonding generated by the oxygenic functional groups.

  6. Metallic Nonsuperconducting Phase and D -Wave Superconductivity in Zn-Substituted La{sub 1.85}Sr{sub 0.15}CuO{sub 4}

    SciTech Connect

    Karpinska, K.; Cieplak, Marta Z.; Guha, S.; Malinowski, A.; Skoskiewicz, T.; Plesiewicz, W.; Berkowski, M.; Boyce, B.; Lemberger, Thomas R.; Lindenfeld, P.

    2000-01-03

    Measurements of the resistivity, magnetoresistance, and penetration depth were made on films of La{sub 1.85} Sr{sub 0.15} CuO{sub 4} , with up to 12 at. % of Zn substituted for the Cu. The results show that the quadratic temperature dependence of the inverse square of the penetration depth, indicative of d -wave superconductivity, is not affected by doping. The suppression of superconductivity leads to a metallic nonsuperconducting phase, as expected for a pairing mechanism related to spin fluctuations. The metal-insulator transition occurs in the vicinity of k{sub F}l{approx_equal}1 , and appears to be disorder driven, with the carrier concentration unaffected by doping. (c) 1999 The American Physical Society.

  7. Static conduction mechanisms in Co2+ and Ti4+ substituted M-type SrCox Tix Fe(12-2x) O19 ferrite

    NASA Astrophysics Data System (ADS)

    Bhikhan, Vikas; Singh, Charanjeet; Kaur, Rajneesh; Jaroszewski, Maciej; Bindra Narang, S.

    2015-12-01

    The static current density ( J)-electric field ( E) characteristics of SrCo x Ti x Fe(12-2 x)O19 ferrite compositions ( x = 0.0, 0.2, 0.3, 0.5, 0.6, 0.7, 1.0) have been investigated from 0.07 kV/m to 5.29 kV/m at room temperature. All compositions obey Ohms Law at low applied field and non-linearity conduction is observed at high field in compositions x = 0.0, 0.2, 0.3, 0.5, 0.6 and 1.0. The non-linear conduction mechanisms, Schottky, Poole-Frenkel, Ionic Hopping and Space Charge Limited Current mechanism, have been discussed. The current density is increased at higher substitution.

  8. A-Site (MCe) Substitution Effects on the Structures and Properties of CaBi4Ti4O15 Ceramics

    NASA Astrophysics Data System (ADS)

    Yan, Haixue; Li, Chengen; Zhou, Jiaguang; Zhu, Weimin; He, Lianxin; Song, Yuxin

    2000-11-01

    We investigated the effect of A-site compound substitution on the structures and properties of Ca0.8(MCe)0.1Bi4Ti4O15 (M denotes Li, Na and K) ceramics. The samples were prepared by the conventional ceramic technique. Sintering characteristics of Ca0.8(MCe)0.1Bi4Ti4O15 and CaBi4Ti4O15 ceramics were discussed. X-ray powder diffraction patterns of the three modified CBT-based compounds show a single phase of bismuth oxide layer type structure with m=4. The hysteresis loops of polarization versus electric field of the four compounds were also measured. A-site compound substitution improves the piezoelectric properties and the high-temperature resistivity of these materials. A-site (LiCe) and (KCe) substitution not only improves the Curie temperature but also decreases the temperature coefficient of dielectric constant (TK\\varepsilon). Among the three modified ceramics, only the Curie temperature of Ca0.8(NaCe)0.1Bi4Ti4O15 is lower than that of CaBi4Ti4O15; however, its TK\\varepsilon is the lowest. As a result, all the three modified CBT-based ceramics were found to be excellent high-temperature piezoelectric materials.

  9. Low loss composition of BaxSryCa1-x-yTiO3: Ba0.12-0.25Sr0.35-0.47Ca0.32-0.53TiO3

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    2001-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  10. Quench degradation limit of multifilamentary AgBi2Sr2CaCu2Ox round wires

    DOE PAGES

    Ye, Liyang; Li, Pei; Shen, Tengming; Schwartz, Justin

    2016-02-02

    Understanding safe operating limits of composite superconducting wires is important for the design of superconducting magnets. Here we report measurements of quench-induced critical current density Jc degradation in commercial Ag/Bi2Sr2CaCu2Ox (Bi-2212) round wires using heater-induced quenches at 4.2 K in self magnetic field that reveal a general degradation behavior. Jc degradation strongly depends on the local hot spot temperature Tmax, and is nearly independent of operating current, the temperature gradient along the conductor dTmax/dx, and the temperature rising rate dTmax/dt. Both Jc and n value (where n is an index of the sharpness of the superconductor-to-normal transition) exhibit small butmore » irreversible degradation when Tmax exceeds 400-450 K, and large degradation occurs when Tmax exceeds 550 K. This behavior was consistently found for a series of Bi-2212 wires with widely variable wire architectures and porosity levels in the Bi-2212 filaments, including a wire processed using a standard partial melt processing and in which Bi-2212 filaments are porous, an overpressure processed wire in which Bi-2212 filaments are nearly porosity-free and that has a Jc(4.2 K, self field) exceeding 8000 A/mm2, and a wire that has nearly no filament to filament bridges after reaction. Microstructural observations of degraded wires reveal cracks in the Bi-2212 filaments perpendicular to the wire axis, indicating that the quench-induced Ic degradation is primarily driven by strain. These results further suggest that the quench degradation temperature limit depends on the strain state of Bi-2212 filaments and this dependence shall be carefully considered when engineering a high-field Bi-2212 magnet.« less

  11. Quench degradation limit of multifilamentary Ag/Bi2Sr2CaCu2O x round wires

    NASA Astrophysics Data System (ADS)

    Ye, Liyang; Li, Pei; Shen, Tengming; Schwartz, Justin

    2016-03-01

    Understanding safe operating limits of composite superconducting wires is important for the design of superconducting magnets. Here we report measurements of quench-induced critical current density J c degradation in commercial Ag/Bi2Sr2CaCu2O x (Bi-2212) round wires using heater-induced quenches at 4.2 K in self magnetic field that reveal a general degradation behavior. J c degradation strongly depends on the local hot spot temperature T max, and is nearly independent of operating current, the temperature gradient along the conductor dT max/dx, and the temperature rising rate dT max/dt. Both J c and n value (where n is an index of the sharpness of the superconductor-to-normal transition) exhibit small but irreversible degradation when T max exceeds 400-450 K, and large degradation occurs when T max exceeds 550 K. This behavior was consistently found for a series of Bi-2212 wires with widely variable wire architectures and porosity levels in the Bi-2212 filaments, including a wire processed using a standard partial melt process and in which Bi-2212 filaments are porous, an overpressure processed wire in which Bi-2212 filaments are nearly porosity-free and that has a J c(4.2 K, self field) exceeding 8000 A mm-2, and a wire that has nearly no filament to filament bridges after reaction. Microstructural observations of degraded wires reveal cracks in the Bi-2212 filaments perpendicular to the wire axis, indicating that the quench-induced I c degradation is primarily driven by strain. These results further suggest that the quench degradation temperature limit depends on the strain state of Bi-2212 filaments and this dependence shall be carefully considered when engineering a high-field Bi-2212 magnet.

  12. The effect of ionic dissolution products of Ca-Sr-Na-Zn-Si bioactive glass on in vitro cytocompatibility.

    PubMed

    Murphy, S; Wren, A W; Towler, M R; Boyd, D

    2010-10-01

    Many commercial bone grafts cannot regenerate healthy bone in place of diseased bone. Bioactive glasses have received much attention in this regard due to the ability of their ionic dissolution products to promote cell proliferation, cell differentiation and activate gene expression. Through the incorporation of certain ions, bioactive glasses can become therapeutic for specific pathological situations. Calcium-strontium-sodium-zinc-silicate glass bone grafts have been shown to release therapeutic levels of zinc and strontium, however the in vitro compatibility of these materials is yet to be reported. In this study, the in vitro cytocompatibility of three different calcium-strontium-sodium-zinc-silicate glasses was examined as a function of their ion release profiles, using Novabone® bioglass as a commercial comparison. Experimental compositions were shown to release Si(4+) ranging from 1 to 81 ppm over 30 days; comparable or enhanced release in comparison to Novabone. The maximum Ca(2+) release detected for experimental compositions was 9.1 ppm, below that reported to stimulate osteoblasts. Sr(2+) release was within known therapeutic ranges, and Zn(2+) release ranged from 0.5 to 1.4 ppm, below reported cytotoxic levels. All examined glass compositions show equivalent or enhanced in vitro compatibility in comparison to Novabone. Cells exposed to BT112 ionic products showed enhanced cell viabilities indicating cell proliferation was induced. The ion release profiles suggest this effect was due to a synergistic interaction between certain combinations and concentrations of ions. Overall, results indicate that the calcium-strontium-sodium-zinc-silicate glass compositions show equivalent or even enhanced in vitro compatibility compared to Novabone®.

  13. Impact of addition of magnetic nanoparticles on vortex pinning and microstructure properties of Bi-Sr-Ca-Cu-O superconductor

    NASA Astrophysics Data System (ADS)

    Albiss, B. A.; Obaidat, I. M.; Gharaibeh, M.; Ghamlouche, H.; Obeidat, S. M.

    2010-09-01

    The major limitations of polycrystalline Bi-based superconductor applications are the weak flux pinning and weak links in granular networks at relatively high temperature and applied magnetic fields. Effective flux pinning centers with various physical properties were artificially introduced into the superconducting matrix to enhance the flux pinning capability. Among these, introduction of nanoscale magnetic pinning sites into high Tc superconductors is still controversial. We have investigated the effects of nanosized NiO addition on the phase formation and flux pinning of the polycrystalline (PbSrCaCuO)1-x( with ( x=0.000, 0.001, 0.002, and 0.005) using XRD, SEM, AFM, and magnetization measurements. The results show that, with the increase of x, the volume fraction of the high critical temperature (Tc) phase (2223) decreases gradually accompanied with an increase in the low Tc phase (2212). However, almost no change in the Tc (onset) for all samples was observed. Measurements of the temperature dependence of the remanent magnetization, MR reveal a nonmonotonic behavior with the nano-NiO addition. A clear enhancement of the pinning strength was observed for the sample with x=0.002 at quite high temperature ( T=90 K). These results were discussed in terms of the interaction of the magnetic nanoparticles with the superconducting matrix especially at elevated temperatures close to Tc and above the depinning line. The relation between the current carrying mechanisms, phase contents, flux pinning and the microstructures of the samples were also discussed for a granular superconductor. It is believed that these magnetic nanoparticles may act as pinning sites in granular superconductors in applied magnetic field. Therefore, it is very important to carefully control all parameters involved in magnetic particles' addition in order to balance the critical current for optimum in-field performance.

  14. Investigating the influence of Na+ and Sr2+ on the structure and solubility of SiO2-TiO2-CaO-Na2O/SrO bioactive glass.

    PubMed

    Li, Y; Placek, L M; Coughlan, A; Laffir, F R; Pradhan, D; Mellott, N P; Wren, A W

    2015-02-01

    This study was conducted to determine the influence that network modifiers, sodium (Na+) and strontium (Sr2+), have on the solubility of a SiO2-TiO2-CaO-Na2O/SrO bioactive glass. Glass characterization determined each composition had a similar structure, i.e. bridging to non-bridging oxygen ratio determined by X-ray photoelectron spectroscopy. Magic angle spinning nuclear magnetic resonance (MAS-NMR) confirmed structural similarities as each glass presented spectral shifts between -84 and -85 ppm. Differential thermal analysis and hardness testing revealed higher glass transition temperatures (Tg 591-760 °C) and hardness values (2.4-6.1 GPa) for the Sr2+ containing glasses. Additionally the Sr2+ (~250 mg/L) containing glasses displayed much lower ion release rates than the Na+ (~1,200 mg/L) containing glass analogues. With the reduction in ion release there was an associated reduction in solution pH. Cytotoxicity and cell adhesion studies were conducted using MC3T3 Osteoblasts. Each glass did not significantly reduce cell numbers and osteoblasts were found to adhere to each glass surface.

  15. Investigating the influence of Na+ and Sr2+ on the structure and solubility of SiO2-TiO2-CaO-Na2O/SrO bioactive glass.

    PubMed

    Li, Y; Placek, L M; Coughlan, A; Laffir, F R; Pradhan, D; Mellott, N P; Wren, A W

    2015-02-01

    This study was conducted to determine the influence that network modifiers, sodium (Na+) and strontium (Sr2+), have on the solubility of a SiO2-TiO2-CaO-Na2O/SrO bioactive glass. Glass characterization determined each composition had a similar structure, i.e. bridging to non-bridging oxygen ratio determined by X-ray photoelectron spectroscopy. Magic angle spinning nuclear magnetic resonance (MAS-NMR) confirmed structural similarities as each glass presented spectral shifts between -84 and -85 ppm. Differential thermal analysis and hardness testing revealed higher glass transition temperatures (Tg 591-760 °C) and hardness values (2.4-6.1 GPa) for the Sr2+ containing glasses. Additionally the Sr2+ (~250 mg/L) containing glasses displayed much lower ion release rates than the Na+ (~1,200 mg/L) containing glass analogues. With the reduction in ion release there was an associated reduction in solution pH. Cytotoxicity and cell adhesion studies were conducted using MC3T3 Osteoblasts. Each glass did not significantly reduce cell numbers and osteoblasts were found to adhere to each glass surface. PMID:25644099

  16. Transformation of AeIn4 Indides (Ae = Ba, Sr) into an AeAu2In2 Structure Type Through Gold Substitution

    SciTech Connect

    Dai, Jing-Cao; Corbett, John D.

    2007-04-17

    The title compounds were prepared from the elements by high-temperature solid-state synthesis techniques. X-ray structural analyses shows that BaAu{sub 2}In{sub 2} (1) and SrAu{sub 2}In{sub 2} (2) crystallize in a new orthorhombic structure, Pnma, Z = 4 (a = 8.755(2), 8.530(2) {angstrom}; b = 4.712(1), 4.598(1) {angstrom}; c = 12.368(3), 12.283(4) {angstrom}, respectively). Gold substitutes for 50% of the indium atoms in the tetragonal BaIn{sub 4} and monoclinic SrIn{sub 4} parents to give this new and more flexible orthorhombic structure. The Ae atoms in this structure are contained within chains of hexagonal prisms built of alternating In and Au that have additional augmenting atoms around their waists from further condensation of parallel displaced chains. The driving forces for these structural changes are in part the shorter Au-In distances (2.72 and 2.69 {angstrom}) relative to d(In-In) in the parents, presumably because of relativistic contractions with Au. Generalities about such centered prismatic building blocks and their condensation modes in these and related phases are described. Band structure calculations (EHTB) demonstrate that the two compounds are metallic, which is confirmed by measurements of the resistivity of 1 and the magnetic susceptibilities of both.

  17. Chemistry of soluble β-diketiminatoalkaline-earth metal complexes with M-X bonds (M=Mg, Ca, Sr; X=OH, Halides, H).

    PubMed

    Sarish, Sankaranarayana Pillai; Nembenna, Sharanappa; Nagendran, Selvarajan; Roesky, Herbert W

    2011-03-15

    Victor Grignard's Nobel Prize-winning preparation of organomagnesium halides (Grignard reagents) marked the formal beginning of organometallic chemistry with alkaline earth metals. Further development of this invaluable synthetic route, RX+Mg→RMgX, with the heavier alkaline earth metals (Ca and Sr) was hampered by limitations in synthetic methodologies. Moreover, the lack of suitable ligands for stabilizing the reactive target molecules, particularly with the more electropositive Ca and Sr, was another obstacle. The absence in the literature, until just recently, of fundamental alkaline earth metal complexes with M-H, M-F, and M-OH (where M is the Group 2 metal Mg, Ca, or Sr) bonds amenable for organometallic reactions is remarkable. The progress in isolating various unstable compounds of p-block elements with β-diketiminate ligands was recently applied to Group 2 chemistry. The monoanionic β-diketiminate ligands are versatile tools for addressing synthetic challenges, as amply demonstrated with alkaline earth complexes: the synthesis and structural characterization of soluble β-diketiminatocalcium hydroxide, β-diketiminatostrontium hydroxide, and β-diketiminatocalcium fluoride are just a few examples of our contribution to this area of research. To advance the chemistry beyond synthesis, we have investigated the reactivity and potential for applications of these species, for example, through the demonstration of dip coating surfaces with CaCO(3) and CaF(2) with solutions of the calcium hydroxide and calcium fluoride complexes, respectively. In this Account, we summarize some recent developments in alkaline earth metal complex chemistry, particularly of Mg, Ca, and Sr, through the utilization of β-diketiminate ligands. We focus on results generated in our laboratory but give due mention to work from other groups as well. We also highlight the closely related chemistry of the Group 12 element Zn, as well as the important chemistry developed by other groups

  18. Investigation of Ca substitution on the gas sensing potential of LaFeO3 nanoparticles towards low concentration SO2 gas.

    PubMed

    Palimar, Sowmya; Kaushik, S D; Siruguri, V; Swain, Diptikanta; Viegas, Alison E; Narayana, Chandrabhas; Sundaram, Nalini G

    2016-09-14

    The present work investigates the superior ability of LaFeO3 (LaFeO) and La0.8Ca0.2FeO2.95 (LaCaFeO) nanoparticles to detect 3 ppm SO2 gas. The influence of calcium substitution on the sensing behaviour of LaFeO has been studied. High resolution TEM images show that the particle sizes of LaFeO and LaCaFeO are less than 100 nm and SEM images show the agglomeration of interconnected nanoparticles. Both LaFeO and LaCaFeO crystallize in the orthorhombic crystal system with the space group Pbnm. Rietveld analysis of neutron diffraction data showed that LaCaFeO has lattice oxygen vacancies. In addition, magnetic refinements on both the samples have been carried out. The presence of lattice oxygen vacancies in LaCaFeO is qualitatively supported by Raman and XPS measurements. Electrical characterization showed increased conductivity for the LaCaFeO sample, influencing their sensing performance significantly. The LaCaFeO nanoparticles exhibit higher sensitivity, faster response time, rapid recovery time and good recyclability for sensing 3 ppm SO2 gas. This enhanced sensing behaviour is attributed to the increased oxygen vacancies in the lattice as well as the surface. As a consequence, increased active sites are created in LaCaFeO, promoting redox reaction between the analyte and the sensing material. The results demonstrated that while LaFeO is a good gas sensor, p-type substitution by Ca(2+) renders this material an improved resistivity based gas sensor to detect low concentration SO2.

  19. Identification and quantification of phases formed during the processing of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}/Ag composite conductors

    SciTech Connect

    Merchant, N.N.; Fischer, A.K.; Maroni, V.A.; Carter, W.L.; Parrella, R.D.

    1996-08-01

    Scanning electron microscopy, energy dispersive x-ray analysis, (including x-ray dot mapping), x-ray diffraction and computer based image analysis have been used to study non-superconducting secondary phases that evolve during the processing of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}/Ag composite superconductors. These investigations have provided new information and insights about specific alkaline earth cuprates (AECs) and lead-rich phases. We can conclusively identify (Ca,Sr){sub 2}CuO{sub 3}, (Ca,Sr){sub 14}(Cu{sub 24})O{sub 41}, and CuO phases, the alkaline earth plumbates, and a (Bi,Pb)-Sr-Ca-Cu-O 3221 phase with a wide range of Pb/Bi ratios. These techniques also help in differentiating voids from secondary phases and alkaline earth plumbates from the lead-rich 3221 phase.

  20. Photoluminescence and cathodoluminescence properties of Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors

    SciTech Connect

    Du, Peng; Yu, Jae Su

    2015-10-15

    Highlights: • Under 393 nm excitation, strong red emission located at 615 nm was observed in all the samples. • The Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest PL properties. • The CIE chromaticity coordinate of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was (0.647,0.352). • The color purity of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was 92.8%. • Strong CL properties were observed in the Eu{sup 3+}-activated CaMoO{sub 4} phosphor. - Abstract: Eu{sup 3+}-activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors were synthesized by a solid-state reaction method. Photoluminescence and cathodoluminescence (CL) spectra as well as X-ray diffraction patterns were measured to characterize the fabricated samples. Under 393 nm excitation, strong red emissions located at ∼615 nm corresponding to the {sup 5}D{sub 0} → {sup 7}F{sub 2} transition of Eu{sup 3+} ions were observed in all the samples. Compared with other Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Sr, Ba) phosphors, Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest red emission intensity with better Commission Internationale de L’Eclairage chromaticity coordinate and higher color purity. Furthermore, the CL results indicated that the Eu{sup 3+}-activated CaMoO{sub 4} phosphor had excellent luminescence properties.

  1. Neutron diffraction study of the crystal structure and structural phase transition of La{sub 0.7}Ca{sub 0.3-x}Sr{sub x}CrO{sub 3} (0<=x<=0.3)

    SciTech Connect

    Omoto, Kazuki; Norberg, Stefan T.; Hull, Steve; Aoto, Akimitsu; Hashimoto, Takuya

    2010-02-15

    The crystal structure of the La{sub 0.7}Ca{sub 0.3-x}Sr{sub x}CrO{sub 3} series, including the compositional and temperature dependence of the structural parameters, has been studied by variable temperature neutron diffraction measurements. The extent of the distortions from the ideal cubic perovskite structure has been evaluated quantitatively using the average bond lengths and the mean volumes of the [CrO{sub 6}] octahedron and [(La/Ca/Sr)O{sub 12}] polyhedron, and has been shown to decrease with increase of Sr content or temperature. At the structural phase transition from the orthorhombic (Pnma) structure to the rhombohedral (R3-barc) one, the volume of the [CrO{sub 6}] octahedron decreases whereas that of the [(La/Ca/Sr)O{sub 12}] polyhedron shows little difference, resulting in an overall decrease in the level of distortion. The change in the degree of distortion at the phase transition decreases with increase of Sr content, in agreement with the smaller variation of the enthalpy and volume for the specimens with higher Sr content. - Graphical abstract: Temperature dependence of parameter, PHI, representing the extent of distortion from the ideal cubic perovskite structure, for La{sub 0.7}Ca{sub 0.3}CrO{sub 3} (diamonds) and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}CrO{sub 3} (circles) calculated from neutron diffraction patterns.

  2. Structural and electrical changes in NdSrNiO{sub 4-{delta}} by substitute nickel with copper

    SciTech Connect

    Chaker, Hanen; Roisnel, T.; Potel, M.; Hassen, R. Ben . E-mail: rached.benhassen@fss.rnu.tn

    2004-11-01

    A novel series of the formula NdSrNi{sub 1-x}Cu{sub x}O{sub 4-{delta}} were synthesized for various values of x ranging from 0 to 1 in 1atm of O{sub 2} gas flow using conventional solid-state methods and were characterized by powder X-ray diffraction and electrical resistivity measurements. The compounds have been shown to adopt the K{sub 2}NiF{sub 4}-type structure. The oxygen stoichiometry of the compounds was determined from thermo-gravimetric analysis (TGA). An analysis of the micro-structure of the neodymium strontium nickel copper oxide is described. All the samples were semi-conducting from room temperature down to 77K. The effect of Cu{sup 2+} incorporation on the structural and electrical properties of NdSrNi{sub 1-x}Cu{sub x}O{sub 4-{delta}}, 0=

  3. Comparative angle-resolved photoemission spectroscopy study of CaRuO3 and SrRuO3 thin films: Pronounced spectral weight transfer and possible precursor of lower Hubbard band

    NASA Astrophysics Data System (ADS)

    Yang, H. F.; Fan, C. C.; Liu, Z. T.; Yao, Q.; Li, M. Y.; Liu, J. S.; Jiang, M. H.; Shen, D. W.

    2016-09-01

    In the prototypical 4 d system (Sr ,Ca ) RuO3 , the degree and origin of electron correlations, and how they correlate with physical properties, still remain elusive, though extensive studies have been performed. In this work we present a comparative electronic structure study of high-quality epitaxial CaRuO3 and SrRuO3 thin films, by means of reactive molecular beam epitaxy and in situ angle-resolved photoemission spectroscopy. We found that while SrRuO3 possesses sharp features signaling the Fermi liquid state, the isostructural CaRuO3 exhibits broad features and its spectral weight is markedly transferred from the Fermi level to -1.2 eV forming a "hump" structure which resembles the Mott-Hubbard system (Sr ,Ca ) VO3 . We suggest that this hump is the precursor of the lower Hubbard band, and the U /W (U and W represent the on-site Coulomb interactions and bandwidth, respectively) of our CaRuO3 thin film is much larger than that of SrRuO3. In addition, we discuss the origin of electron correlations as well as the ferromagnetism in SrRuO3 which is absent in CaRuO3. Our findings put constraints on future studies, and also show that perovskite ruthenates are indeed an experimentally tunable system for the study of electron correlations.

  4. Eu(2+)-Activated Alkaline-Earth Halophosphates, M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) for NUV-LEDs: Site-Selective Crystal Field Effect.

    PubMed

    Kim, Donghyeon; Kim, Sung-Chul; Bae, Jong-Seong; Kim, Sungyun; Kim, Seung-Joo; Park, Jung-Chul

    2016-09-01

    Eu(2+)-activated M5(PO4)3X (M = Ca, Sr, Ba; X = F, Cl, Br) compounds providing different alkaline-earth metal and halide ions were successfully synthesized and characterized. The emission peak maxima of the M5(PO4)3Cl:Eu(2+) (M = Ca, Sr, Ba) compounds were blue-shifted from Ca to Ba (454 nm for Ca, 444 nm for Sr, and 434 nm for Ba), and those of the Sr5(PO4)3X:Eu(2+) (X = F, Cl, Br) compounds were red-shifted along the series of halides, F → Cl → Br (437 nm for F, 444 nm for Cl, and 448 nm for Br). The site selectivity and occupancy of the activator ions (Eu(2+)) in the M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) crystal lattices were estimated based on theoretical calculation of the 5d → 4f transition energies of Eu(2+) using LCAO. In combination with the photoluminescence measurements and theoretical calculation, it was elucidated that the Eu(2+) ions preferably enter the fully oxygen-coordinated sites in the M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) compounds. This trend can be well explained by "Pauling's rules". These compounds may provide a platform for modeling a new phosphor and application in the solid-state lighting field. PMID:27494550

  5. Effect of La-CO substitution on the crystal structure and magnetic properties of low temperature sintered Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites

    NASA Astrophysics Data System (ADS)

    Peng, Long; Li, Lezhong; Wang, Rui; Hu, Yun; Tu, Xiaoqiang; Zhong, Xiaoxi

    2015-11-01

    The La-Co substituted Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites with appropriate Bi2O3 additive were prepared at a low sintering temperature of 890 °C compatible with LTCC (low temperature co-fired ceramics) systems, and the effect of La-Co substitution on their crystal structure and magnetic properties was investigated. The results show that the pure M-type phase is successfully obtained when the La-Co substitution amount x does not exceed 0.3. However, the single M-type phase structure transforms to multiphase structure with further increased x, where the α-Fe2O3 phase and La2O3 phase coexist with the M-type phase. Moreover, the saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC of the ferrites depend on the La-Co substitution amount strongly, which are suggested to be determined by the partially substitution of La3+-Co2+ ions for Sr2+-Fe3+ ions with x not higher than 0.3. It is found that the obtained Sr1-xLaxFe12-xCoxO19 (x=0.2 and 0.3) ferrites can provide improved magnetic properties (Ms>62 emu/g, Ha>1400 kA/m, and Hci>320 kA/m) as low temperature sintered M-type hexaferrites for microwave LTCC applications.

  6. First-Principles Studies of Pressure-Induced Structural and Insulator-To Transitions in Alkaline-Earth Dicarbides MC2 (M = Ca, Sr and Ba)

    NASA Astrophysics Data System (ADS)

    Jiang, Li-Na

    2013-12-01

    Pressure-induced phase transitions in MC2 (M = Ca, Sr and Ba) are investigated by using the first-principles plane wave pseudopotential method within the generalized gradient approximation. The first-order phase transition from tetragonal phase (CaC2-type, space group I4/mmm) to rhombohedral (CsCl-type, space group R/line{3}m) structure is predicted to occur at 22.2, 10.0 and 3.6 GPa, respectively, and transition pressure point of BaC2 agrees well with recent theoretical works. Based on the electronic analysis, the ionic Ca-C bond character becomes stronger with increasing pressure in both I4/mmm and R/line{3}m phases. In particular, there will occur a transition from insulator to metal with increasing pressure due to the reason that the calculated band gap gets narrower and finally closes at some high pressure.

  7. Effect of La-substitution on the structure, dielectric and ferroelectric properties of Nb modified SrBi{sub 8}Ti{sub 7}O{sub 27} ceramics

    SciTech Connect

    Parida, Geetanjali Bera, J.

    2015-08-15

    Graphical abstract: The ferroelectric properties of Nb modified Bi{sub 4}Ti{sub 3}O{sub 12}–SrBi{sub 4}Ti{sub 4}O{sub 15} intergrowth ceramics increases significantly when Bi is substituted by La. - Highlights: • La{sup 3+} substitution for Bi{sup 3+} in Nb doped Bi{sub 4}Ti{sub 3}O{sub 12}–SrBi{sub 4}Ti{sub 4}O{sub 15} ferroelectrics is reported. • The orthorhombic distortion of the structure decreased with the increasing La. • La acts as a grain growth inhibitor in the ceramics. • The remnant polarization of the ferroelectrics increased significantly with La substitution. - Abstract: The effect of La substitution on the electrical properties of SrLa{sub x}Bi{sub 8−x}Ti{sub 6.88}Nb{sub 0}.{sub 12}O{sub 27} intergrowth Aurivillius phase ferroelectric ceramic was investigated. La content ‘x’ was ranging from 0.0 to 1.0 in a step of 0.2. The ceramic phase was synthesized through a modified oxalate route. X-ray diffraction was used to identify the phase and to investigate the change in lattice parameter and microstrain with the substitution. La-substitution does not affect the crystal structure of the intergrowth. Microstructural investigation revealed that the grain size of the ceramic decreases with La addition. The lattice parameters and orthorhombicity of intergrowth structure were found to decrease with increasing La substitution. The temperature dependence of dielectric behavior was investigated in the temperature range 30–700 °C and the frequency of 100 kHz. The remnant polarization 2P{sub r} increased and the Curie temperature T{sub c} decreased with the increase in the La substitution.

  8. Reduced Expression of the Extracellular Calcium-Sensing Receptor (CaSR) Is Associated with Activation of the Renin-Angiotensin System (RAS) to Promote Vascular Remodeling in the Pathogenesis of Essential Hypertension

    PubMed Central

    Wang, La-mei; Tang, Na; Zhong, Hua; Liu, Yong-min; Li, Zhen; Feng, Qian; He, Fang

    2016-01-01

    The proliferation of vascular smooth muscle cells (VSMCs), remodeling of the vasculature, and the renin-angiotensin system (RAS) play important roles in the development of essential hypertension (EH), which is defined as high blood pressure (BP) in which secondary causes, such as renovascular disease, are absent. The calcium-sensing receptor (CaSR) is involved in the regulation of BP. However, the underlying mechanisms by which the CaSR regulates BP are poorly understood. In the present study, the role of the CaSR in EH was investigated using male spontaneously hypertensive rats (SHRs) and rat and human plasma samples. The percentages of medial wall thickness to external diameter (WT%), total vessel wall cross-sectional area to the total area (WA%) of thoracic arteries, as well as the percentage of wall area occupied by collagen to total vessel wall area (CA%) were determined. Tissue protein expression and plasma concentrations of the CaSR, cyclic adenosine monophosphate (cAMP), renin, and angiotensin II (Ang II) were additionally assessed. WT%, WA%, and CA% were found to increase with increasing BP, whereas the plasma concentration of CaSR was found to decrease. With increasing BP, the levels of smooth muscle actin and calponin decreased, whereas those of osteopontin and proliferating cell nuclear antigen increased. The CaSR level negatively correlated with the levels of cAMP and Ang II, but positively correlated with those of renin. Our data suggest that reduced expression of the CaSR is correlated with activation of the RAS, which induces increased vascular remodeling and VSMC proliferation, and thereby associated with EH in the SHR model and in the Han Chinese population. Our findings provide new insights into the pathogenesis of EH. PMID:27391973

  9. New-Structure-Type Fe-Based Superconductors: CaAFe4As4 (A = K, Rb, Cs) and SrAFe4As4 (A = Rb, Cs).

    PubMed

    Iyo, Akira; Kawashima, Kenji; Kinjo, Tatsuya; Nishio, Taichiro; Ishida, Shigeyuki; Fujihisa, Hiroshi; Gotoh, Yoshito; Kihou, Kunihiro; Eisaki, Hiroshi; Yoshida, Yoshiyuki

    2016-03-16

    Fe-based superconductors have attracted research interest because of their rich structural variety, which is due to their layered crystal structures. Here we report the new-structure-type Fe-based superconductors CaAFe4As4 (A = K, Rb, Cs) and SrAFe4As4 (A = Rb, Cs), which can be regarded as hybrid phases between AeFe2As2 (Ae = Ca, Sr) and AFe2As2. Unlike solid solutions such as (Ba(1-x)K(x))Fe2As2 and (Sr(1-x)Na(x))Fe2As2, Ae and A do not occupy crystallographically equivalent sites because of the large differences between their ionic radii. Rather, the Ae and A layers are inserted alternately between the Fe2As2 layers in the c-axis direction in AeAFe4As4 (AeA1144). The ordering of the Ae and A layers causes a change in the space group from I4/mmm to P4/mmm, which is clearly apparent in powder X-ray diffraction patterns. AeA1144 is the first known structure of this type among not only Fe-based superconductors but also other materials. AeA1144 is formed as a line compound, and therefore, each AeA1144 has its own superconducting transition temperature of approximately 31-36 K. PMID:26943024

  10. Controlled peak wavelength shift of Ca{sub 1-} {sub x} Sr {sub x} (S {sub y} Se{sub 1-} {sub y} ):Eu{sup 2+} phosphor for LED application

    SciTech Connect

    Nazarov, Mihail . E-mail: nazarov.mihail@samsung.com; Yoon, Chulsoo

    2006-08-15

    The highly efficient red-orange-yellow-emitting phosphor (Ca{sub 1-} {sub x} Sr {sub x} )(S{sub 1-} {sub y} Se {sub y} ):Eu{sup 2+} in combination with commercial green phosphor SrGa{sub 2}S{sub 4}:Eu{sup 2+} and blue LED are proposed for a three-band white LED. The luminescence mechanism and optimization parameters are discussed on the basis of proposed peak wavelength diagram. - Graphical abstract: 'Peak wavelength diagram for (Ca{sub 1-} {sub x} Sr {sub x} )(S{sub 1-} {sub y} Se {sub y} ):Eu{sup 2+}'.

  11. Probing the phase diagram of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+delta} with tunneling spectroscopy.

    SciTech Connect

    Ozyuzer, L.; Zasadzinski, J. F.; Gray, K. E.; Hinks, D. G.; Miyakawa, N.

    2002-08-29

    Tunneling measurements are performed on Ca-rich single crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212), with various oxygen doping levels, using a novel point contact method. At 4.2 K, SIN and SIS tunnel junctions are obtained with well-defined quasi-particle peaks, robust dip and hump features and in some cases Josephson currents. The doping dependence of tunneling conductances of Ca-rich Bi2212 are analyzed and compared to stoichiometric Bi2212. A similar profile of energy gap vs. doping concentration is found although the Ca-rich samples have a slightly smaller optimum T{sub c} and therefore smaller gap values for any doping level. The evolution of tunneling conductance peak height to background ratios with hole concentration are compared. For a given doping level, the Ca-rich spectra showed more broadened features compared to the stoichiometric counterparts, most likely due to increased disorder from the excess Ca. Comparison of the dip and hump features has provided some potential insights into their origins.

  12. Electronic structure and x-ray magnetic circular dichroism in A2FeReO6 (A =Ca ,Sr ,andBa ) oxides

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Bekenov, L. V.; Ernst, A.

    2016-07-01

    A systematic electronic structure study of A2FeReO6 (A =Ba ,Sr ,andCa ) has been performed by employing the local-spin-density approximation (LSDA) and LSDA +U methods using the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We investigated the effects of the subtle interplay between spin-orbit coupling, electron correlations, and lattice distortion on the electronic structure of double perovskites. Ca2FeReO6 has a large distortion in the Fe-O-Re bond, and the electronic structure is mainly determined by electron correlations and lattice distortion. In the Ba -Sr -Ca row, the correlation effects at the Fe site are increased. The correlations at the Re site are small in the Ba- and Sr-based compounds but significant in Ca2FeReO6 . Ca2FeReO6 behaves like an insulator only if considered with a relatively large value of Coulomb repulsion Ueff=2.3 eV at the Re site in addition to Ueff=3.1 eV at the Fe site. Ca2FeReO6 possesses a phase transition at 140 K where the metal-insulator transition (MIT) occurs between metallic high-temperat