Science.gov

Sample records for ca sr substitution

  1. 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.

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

    PubMed Central

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

    2015-01-01

    Proton matrix ENDOR spectra were measured for Ca2+-depleted and Sr2+-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 Ca2+-containing and Sr2+-substituted PSII, indicating that the proton arrangements around the manganese cluster in cyanobacterial and higher plant PSII and Ca2+-containing and Sr2+-substituted PSII are similar in the S2 state, in agreement with the similarity of the crystal structure of both Ca2+-containing and Sr2+-substituted PSII in the S1 state. Nevertheless, slightly different hyperfine separations were found between Ca2+-containing and Sr2+-substituted PSII because of modifications of the water protons ligating to the Sr2+ ion. Importantly, Ca2+ depletion caused the loss of ENDOR signals with a 1.36-MHz separation because of the loss of the water proton W4 connecting Ca2+ and YZ directly. With respect to the crystal structure and the functions of Ca2+ in oxygen evolution, it was concluded that the roles of Ca2+ and Sr2+ involve the maintenance of the hydrogen bond network near the Ca2+ site and electron transfer pathway to the manganese cluster. PMID:26438823

  3. Magnetic and microstructural properties of Al substituted M-type Ca-Sr hexaferrites

    NASA Astrophysics Data System (ADS)

    Yang, Yujie; Wang, Fanhou; Liu, Xiansong; Shao, Juxiang; Huang, Duohui

    2017-01-01

    In the current study, Al substituted M-type Ca-Sr hexaferrites, with composition Ca0.6Sr0.1La0.3Fe12-xAlxO19 (0≤x≤1.4), have been prepared using the conventional ceramic techniques. The phase composition of the magnetic powders was characterized by X-ray diffraction (XRD). The XRD data show that the magnetic powders with Al content (x) from 0 to 0.8 show α-Fe2O3 as a second phase, while the magnetic powders with x from 1.0 to 1.4 consist of pure magnetoplumbite without any other impurity phases. A field emission scanning electron microscopy (FE-SEM) was used to observe the morphologies of the magnetic powders. FE-SEM images of the magnetic powders show the hexagonal platelet-like shape. The magnetic properties of the magnetic powders were measured by a physical property measurement system-vibrating sample magnetometer (PPMS-VSM). The saturation magnetization (Ms) linearly decreases with Al content (x) from 0 to 1.4. While the remanent magnetization (Mr) first increases with Al content (x) from 0 to 0.2 and then decreases when Al content (x)≥0.2. However, the coercivity (Hc) increases with Al content (x) from 0 to 1.4.

  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.

  5. Magnetic comparison of BaCa and BaSr substituted hexaferrite powders

    NASA Astrophysics Data System (ADS)

    González-Angeles, A.; Lipka, J.; Grusková, A.; Sláma, J.; Jančárik, V.; Slugeň, V.

    2010-03-01

    Results on magnetic studies of Ba0.5Sr0.5Fe12-2x(ZnTi)xO19 and Ba0.75Ca0.25Fe12-2x(ZnTi)xO19, where x = 0.2 to 0.6, ferromagnetic powders prepared by mechanical alloying are discussed. The structural and magnetic properties of the resulting powders were analyzed by thermo-magnetic analysis, X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy and magnetic measurements. Curie temperature, Tc decreased dramatically (drop ~ 39%) for BaCa samples, whilst for BaSr samples remained almost without change (diminution ~ 2%) at x <= 0.2. SEM studies showed that all the particles present nearly hexagonal platelet shape.

  6. Combined effects of Sr substitution and pressure on the ground states in CaFe2As2

    NASA Astrophysics Data System (ADS)

    Knöner, S.; Gati, E.; Köhler, S.; Wolf, B.; Tutsch, U.; Ran, S.; Torikachvili, M. S.; Bud'ko, S. L.; Canfield, P. C.; Lang, M.

    2016-10-01

    We present a detailed study of the combined effects of Sr substitution and hydrostatic pressure on the ground-state properties of CaFe2As2 . Measurements of the electrical resistance and magnetic susceptibility, both at ambient and finite pressure P ≤2 GPa, were performed on Ca1 -xSrxFe2As2 single crystals grown out of Sn flux. We find that by Sr substitution the transition temperature to the magnetic/structural phase is enhanced and therefore a higher pressure is needed to suppress the transition to lowest temperature. In addition, the transition to the collapsed tetragonal phase is found at a pressure, which is distinctly higher than in the pure compound. This implies that the stability ranges of both phases shift on the pressure-axis upon doping, but the latter one with a higher rate. These observations suggest the possibility of separating the two phase lines, which intersect already at elevated temperatures for x =0 and low Sr concentration levels. For x =0.177 , we find strong evidence that both phases remain separated down to the lowest temperature and that a zero-resistance state emerges in this intermediate pressure window. This observation indicates that Sr substitution combined with hydrostatic pressure provides another route for stabilizing superconductivity in CaFe2As2 . Our results are consistent with the notion that (i) preserving the fluctuations associated with the structural-magnetic transition to low temperatures is vital for superconductivity to form in this material and that (ii) the nonmagnetic collapsed tetragonal phase is detrimental for superconductivity.

  7. Combined effects of Sr substitution and pressure on the ground states in CaFe2As2

    DOE PAGES

    Knoner, S.; Gati, E.; Kohler, S.; ...

    2016-10-21

    Here, we present a detailed study of the combined effects of Sr substitution and hydrostatic pressure on the ground-state properties of CaFe2As2. Measurements of the electrical resistance and magnetic susceptibility, both at ambient and finite pressure P ≤ 2 GPa, were performed on Ca1–xSrxFe2As2 single crystals grown out of Sn flux. We find that by Sr substitution the transition temperature to the magnetic/structural phase is enhanced and therefore a higher pressure is needed to suppress the transition to lowest temperature. In addition, the transition to the collapsed tetragonal phase is found at a pressure, which is distinctly higher than inmore » the pure compound. This implies that the stability ranges of both phases shift on the pressure-axis upon doping, but the latter one with a higher rate. These observations suggest the possibility of separating the two phase lines, which intersect already at elevated temperatures for x = 0 and low Sr concentration levels. For x = 0.177, we find strong evidence that both phases remain separated down to the lowest temperature and that a zero-resistance state emerges in this intermediate pressure window. This observation indicates that Sr substitution combined with hydrostatic pressure provides another route for stabilizing superconductivity in CaFe2As2. Lastly, our results are consistent with the notion that (i) preserving the fluctuations associated with the structural-magnetic transition to low temperatures is vital for superconductivity to form in this material and that (ii) the nonmagnetic collapsed tetragonal phase is detrimental for superconductivity.« less

  8. Computational insights on crystal structures of the oxygen-evolving complex of photosystem II with either Ca(2+) or Ca(2+) substituted by Sr(2+).

    PubMed

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

    2015-01-27

    The oxygen-evolving complex of photosystem II can function with either Ca(2+) or Sr(2+) as the heterocation, but the reason for different 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 the X-ray crystal structures with either Ca(2+) or Sr(2+) are most consistent with the S-2 state (i.e., Mn4[III,III,III,II] with O4 and O5 protonated). As expected, the QM/MM models show that Ca(2+)/Sr(2+) substitution results in the elongation of the heterocation bonds and the displacement of terminal waters W3 and W4. The optimized structures also show that hydrogen-bonded W5 is displaced in all S states with Sr(2+) as the heterocation, suggesting that this water may play a critical role during water oxidation.

  9. 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.

  10. 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.

  11. 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.

  12. Band-gap tuning and magnetic properties of heterovalent ions (Ba, Sr and Ca) substituted BiFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Chauhan, Sunil; Kumar, Manoj; Katyal, S. C.

    2016-05-01

    A Comparative study of heterovalent Ba, Sr and Ca ions substitution on the structural, vibrational, optical and magnetic properties of BiFeO3 nanoparticles was carried out. The distorted rhombohedral structure was confirmed from both X-ray diffraction and Raman spectroscopy techniques in pure BiFeO3 and Bi0.85A0.15FeO3 (A= Ba, Sr and Ca) samples. UV-Visible spectroscopy results show that the band-gap of BiFeO3 nanoparticles can be tuned by heterovalent ions substitution from 2.12 eV for BiFeO3 to 2.10, 2.06 and 2.03 eV for Ca, Sr and Ba substituted BiFeO3 nanoparticles respectively. The magnetic measurements indicate enhancement in magnetization for heterovalent A2+ substituted BiFeO3 samples and the magnetization increases with increase of ionic radius of the substituted ions.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Jaiganesh, G.; Jaya, S. Mathi

    2015-06-01

    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.

  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. Influences of alkaline earth metal substitution on the crystal structure and physical properties of magnetic RuSr1.9A0.1GdCu2O8 (A = Ca, Sr, and Ba) superconductors.

    PubMed

    Hur, Su Gil; Park, Dae Hoon; Hwang, Seong-Ju; Kim, Seung Joo; Lee, J H; Lee, Sang Young

    2005-11-24

    We have investigated the effect of alkaline earth metal substitution on the crystal structure and physical properties of magnetic superconductors RuSr(1.9)A(0.1)GdCu(2)O(8) (A = Ca, Sr, and Ba) in order to probe an interaction between the magnetic coupling of the RuO(2) layer and the superconductivity of the CuO(2) layer. X-ray diffraction and X-ray absorption spectroscopic analyses demonstrate that the isovalent substitution of Sr ions with Ca or Ba ions makes it possible to tune the interlayer distance between the CuO(2) and the RuO(2) layers. From the measurements of electrical resistance and magnetic susceptibility, it was found that, in contrast to negligible change of magnetization, both of the alkaline earth metal substitutions lead to a notable depression of zero-resistance temperature T(c) (DeltaT(c) approximately 17-19 K). On the basis of the absence of a systematic correlation between the T(c) and the interlayer distance/magnetization, we have concluded that the internal magnetic field of the RuO(2) layer has insignificant influence on the superconducting property of the CuO(2) layer in the ruthenocuprate.

  17. 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.

  18. Combined effects of Sr substitution and pressure on the ground states in CaFe2As2

    SciTech Connect

    Knoner, S.; Gati, E.; Kohler, S.; Wolf, B.; Tutsch, U.; Ran, S.; Torikachvili, M. S.; Bud'ko, S. L.; Canfield, P. C.; Lang, M.

    2016-10-21

    Here, we present a detailed study of the combined effects of Sr substitution and hydrostatic pressure on the ground-state properties of CaFe2As2. Measurements of the electrical resistance and magnetic susceptibility, both at ambient and finite pressure P ≤ 2 GPa, were performed on Ca1–xSrxFe2As2 single crystals grown out of Sn flux. We find that by Sr substitution the transition temperature to the magnetic/structural phase is enhanced and therefore a higher pressure is needed to suppress the transition to lowest temperature. In addition, the transition to the collapsed tetragonal phase is found at a pressure, which is distinctly higher than in the pure compound. This implies that the stability ranges of both phases shift on the pressure-axis upon doping, but the latter one with a higher rate. These observations suggest the possibility of separating the two phase lines, which intersect already at elevated temperatures for x = 0 and low Sr concentration levels. For x = 0.177, we find strong evidence that both phases remain separated down to the lowest temperature and that a zero-resistance state emerges in this intermediate pressure window. This observation indicates that Sr substitution combined with hydrostatic pressure provides another route for stabilizing superconductivity in CaFe2As2. Lastly, our results are consistent with the notion that (i) preserving the fluctuations associated with the structural-magnetic transition to low temperatures is vital for superconductivity to form in this material and that (ii) the nonmagnetic collapsed tetragonal phase is detrimental for superconductivity.

  19. Angular properties of pure and Ca-substituted YBa2Cu3O7-δ superconducting thin films grown on SrTiO3 and CeO2 buffered Al2O3 substrates

    NASA Astrophysics Data System (ADS)

    Augieri, A.; Celentano, G.; Ciontea, L.; Galluzzi, V.; Gambardella, U.; Halbritter, J.; Petrisor, T.; Rufoloni, A.; Vannozzi, A.

    2007-09-01

    In this work transport properties of superconducting 10 at.% Ca-substituted YBCO thin films grown on (1 0 0)-SrTiO 3 single crystal substrate (STO) and superconducting pure and 10 at.% Ca-substituted YBCO thin films grown on CeO 2 buffered Al 2O 3 substrates (CAO) have been analyzed as a function of the temperature, applied magnetic field and angle between magnetic field direction and the direction normal to the film surfaces. Particularly, the angular analysis provides an easy way to discriminate between isotropic point defects and correlated pinning sites. Despite the intragrain pinning mechanisms remained unaffected by Ca substitution, a detrimental effect on grain boundary properties clearly emerged for 10 at.% Ca concentration. This effect is enhanced in sample grown on CeO 2 buffered sapphire where a more disturbed grain boundary is expected resulting in an enhancement of the correlated pinning, already observed in pure YBCO films grown on CAO, and in a reduction of the intrinsic pinning efficiency.

  20. Synthesis of BiSrCa(Y)CuO superconductor from the sol-gel method and the effect of Y substitution

    SciTech Connect

    Menassel, S.; Mosbah, M-F.; Altintas, S. P.; Varilci, A.; Bouaicha, F.

    2012-09-06

    Superconducting Bi{sub 2}Sr{sub 2}Ca{sub 1-x}Y{sub x}Cu{sub 2}O{sub 8} ceramics samples have been prepared by Sol-Gel methods using citrate process. The influences of the conditions of preparation of oxide powder compound on structural and superconducting properties have been investigated by X ray diffraction (XRD), Scanning Electron Microscopy (SEM) equipped with EDS. The critical transition temperatures Tc have been determined by resistivity versus temperature measurements. Cell parameters samples were calculated from XRD patterns. The polyacryl amide gel makes the citrate process easier, more rapid and affords the possibility of synthesis of high quality oxide powders.

  1. 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.

  2. Effect of Hf substitutions on the formation and superconductivity of Tl-1212 type phase TlSr{sub 2}(Ca{sub 1−x}Hf{sub x})Cu{sub 2}O{sub 7−δ}

    SciTech Connect

    Al-Sharabi, Annas; Abd-Shukor, R.

    2013-11-27

    The TlSr{sub 2}(Ca{sub 1−x}Hf{sub x})Cu{sub 2}O{sub 7−δ} (Tl-1212) superconductor for x = 0.0 to 0.4 has been prepared by the solid state reaction method and studied by powder X-ray diffraction method, electrical resistance and scanning electron microscope (SEM). Most of the samples showed the Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Hf-substitution (x ≤ 0.15 or x ≤ 0.25) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature (T{sub c} {sub onset}) between 38 and 47 K for Hf substitution.

  3. 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; ...

    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

  4. Paraconductivity measurements and comparative studies of fluctuations in BiSrCaCuO, YBaCuO and YBaCuO with Gd substitution

    SciTech Connect

    Patapis, S.K.; Sideridis, L.; Apostolopoulos, G.; Ausloos, M.; Luo, H.L.; Politis, C.; Puig, T.; Pont, M.; Munoz, J.S.; Balachadran, U.

    1991-12-31

    Information concerning the dimensionality of the superconductive fluctuations in the new high temperature superconductors can be derived from the excess conductivity (or paraconductivity) near the transition temperature. Here the `lowering`` of the sample resistance in the same temperature regions is used for extraction of dimensionality and generally for comparative studies of the critical behaviour of three different samples such as YBa{sub 2}Cu{sub 3}O{sub 7}, Y{sub 0.8}Gd{sub 0.2}Ba{sub 2}Cu{sub 3}O{sub 7} and Bi{sub 0. 85}Pb{sub 0.15}SrCa{sub 1.2}Cu{sub 2}O{sub 6}. The experimental data of the three samples show a similar behaviour with some distinct differences depending rather on the ``metallurgical`` state of the material than the composition itself. A logarithmic behaviour is present for YBaCuO and Y(Gd)BaCuO samples not close to the critical temperature and, the most important, closer to {Tc} YBaCuO shows a fractal behaviour, observed for the first time, similar to the one of Bi-compound observed many times before.

  5. Paraconductivity measurements and comparative studies of fluctuations in BiSrCaCuO, YBaCuO and YBaCuO with Gd substitution

    SciTech Connect

    Patapis, S.K.; Sideridis, L.; Apostolopoulos, G. . Dept. of Physics); Ausloos, M. . Inst. de Physique); Luo, H.L. . Dept. of Electrical and Computer Engineering); Politis, C. . Inst. fuer Nukleare Festkoerperphysik); Puig, T.; Pont, M.; Munoz, J.S. (Univ

    1991-01-01

    Information concerning the dimensionality of the superconductive fluctuations in the new high temperature superconductors can be derived from the excess conductivity (or paraconductivity) near the transition temperature. Here the lowering'' of the sample resistance in the same temperature regions is used for extraction of dimensionality and generally for comparative studies of the critical behaviour of three different samples such as YBa{sub 2}Cu{sub 3}O{sub 7}, Y{sub 0.8}Gd{sub 0.2}Ba{sub 2}Cu{sub 3}O{sub 7} and Bi{sub 0. 85}Pb{sub 0.15}SrCa{sub 1.2}Cu{sub 2}O{sub 6}. The experimental data of the three samples show a similar behaviour with some distinct differences depending rather on the metallurgical'' state of the material than the composition itself. A logarithmic behaviour is present for YBaCuO and Y(Gd)BaCuO samples not close to the critical temperature and, the most important, closer to {Tc} YBaCuO shows a fractal behaviour, observed for the first time, similar to the one of Bi-compound observed many times before.

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

    DOE PAGES

    Naamneh, M.; Lubashevsky, Y.; Lahoud, E.; ...

    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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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

  13. Are seawater Sr/Ca variations preserved in Quaternary foraminifera?

    SciTech Connect

    Stoll, H.M.; Schrag, D.P.; Clemens, S.C.

    1999-11-01

    High precision measurements of Sr/Ca in planktonic foraminifera for the last 150 ka reveal Sr/Ca variations of up to 12% on glacial/interglacial time scales. Although records showing the largest variations appear to be strongly influenced by selective dissolution, other records show Sr/Ca variations of 3--5% that do not covary with indicators of dissolution intensity and that are reproduced in sites of contrasting Quaternary dissolution histories. These systematic variations are characterized by high Sr/Ca ratios during glacial maxima, followed by steep decreases during deglaciation and gradual increases through interstadial periods, closely following {delta}{sup 18}O curves. Foraminiferal Sr/Ca variations may reflect changes in the Sr/Ca ratio of seawater, or they may be due to kinetically or biologically induced changes in Sr partitioning. Coupled numerical models of the Sr and Ca budgets of the ocean reveal that sea level changes, together with large changes in river fluxes and carbonate accumulation rates, can produce seawater Sr/Ca variations that approximate both the shape and amplitude of foraminiferal Sr/Ca variations. However, such extreme changes in river and carbonate fluxes conflict with existing data on carbonate accumulation rates and Sr isotopic constraints on the magnitude of variations in the river flux. Smaller variations (1--3%) in the Sr/Ca ratio of seawater likely characterize Quaternary glacial cycles. Changes in Sr partitioning due to glacial-interglacial changes in the carbonate ion concentration and other environmental factors likely produce additional variation in the Sr/Ca record of planktonic foraminifera.

  14. 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.

  15. Newly developed Sr-substituted alpha-TCP bone cements.

    PubMed

    Pina, S; Torres, P M; Goetz-Neunhoeffer, F; Neubauer, J; Ferreira, J M F

    2010-03-01

    New bone cements made of Sr-substituted brushite-forming alpha-tricalcium phosphate (alpha-TCP) were prepared and characterized in the present work. The quantitative phase analysis and structural refinement of the starting powders and of hardened cements were performed by X-ray powder diffraction and the Rietveld refinement technique. Isothermal calorimetry along with setting time analysis allowed a precise tracing of the setting process of the pastes. The pastes showed exothermic reactions within the first 10-15 min after mixing and further release of heat after about 1h. An apatitic phase formed upon immersion of the hardened cements in simulated body fluid for 15 and 30 days due to the conversion of brushite into apatite confirming their in vitro mineralization capability. The compressive strength of the wet cement specimens decreased with increasing curing time, being higher in the case of Sr-substituted CPC. The results suggest that the newly developed Sr-substituted brushite-forming alpha-TCP cements show promise for uses in orthopaedic and trauma surgery such as in filling bone defects.

  16. 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.

  17. 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+).

  18. Heteronuclear Mn-Ca/Sr Complexes, and Ca/Sr EXAFS SpectralComparisons with the Oxygen-Evolving Complex of Photosystem II

    SciTech Connect

    Mishra, A.; Yano, J.; Pushkar, Y.; Yachandra, V.K.; Abboud, K.A.; Christou, G.

    2007-12-19

    HeterometallicMn Ca and Mn Sr complexes have been preparedand employed as model complexes for Ca and Sr EXAFS spectral comparisonswith the Oxygen-Evolving Complex (OEC) of Photosystem II (PS II); thesehave revealed similarities that support the presence of at least one Oatom bridge between the Mn and Ca/Sr in the OEC.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. The luminescent characterization of (Sr, Ca)2SiO4:Eu2+ nanopowders synthesized by a co-precipitation method.

    PubMed

    Lee, Jun Seong; Kim, Young Jin

    2013-05-01

    (Sr, Ca)2SiO4:Eu2+ nanopowders were prepared by a co-precipitation method, and then the effects of Ca2+ ions on the structural and luminescent properties were investigated. The pure Sr2SiO4:Eu2+ powders were perfectly composed of the beta-phase, whereas the substitution of Ca2+ ions led to the beta --> alpha' phase transition. The photoluminescence spectra of Sr2SiO4:Eu2+ exhibited two excitation bands at around 330 and 375 nm assigned to Eu(I) and (II) sites, respectively, resulting in two emission bands at around 473 and 543 nm. Meanwhile, the dominant peak wavelengths of the emission spectra of (Sr, Ca)2SiO4:Eu2+ could be tuned, depending on the cation ratio of Ca2+ to Sr2+. The substitution of Ca2+ ions for Sr2+ ions caused the red-shift of the emission peaks of Sr(2-x)Ca(x)SiO4:Eu2+ powders with increasing Ca2+ content (x = 0-1.0) due to the increase in the crystal field strength.

  7. 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.

  8. Sr/Ca and Ba/Ca variations in environmental and biological sources: A survey of marine and terrestrial systems

    NASA Astrophysics Data System (ADS)

    Peek, Stephanie; Clementz, Mark T.

    2012-10-01

    The relative concentrations of strontium to calcium (Sr/Ca) and barium to calcium (Ba/Ca) in mammalian bioapatite are common biogeochemical indicators for trophic level and/or dietary preferences in terrestrial foodwebs; however, similar research in marine foodwebs is lacking. This study combined environmental and biological Sr/Ca and Ba/Ca data from both terrestrial and marine settings from 62 published books, reports, and studies along with original data collected from 149 marine mammals (30 species) and 83 prey items (18 species) and found that variations in Sr/Ca and Ba/Ca ratios of biological and environmental samples are appreciably different in terrestrial and marine systems. In terrestrial systems, environmental sources account for most of the variations in Sr/Ca and Ba/Ca ratios. In contrast, environmental sources in marine systems (i.e., seawater) are comparatively invariant, meaning most of the variations in Sr/Ca and Ba/Ca ratios originate from biological processes. Marine consumers, particularly non-mammalian and mammalian vertebrates, show evidence of biopurification of Ca relative to Sr and Ba, similar to what is observed in terrestrial systems; however, unlike terrestrial systems, variations in Sr/Ca and Ba/Ca ratios of environmental sources are overprinted by bioaccumulation of Sr and Ba at the base of marine foodwebs. This demonstrates that in marine systems, spatial or temporal differences may have little to no effect on Sr/Ca and Ba/Ca ratios of marine vertebrates, making Sr/Ca, and to a lesser extent Ba/Ca, potentially useful global proxies for trophic level and dietary preferences of marine vertebrates.

  9. 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.

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

    PubMed

    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.

  11. 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.

  12. Determination of the Bond Lengths in MgCCH, CaCCH and SrCCH

    NASA Astrophysics Data System (ADS)

    Forthomme, D.; Tokaryk, D. W.; Linton, C.; Adam, A. G.

    2011-06-01

    %High resolution spectra have been analyzed for the tilde{A}2E-tilde{X}2A_1 transition of M-12C12CH, M-12C12CD and M-13C13CH, where M refers to Mg, Ca and Sr. All the molecules except CaCCH have been recorded and analyzed in our laboratory in a laser ablation molecular jet source. The rotational constants extracted from the fits allowed us to calculate accurate bond lengths in MgCCH, CaCCH and SrCCH. This study is of particular interest since it shows how the structure of the molecules evolves as we substitute the alkaline earth atom by another one from the same family. The results showed clear trends in how the molecules account for changes in the mass of the metal atom and how the bond lengths in the ligand CCH are significantly different from the bond lengths in HCCH. Surprisingly, the triple bond between the two carbon atoms happens to be the one that experiences the greatest change. To determine the three bond lengths in a linear four atom molecule, one requires spectral data from three isotopologues of that molecule. By combining information from previously published analyses with new high resolution isotopically substituted spectra, we have determined the bond lengths for MgCCH, CaCCH and SrCCH. In each case, the tilde{A}2Π-tilde{X}2Σ^+ spectra of the M-12C12CH, M-12C12CD and M-13C13CH isotopologues were considered, where M refers to Mg, Ca and Sr. This study is of particular interest since it shows how the structure of this family of molecules evolves as we change the alkaline earth atom attached to the CCH ligand. In MgCCH, the structure of the CCH ligand is nearly the same as it is in acetylene, HCCH. Surprisingly, the bonding in the ligand is quite different from that of acetylene for the two heavier acetylide molecules, with the triple bond between the two carbon atoms experiencing the greatest change. M. Li and J. A. Coxon, J. Mol. Spectrosc. 176 (1996) 206-210 M. J. Dick, P. M. Sheridan, J. -G. Wang and P. F. Bernath, J. Mol. Spectrosc. 233 (2005

  13. Variations in seawater Sr/Ca recorded in deep-sea bamboo corals

    NASA Astrophysics Data System (ADS)

    Hill, T. M.; Lavigne, M.; Spero, H. J.; Guilderson, T.; Gaylord, B.; Clague, D.

    2012-09-01

    A depth transect of deep-sea bamboo corals along the California margin provides evidence that coral strontium to calcium ratios (Sr/Cacoral) record seawater Sr/Ca ratios (Sr/Casw). A calibration was constructed utilizing Sr/Cacoral ratios and previously published Pacific Sr/Casw data (R2 = 0.53, n = 12, p < 0.01): Sr/Cacoral (mmol/mol) = 4.62*Sr/Casw (mmol/mol) - 36.64. Sr/Casw is ultimately governed by the remineralization of Sr-containing shells of surface water-derived marine organisms (e.g., Acantharia) at intermediate water depths. California margin Sr/Cacoral records from 792 and 1295 m document fluctuations in Sr/Casw that appear decadal-scale. These results suggest that Sr/Casw may not be as stable as previously assumed and may be influenced by surface productivity on short timescales.

  14. A study of the pseudogap state in Bi2Sr2CaCu2Ox and Bi2Sr2ZnCu2Oy HTSC materials

    NASA Astrophysics Data System (ADS)

    Aliev, V. M.; Mamedova, A. N.; Raqimov, S. S.; Selim-zade, R. I.; Tairov, B. A.

    2016-10-01

    We examine the effect of replacing calcium by zinc has on the transport properties of the BiSrCaCuO-2221 system. It is shown that the critical temperatures Tc of the Bi2Sr2CaCu2Ox(B1) and Bi2Sr2ZnCu2Oy(B2) samples are close (81 K and 80.72 K). However, the resistivity ρ of the Bi2Sr2ZnCu2Oy sample increases considerably, and the ratio ρB2/ρB1 ≈ 10 at 100 K. We use the local pair model to analyze the mechanism behind the formation of excess conductivity in Bi2Sr2CaCu2Ox and Bi2Sr2ZnCu2Oy(B2), with consideration of the Aslamazov-Larkin theory near Tc. We determined the temperature T0 of the transition from the 2D fluctuation area to the 3D region (i.e., the 2D-3D crossover temperature). We calculated the coherence length of the fluctuation Cooper pairs along the c axis, ξc(0). It is shown that substituting Zn for Ca reduces ξc(0) by almost 1.5 times (4.8 Å and 3.3 Å, respectively), and also leads to a narrowing of both the pseudogap region and the superconducting fluctuation area near Tc. We determined the temperature dependence of the pseudogap Δ * T and Δ * (Tc). The increase of ρ, its specific temperature dependence and the significant decrease of T * in sample B2, all point to the destruction of local pairs at all high temperatures, i.e., to the suppression of the pseudogap by Zn doping.

  15. A Study on the Effect of Ni Dopping on Bi-Pb-Sr-Ca-Cu-O System

    NASA Astrophysics Data System (ADS)

    Tepe, M.; Abukay, D.

    1998-01-01

    The effect of Ni doping on superconductivity properties of the Bi1.7Pb0.3Sr2Ca2(Cu1-xNix)3Oy system has been investigated by means of x-ray diffraction, ac electrical resistance, ac magnetic susceptibility and critical current measurements. The volume fraction of the 2223 phase decreases with increasing Ni concentration. The zero-resistance temperature and the critical current density are suppressed with Ni substitution.

  16. Probing the links between structure and magnetism in Sr(2-x)Ca(x)FeOsO₆ double perovskites.

    PubMed

    Morrow, Ryan; Freeland, John W; Woodward, Patrick M

    2014-08-04

    The synthesis, structure, and properties of the ordered double perovskites Sr2FeOsO6, Ca2FeOsO6, and SrCaFeOsO6 are reported. The latter two compounds have monoclinic P2₁/n symmetry and a(-)a(-)b(+) tilting of the octahedra, while Sr2FeOsO6 is tetragonal with I4/m symmetry and a(0)a(0)c(-) tilting. Magnetic measurements indicate and neutron powder diffraction studies confirm that Ca2FeOsO6 is a ferrimagnet with a Curie temperature of 350 K. The ferrimagnetism is retained if half of the Ca(2+) ions are replaced with larger Sr(2+) ions to form SrCaFeOsO6 (T(C) = 210 K). This substitution reduces the degree of octahedral tilting, but unlike most perovskites, the magnetic ordering temperature decreases as the Fe-O-Os bond angles approach a linear geometry. In contrast, Sr2FeOsO6 orders antiferromagnetically, as previously reported. X-ray absorption spectroscopy confirms the assignment of Fe(III) and Os(V) oxidation states for all three compounds. In these insulating double perovskites, the magnetic ground state is governed by a competition between the four-bond Fe-O-Os-O-Fe antiferromagnetic superexchange coupling of Fe(III) ions and the two-bond Fe-O-Os antiferromagnetic superexchange coupling between neighboring Fe(III) and Os(V) ions. When the Fe-O-Os bonds are linear, as they are in the c direction in Sr2FeOsO6, the four-bond coupling between Fe(III) ions prevails. The competition shifts in favor of antiferromagnetic coupling of Fe(III) and Os(V) as the Fe-O-Os bond angles bend in response to chemical pressure.

  17. Continuous drawing of Bi-Ca-Sr-Cu-O glass fibers from a preform

    SciTech Connect

    Zheng, H.; Hu, Y.; Mackenzie, J.D. )

    1991-04-15

    Several issues related to drawing Bi-Ca-Sr-Cu-O glass fibers from a preform are discussed. Continuous drawing of Bi-Ca-Sr-Cu-O glass fibers was successfully accomplished. Bi-Ca-Sr-Cu-O glass fibers are drawn above the crystallization temperature. Minimizing crystallization of the glass preforms is a key for successful drawing of the glass fibers. Two effective means, high glass melting temperature and V{sub 2}O{sub 5} doping, have been used to minimize the crystallization of the preforms, thus assuring the continuous drawing of Bi-Ca-Sr-Cu-O glass fibers.

  18. Late INa increases diastolic SR-Ca2+-leak in atrial myocardium by activating PKA and CaMKII

    PubMed Central

    Fischer, Thomas H.; Herting, Jonas; Mason, Fleur E.; Hartmann, Nico; Watanabe, Saera; Nikolaev, Viacheslav O.; Sprenger, Julia U.; Fan, Peidong; Yao, Lina; Popov, Aron-Frederik; Danner, Bernhard C.; Schöndube, Friedrich; Belardinelli, Luiz; Hasenfuss, Gerd; Maier, Lars S.; Sossalla, Samuel

    2015-01-01

    Aims Enhanced cardiac late Na current (late INa) and increased sarcoplasmic reticulum (SR)-Ca2+-leak are both highly arrhythmogenic. This study seeks to identify signalling pathways interconnecting late INa and SR-Ca2+-leak in atrial cardiomyocytes (CMs). Methods and results In murine atrial CMs, SR-Ca2+-leak was increased by the late INa enhancer Anemonia sulcata toxin II (ATX-II). An inhibition of Ca2+/calmodulin-dependent protein kinase II (Autocamide-2-related inhibitory peptide), protein kinase A (H89), or late INa (Ranolazine or Tetrodotoxin) all prevented ATX-II-dependent SR-Ca2+-leak. The SR-Ca2+-leak induction by ATX-II was not detected when either the Na+/Ca2+ exchanger was inhibited (KBR) or in CaMKIIδc-knockout mice. FRET measurements revealed increased cAMP levels upon ATX-II stimulation, which could be prevented by inhibition of adenylyl cyclases (ACs) 5 and 6 (NKY 80) but not by inhibition of phosphodiesterases (IBMX), suggesting PKA activation via an AC-dependent increase of cAMP levels. Western blots showed late INa-dependent hyperphosphorylation of CaMKII as well as PKA target sites at ryanodine receptor type-2 (-S2814 and -S2808) and phospholamban (-Thr17, -S16). Enhancement of late INa did not alter Ca2+-transient amplitude or SR-Ca2+-load. However, upon late INa activation and simultaneous CaMKII inhibition, Ca2+-transient amplitude and SR-Ca2+-load were increased, whereas PKA inhibition reduced Ca2+-transient amplitude and load and additionally slowed Ca2+ elimination. In atrial CMs from patients with atrial fibrillation, inhibition of late INa, CaMKII, or PKA reduced the SR-Ca2+-leak. Conclusion Late INa exerts distinct effects on Ca2+ homeostasis in atrial myocardium through activation of CaMKII and PKA. Inhibition of late INa represents a potential approach to attenuate CaMKII activation and decreases SR-Ca2+-leak in atrial rhythm disorders. The interconnection with the cAMP/PKA system further increases the antiarrhythmic potential of late

  19. 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.

  20. 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.

  1. Planktonic Foram Sr/Ca Indicates Long-Term Stability of Carbonate Saturation State and Seawater Sr/Ca during the Cenozoic

    NASA Astrophysics Data System (ADS)

    Caves, J. K.; Opdyke, B.; Owens, R.

    2012-12-01

    Changes in ocean chemistry are poorly understood over timescales of tens of millions of years; yet, such changes reflect the interplay of fundamental Earth processes, such as the long-term carbon-cycle, evolution, tectonics, and weathering. Simultaneously constraining two ocean chemical parameters could help deconvolve these processes and improve our understanding of the marine response to anthropogenic perturbations to the carbon cycle. We use a multi-proxy and modeling approach, utilizing planktonic foram Sr/Ca, calcite cements, and box-modeling to produce a first-attempt at a Cenozoic carbonate saturation state (Ω) curve and to improve estimates of long-term seawater Sr/Ca variability. Evidence from both culturing studies and glacial-interglacial records indicate that foram Sr/Ca is dominantly sensitive to Ω, suggesting that foram Sr/Ca can be used to reconstruct Ω if seawater Sr/Ca can be constrained. We apply this new proxy to an updated Cenozoic planktonic foram Sr/Ca record, comprising 1680 records from 18 publications. Our foram Sr/Ca record is largely constant during the Cenozoic, with a minimum at the Miocene-Pliocene boundary and a pronounced shift at 38Mya, corresponding to a major planktonic foram overturning event, which we interpret as a species offset. To constrain seawater Sr/Ca, we use both trace element data from calcite cements and a box-model linked to the 87Sr/86Sr record. Both the model and calcite cement data suggest seawater Sr/Ca has remained relatively stable, with slightly higher values during the Paleogene, a minimum during the mid-Miocene, and variability driven by changes in carbonate deposition and mineralogy. Relative to calcite, Ω was low (~4) during much of the Paleogene, but increased during the Oligocene, reaching a maximum during the mid-Miocene. Ω declined to a local minimum at the Miocene-Pliocene boundary, and has since increased to pre-industrial values of 5-6. This record helps explain the lag between the aragonite

  2. Preparation, crystal structure and superconductivity of (C, Cu)(Sr, Ca) 2(Y, Ca, Sr)Cu 2O 7

    NASA Astrophysics Data System (ADS)

    Miyazaki, Y.; Yamane, H.; Kajitani, T.; Kobayashi, N.; Hiraga, K.; Morii, Y.; Funahashi, S.; Hirai, T.

    1994-09-01

    A series of solid solutioins containing CO 3 groups, (c ycu 1-y)(Sr 1-z/2Ca z/2) 2(Y 1-xCa x-zSr z)Cu 2 O dd with 0.30≤ x≤0.70, was prepared at 1313 K under the atmosphere of O 2-CO 2. The values of y (0.48-0.67) and z (0.14-0.28) depend on the total Ca content, x. The length of the a-axis increase from 3.8374(2) Å ( x=0.30) to 3.8591(9) Å ( x=0.70) with increasing x, while the c-axis length decreases from 11.1198(6) to 10.9410(6) Å. All the as-prepared solid solutions are semiconductors, but superconducting transition is observed for the samples with 0.35≤ × ≤0.70 after annealing at 1273 K and an oxygen pressure of 4.0 MPa. The transition temperature ( T c increases with increasing x, and the highest Tc=60 K is measured for the samples with 0.60≤ x≤0.70. All the annealed samples show appreciable expansion of the c-axis length and contraction of the a-axis length relative to the as-prepared ones. The crystal structures of the as-prepared and annealed samples with x = .50 were refined from neutron powder diffraction data by means of the Rietveld method. On the basis of the refined crystal structure data and wet chemical analysis, it is suggested that hole doping is caused, during high-pressure oxygen annealing, by the release of some CO 3 groups and by the introduction of oxygen atoms into the vacant “apical” oxygen site, where the CO 3 group is not present.

  3. 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

  4. 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.

  5. Intracellular Ca2+ oscillations generated via the extracellular Ca2+-sensing receptor (CaSR) in response to extracellular Ca2+ or L-phenylalanine: impact of the highly conservative mutation Ser170Thr

    PubMed Central

    Young, Steven H.; Rey, Osvaldo; Rozengurt, Enrique

    2015-01-01

    The extracellular Ca2+-sensing receptor (CaSR) is an allosteric protein that responds to changes in the extracellular concentration of Ca2+ ([Ca2+]e) and aromatic amino acids with the production of different patterns of oscillations in intracellular Ca2+ concentration ([Ca2+]i). An increase in [Ca2+]e stimulates sinusoidal oscillations in [Ca2+]i whereas aromatic amino acid-induced CaR activation in the presence of a threshold [Ca2+]e promotes transient oscillations in [Ca2+]i. Here, we examined spontaneous and ligand-evoked [Ca2+]i oscillations in single HEK-293 cells transfected with the wild type CaSR or with a mutant CaSR in which Ser170 was converted to Thr (CaSRS170T). Our analysis demonstrates that cells expressing CaSRS170T display [Ca2+]i oscillations in the presence of low concentrations of extracellular Ca2+ and respond to L-Phe with robust transient [Ca2+]i oscillations. Our results indicate that the S170T mutation induces a marked increase in CaSR sensitivity to [Ca2+]e and imply that the allosteric regulation of the CaSR by aromatic amino acids is not only mediated by an heterotropic positive effect on Ca2+ binding cooperativity but, as biased agonists, aromatic amino acids stabilize a CaSR conformation that couples to a different signaling pathway leading to transient [Ca2+]i oscillations. PMID:26431875

  6. 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.

  7. Gulf of Alaska and California bamboo corals: Ba/Ca and Sr/Ca records

    NASA Astrophysics Data System (ADS)

    Sauthoff, W.; LaVigne, M.; Hill, T. M.; Roark, E.; Dunbar, R. B.; Guilderson, T. P.; Spero, H. J.

    2012-12-01

    Deep-sea bamboo coral communities form on seamounts and along continental margins with near global distribution. Bamboo [Isididae] corals record surrounding ocean geochemistry presenting reliable proxy records of changes in seawater conditions, including productivity and nutrient content. Here we investigate bamboo coral specimens from the California margin and Gulf of Alaska (634-1288 m water depth; ~37oN-48oN), to provide insight into latitudinal and temporal differences in eastern Pacific Ocean climate processes. Past oceanic conditions were reconstructed in this investigation by trace element analyses (Ba/Ca, Sr/Ca) using laser ablation ICP-MS, using a 85 μm spot size at 10 μm/s, 4.45 J/cm2 fluence, and 10 Hz repetition rate. Two California specimens show differences in mean Ba/Ca content: 13.73 compared to 18.55 μmol/mol, which we attribute to differences in collection depth (T1104 A10: 833 m and T1100 A04: 1288 m, respectively). Gulf of Alaska corals show a more subdued nutrient signal with lower mean Ba/Ca values of 10.56 and 10.05 μmol/mol across a narrower depth range (ALV3803 #3: 720 m; ALV3803 #5: 634 m, respectively). This trend of increasing Ba/Ca with depth is in consensus with eastern Pacific dissolved barium and California margin bamboo coral depth transects. Sr/Ca content was uniform between four coral specimens with values ranging from 3.01 to 3.06 mmol/mol. Coral chronologies were compared against indices of climate oscillations, including El Niño Southern Oscillation and Pacific Decadal Oscillation, using time series based upon radiocarbon dating. The corals investigated here show a limited connection with El Niño Southern Oscillation; longer-term changes related Pacific Decadal Oscillation may be evidenced in this climate archive.

  8. Compensatory up-regulation of cardiac SR Ca2+-pump by heat-shock counteracts SR Ca2+-channel activation by ischemia/reperfusion.

    PubMed

    O'Brien, P J; Li, G O; Locke, M; Klabunde, R E; Ianuzzo, C D

    1997-08-01

    We tested the hypothesis that heat-shock protected myocardial Ca2+-cycling by sarcoplasmic reticulum from ischemia and reperfusion (I/R) injury. Twenty-four hours after increasing body temperature to 42 degrees C for 15 min, rat hearts were isolated, Langendorff-perfused, and subjected to 30 min ischemia then 30 min reperfusion. Left ventricles were homogenized and their ionized Ca2+ concentration monitored with indo- during Ca2+-uptake in the presence and absence of the Ca2+-release channel (CRC) modulator ryanodine. Tissue content of heat-shock protein 72 (HSP 72) was analyzed. Exposure to I/R resulted in a 37% enhancement of CRC activity but no effect on Ca2+-pumping activity, resulting in 25% decreased net Ca2+-uptake activity. Pre-exposure to heat-shock resulted in a 10-fold increase in HSP 72, and a 25% enhancement of maximal Ca2+-pumping activity which counteracted the effect of I/R on CRC and net Ca2+-uptake activities. This protection of SR Ca2+-cycling was associated with partial protection of myocardial physiological performance. Net Ca2+-uptake activity was correlated with the left ventricular developed pressure and its rate of change. We conclude that one of the mechanisms by which heat-shock protects myocardium from I/R injury is to upregulate SR Ca2+-pumping activity to counteract the enhanced SR Ca2+-release produced by I/R.

  9. Reconstructing past seawater Mg/Ca and Sr/Ca from mid-ocean ridge flank calcium carbonate veins.

    PubMed

    Coggon, Rosalind M; Teagle, Damon A H; Smith-Duque, Christopher E; Alt, Jeffrey C; Cooper, Matthew J

    2010-02-26

    Proxies for past seawater chemistry, such as Mg/Ca and Sr/Ca ratios, provide a record of the dynamic exchanges of elements between the solid Earth, the atmosphere, and the hydrosphere and the evolving influence of life. We estimated past oceanic Mg/Ca and Sr/Ca ratios from suites of 1.6- to 170-million-year-old calcium carbonate veins that had precipitated from seawater-derived fluids in ocean ridge flank basalts. Our data indicate that before the Neogene, oceanic Mg/Ca and Sr/Ca ratios were lower than in the modern ocean. Decreased ocean spreading since the Cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early Tertiary may explain the recent rise in these ratios.

  10. 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.

  11. Comparison of the EXAFS Spectra of Heteronuclear MnCa/Sr Model Complexes to the Oxygen-Evolving Mn(4)Ca Complex of Photosystem II

    SciTech Connect

    Mishra, A.; Yano, J.; Pushkar, Y.; Abboud, K.A.; Yachandra, V.K.; Christou, G.

    2009-06-03

    Heterometallic Mn-Ca and Mn-Sr complexes have been prepared and employed as model complexes for Ca and Sr EXAFS spectral comparisons with the Oxygen-Evolving Complex (OEC) of Photosystem II (PS II); these have revealed similarities that support the presence of at least one O atom bridge between the Mn and Ca/Sr in the OEC.

  12. Intercolony Sr/Ca variability in Palmyra Island corals: Implications for paleo-SST reconstructions

    NASA Astrophysics Data System (ADS)

    Sayani, H. R.; Cobb, K.; Cohen, A. L.; Druffel, E. R.; Monteleone, B. D.

    2011-12-01

    The ratio of strontium to calcium (Sr/Ca) in coral skeletons is widely used to construct continuous, highly-resolved records of past sea-surface temperature (SST) variability. Typically, paleo-SST estimates are derived using Sr/Ca-SST functions created by regressing Sr/Ca from a single modern coral against instrumental SST. However, several studies have found that while coral Sr/Ca may strongly covary with SST, the absolute Sr/Ca values in corals growing on the same reef often differ significantly. As such, the uncertainties associated with coral-derived paleo-SST estimates based on the calibration approach outlined above are poorly constrained. To assess reproducibility of coral Sr/Ca and extent of intercolony variability at Palmyra Island (6°N, 162°W; Cobb et al., 2003; Nurhati et al., 2011), we measure mm- and μm-scale Sr/Ca in four overlapping modern Porites cores. Conventional mm-scale Sr/Ca records from these modern cores are well correlated with each other (R = 0.65 to 0.68) and with SST (R = -0.73 to -0.85), but the absolute Sr/Ca values of these records exhibit baseline offsets of ×0.11mmol/mol (1σ). Secondary ion mass spectrometry (SIMS) is used to generate 2-3 year long, weekly-resolved, Sr/Ca records from 3 overlapping modern coral segments. While the SIMS Sr/Ca analyses from each core exhibit relatively large point-to-point variations of ~0.17mmol/mol (1σ), compared to ~0.06mmol/mol (1σ) in mm-scale Sr/Ca, their monthly-scale variability resolves the annual SST cycles observed at Palmyra reasonably well (R = -0.46 to -0.64). Furthermore, the intercolony offsets observed in mm-scale Sr/Ca records are reproduced in the SIMS Sr/Ca records. These large offsets imply that paleo-SST estimates derived from a single fossil coral Sr/Ca dataset would be associated with uncertainties of ×1.4°C (1σ). We build a coral Sr/Ca 'stack' for Palmyra Island using Sr/Ca records from the 4 modern cores. This composite Sr/Ca record is more strongly correlated with

  13. Intercolony Sr/Ca variability in Palmyra Island corals: Implications for paleo-SST reconstructions

    NASA Astrophysics Data System (ADS)

    Sayani, H. R.; Cobb, K.; Cohen, A. L.; Druffel, E. R.; Monteleone, B. D.

    2013-12-01

    The ratio of strontium to calcium (Sr/Ca) in coral skeletons is widely used to construct continuous, highly-resolved records of past sea-surface temperature (SST) variability. Typically, paleo-SST estimates are derived using Sr/Ca-SST functions created by regressing Sr/Ca from a single modern coral against instrumental SST. However, several studies have found that while coral Sr/Ca may strongly covary with SST, the absolute Sr/Ca values in corals growing on the same reef often differ significantly. As such, the uncertainties associated with coral-derived paleo-SST estimates based on the calibration approach outlined above are poorly constrained. To assess reproducibility of coral Sr/Ca and extent of intercolony variability at Palmyra Island (6°N, 162°W; Cobb et al., 2003; Nurhati et al., 2011), we measure mm- and μm-scale Sr/Ca in four overlapping modern Porites cores. Conventional mm-scale Sr/Ca records from these modern cores are well correlated with each other (R = 0.65 to 0.68) and with SST (R = -0.73 to -0.85), but the absolute Sr/Ca values of these records exhibit baseline offsets of ×0.11mmol/mol (1σ). Secondary ion mass spectrometry (SIMS) is used to generate 2-3 year long, weekly-resolved, Sr/Ca records from 3 overlapping modern coral segments. While the SIMS Sr/Ca analyses from each core exhibit relatively large point-to-point variations of ~0.17mmol/mol (1σ), compared to ~0.06mmol/mol (1σ) in mm-scale Sr/Ca, their monthly-scale variability resolves the annual SST cycles observed at Palmyra reasonably well (R = -0.46 to -0.64). Furthermore, the intercolony offsets observed in mm-scale Sr/Ca records are reproduced in the SIMS Sr/Ca records. These large offsets imply that paleo-SST estimates derived from a single fossil coral Sr/Ca dataset would be associated with uncertainties of ×1.4°C (1σ). We build a coral Sr/Ca 'stack' for Palmyra Island using Sr/Ca records from the 4 modern cores. This composite Sr/Ca record is more strongly correlated with

  14. The Unusual Metal-Insulator Transition in Ca(2-x)Sr(x)RuO(4)

    NASA Astrophysics Data System (ADS)

    Rice, T. Maurice

    2002-03-01

    The isoelectronic compounds Ca_2-xSr_xRuO4 offer a rare opportunity to follow the evolution of the electronic structure from a multiband metal, Sr_2RuO_4, to a Mott insulator, Ca_2RuO_4. The evolution is not at all monotonic but proceeds through a series of intermediate regions with unexpected behavior [1]. Sr_2RuO4 is a good metal with the 4 electrons in the t_2g-subshell of the Ru^4+-ions distributed equally in 3 bands. These in turn separate into a d_xy-band which disperses in both directions in the RuO_2-planes and d_xz/d_yz-bands dispersing only in one direction. The hybridization between these components occurs only through very weak interplanar processes. Substituting Ca for Sr leads to band narrowing through a rotation of the RuO_4-octahedra. A series of electronic structure calculations [2] using the LDA+DMFT method to incorporate strong correlations, predict an unusual state with 3 electrons localizing in the narrower d_xz/d_yz bands while the last electron remains itinerant in the broader d_xy-band. The observation of a strongly enhanced and temperature dependent spin susceptibility in the metallic state at x=0.5 is attributed to the S=1/2 local moments of the localized hole in the d_xz/d_yz-orbitals. The superexchange interaction between the local moments is strongly dependent on the specific orbital occupation and so glassy behavior in the orbital ordering can account for the glassy behavior observed in the susceptibility in the range 0.2 < x < 0.5. The final transition to a Mott insulator at x < 0.2 is driven by a compression of the RuO_4-octahedra and a switch to an electronic configuration with a filled d_xy-orbital and 2 electrons in the d_xz/d_yz orbitals which has a S=1 local moment expected for a Ru^4+-ion. [1] S. Nakatsuji and Y. Maeno, Phys. Rev. Lett. 84, 2666 (2000). [2] V.I. Anisimov, I.A. Nekrasov, D.E. Kondakov, T.M. Rice, and M. Sigrist, cond-mat0107095 and Eur. Phys. Jour. B (in press).

  15. Geometry and Vibrational Spectra of the Alkaline Earth Dihalides. III. MgCl2, CaCl2, SrCl2 and BaCl2.

    DTIC Science & Technology

    The infrared spectra of MgCl2 , CaCl2, SrCl2 and BaCl2 trapped in solid krypton matrices at 20K are reported. From precise measurements of changes in...the vibrational modes on isotopic substitution, a linear configuration for MgCl2 and CaCl2 is confirmed and an apex angle of 120 degrees is...established for SrCl. For BaCl2 the bond angle has been estimated at 100 degrees. Using a valence force field a set of force constants has been obtained from

  16. 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

  17. Large enhancement of superconducting transition temperature of SrBi3 induced by Na substitution for Sr

    PubMed Central

    Iyo, Akira; Yanagi, Yousuke; Kinjo, Tatsuya; Nishio, Taichiro; Hase, Izumi; Yanagisawa, Takashi; Ishida, Shigeyuki; Kito, Hijiri; Takeshita, Nao; Oka, Kunihiko; Yoshida, Yoshiyuki; Eisaki, Hiroshi

    2015-01-01

    The Matthias rule, which is an empirical correlation between the superconducting transition temperature (Tc) and the average number of valence electrons per atom (n) in alloys and intermetallic compounds, has been used in the past as a guiding principle to search for new superconductors with higher Tc. The intermetallic compound SrBi3 (AuCu3 structure) exhibits a Tc of 5.6 K. An ab-initio electronic band structure calculation for SrBi3 predicted that Tc increases on decreasing the Fermi energy, i.e., on decreasing n, because of a steep increase in the density of states. In this study, we demonstrated that high-pressure (~ 3 GPa) and low-temperature ( < 350 °C) synthesis conditions enables the substitution of Na for about 40 at.% of Sr. With a consequent decrease in n, the Tc of (Sr,Na)Bi3 increases to 9.0 K. A new high-Tc peak is observed in the oscillatory dependence of Tc on n in compounds with the AuCu3 structure. We have shown that the oscillatory dependence of Tc is in good agreement with the band structure calculation. Our experiments reaffirm the importance of controlling the number of electrons in intermetallic compounds. PMID:25965162

  18. Injectability of brushite-forming Mg-substituted and Sr-substituted alpha-TCP bone cements.

    PubMed

    Pina, S; Torres, P M C; Ferreira, J M F

    2010-02-01

    The influence of magnesium- and strontium-substitutions on injectability and mechanical performance of brushite-forming alpha-TCP cements has been evaluated in the present work. The effects of Mg- and Sr-substitutions on crystalline phase composition and lattice parameters were determined through quantitative X-ray phase analysis and structural Rietveld refinement of the starting calcium phosphate powders and of the hardened cements. A noticeable dependence of injectability on the liquid-to-powder ratio (LPR), smooth plots of extrusion force versus syringe plunger displacement and the absence of filter pressing effects were observed. For LPR values up to 0.36 ml g(-1), the percentage of injectability was always higher and lower for Mg-containing cements and for Sr-containing cements, respectively, while all the pastes could be fully injected for LPR > 0.36 ml g(-1). The hardened cements exhibited relatively high wet compressive strength values (~17-25 MPa) being the Sr- and Mg-containing cements the strongest and the weakest, respectively, holding an interesting promise for uses in trauma surgery such as for filling bone defects and in minimally invasive techniques such as percutaneous vertebroplasty to fill lesions and strengthen the osteoporotic bone.

  19. Magnetic excitations in the S = {1/2} quasi-one-dimensional magnet Sr{sub 14{minus}x}Ca{sub x}Cu{sub 24}O{sub 41}

    SciTech Connect

    Matsuda, M.; Katsumata, K.; Shapiro, S.M.; Shirane, G.

    1998-08-20

    Neutron scattering experiments have been performed on Sr{sub 14{minus}x}Ca{sub x}Cu{sub 24}O{sub 41} (x = 3 and 6), which consists of CuO{sub 2} chains and CuO{sub 2}O{sub 3} ladders, in order to study the effect of Ca substitution on the dimerized state in the chains. The Ca substitution broadens the excitation peak although the excitation energy is almost unchanged. The effects of Ca and Y substitution on the dimerized state are compared.

  20. Application of K/Sr co-doped calcium polyphosphate bioceramic as scaffolds for bone substitutes.

    PubMed

    Xie, Huixu; Wang, Qianbin; Ye, Qingsong; Wan, Changxiu; Li, Longjiang

    2012-04-01

    Ion doping is one of the most important methods to modify the properties of bioceramics for better biodegrade abilities, biomechanical properties, and biocompatibilities. This paper presents a novel ion doping method applied in calcium polyphosphate (CPP)-based bioceramic scaffolds substituted by potassium and strontium ions (K/Sr) to form (K/Sr-CPP) scaffolds for bone tissue regeneration. The microstructure and crystallization of the scaffolds were detected by scanning electron microscopy and X-ray diffraction. Compressive strength and degradation tests were assessed to evaluate the mechanical and chemical stabilities of K/Sr-CPP in vitro. The cell biocompatibility was measured with respect to the cytotoxicity of the extractions of scaffolds. Muscle pouches and bone implantation were performed to evaluate the biodegradability and osteoconductivity of the scaffolds. The results indicated that the obtained K/Sr-CPP scaffolds had a single beta-CPP phase. The unit cell volume and average grain size increased but the crystallization decreased after the ions were doped into the CPP structure. The K/Sr-CPP scaffolds yielded a higher compressive strength and a better degradation property than the pure CPP scaffold. The MTT assay and in vivo results reveal that the K/Sr-CPP scaffolds exhibited a better cell biocompatibility and a tissue biocompatibility than CPP and hydroxyapatite scaffolds. This study proves the potential applications of K/Sr-CPP scaffolds in bone repair.

  1. (Ca/Sr)Au xCd 1- x: Stacking variants of the CrB-FeB series

    NASA Astrophysics Data System (ADS)

    Harms, Wiebke; Dürr, Ines; Daub, Michael; Röhr, Caroline

    2010-01-01

    The structural chemistry of binary 1:1 alkaline earth metallides AIIM ( M=p-block or late transition element) is dominated by planar M zig-zag chains, which are stacked in different orientations (CrB ( c) to FeB ( h) type) and with variable stacking distances (types I and II). As a case study of the electronic influences, the substitution of Au against Cd in the respective Ca and Sr aurides was examined by means of experimental, crystallographic and computational methods. Starting from CaAu, up to 11% of Au can be substituted by Cd without a change in the CrB structure type (orthorhombic, space group Cmcm, a=398.2(1), b=1122.6(6), c=460.9(2) pm, Z=4, R1=0.0303). Starting from SrAu (stacking sequence (hc)2(h2c)2), depending on the proportion of the Cd substitution a successive change to structures with increased hexagonality is observed: In SrAu0.93Cd0.07 (monoclinic, space group P21/m, a=621.3(4), b=472.4(2), c=1216.1(9) pm, β=96.97(5)∘, Z=6, R1=0.0467) the stacking sequence is h2 c, i.e. the hexagonality is 66.67%. A slightly more increased Cd content in SrAu0.78Cd0.22 (orthorhombic, space group Pnma, a=3243.3(8), b=474.17(8), c=626.20(9) pm, Z=16, R1=0.0682) drives the hexagonality to 75%, with a (h3c)2 stacking sequence known from several rare earth nickel compounds. Further Cd substitution is not possible. However, in the Cd-rich section of the two series, where the CsCl/β-brass structure type occurs for both alkaline earth elements, a small Au substitution, as determined from powder data by Rietveld refinements, is possible. The substitution limit and the stability ranges of the CsCl and the CrB type can be rationalized from the calculated band structures. Geometrical and electronic criteria are used to compare and discuss the stability ranges in a structural map.

  2. Variation of the Ru moment in the Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O3 system.

    PubMed

    Mizusaki, S; Naito, M; Taniguchi, T; Nagata, Y; Itou, M; Sakurai, Y; Noro, Y; Ozawa, T C; Samata, H

    2010-04-14

    The variation of the magnetic moment on Ru and Mn atoms in the Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O(3) system was investigated by the magnetic Compton scattering technique using synchrotron radiation. The Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O(3) system has ferrimagnetism with an antiferromagnetic coupling between Ru and Mn, and the dominant magnetic component changes from ferromagnetic Ru to ferromagnetic Mn at x ∼0.25 as the Mn substitution proceeds. The mechanism for the change in the magnetism of Ca(0.3)Sr(0.7)Ru(1-x)Mn(x)O(3) is discussed.

  3. 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

    2015-03-06

    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.

  4. Extracellular calcium and CaSR drive osteoinduction in mesenchymal stromal cells.

    PubMed

    González-Vázquez, Arlyng; Planell, Josep A; Engel, Elisabeth

    2014-06-01

    Bone is the main store of calcium and progenitor cells in the body. During the resorption process, the local calcium concentration reaches 8-40mM, and the surrounding cells are exposed to these fluctuations in calcium. This stimulus is a signal that is detected through the calcium sensing receptor (CaSR), which modulates chemotactic and proliferative G protein-dependent signaling pathways. The objective of the present work is to evaluate the roles of extracellular calcium ([Ca(2+)]o) and the CaSR in osteoinduction. Rat bone marrow mesenchymal stromal cells (rBMSCs) were stimulated with 10mM of Ca(2+). Several experiments were conducted to demonstrate the effect of [Ca(2+)]o on chemotaxis, proliferation and differentiation on the osteoblastic lineage. It was found that [Ca(2+)]o induces rBMSCs to migrate and proliferate in a concentration-dependent manner. Real-time polymerase chain reaction and immunofluorescence also revealed that 10mM Ca(2+) stimulates overexpression of osteogenic markers in rBMSCs, including alkaline phosphatase (ALP), bone sialoprotein, collagen Ia1 and osteocalcin. Functional assays determining ALP activity and mineralization tests both corroborate the increased expression of these markers in rBMSCs stimulated with Ca(2+). Moreover, CaSR blockage inhibited the cellular response to stimulation with high concentrations of [Ca(2+)]o, revealing that the CaSR is a key modulator of these cellular responses.

  5. 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.

  6. 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.

  7. 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.

  8. Yellow-to-orange emission from B2+-doped RF2 (R = Ca and Sr) phosphors.

    PubMed

    Cao, Renping; Zhang, Fangteng; Liao, Chenxing; Qiu, Jianrong

    2013-07-01

    RF2:Bi (R = Ca and Sr) phosphors were synthesized by solid state reaction method in air and their luminescence properties were investigated. Broad yellow-to-orange emissions peaking at ~550 nm (CaF2:Bi) and ~600 nm (SrF2:Bi) were observed under ~260 nm excitation. The emission centers inRF2:Bi (R = Ca and Sr) phosphors are Bi2+ ions, and the excitation and emission bands of RF2:Bi (R = Ca and Sr) phosphors can be attributed to 2P 1/2 → 2S 1/2 and 2P 3/2(1) → 2P 1/2 transitions of Bi2+ ions, respectively. The phosphors are promising for application in lighting due to broad yellow-to-orange emission.

  9. 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.

  10. 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.

  11. Bamboo coral skeletal Sr/Ca: An indicator of growth rate or other vital effects?

    NASA Astrophysics Data System (ADS)

    Hill, T. M.; Lavigne, M.; Spero, H. J.; Guilderson, T. P.

    2009-12-01

    Research has demonstrated that intermediate waters (300-2000m) may play an important role in forcing and responding to perturbations to the climate system, via circulation (ventilation), temperature, carbon cycling, and nutrients. Here we investigate the geochemistry of deep-sea bamboo corals, collected on a transect across intermediate water depths (250-2500m) on the California margin. Radiocarbon dating of the calcite skeleton of coral specimens indicates that bamboo corals live for centuries, with growth rates of ~50-100 microns/year, consistent with previous bamboo coral investigations (Roark et al., 2005). Although skeletal Sr/Ca is typically interpreted as a temperature proxy in aragonitic surface corals, it is less clear what factors influence the incorporation of Sr/Ca in calcitic deep sea corals. Recent results indicate that while a strong vital effect is present in bamboo coral stable isotopes (d18O, d13C), Sr/Ca ratios do not covary with isotopic values, indicating different biological or growth factors must control these tracers. Laser ablation ICPMS results from California margin bamboo corals show reproducible Sr/Ca variations in agreement with the timing of PDO shifts for corals collected from different California margin locations. Synchronous coral Sr/Ca and PDO index variability suggest that bamboo coral Sr/Ca trends are related to PDO phase, and may be dictated by surface-driven processes such as food source, quality, or quantity. These results suggest that intermediate waters are impacted by surface water environmental shifts such as changes in productivity and carbon export. Additional work is required to determine whether such shifts in Sr/Ca are apparent through multiple PDO cycles, and to understand the origin of Sr/Ca shifts.

  12. 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.

  13. Non-traditional stable Ca, Sr isotopic composition in rainwater from Guiyang city, southwest China

    NASA Astrophysics Data System (ADS)

    Han, G.; Tang, Y.

    2013-12-01

    The major ions, strontium concentrations, δ[44/40]Ca, [87]Sr/^[86]Sr and δ[88/86]Sr ratios were measured in rainwater samples collected at an urban site in Guiyang, southwest China, over a period of one year. The pH values ranged between 4.2 and 8.6, with a volume-weighted mean (VWM) of 6.2. About 30% of the rainwater studied were acidic rain with pH values less than 5.6. Ca[2+] was the most dominant cation in rainwater samples and the VWM value was175μmol/L (21-1631 μmol/L). SO[4][2-] was the predominant anion with VWM value of 137 μmol/L (5-2019 μmol/L), next was NO3- with VWM value of 26 μmol/L(1.4-444 μmol/L).Using Na as an indicator of marine origin, and Al for the terrestrial inputs, the proportions of sea salt and terrestrial elements were estimated from elemental ratios. More than 99% of Ca[2+] and 98% of SO[4][2-] in rainwater samples are non-sea-salt origin. The δ[44/40]Ca values of rainwater samples from Guiyang city, ranged from 0.51×0.18‰to 1.09×0.14‰, are very similar to the range of δ[44/40]Ca values in natural rivers. The [87]Sr/^[86]Sr ratios spanned a range of 0.70800 to 0.72742, with a mean value of 0.71080. The δ[88/86]Sr of rainwater samples ranged from 0.215×0.004‰ to 0.333×0.004‰, with a mean δ88/86Sr of rainwater is 0.296×0.01‰. The radiogenic strontium isotope data ([87]Sr/^[86]Sr) can infer the sources of Sr of the rainwater samples. The [87]Sr/^[86]Sr vs. Cl/Na suggests that the sources of rainwater samples come from dissolved carbonate minerals and anthropogenic inputs. The δ[44/40]Ca values and the stable Sr isotope (δ[88/86]Sr) may be affected by biological processes.

  14. Constraints on Ca/Sr as a Proxy for Calcium in Forest Ecosystems

    NASA Astrophysics Data System (ADS)

    Hoff, C. J.; Hobbie, E. A.; Hallett, R.; Colpaert, J.; Bryce, J. G.

    2004-05-01

    Calcium is a key plant nutrient and important base cation in ecosystems. Our current efforts to quantify Ca cycling in ecosystems rely on indirect proxies, e.g., Ca/Sr or Sr isotopic systems (1). An important assumption in these applications is that the elemental ratio of calcium to strontium faithfully represents calcium cycling and that little fractionation occurs through biogeochemical and physiological processes. However, several researchers have reported variations in Ca/Sr, e.g. among different tree tissues (2) and during weathering processes (3), raising doubts about the suitability of the proxy. To address the question of reliability, we measured Ca/Sr values in a culture study in which Scots pines were grown at low or high nutrient supply rates (3% per day or 5% per day). Because mycorrhizal fungi are intimately involved in plant nutrient supply, plants were also grown either uncolonized or colonized with one of two different species of mycorrhizal fungi (Suillus luteus and Thelephora terrestris). Our preliminary results indicate that Ca/Sr values differ between high and low nutrient treatments, root and foliage, and mycorrhizal treatments. In individual seedlings, roots have lower Ca/Sr than foliage by absolute factors of 2-5. The magnitude of the effect is apparently determined by a combination of environmental factors including both the nutrient and mycorrhizal treatments. These results indicate that Ca and Sr are partitioned differently between nutrient and mycorrhizal treatments and between plant fractions despite the common nutrient broth and substrate. Thus, Ca/Sr values alone are not reliable tracers of Ca within an ecosystem because of partitioning of Ca and Sr during nutrient transport within the plant-mycorrhizal system. We are presently refining analytical techniques and conducting leachate experiments to improve the quantification of this Ca/Sr fractionation. We are also exploring the use of isotopic tracers to study calcium biogeochemical

  15. Exploring foraminiferal Sr/Ca as a new carbonate system proxy

    NASA Astrophysics Data System (ADS)

    Keul, Nina; Langer, Gerald; Thoms, Silke; de Nooijer, Lennart Jan; Reichart, Gert-Jan; Bijma, Jelle

    2017-04-01

    In present day paleoclimate research one of the most pressing challenges is the reconstruction of atmospheric CO2 concentrations. A variety of proxies for several components of the marine inorganic carbon system have been developed in this context (e.g. B isotopes, B/Ca, U/Ca) to allow reconstruction of past seawater pH, HCO3- and CO32- and thereby facilitate estimates of past atmospheric pCO2. Based on culture experiments using the benthic foraminifera Ammonia sp. we describe a positive correlation between Sr/Ca and the carbonate system, namely DIC/bicarbonate ion concentration. Foraminiferal Sr/Ca ratios provide potentially additional constraints on the carbonate system proxy, because the analysis of foraminiferal carbonate Sr/Ca is straightforward and not easily contaminated. Applying our calibration to a published dataset of paleo-Sr/Ca suggests the validity of Sr/Ca as a carbonate system proxy. Furthermore, we explore how our data can be used to advance conceptual understanding of the foraminiferal biomineralization mechanism.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. A new aspect of single-layered cuprate superconductors — 90 K superconductors for Ca-doped Bi2Sr2CuO6+δ single crystals

    NASA Astrophysics Data System (ADS)

    Yoshizaki, R.; Yamamoto, T.; Ikeda, H.; Kadowaki, K.

    2012-12-01

    We found that the highest Tc (Tc max) of the superconductors in Bi-2201 phase was 80-90 K for the partially Ca substituted Bi2Sr2CuO6+δ for Sr. The superconductivity was confirmed to be bulk effect from a specific heat jump around Tc. By the findings the correlation between the structure and Tc max has been made clear and simple with respect to the distance between Cu and the apical oxygen for the single-layered cuprate superconductors in the hole doped system.

  2. Preparation and characterization of members of the system La 2- xA1+ xCu 2O 6± y where A = Ca,Sr

    NASA Astrophysics Data System (ADS)

    Doverspike, K.; Liu, J.-H.; Dwight, K.; Wold, A.

    1989-09-01

    Members of the system La 2- xA1+ xCu 2O 6± y, where A = Ca,Sr, were prepared by decomposition of the nitrates. The tolerance of these compounds for oxygen uptake, as well as the ease of substitution for the A-site ions, is shown to be closely related to the distribution of the alkaline-earth ions on the 8- and 9-coordinated A-sites.

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

    USGS Publications Warehouse

    Hedrick, J.B.; Sinha, S.P.; Kosynkin, V.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.

  4. 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

  5. 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.

  6. 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.

  7. Luminescence in Eu2+ and Ce3+ doped SrCaP2O7 phosphors

    NASA Astrophysics Data System (ADS)

    Shinde, K. N.

    Eu2+ and Ce3+ doped SrCaP2O7 has been achieved by modified solid state diffusion in reducing atmosphere. The prepared phosphor powders have been identified by their characteristic X-ray diffraction patterns. The mixed phases of α-Sr2P2O7 type with orthorhombic and α-Ca2P2O7 type with monoclinic form were investigated. Its excitation wavelength ranging from 250 to 430 nm fits well with the characteristic emission of UV light-emitting diode (LED). The excitation and emission spectra indicate that these phosphors can be effectively excited by the near-UV light, and emits blue (visible range due to 4f7 → 4f65d1 transition of Eu2+) particularly, SrCaP2O7: Eu2+ whereas, photoluminescence excitation spectrum measurements of Ce3+ activated SrCaP2O7 shows that the phosphor can be efficiently excited by UV-Vis light from 280 to 310 nm to realize emission in the near visible range due to the 5d-4f transition of Ce3+ ions which is applicable for scintillation purpose. The impacts of doping of divalent europium and trivalent cerium on photoluminescence properties on SrCaP2O7 pyrophosphate phosphors were investigated and I propose a feasible interpretation.

  8. Direct measurement of SR release flux by tracking 'Ca2+ spikes' in rat cardiac myocytes.

    PubMed

    Song, L S; Sham, J S; Stern, M D; Lakatta, E G; Cheng, H

    1998-11-01

    1. Ca2+ release flux across the sarcoplasmic reticulum (SR) during cardiac excitation-contraction coupling was investigated using a novel fluorescence method. Under whole-cell voltage-clamp conditions, rat ventricular myocytes were dialysed with a high concentration of EGTA (4.0 mM, 150 nM free Ca2+), to minimize the residence time of released Ca2+ in the cytoplasm, and a low-affinity, fast Ca2+ indicator, Oregon Green 488 BAPTA-5N (OG-5N; 1.0 mM, Kd approximately 31 microM), to optimize the detection of localized high [Ca2+] in release site microdomains. Confocal microscopy was employed to resolve intracellular [Ca2+] at high spatial and temporal resolution. 2. Analytical and numerical analyses indicated that, under conditions of high EGTA concentration, the free [Ca2+] change is the sum of two terms: one major term proportional to the SR release flux/Ca2+ influx, and the other reflecting the running integral of the released Ca2+. 3. Indeed, the OG-5N transients in EGTA-containing cells consisted of a prominent spike followed by a small pedestal. The OG-5N spike closely resembled the first derivative (d[Ca2+]/dt) of the conventional Ca2+ transient (with no EGTA), and mimicked the model-derived SR Ca2+ release function reported previously. In SR Ca2+-depleted cells, the OG-5N transient also closely followed the waveform of L-type Ca2+ current (ICa). Using ICa as a known source of Ca2+ influx, SR flux can be calibrated in vivo by a linear extrapolation of the ICa-elicited OG-5N signal. 4. The OG-5N image signal was localized to discrete release sites at the Z-line level of sarcomeres, indicating that the local OG-5N spike arises from 'Ca2+ spikes' at transverse (T) tubule-SR junctions (due to the imbalance between calcium ions entering the cytosol and the buffer molecules). 5. Both peak SR release flux and total amount of released Ca2+ exhibited a bell-shaped voltage dependence. The temporal pattern of SR release also varied with membrane voltage: Ca2+ release was

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. Preparation of the High-Tc Phase of Bi-Sr-Ca-Cu-O Superconductor

    NASA Astrophysics Data System (ADS)

    Endo, Utako; Koyama, Satoshi; Kawai, Tomoji

    1988-08-01

    Co-decomposition of mixed nitrates of Bi, Pb, Sr, Ca and Cu around 830°C under low oxygen pressure led to the formation of a high-Tc superconducting phase of Bi(Pb)-Sr-Ca-Cu-O with Tc(zero) at 107.5 K. A sample prepared by a conventional solid state reaction method under low oxygen pressure also showed the superconducting transition at 107.5 K. X-ray powder diffraction and magnetic susceptibility measurements on these samples revealed the high-Tc phase without 80 K or semiconducting phase. The reaction under low oxygen pressure has an effect to lower the temperature with broad ranges to render the high-Tc phase of the Bi-Sr-Ca-Cu-O.

  14. 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.

  15. 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.

  16. 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

  17. Control of mean ionic radius at Ca site by Sr co-doping for Ce doped LiCaAlF6 single crystals and the effects on optical and scintillation properties

    NASA Astrophysics Data System (ADS)

    Yokota, Yuui; Yamaji, Akihiro; Kurosawa, Shunsuke; Kamada, Kei; Yoshikawa, Akira

    2014-10-01

    Sr co-doped Ce:LiCaAlF6 [Ce:Li(Ca,Sr)AlF6] crystals with various Ca/Sr ratios were grown by a micro-pulling-down (μ-PD) method and effects of Sr co-doping on crystal structure, chemical composition, optical and scintillation properties for Ce:LiCaAlF6 crystals were investigated as a neutron scintillator. High transparent Ce2%:Li(Ca,Sr)AlF6 crystals with 2% and 5% Sr contents were obtained while Ce2%:Li(Ca,Sr)AlF6 crystals with 10% and 20% Sr contents included milky parts in the crystals. a- and c-axis lengths of Ce:Li(Ca,Sr)AlF6 phase systematically increased with an increase of Sr content. In addition to the emission at 284 and 308 nm from Ce3+ ion, emission peaks at 367 nm appeared by Sr co-doping.

  18. 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.

  19. 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.

  20. 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.

  1. Superconducting thin films of Bi-Sr-Ca-Cu-O obtained by laser ablation processing

    SciTech Connect

    Kim, B.F.; Bohandy, J.; Phillips, T.E.; Green, W.J.; Agostinelli, E.; Adrian, F.J.; Moorjani, K.; Swartzendruber, L.J.; Shull, R.D.; Bennett, L.H.; and others

    1988-07-25

    Thin films of Bi-Sr-Ca-Cu-O, deposited on (100) cubic zirconia by laser ablation from a bulk superconducting target of nominal composition BiSrCaCu/sub 2/ O/sub x/ , have been investigated by dc resistance and magnetically modulated microwave absorption measurements. The latter technique reveals important features regarding the phase purity of superconducting samples that are masked in the dc resistance measurements. The superconducting behavior of the films, as a function of the substrate temperature during deposition and the post-deposition annealing conditions, is discussed.

  2. Influence of carbonate ion in the crystallization medium on the formation and chemical composition of CaHA-SrHA solid solutions

    NASA Astrophysics Data System (ADS)

    Nikolaev, Anton; Kuz'mina, Maria; Frank-Kamenetskaya, Olga; Zorina, Maina

    2015-06-01

    The study of the influence of carbonate ions in a solution to Sr-distribution in system «solution-crystal» and to ion substitutions and the non-stoichiometry of formed CaHA-SrHA solid solutions was carried out. The CaHA-SrHA solid solutions were synthesized by precipitation from aqueous solutions with the atomic C/P ratio equal to 0, 0.05 and 0.1 at T = 90 °C. Resulting precipitates were studied using various methods including X-ray powder diffraction, infrared spectroscopy and different chemical analyses. The results of the study have shown that in the range of values of (Ca + Sr)/P in the water solution from 40% to 85%, the presence of carbonate ions (C/P = 0.05-0.1) promotes the incorporation of strontium in the apatite. Crystalline apatite solid solutions formed from water solutions of such composition are more defective compared to apatites that are mainly calcium or strontium. They are characterized by a smaller size coherence scattering domain length along [0 0 1] direction and a greater number of carbonate ions, water molecules and vacancies at the Ca-sites.

  3. 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.

  4. 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.

  5. 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

  6. Preparation of single 110 K phase of the Bi-Pb-Sr-Ca-Cu-O superconductor

    NASA Astrophysics Data System (ADS)

    Koyama, Satoshi; Endo, Utako; Kawai, Tomoji

    1988-10-01

    A pure 110 K phase of the Bi-Pb-Sr-Ca-Cu-O superconductor was obtained by co-decomposition of metal nitrates and a solid reaction under low oxygen pressure. The best starting compositions were in the region close to Bi(1.84)Pb(0.34)Sr2Ca2Cu3O(y) with a little excess of Ca and Cu. In this region, the samples showed the absence of the 80 K and semiconducting phase, and there was no indication of impurities at all. The 110 K phase without stacking faults is stabilized by the addition of Pb, so that the nominal composition close to the ideal one is required at the start. A little excess of Ca and Cu, however, effectively decreases the 80 K phase.

  7. Microstructure-property correlations in the Bi(Pb)-Sr-Ca-Cu-O superconducting system

    SciTech Connect

    Ramesh, R.; Green, S. M.; Mei, Y.; Manzi, A. E.; Luo, H. L.

    1989-08-01

    The microstructure of solid-state processed (Bi,Pb)-Sr-Ca-Cu-O ceramics was characterized using transmission electron microscopy techniques. A strong sensitivity of the transport properties to small deviations in the nominal Bi-Ca ratio is evidenced. Significant differences in the microstructure are shown to correlate to the changes in the transport properties. It is suggested that the microstructure can be predicted by combining the results of resistivity, Meissner, and shielding experiments.

  8. The calcium-sensing receptor (CaSR) defends against hypercalcemia independently of its regulation of parathyroid hormone secretion

    PubMed Central

    Quinn, Steven J.; Egbuna, Ogo I.; Baxi, Khanjan; Butters, Robert; Pang, Jian L.; Pollak, Martin R.; Goltzman, David; Brown, Edward M.

    2009-01-01

    The calcium-sensing receptor (CaSR) controls parathyroid hormone (PTH) secretion, which, in turn, via direct and indirect actions on kidney, bone, and intestine, maintains a normal extracellular ionized calcium concentration (Ca2+o). There is less understanding of the CaSR's homeostatic importance outside of the parathyroid gland. We have employed single and double knockout mouse models, namely mice lacking PTH alone (CaSR+/+ PTH−/−, referred to as C+P−), lacking both CaSR and PTH (CaSR−/− PTH−/−, C−P−) or wild-type (CaSR+/+ PTH+/+, C+P+) mice to study CaSR-specific functions without confounding CaSR-mediated changes in PTH. The mice received three hypercalcemic challenges: an oral Ca2+ load, injection or constant infusion of PTH via osmotic pump, or a phosphate-deficient diet. C−P− mice show increased susceptibility to developing hypercalcemia with all three challenges compared with the other two genotypes, whereas C+P− mice defend against hypercalcemia similarly to C+P+ mice. Reduced renal Ca2+ clearance contributes to the intolerance of the C−P− mice to Ca2+ loads, as they excrete less Ca2+ at any given Ca2+o than the other two genotypes, confirming the CaSR's direct role in regulating renal Ca2+ handling. In addition, C+P+ and C+P−, but not C−P−, mice showed increases in serum calcitonin (CT) levels during hypercalcemia. The level of 1,25(OH)2D3 in C−P− mice, in contrast, was similar to those in C+P− and C+P+ mice during an oral Ca2+ load, indicating that increased 1,25(OH)2D3 production cannot account for the oral Ca2+-induced hypercalcemia in the C−P− mice. Thus, CaSR-stimulated PTH release serves as a “floor” to defend against hypocalcemia. In contrast, high-Ca2+o-induced inhibition of PTH is not required for a robust defense against hypercalcemia, at least in mice, whereas high-Ca2+o-stimulated, CaSR-mediated CT secretion and renal Ca2+ excretion, and perhaps other factors, serve as a “ceiling” to limit

  9. Mechanical and corrosion properties of biodegradable Mg-1.5Mn-1Ca-xSr alloys

    NASA Astrophysics Data System (ADS)

    Sun, X.; Sun, S. Y.; Ning, Y. H.; Ning, Y. T.

    2017-03-01

    The mechanical properties and corrosion mechanism of both as-cast and solution-naturally age (T4) treated Mg-1.5Mn-1Ca-xSr alloys were investigated. The results showed that Sr is helpful to decrease grain size and increase the strength. The corrosion process of alloys was mainly determined by the quantity and distribution of second phases. Mg17Sr2, α-Mn and Ca-Sr phases acted as cathodes accelerated the corrosion of Mg2Ca anodic phase and α-Mg matrix. However, continuous distributed Mg17Sr2 was beneficial to resist the happening of localized corrosion because of its barrier effect. T4 treatment could significantly improve the mechanical properties and corrosion resistance of Mg alloys because of the dissolution of Mg2Ca phase and the dispersive distribution of Mg17Sr2 and α-Mn phases.

  10. 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.

  11. 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.

  12. Some Experiments on Flux Pinning in Pb Doped Bi-Sr-Ca-Cu-O System

    NASA Astrophysics Data System (ADS)

    Nagashima, Toshio; Watanabe, Kenji; Watahiki, Masaya; Fukai, Yuh

    1989-02-01

    In order to investigate the mechanism of energy dissipation by irreversible motion of fluxoids, we performed two different types of experiments; the oscillating-pendulum in magnetic field and the magnetic hysteresis including both major and minor loops. Results obtained for Pb-doped Bi-Sr-Ca-Cu-O system at 77 K are presented and some preliminary discussions are made.

  13. 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

  14. Properties of superconducting Bi-Sr-Ca-Cu-O system remelted under higher gravity conditions

    NASA Astrophysics Data System (ADS)

    Volkov, M. P.; Melekh, B. T.; Parfeniev, R. V.; Kartenko, N. F.; Regel, L. L.; Turchaninov, A. M.

    1992-04-01

    The structure and magnetic properties of high Tc superconductor Bi-Sr-Ca-Cu-O samples remelted under 1 g0, 8 g0 and 12 g0 gravity levels have been investigated. Superconducting properties make a change along the ingots. The dependence of structural and superconducting properties on the gravity level and their time degradation have been observed.

  15. Stratification of the Bi-Sr-Ca-Cu-O system melted under high gravity conditions

    NASA Astrophysics Data System (ADS)

    Volkov, M. P.; Melekh, B. T.; Parfen'ev, R. V.; Kartenko, N. F.; Turchaninov, A. M.; Regel, L. L.

    1992-08-01

    The structure and magnetic properties of high Tc superconductor Bi-Sr-Ca-Cu-O samples remelted under gravity levels have been investigated. Superconducting properties make a change along the ingots. The dependence of structural and superconducting properties on the gravity level and their time degradation have been observed.

  16. 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.

  17. Nonequilibrium THz Conductivity of Bi2Sr2CaCu2O8+d

    SciTech Connect

    Carnahan, M.A.; Kaindl, R.A.; Orenstein, J.; Chemla, D.S.; Oh,S.; Eckstein, J.N.

    2003-05-27

    Using high sensitivity visible-pump/THz-probe spectroscopywe investigate the dynamics of the complex optical conductivity inoptimally-doped Bi2Sr2CaCu2O8+d films directly after photoexcitation. Thephotoinduced change in the imaginary part, indicative of a reduction inthe superconducting condensate density, saturates at higherlaser-fluences and shows a complete destruction of thecondensate.

  18. Enthalpies of Formation of La 1- xAxMnO 3± δ ( A=Ca and Sr) Measured by High-Temperature Solution Calorimetry

    NASA Astrophysics Data System (ADS)

    Rørmark, Lisbeth; Stølen, Svein; Wiik, Kjell; Grande, Tor

    2002-01-01

    High-temperature reaction calorimetry using molten lead borate as a solvent has been used to study the thermochemistry of La1-xAxMnO3 (A=Ca and Sr, 0≤x≤1). The structural properties and the oxygen stoichiometry of the calcined powders were characterized by powder X-ray diffraction, thermogravimetry, and iodometry. The enthalpy of formation of the materials from their binary constituents has been calculated from measured enthalpy of solutions. The enthalpy of formation of La1-xCaxMnO3 from the component oxides becomes more exothermic with increasing substitution level x due to the increasing valence state of Mn, and demonstrates a nearly linear dependence of the average valence state of manganese. La1-xSrxMnO3 has a significantly more exothermic enthalpy of formation from the binary constituents than the Ca-substituted materials, and demonstrates a negative deviation from ideal behavior. The present thermodynamic data are discussed in relation to the Goldschmidt tolerance factor for the perovskite structure. Finally, the phase stability of Sr- and Ca-substituted LaMnO3 is addressed in relation to the application of these materials in solid oxide fuel cells.

  19. 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.

  20. Sr/Ca Ratios of Vaceletia: Implication for Biocalcification Mechanisms of Sclerosponges

    NASA Astrophysics Data System (ADS)

    Haase-Schramm, A.; Boehm, F.; Eisenhauer, A.; Garbe-Schoenberg, D.; Reitner, J.; Woerheide, G.

    2005-12-01

    Sclerosponges have been established as reliable proxy recorders for several environmental parameters like the radiocarbon and stable carbon isotopic composition, lead concentration, temperature and salinity of ambient water. Specifically, Sr/Ca ratios in skeletons of the Caribbean species Ceratoporella nicholsoni have been shown to record water temperatures with a very high precision. In order to study the variability of strontium incorporation and its temperature dependence in the skeletons of different sclerosponge species, we investigated the Sr/Ca ratios of various specimens of Vaceletia crypta and Vaceletia sp. from different sites and water depths in the Pacific. We determined Sr/Ca ratios and their temperature dependence in Vaceletia skeletons and compared them with published data of Ceratoporella and Astrosclera, inorganic aragonite and ooids. The Sr/Ca-temperature relation in Vaceletia and Ceratoporella is identical within errors (-0.1mmol/mol/K) and stronger than in inorganic aragonites and corals. The distribution coefficient of Sr/Ca in aragonite relative to sea water is similar in Ceratoporella and inorganic aragonite, however it is higher in Vaceletia, Astrosclera and ooids. The sclerosponges Ceratoporella, Vaceletia and Astrosclera precipitate the bulk of skeletal aragonite extracellularly as synvivo-diagenetic, epitactic overgrowth, in carbon and oxygen isotopic equilibrium with ambient sea water. Thus sea water derived carbonate ions are incorporated into the skeleton without biologic modifications. In contrast, the observed interspecific differences of skeletal cation ratios indicate an incorporation process, which involves the biologically controlled modification of the sea water ion composition. I. e. sclerosponges use a calcification mechanism that does not affect carbonate anions, but selectively incorporates certain cations.

  1. Crystal structure of new Li + ion conducting perovskites: Li 2 xCa 0.5- xTaO 3 and Li 0.2[Ca 1- ySr y] 0.4TaO 3

    NASA Astrophysics Data System (ADS)

    Pham, Quoc Nghi; Crosnier-Lopez, Marie-Pierre; Le Berre, Françoise; Fauth, François; Fourquet, Jean-Louis

    2004-09-01

    Two new solid solutions—Li 2 xCa 0.5- xTaO 3 (0.05⩽ x⩽0.25) and Li 0.2[Ca 1- ySr y] 0.4TaO 3 (0< y⩽0.15)—based on the A defective ABO 3 perovskite structural type, are synthesized. The crystal structures of these Li + ion conducting compounds are solved from synchrotron radiation and conventional X-ray powder diffraction data. The unit cells exhibit a classical orthorhombic distortion of the cubic perovskite model (space group Pnma No. 62) with parameters close to 2a p, 2 ap, 2a p ( ap, primitive cubic cell parameter). The distortion of the cubic aristotype arises from the three tilts system a+b-b- of the TaO 6 octahedra. For the same lithium content ( x=0.10), the Sr 2+ substitution to Ca 2+ is found to enhance the electrical conductivity by quasi-one order of magnitude (at 200 °C, bulk dc conductivity values are close to 2.3×10 -6 and 1.1×10 -5 S cm -1 for Li 0.2Ca 0.4TaO 3 and Li 0.2[Ca 0.9Sr 0.1] 0.4TaO 3, respectively).

  2. 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.

  3. 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.

  4. 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.

  5. CaSR-mediated interactions between calcium and magnesium homeostasis in mice

    PubMed Central

    Quinn, Stephen J.; Thomsen, Alex R. B.; Egbuna, Ogo; Pang, Jian; Baxi, Khanjan; Goltzman, David; Pollak, Martin

    2013-01-01

    Calcium (Ca) and magnesium (Mg) homeostasis are interrelated and share common regulatory hormones, including parathyroid hormone (PTH) and vitamin D. However, the role of the calcium-sensing receptor (CaSR) in Mg homeostasis in vivo is not well understood. We sought to investigate the interactions between Mg and Ca homeostasis using genetic mouse models with targeted inactivation of PTH (PTH KO) or both PTH and the calcium-sensing receptor (CaSR) (double knockout, DKO). Serum Mg is lower in PTH KO and DKO mice than in WT mice on standard chow, whereas supplemental dietary Ca leads to equivalent Mg levels for all three genotypes. Mg loading increases serum Mg in all genotypes; however, the increase in serum Mg is most pronounced in the DKO mice. Serum Ca is increased with Mg loading in the PTH KO and DKO mice but not in the WT mice. Here, too, the hypercalcemia is much greater in the DKO mice. Serum and especially urinary phosphate are reduced during Mg loading, which is likely due to intestinal chelation of phosphate by Mg. Mg loading decreases serum PTH in WT mice and increases serum calcitonin in both WT and PTH KO mice but not DKO mice. Furthermore, Mg loading elevates serum 1,25-dihydroxyvitamin D in all genotypes, with greater effects in PTH KO and DKO mice, possibly due to reduced levels of serum phosphorus and FGF23. These hormonal responses to Mg loading and the CaSR's role in regulating renal function may help to explain changes in serum Mg and Ca found during Mg loading. PMID:23360827

  6. 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.

  7. Induced overexpression of Na+/Ca2+ exchanger transgene: altered myocyte contractility, [Ca2+]i transients, SR Ca2+ contents, and action potential duration.

    PubMed

    Wang, JuFang; Chan, Tung O; Zhang, Xue-Qian; Gao, Erhe; Song, Jianliang; Koch, Walter J; Feldman, Arthur M; Cheung, Joseph Y

    2009-08-01

    We have produced mice in which expression of the rat cardiac Na(+)/Ca(2+) exchanger (NCX1) transgene was switched on when doxycycline was removed from the feed at 5 wk. At 8 to 10 wk, NCX1 expression in induced (Ind) mouse hearts was 2.5-fold higher but protein levels of sarco(endo)plasmic reticulum Ca(2+)-ATPase, alpha(1)- and alpha(2)-subunits of Na(+)-K(+)-ATPase, phospholamban, ryanodine receptor, calsequestrin, and unphosphorylated and phosphorylated phospholemman were unchanged compared with wild-type (WT) or noninduced (non-Ind) hearts. There was no cellular hypertrophy since WT, non-Ind, and Ind myocytes had similar whole cell membrane capacitance. In Ind myocytes, NCX1 current amplitude was approximately 42% higher, L-type Ca(2+) current amplitude was unchanged, and action potential duration was prolonged compared with WT or non-Ind myocytes. Contraction and intracellular Ca(2+) concentration ([Ca(2+)](i)) transient amplitudes in Ind myocytes were lower at 0.6, not different at 1.8, and higher at 5.0 mM extracellular Ca(2+) concentration ([Ca(2+)](o)) compared with WT or non-Ind myocytes. Despite similar Ca(2+) current amplitude and sarcoplasmic reticulum (SR) Ca(2+) uptake, SR Ca(2+) content at 5.0 mM [Ca(2+)](o) was significantly higher in Ind compared with non-Ind myocytes, indicating that NCX1 directly contributed to SR Ca(2+) loading. Echocardiography demonstrated that heart rate, left ventricular mass, ejection fraction, stroke volume, and cardiac output were similar among the three groups of animals. In vivo close-chest catheterization demonstrated similar contractility and relaxation among the three groups of mice, both at baseline and after stimulation with isoproterenol. We conclude that induced expression of NCX1 transgene resulted in altered [Ca(2+)](i) homeostasis, myocyte contractility, and action potential morphology. In addition, heart failure did not occur 3 to 5 wk after NCX1 transgene was induced to be expressed at levels found in

  8. BN-coated Ca(1-x)Sr(x)S:Eu solid-solution nanowires with tunable red light emission.

    PubMed

    Lin, Jing; Huang, Yang; Mi, Jiao; Zhang, Xinghua; Lu, Zunming; Xu, Xuewen; Fan, Ying; Zou, Jin; Tang, Chengchun

    2013-10-11

    We report on the controlled growth of novel BN-coated Ca(1-x)Sr(x)S:Eu nanowires via a solid-liquid-solid process. The Ca(1-x)Sr(x)S solid solution forms as one-dimensional nanowires and has been coated with homogeneous protective BN nanolayers. The structure and luminescence properties of this new nanocomposite have been systematically investigated. High-spatial-resolution cathodoluminescence investigations reveal that effective red color tuning has been achieved by tailoring the composition of the Ca(1-x)Sr(x)S nanowires. Moreover, codoping of Ce(3+) and Eu(2+) in the CaS nanowire can induce energy transfer in the matrix and make it possible to obtain enhanced orange color in the nanowires. The BN-coated Ca(1-x)Sr(x)S:Eu solid-solution nanowires are envisaged to be valuable red-emitting nanophosphors and useful in advanced nanodevices and white LEDs.

  9. 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.

  10. 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.

  11. Percolation metal-insullator transition in BiSrCaCuO films

    NASA Astrophysics Data System (ADS)

    Okunev, V. D.; Pafomov, N. N.; Svistunov, V. M.; Lewandowski, S. J.; Gierlowski, P.; Kula, W.

    1996-02-01

    An experimental investigation of the metal-insulator trnasition in BiSrCaCuO (BSCCO) films is reported. We performed resistivity, optical-absorption and critical-temperature measurements on several samples obtained by different technological methods. The results agree well with the percolation mechanism of the metal-insulator transition and show interesting correlations between room-temperature conductivity and superconducting properties of the investigated films.

  12. Angular scaling of the magnetoresistance of BiSrCaCuO thin films below Tc

    NASA Astrophysics Data System (ADS)

    Raffy, H.; Labdi, S.; Laborde, O.; Monceau, P.

    1991-12-01

    We have studied the magnetoresistance (MR) of c-axis oriented superconducting BiSrCaCuO thin films at various temperature (T⩽Tc) and various orientations of the magnetic field (H⩽20T) with respect to the crystallographic c-axis. A scaling law of the MR for different tilt angle of the magnetic field is presented. It results from the predominant role of the component of the magnetic field along the c-axis.

  13. 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.

  14. Temperature and carbonate ion effects on Mg/Ca and Sr/Ca ratios in benthic foraminifera: Aragonitic species Hoeglundina elegans

    NASA Astrophysics Data System (ADS)

    Rosenthal, Yair; Lear, Caroline H.; Oppo, Delia W.; Linsley, Braddock K.

    2006-03-01

    Core top samples from Atlantic (Little Bahama Banks (LBB)) and Pacific (Hawaii and Indonesia) depth transects have been analyzed in order to assess the influence of bottom water temperature (BWT) and aragonite saturation levels on Mg/Ca and Sr/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans. Both the Mg/Ca and Sr/Ca ratios in H. elegans tests show a general decrease with increasing water depth. Although at each site the decreasing trends are consistent with the in situ temperature profile, Mg/Ca and Sr/Ca ratios in LBB are substantially higher than in Indonesia and Hawaii at comparable water depths with a greater difference observed with increasing water depth. Because we find no significant difference between results obtained on "live" and "dead" specimens, we propose that these differences are due to primary effects on the metal uptake during test formation. Evaluation of the water column properties at each site suggests that in situ CO3 ion concentrations play an important role in determining the H. elegans Mg/Ca and Sr/Ca ratios. The CO3 ion effect is limited, however, only to aragonite saturation levels ([ΔCO3]aragonite) below 15 μmol kg-1. Above this level, temperature exerts a dominant effect. Accordingly, we propose that Mg/Ca and Sr/Ca in H. elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships: Mg/Ca = (0.034 ± 0.002)BWT + (0.96 ± 0.03) and Sr/Ca = (0.060 ± 0.002)BWT + (1.53 ± 0.03) (for [ΔCO3]aragonite > 15 μmol kg-1). The standard error associated with these equations is about ±1.1°C. Reconstruction of deeper water temperatures is complicated because in undersaturated waters, changes in Mg/Ca and Sr/Ca ratios reflect a combination of changes in [CO3] and BWT. Overall, we find that Sr/Ca, rather than Mg/Ca, in H. elegans may be a more accurate proxy for reconstructing paleotemperatures.

  15. Investigation into the effect of Si doping on the performance of Sr(1-y)Ca(y)MnO(3-δ) SOFC cathode materials.

    PubMed

    Porras-Vazquez, Jose M; Losilla, Enrique R; Keenan, Philip J; Hancock, Cathryn A; Kemp, Thomas F; Hanna, John V; Slater, Peter R

    2013-04-21

    In this paper we report the successful incorporation of silicon into Sr1-yCayMnO3-δ perovskite materials for potential applications in cathodes for solid oxide fuel cells. The Si substitution onto the B site of a (29)Si enriched Sr1-yCayMn1-xSixO3-δ perovskite system is confirmed by (29)Si MAS NMR measurements at low B0 field. The very large paramagnetic shift (~3000-3500 ppm) and anisotropy (span ~4000 ppm) suggests that the Si(4+) species experiences both Fermi contact and electron-nuclear dipolar contributions to the paramagnetic interaction with the Mn(3+/4+) centres. An improvement in the conductivity is observed for low level Si doping, which can be attributed to two factors. The first of these is attributed to the tetrahedral coordination preference of Si leading to the introduction of oxide ion vacancies, and hence a partial reduction of Mn(4+) to give mixed valence Mn. Secondly, for samples with high Sr levels, the undoped systems adopt a hexagonal perovskite structure containing face sharing of MnO6 octahedra, while Si doping is shown to help to stabilise the more highly conducting cubic perovskite containing corner linked octahedra. The level of Si, x, required to stabilise the cubic Sr1-yCayMn1-xSixO3-δ perovskite in these cases is shown to decrease with increasing Ca content; thus cubic symmetry is achieved at x = 0.05 for the Sr0.5Ca0.5Mn1-xSixO3-δ series; x = 0.075 for Sr0.7Ca0.3Mn1-xSixO3-δ; x = 0.10 for Sr0.8Ca0.2Mn1-xSixO3-δ; and x = 0.15 for SrMn1-xSixO3-δ. Composites with 50% Ce0.9Gd0.1O1.95 were examined on dense Ce0.9Gd0.1O1.95 pellets. For all series an improvement in the area specific resistances (ASR) values is observed for the Si-doped samples. Thus these preliminary results show that silicon can be incorporated into perovskite cathode materials and can have a beneficial effect on the performance.

  16. 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

  17. Effect of local A-site strain on dipole stability in A6GaNb9O30 (A = Ba, Sr, Ca) tetragonal tungsten bronze relaxor dielectrics.

    PubMed

    Miller, Andrew J; Rotaru, Andrei; Arnold, Donna C; Morrison, Finlay D

    2015-06-21

    A series of isovalently A-site substituted relaxor dielectric tetragonal tungsten bronzes of general formula Ba(6-x-y)Sr(x)Ca(y)GaNb(9)O(30) were investigated. The long-range (average) crystal structure as determined by conventional diffraction techniques varies monotonically according to Vegard's law. The dielectric properties, however, do not display a similar, simple "average size" dependence and instead show a dependence on the statistical size variance, i.e. size mismatch, of the A-cation. The difficulties in Vogel-Fulcher analysis of relative permittivity and the complementary approach of using dielectric loss data fitted to Jonscher's empirical universal dielectric relaxation model is discussed.

  18. Preliminary results of Sr/Ca ratio study of teeth samples by photoactivation analysis

    NASA Astrophysics Data System (ADS)

    Kavun, Yusuf; Boztosun, Ismail; Maraş, Ismail; Ðapo, Haris; Segebade, Christian

    2016-11-01

    In this paper, we have performed Photoactivation Analysis (PAA), a non-destructive method, which is used to determine elemental concentration of any sample. This paper presents the first use of this method in medical sciences in Turkey. The method was applied to the determination of Sr/Ca ratios in teeth. The collected teeth samples and standards (SrO and CaCO3) have been irradiated for a fixed time interval with high energy photons. The photons were generated by a clinical linear accelerator (cLINAC). The photon end-point energy was 18 MeV. The energy and the time interval were sufficient to achieve good activation. Afterward, the samples and standards have been analysed with gamma spectroscopic analysis by using an HPGe detector system. By analysing many samples, a database of Sr/Ca ratios will be created at Nuclear Research and Application Center (NUBA). In this paper we present a small subset of the already analysed data as an example of our capabilities and goal. We hope to set an example for future studies.

  19. 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

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

    PubMed

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

    2016-02-24

    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.

  1. 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.

  2. 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.

  3. 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.

  4. Structural and thermoelectric properties of A-site substituted (Sr1-x-yCaxNdy)TiO3 perovskites

    NASA Astrophysics Data System (ADS)

    Somaily, Hamoud H.

    Detailed structural results and models are reported for a special class of A-site substituted perovskites, (Sr1-x-yCaxNd y)TiO3, obtained with high resolution NPD data as a function of temperature and Nd composition. Two series with various A-site concentrations were synthesized and investigated. Each series was designed to have a nominally constant tolerance factor. At room temperature (RT), I determine the space groups of the Sr-rich and Sr poor series as being tetragonal I4/mcm and orthorhombic Pbnm, respectively. The RT structures remain unchanged upon increasing the Nd3+ content. However, three different orthorhombic phases, Pbnm, Ibmm, Pbcm, are determined for the Sr-rich series as a function of decreasing temperature; whereas, for the Sr-poor series the orthorhombic Pbnm structure is found to persist throughout the full range of measured temperatures. A phase diagram is constructed and proposed in the temperature range 0-1000 K. Thermoelectric properties of (Sr 1-x-yCaxNdy)TiO3 were also investigated and the best figure of merit ZT=0.07 was obtained with the Sr-rich series.

  5. Influence of MO/MF2 modifiers (M = Ca, Sr, Ba) on spectroscopic properties of Eu3+ ions in germanate and borate glasses

    NASA Astrophysics Data System (ADS)

    Zur, Lidia; Janek, Joanna; Pietrasik, Ewa; Sołtys, Marta; Pisarska, Joanna; Pisarski, Wojciech A.

    2016-11-01

    Series of Eu3+-doped lead-free germanate and borate glasses were synthesized. The MO glass modifiers (M = Ca, Sr or Ba) were partially or totally substituted by MF2 in chemical composition. In contrast to samples modified by CaO/CaF2 or SrO/SrF2, the germanate glass samples containing BaO and/or BaF2 are fully amorphous, while the lead-free borate glasses are fully amorphous, independently from glass modifiers. Effect of glass modifiers on spectroscopic properties of Eu3+ were systematically investigated. For that reason, excitation and emission spectra of Eu3+ ions in examined systems were registered. Based on the emission spectra, ratio of integrated luminescence intensity of the 5D0 → 7F2 transition to that of the 5D0 → 7F1 transition (R factor) was calculated. Moreover, the luminescence decay curves were collected and the luminescence lifetimes of the 5D0 excited state of Eu3+ ions were determined in function of MF2 concentration.

  6. 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

  7. Growth of Nucleation Sites on Pd-doped Bi_2Sr_2Ca1 Cu_2O_8+δ

    NASA Astrophysics Data System (ADS)

    Kouzoudis, D.; Finnemore, D. K.; Xu, Ming; Balachandran

    1996-03-01

    Enviromental Scanning Electron Microscope has shown evidence that during the growth of Bi_2Sr_2Ca_2Cu_3O_10+δ from mixed powders of Pb-doped Bi_2Sr_2Ca_1Cu_2O_8+δ and other oxides, a dense array of hillocks or mesas grow at the interface between an Ag overlay and Pb doped Bi_2Sr_2Ca_1Cu_2O_8+δ grains. These hillocks develop a texture that looks like ''chicken pox'' during the ramp up to the reaction temperature starting at about 700^circ C and they are about 500 to 1000 nm across and are spaced at about 500 to 1000 nm. If there is no Ag, this texture does not develop. Preliminary measurments indicate that the hillocks are re-crystallization of (Bi,Pb)_2Sr_2Ca_1Cu_2O_8+δ and are definetely not a Pb rich phase

  8. 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

  9. Site-related near-infrared luminescence in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):Fe{sup 3+} phosphors

    SciTech Connect

    Li, Y.J.; Ma, Y.Y.; Ye, S.; Hu, G.P.; Zhang, Q.Y.

    2014-03-01

    Graphical abstract: - Highlights: • Intense 700–850 nm NIR emissions in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):1%Fe{sup 3+} has been obtained. • The NIR emissions can be ascribed to the octahedral Fe{sup 3+} sites. • The site symmetry of Fe{sup 3+} in CA{sub 6} and SA{sub 6} may be lower than that in BA{sub 6}. • The phosphors may be potentially applied in the high-resolution bioimaging. - Abstract: Intense and broad near-infrared (NIR) photoluminescence (PL) peaks locating at 777, 808 and 810 nm is observed for BaAl{sub 12}O{sub 19} (BA{sub 6}):1%Fe{sup 3+}, CaAl{sub 12}O{sub 19} (CA{sub 6}):1%Fe{sup 3+} and SrAl{sub 12}O{sub 19} (SA{sub 6}):1%Fe{sup 3+}, respectively. Electron paramagnetic resonance (EPR) spectra show that Fe{sup 3+} ions substitute for the different types of Al{sup 3+} sites simultaneously. Meanwhile, the luminescence of Fe{sup 3+} in MAl{sub 12}O{sub 19} (M = Ca, Sr and Ba) are ascribed to octahedral Fe{sup 3+}. In addition, the site symmetry of Fe{sup 3+} in CA{sub 6}/SA{sub 6} is lower compared with BA{sub 6}, deduced from the photoluminescence excitation (PLE), EPR and Fourier-transform infrared (FT-IR) spectra. These phosphors can be considered as good candidates for the applications in the field of high-resolution bioimaging.

  10. Effects of chemical pressure on the magnetic ground states of the osmate double perovskites SrCaCoOs6 and Ca2CoOsO6

    DOE PAGES

    Morrow, Ryan; Yan, Jiaqiang; McGuire, Michael A.; ...

    2015-09-21

    The magnetic ground state in the double perovskite system Sr2-xCaxCoOsO6 changes from an antiferromagnet (x=0), to a spin glass (x=1), to a ferrimagnet (x=2) as the Ca content increases. Moreover, this crossover is driven by chemical pressure effects that control the relative strength of magnetic exchange interactions. The synthesis, crystal structure, and magnetism of SrCaCoOsO6 and Ca2CoOsO6 are investigated and compared with Sr2CoOsO6. Both compounds adopt a monoclinic crystal structure with rock-salt ordering of Co2+ and Os6+ and a-a-b+ octahedral tilting, but the average Co–O–Os bond angle evolves from 158.0(3) in SrCaCoOsO6 to 150.54(9)° in Ca2CoOsO6 as the smaller Ca2+more » ion replaces Sr2+. And while this change may seem minor, it has a profound effect on the magnetism, changing the magnetic ground state from antiferromagnetic in Sr2CoOsO6 (TN1=108K, TN2=70K), to a spin glass in SrCaCoOsO6 (Tf1=32K, Tf2=13K), to ferrimagnetic in Ca2CoOsO6 (TC=145K). Finally, in the first two compounds the observation of two transitions is consistent with weak coupling between the Co and Os sublattices.« less

  11. The effect of shell secretion rate on Mg / Ca and Sr / Ca ratios in biogenic calcite as observed in a belemnite rostrum

    NASA Astrophysics Data System (ADS)

    Vinzenz Ullmann, Clemens; Pogge von Strandmann, Philip A. E.

    2017-01-01

    Isotopic ratios and concentrations of the alkaline earth metals Mg and Sr in biogenic calcite are of great importance as proxies for environmental parameters. In particular, the Mg / Ca ratio as a temperature proxy has had considerable success. It is often hard to determine, however, which parameter ultimately controls the concentration of these elements in calcite. Here, multiple Mg / Ca and Sr / Ca transects through a belemnite rostrum of Passaloteuthis bisulcata (Blainville, 1827) are used to isolate the effect of calcite secretion rate on incorporation of Mg and Sr into the calcite. With increasing calcite secretion rate Mg / Ca ratios decrease and Sr / Ca ratios in the rostrum increase. In the studied specimen this effect is found to be linear for both element ratios over a calcite secretion rate increase of ca. 150 %. Mg / Ca ratios and Sr / Ca ratios show a linear co-variation with increasing relative growth rate, where a 100 % increase in growth rate leads to a (8.1 ± 0.9) % depletion in Mg and a (5.9 ± 0.7) % enrichment in Sr. The magnitude of the calcite secretion rate effect on Mg is (37 ± 4) % greater than that on Sr. These findings are qualitatively confirmed by a geochemical transect through a second rostrum of Passaloteuthis sp. Growth rate effects are well defined in rostra of Passaloteuthis, but only account for a minor part of chemical heterogeneity. Biasing effects on palaeoenvironmental studies can be minimized by informed sampling, whereby the apex and apical line of the rostrum are avoided.

  12. 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.

  13. 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.

  14. Evidence for the non-influence of salinity variability on the Porites coral Sr/Ca palaeothermometer

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Porites coral-based sea surface temperature (SST) reconstructions are obtained from the measurement of skeleton Sr/Ca ratio. However, the influence of salinity in the incorporation of these trace elements in the Porites aragonitic skeleton is still poorly documented. Laboratory experiments indicate that in three different 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 Porites Sr/Ca-based SST reconstructions at monthly and interannual timescales in open-ocean environmental conditions. We use a large spatial compilation of published Porites data from the Red Sea and Pacific and Indian oceans. Additionally to those published records, we add a new eastern Pacific coral Sr/Ca record from Clipperton Atoll. Using two different salinity products (Simple Ocean Data Assimilation (SODA) SSS reanalyses version 2.2.4, Carton and Giese, 2008; and instrumental SSS from the Institut de Recherche pour le Développement, France (IRD) Delcroix et al., 2011), we find no evidence of salinity bias on the Sr/Ca SST proxy at monthly and interannual timescales. We conclude that Porites Sr/Ca is a reliable palaeothermometer that is not influenced by salinity variability.

  15. 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.

  16. Electronic structure, chemical bonding, and geometry of pure and Sr-doped CaCO3.

    PubMed

    Stashans, Arvids; Chamba, Gaston; Pinto, Henry

    2008-02-01

    The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures.

  17. 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

  18. Comparison of Equatorial Pacific Sea Surface Variability and Trends with Sr/Ca Records from Multiple Corals

    NASA Astrophysics Data System (ADS)

    Alpert, A.; Cohen, A. L.; Oppo, D.; Gove, J.; Young, C.; Decarlo, T. M.

    2015-12-01

    The short duration of instrumental SST records makes it difficult to reliably separate anthropogenic-related trends from natural variability, especially in the tropical Pacific. The Sr/Ca ratio of massive corals has been used to lengthen the record and fill data gaps but its reliability has been questioned because different coral colonies on the same reef can have different Sr/Ca-temperature relationships and yield opposing derived SST trends. We exploited a unique multi-year dataset of in situ temperature data to assess whether inter-colony differences are attributable to small-scale oceanographic variability or "vital effects" and to quantify the effect of these 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 temperature data from in situ loggers also placed on the east and west sides. In general, Sr/Ca captured - albeit inconsistently - the occurrence of inter-annual SST events but their amplitude was not consistently recorded by any of the corals. However, the Sr/Ca-temperature regressions derived from the four different colonies were statistically distinct. Assuming these relationships represent the full range of Sr/Ca-temperature calibrations in Jarvis Porites, we assessed how well Sr/Ca of a fossil coral with an unknown Sr/Ca-temperature relationship can constrain past temperatures. Our results indicate that the standard error of prediction methods underestimate the actual error as we could not reliably reconstruct the amplitude or frequency of ENSO events as large as ±2°C. Further, Sr/Ca of one coral implied a statistically significant cooling trend while that of its neighbor implied a warming trend whereas no long-term trend was identified in the instrumental data. This observation of a derived trend where none exists is consistent with observations made independently at other coral reef sites in the

  19. Analysis of the structure and Mössbauer study of the neodymium substitution in the Sr-hexaferrite

    NASA Astrophysics Data System (ADS)

    Pérez-Juache, T. J.; Guerrero, A. L.; Cabal-Velarde, J. G.; Mirabal-García, M.; Palomares-Sánchez, S. A.; Matutes-Aquino, J. A.

    2016-12-01

    This work reads on the obtainment of the strontium hexaferrite substituted with neodymium in its pure phase using the solid state reaction method. The solubility of neodymium on the strontium hexaferrite was investigated according with the formula Sr1-xNdxFe12O19, for x=0.00, 0.05, 0.10, 0.15, 0.20 and 0.25. Results indicate that neodymium is soluble in the hexaferrite until x=0.15. In samples with higher neodymium content there are traces of secondary phases. Analysis of magnetic and structural properties was performed in function of the neodymium content, always in its solubility range. From the structural properties, it was observed that the addition of a little neodymium quantity in the Sr-hexaferrite causes an important reduction of the unit cell volume. Also, magnetic properties are strongly linked to the structural behavior, in this case a trend to reduce the magnetization of the samples was detected when neodymium content increased, which can be explained in terms of fluctuations of the superexchange coupling conducted by the neodymium interactions with the structure. Mössbauer analysis was carried out in order to analyze the effects of the neodymium substitution on the hyperfine parameters, as well as to confirm the preferential site of the neodymium substitution in the Sr-hexaferrite.

  20. NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7: novel single crystal pyrochlore antiferromagnets

    NASA Astrophysics Data System (ADS)

    Sanders, M. B.; Krizan, J. W.; Plumb, K. W.; McQueen, T. M.; Cava, R. J.

    2017-02-01

    The crystal structures and magnetic properties of three previously unreported A2B2F7 pyrochlore materials, NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7 are presented. In these compounds, either S  =  2Fe2+ or S  =  5/2Mn2+ is on the B site, while nonmagnetic Na and Ca (Na and Sr) are disordered on the A site. The materials, which were grown as crystals via the floating zone method, display high effective magnetic moments and large Curie-Weiss thetas. Despite these characteristics, no ordering transition is detected. However, freezing of the magnetic spins, characterized by peaks in the susceptibility or specific heat, is observed at very low temperatures. The empirical frustration index, f  =  -θ CW/T f, for the materials are 36 (NaSrMn2F7), 27 (NaSrFe2F7), and 19 (NaCaFe2F7). AC susceptibility, DC susceptibility, and heat capacity measurements are used to characterize the observed spin glass behavior. The results suggest that the compounds are frustrated pyrochlore antiferromagnets with weak bond disorder. The magnetic phenomena that these fluoride pyrochlores exhibit, in addition to their availability as relatively large single crystals, make them promising candidates for the study of geometric magnetic frustration.

  1. Influence of Ca Substitution on Piezoelectric Properties of Ba1-x Ca x TiO3

    NASA Astrophysics Data System (ADS)

    Nguyen, Van Khien; Le, Thi Hong Phong; Tran, Thi Kim Chi; Truong, Van Chuong; Than, Trong Huy; Le, Van Hong

    2017-02-01

    Ca has been partially substituted for Ba in the structure of BaTiO3 to investigate the influence on its dielectric relaxation time and piezoelectric properties. Ba1-x Ca x TiO3 samples with x = 0.120, 0.140, 0.142, 0.144, 0.146, 0.148, 0.150, 0.152, and 0.160 were fabricated by the solid-state reaction method. The phase composition of the samples was identified by x-ray diffraction analysis. The impedance versus frequency characteristic in a range from 100 Hz to 2.5 MHz was measured at room temperature for all samples in both disk and cylinder shape. The results showed that Ca substitution considerably affected the piezoelectric properties of the fabricated samples. The piezoelectric properties were improved and optimized for x = 0.148, for which the relaxation time reached its minimal value. The relationship between the dielectric relaxation time and piezoelectric properties was found to be associated with structural phase competition as identified by high-resolution transmission electron microscopy analysis.

  2. Flux creep in Bi2Sr2Ca1Cu2O(8+x) single crystals

    NASA Technical Reports Server (NTRS)

    Agostinelli, E.; Fiorani, D.; Testa, A. M.; Tejada, J.

    1991-01-01

    Dissipative effects were investigated in Bi2Sr2Ca1Cu2O(8+x) single crystals by critical current and magnetic relaxation measurements. Activation energies for the flux motion were determined from the temperature dependence of the critical current and from the time decay of the zero field cooled and the remanent magnetization. The effective activation energy was found to increase with temperature, in agreement with the existence of a distribution of activation energies (E sub o 20 meV at 4.2 K for H + 10 kOe applied parallel to the c-axis.).

  3. 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.

  4. Spectroscopy of LiCa and RbSr Molecules on Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.

    2013-06-01

    We report on the investigation of mixed alkali metal (Ak) - alkaline earth metal (Ake) molecules on the surface of helium nanodroplets (He_{N}). These molecules have recently attracted considerable attention as candidates for the formation of ultracold molecules with a magnetic and an electronic dipole moment. In our experiments, LiCa and RbSr molecules are formed in a sequential pick-up process in their X^{2}Σ^{+} ground state and cool down rapidly to the droplet temperature of 0.38 K. Excitation spectra of LiCa and RbSr were recorded by using resonance enhanced multi-photon ionization time-of-flight (REMPI-TOF) spectroscopy and laser induced fluorescence (LIF) spectroscopy. On the helium droplet, vibronic transitions in Ak-Ake molecules are broadened and show a characteristic asymmetric peak form, which is caused by the interaction between the molecule and the superfluid He_{N} environment. For the lower electronic transitions in LiCa and RbSr progressions of vibrational bands excited from the X^{2}Σ^{+} (ν'' = 0) state are observed. The LiCa spectra can be compared to molecular beam experiments, which enables the assignment of three band systems near 15260 cm^{-1}, 19300 cm^{-1} and 22120 cm^{-1} as ^{2}Σ^{+}, ^{2}Π_{Ω} and ^{2}Π band, respectively. In the RbSr excitation spectrum we observe a vibrationally resolved band system near 14020 cm^{-1}. Upon electronic excitation, a fraction of the molecules desorb from the droplet surface and dispersed fluorescence spectra allow to study the X^{2}Σ^{+} ground state and excited states of free Ak-Ake molecules. H. Hara, Y. Takasu, Y. Yamaoka, J.M. Doyle, Y. Takahashi, Phys. Rev. Lett. 106, 205304 (2011) C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) L. M. Russon, G. K. Rothschopf, M. D. Morse, A. I

  5. Rare gases and Ca, Sr, and Ba in Apollo 17 drill-core fines

    NASA Technical Reports Server (NTRS)

    Pepin, R. O.; Dragon, J. C.; Johnson, N. L.; Bates, A.; Coscio, M. R., Jr.; Murthy, V. R.

    1975-01-01

    Trapped gas isotopic compositions and spallation gas concentrations as functions of depth in the Apollo 17 drill core were determined from mass spectrometer studies by means of correlation techniques. The distribution of He, Ne, Ar, Kr, and Xe as well as Ca, Sr, and Ba was investigated, and rare-gas spallation and neutron capture profiles are compared with attention to proposed depositional models for the Taurus-Littrow regolith. The data exclude a sedimentation pattern similar to that found at the Apollo 15 site but are possibly compatible with long-term continuous accretion models or models of very recent rapid accumulation of regolith.

  6. Preparation of Bulky Bi(Pb)-Sr-Ca-Cu-O Superconductor by Magnetized Twin-Roll

    NASA Astrophysics Data System (ADS)

    Kawahara, Nobuaki; Kawabata, Sanemasa; Enami, Hiroyoshi; Shinohara, Toshiyuki; Hoshizaki, Hiroki; Hasegawa, Masashi; Asai, Shigeo; Imura, Toru

    1990-02-01

    A highly oriented (Bi, Pb)2Sr2Ca2Cu3Ox bulk superconductor has been prepared by magnetized twin-roll processing. In these bulks, plate-like crystal grains were highly oriented by a magnetic and mechanical force. The grain c-axes were parallel to the magnetic field and pressing directions. In fact, both critical current density (Jc) and orientation degree of the sample rolled under 2 T were higher than those of the sample rolled with no magnetic field. The magnetized twin-roll processing is effective not only in enhancing grain-orientation but also in packing to improve Jc.

  7. 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}.

  8. 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.

  9. Ca2+_, Sr2+_force relationships and kinetic properties of fast-twitch rat leg muscle fibre subtypes.

    PubMed

    Galler, S

    1999-10-01

    Force generation of fast-twitch and slow-twitch fibres exhibits large differences in its sensitivity to Ca2+ and Sr2+ (e.g. Fink et al. 1986). Little is known about fast-twitch fibre subtypes. Thus, a variety of mechanical measurements on segments of rehydrated freeze-dried fast-twitch rat leg muscle fibres were executed in this study. Among these, the Ca2+- and Sr2+-force relationship and the unloaded shortening velocity were determined. The fibres were classified into subtypes according to their kinetics of stretch activation (Galler et al. 1994). In all fibres, the maximal force under Sr2+ activation was about 0.9 of that under Ca2+ activation. The Ca2+- and Sr2+-force relationship exhibited a biphasic shape with a steeper part (Hill coefficient, n1) below 50% and a flatter part (Hill coefficient, n2) above 50% of maximal force. The difference between the Ca2+ - and Sr2+ -sensitivity was independent of the fibre subtypes. The Hill coefficients were only partially correlated with kinetic properties. The correlation was more pronounced for the unloaded shortening velocity than for the kinetics of stretch activation. The data are consistent with the idea that the Ca2+ and Sr2+ sensitivities of fast-twitch fibres are mainly determined by a single isoform of troponin C. Among several protein isoforms, the isoforms of the myosin light chains seem to be involved for determining the slope of the Ca2+- and Sr2+-force relationship of fast-twitch muscle fibres.

  10. Effect of Eu/Sr Ratios on Ferroelectric and Fluorescent Properties of Eu-Substituted Strontium Bismuth Tantalate Films

    NASA Astrophysics Data System (ADS)

    Aizawa, Koji; Ohtani, Yusuke

    2008-09-01

    The ferroelectric and fluorescent properties of Eu-substituted strontium bismuth tantalate (Eu-SBT) films grown on Pt/Ti/SiO2/Si substrates by spin coating were investigated. The polycrystalline Eu-SBT films with Aurivillius phases were grown at Eu/Sr ratios between 0 and 0.25. Moreover, the lattice constants along the a- and c-axes at Eu/Sr=0.25 in comparison with Eu/Sr=0 decreased by approximately 0.36 and 0.19%, respectively. The remnant polarization values of the Eu-SBT films with Eu/Sr ratios of 0 and 0.25 were approximately 6.6 and 5.8 µC/cm2, respectively. The 80%-fatigue endurance of a Eu-SBT film with Eu/Sr=0.25 was approximately 3.1×109 cycles when a 10 kHz triangular wave with an amplitude of 8 V (approximately 530 kV/cm electric field) was used. The photoluminescence intensity of the Eu-SBT films was increased by Eu doping with negligible change of the remnant polarization. Emission peaks at approximately 600 nm in wavelength, which were associated with the 5D0-7F transitions of Eu3+, were observed in the Eu-SBT films.

  11. 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.

  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. 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.

  14. Sr-90 Immobilization by Infiltration of a Ca-Citrate-PO4 Solution into the Hanford 100-N Area Vadose Zone

    SciTech Connect

    Szecsody, Jim E.; Fruchter, Jonathan S.; Burns, Carolyn A.; Rockhold, Mark L.; Oostrom, Mart; Williams, Mark D.; Vermeul, Vince R.

    2008-01-11

    This project was initiated to develop a strategy for infiltration of a Ca-citrate-PO4 solution in order to precipitate apatite [Ca6(PO4)10(OH)2] in desired locations in the vadose zone for Sr-90 remediation. Laboratory experiments have demonstrated that infiltration of a Ca-citrate-PO4 solution into sediments at low and high water saturation results in citrate biodegradation and formation of apatite. The citrate biodegradation rate was relatively uniform, in spite of the spatial variability of sediment microbial biomass, likely because of microbial transport processes that occur during solution infiltration. The precipitate was characterized as hydroxyapatite, and the Sr-90 substitution into apatite was shown to have a half-life of 5.5 to 16 months. 1-D and 2-D laboratory infiltration experiments quantified the spatial distribution of apatite that formed during solution infiltration. Slow infiltration in 2-D experiments at low water saturation show the apatite precipitate concentrated in the upper third of the infiltration zone. More rapid 1-D infiltration studies show the apatite precipitate concentrated at greater depth.

  15. 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.

  16. 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

  17. Electrical and magnetic properties of honeycomb-type Bi(Pb)-Sr-Ca-Cu-O superconductors

    NASA Astrophysics Data System (ADS)

    Altunbas, M.; Yanmaz, E.; Nezir, S.; Karal, H.; Vidadi, Yu. A.

    1994-11-01

    Bi2O3, PbO, SrCO3, CaO and CuO compounds have been dissolved in liquid ammonium nitrate in order to produce Bi(1.8)Pb(0.2)Sr2Ca2Cu3O10 (2223) superconductors of honeycomb-type structure. The resulting metal nitrate and nitrate complexes have been decomposed in an environment activated by the exothermic reaction. Powders, homogeneous on the molecular scale, containing the binary and ternary oxides as the necessary constituents have been produced. Samples in the form of pellets have been annealed at 845 deg C for 25-125 h. This honeycomb-type BSCCO superconductor with a critical temperature T(sub c) = 110 K and a density of 3 g/cc has been produced. The volume of the sample has increased by about 25%-40% after annealing. Electrical and magnetic properties of the samples have been investigated in three regions: the superconducting region T less than T(sub c), the region T(sub c) less than T less than T(sub c) + Delta T(sub F) where the Flicker effect has been observed (Delta T(sub F) = 20 K), and the normal region T greater than T(sub c) Delta T(sub F). It has been found that it is possible to have a controllable variation in critical current density and that the optimum annealing time was about 100 h in order to obtain its maximum value.

  18. 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.

  19. Characterization of MeWO 4 (Me = Ba, Sr and Ca) nanocrystallines prepared by sonochemical method

    NASA Astrophysics Data System (ADS)

    Thongtem, Titipun; Phuruangrat, Anukorn; Thongtem, Somchai

    2008-09-01

    Metal tungstates (MeWO 4, Me = Ba, Sr and Ca) were successfully prepared using the corresponding Me(NO 3) 2·2H 2O and Na 2WO 4·2H 2O in ethylene glycol by the 5 h sonochemical process. The tungstate phases with scheelite structure were detected with X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their calculated lattice parameters are in accord with those of the JCPDS cards. Transmission electron microscopy (TEM) revealed the presence of nanoparticles composing the products. Their average sizes are 42.0 ± 10.4, 18.5 ± 5.1 and 13.1 ± 3.3 nm for Me = Ba, Sr and Ca, respectively. Interplanar spaces of the crystals were also characterized with high-resolution TEM (HRTEM). Their crystallographic planes are aligned in systematic array. Six different vibration wavenumbers were detected using Raman spectrometer and are specified as ν1(A g), ν3(B g), ν3(E g), ν4(B g), ν2(A g) and free rotation. Fourier transform infrared (FTIR) spectra provided the evidence of scheelite structure with W-O anti-symmetric stretching vibration of [WO 4] 2- tetrahedrons at 786-883 cm -1. Photoluminescence emission of the products was detected over the range of 384-416 nm.

  20. Temperature and [CO3 ] Effects on Mg/Ca and Sr/Ca in the Benthic Foraminifera Species of Hoeglundina Elegans and Cibicidoides

    NASA Astrophysics Data System (ADS)

    Lear, C. H.; Rosenthal, Y.; Oppo, D. W.; Linsley, B. K.

    2005-12-01

    Current core-top calibrations suggest that the temperature sensitivity of Mg/Ca in Cibicidoides sp. tests is essentially identical with the 10% increase in Mg/Ca per 1°C observed in many planktonic species. However, there is also evidence suggesting that non temperature-related effects may exert additional control on Mg/Ca in foraminiferal calcite. Here we use core-top samples from Atlantic (Little Bahama Banks, LBB; Arctic) and Pacific (Hawaii, and Indonesia) depth transects to assess the influence of bottom water temperature (BWT) and carbonate saturation levels on metal/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans and calcitic Cibicidoides sp. We find that in situ CO3 ion concentrations play an important role in determining the Mg/Ca ratios in Cibicidoides sp. and Mg/Ca and Sr/Ca in H. elegans. The CO3 ion effect is limited, however, only to relatively low saturation levels, whereas at over-saturated levels, temperature exert the dominant effect on these metal ratios. Because we find no significant difference between results obtained on ``live'' and ``dead'' specimens, we propose that these differences are due to primary effects on metal uptake during test formations and not because of dissolution. Based on the new results we reappraise the Mg/Ca-temperature relationship of Cibicidoides sp. and propose a new calibration. We also propose that Sr/Ca and Mg/Ca in H. elegans tests can be used to reconstruct thermocline temperatures. Sr/Ca-thermometry in H. elegans may be especially useful in cases where the use of Mg/Ca thermometry in calcitic foraminfera has been compromised by contamination issues. In both cases, temperature estimates in low carbonate saturation levels may be grossly inaccurate.

  1. Biogeochemistry of stable Ca and radiogenic Sr isotopes in a larch-covered permafrost-dominated watershed of Central Siberia

    NASA Astrophysics Data System (ADS)

    Bagard, Marie-Laure; Schmitt, Anne-Désirée; Chabaux, François; Pokrovsky, Oleg S.; Viers, Jérôme; Stille, Peter; Labolle, François; Prokushkin, Anatoly S.

    2013-08-01

    Stable Ca and radiogenic Sr isotope compositions were measured in different compartments (stream water, soil solutions, rocks, soils and soil leachates and vegetation) of a small permafrost-dominated watershed in the Central Siberian Plateau. The Sr and Ca in the area are supplied by basalt weathering and atmospheric depositions, which significantly impact the Sr isotopic compositions. Only vegetation significantly fractionates the calcium isotopes within the watershed. These fractionations occur during Ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and Ca oxalate crystallisations during Ca circulation or storage within plant organs. Biomass degradation significantly influences the Ca isotopic compositions of soil solutions and soil leachates via the release of light Ca, and organic and organo-mineral colloids are thought to affect the Ca isotopic compositions of soil solutions by preferential scavenging of 40Ca. The imprint of organic matter degradation on the δ44/40Ca of soil solutions is much more significant for the warmer south-facing slope of the watershed than for the shallow and cold soil active layer of the north-facing slope. As a result, the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil-water system in permafrost areas. Finally, the obtained δ44/40Ca patterns contrast with those described for permafrost-free environments with a much lower δ44/40Ca fractionation factor between soils and plants, suggesting specific features of organic matter decomposition in permafrost environments. The biologically induced Ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the δ44/40Ca signature may be controlled by the heterogeneity of lithological sources.

  2. (Ca,Sr)CO 3 aqueous-solid solution systems: From atomistic simulations to thermodynamic modelling

    NASA Astrophysics Data System (ADS)

    Kulik, D. A.; Vinograd, V. L.; Paulsen, N.; Winkler, B.

    The uptake of strontium in calcium carbonates is a topic of sustained interest in (radio)geochemistry. The available data on (Ca,Sr)CO 3 aqueous-solid solution (Aq-SS) systems with the calcite ( R3barc) and aragonite ( Pmcn) structures are reconciled using a stepwise approach from atomistic to thermodynamic modelling consisting of: (1) Quantum-mechanical and force-field calculations aimed at the prediction of standard thermodynamic properties of a hypothetical pure SrCO 3( R3barc) compound; (2) Force-field calculations on supercell structures of end members with defects of incoherent atoms in the cluster expansion framework, followed by Monte Carlo simulations of the excess SS mixing properties in both R3barc and Pmcn structures; (3) Thermodynamic modelling of Aq-SS systems with SS phases of both structures using the Gibbs Energy Minimization (GEM) code in two scenarios: (i) aqueous solution in equilibrium with one SS phase of either Pmcn or R3barc structure; (ii) aqueous solution equilibrated with two SS phases having different structures. The (ii) case was investigated using two approaches: (A) The two SS introduced as separate phases, with the excess mixing in each phase described by an own Guggenheim polynomial and (B) End members of different structures combined into a single calcite-strontianite phase using the Darken’s Quadratic Formulation (DQF) mixing model. For the aragonite-strontianite SS system, a nearly symmetric solvus is predicted in good agreement with the available calorimetric and electrochemical data. The solubility data at low Sr concentrations are qualitatively reproduced with the DQF model. For the (Ca,Sr)CO 3 SS with the calcite structure, a slightly asymmetric, moderately positive excess Gibbs free energy of mixing is predicted and shown to agree well with known equilibrium distribution coefficients for trace Sr in calcite and with the predicted solubility product of the hypothetical SrCO 3( R3barc) end member. Although each SS system

  3. New T1-based superconductor T1PbSrRCuO without Ca with Tc above 100 K

    NASA Astrophysics Data System (ADS)

    Sheng, Z. Z.; Xin, Y.; Meason, J. M.

    1991-04-01

    Ca-free T1PbSrRCuO samples (R=rare earths) with Tc up to above 100 K were prepared, and studied by resistance and ac susceptibility measurements and by powder x-ray diffraction analyses. A 1212-type phase (Tl1-xPbx)Sr2(Sr1-yRy)Cu2Oz is responsible for the observed supercondcutivity. A rare-earth is required for the formation of the 1212 phase. Pb-dopping is necessary to increase the Tc of the 1212 phase from 90 K to above 100 K.

  4. Hydrogen adsorption on Be, Mg, Ca and Sr doped graphenes: The role of the dopant in the IIA main group

    NASA Astrophysics Data System (ADS)

    Luo, Huijuan; Li, Hejun; Fu, Qiangang

    2017-02-01

    Hydrogen (H2) adsorption on the IIA elements doped double-vacancy graphenes (BeG, MgG, CaG and SrG) was studied by using dispersion-corrected density functional theory calculations. Through investigation of different numbers of hydrogen dockings from two directions, it is found that 1H2/BeG, 1H2/MgG, 8H2/CaG and 8H2/SrG are the most stable adsorption configurations for Be, Mg, Ca and Sr doped graphenes, respectively. Atomic radius, electronegativity and ionization potential of the IIA dopant contribute to the dominating adsorption mechanism under specific H2 concentration. The study would facilitate exploration of high performance graphene-related supports for hydrogen storage.

  5. Effect of Sr substitution on irreversibility line, lattice dynamics and formation of Hg,Pb-1223 superconductors

    NASA Astrophysics Data System (ADS)

    Lee, Sergey; Kiryakov, N. P.; Emelyanov, D. A.; Kuznetsov, M. S.; Tretyakov, Yu. D.; Petrykin, V. V.; Kakihana, M.; Yamauchi, H.; Zhuo, Yi; Kim, Mun-Seog; Lee, Sung-Ik

    1998-09-01

    Effect of Sr substitution on irreversible properties and lattice dynamics of Hg,Pb-1223 phases was studied. We found that flux pinning properties in high magnetic fields essentially improved by substitutions of Hg by Pb and Ba by Sr. Consideration of lattice dynamics figured out the role of lead and strontium on phase stability and hole doping of CuO 2 layers. Investigation of phase composition and microstructural features of the samples allowed us to suggest a possible mechanism of Hg,Pb-1223 phase formation. The substituted samples possessed an improved chemical stability and allowed their further utilization for materials preparation. As an example, nearly single phase thick film on MgO substrate with the Tc of 120 K was obtained by screen printing method. Despite of the very high intragrain critical current density ( jc=3×10 5 A/cm 2, H=0, 77 K), transport jc was restricted by formation of `weak links' on the grain boundaries.

  6. Electronic structures of non-half-metallic antiferromagnetic double perovskites ALaVMoO6 (A = Ca, Sr, and Ba)

    NASA Astrophysics Data System (ADS)

    Kim, I. G.; Park, M. S.

    2005-03-01

    Recently, double perovskites ALaVMoO6 (A= Ca and Sr) of the Fm3m space group were proposed experimentally to be half-metallic antiferromagnets.ootnotetextUehara, Yamada, and Kimishima, Solid St. Commun. 129, 385 (2004). The electronic structures and magnetism of the double perovskites ALaVMoO6 (A= Ca, Sr, and Ba) were determined within the generalized gradient approximation to density functional theory using the all-electron full-potential linearized augmented plane wave (FLAPW) method.ootnotetextWimmer, Krakauer, Weinert, and Freeman, PRB 24, 864 (1981). The A= Ca case shows metallic ferrimagnetism as the most stable phase, with magnetic moments of 1.15;μB for V and -0.53;μB for Mo, whereas the Sr and Ba cases are calculated to be almost non-magnetic metals. Comparing the calculated density of states, we find that the heavier A implies stronger hybridization between the divalent atom sp states and the transition metal atom d states. The stronger sp-d hybridization is considered to be responsible for the suppression of magnetism for the Sr and Ba cases. These results, at least for the Fm3m space group, are in contrast with the recent experimental result proposing half-metallic antiferromagnetism for A= Ca and Sr.

  7. 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

  8. 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.

  9. Chemical inhomogeneity and reactions of BiSrCaCuO surfaces detected by synchrotron imaging spectromicroscopy

    NASA Astrophysics Data System (ADS)

    Hwu, Y.; Cheng, N.-F.; Lee, S.-D.; Tung, C.-Y.; Alméras, P.; Berger, H.

    1996-11-01

    A microscopic chemical analysis of BiSrCaCuO (BSCCO) 2212 single crystals was performed with an unprecedented combination of high (submicron) lateral resolution and high energy resolution (100 meV or better). These performances, achieved with imaging synchrotron spectromicroscopy, enabled us to detect in a very small fraction of the investigated specimens, morphological and chemical inhomogeneities. Specifically, we found deviations from stoichiometry in the surface Sr content which have a subtle effect on the chemical environment of at least one other element, Ca. The different chemical environment was found to influence surface chemical reactions.

  10. 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.

  11. Low-temperature AC conductivity of Bi 2Sr 2CaCu 2O 8+ δ

    NASA Astrophysics Data System (ADS)

    Corson, J.; Orenstein, J.; Eckstein, J. N.; Bozovic, I.

    2000-05-01

    We report measurements of anamolously large dissipative conductivities, σ1, in Bi 2Sr 2CaCu 2O 8+ δ at low temperatures. We have measured the complex conductivity of Bi 2Sr 2CaCu 2O 8+ δ thin films at 100-600 GHz as a function of doping from the underdoped to the overdoped state. At low temperatures there exists a residual σ1 which scales with the T=0 superfluid density as the doping is varied. This residual σ1 is larger than the possible contribution to σ1 from a thermal population of quasiparticles (QP) at the d-wave gap nodes.

  12. 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; ...

    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

  13. High resolution windows into early Holocene climate: Sr/(Ca) coral records from the Huon Peninsula

    NASA Astrophysics Data System (ADS)

    McCulloch, Malcolm; Mortimer, Graham; Esat, Tezer; Xianhua, Li; Pillans, Brad; Chappell, John

    1996-02-01

    High-precision measurements of Sr/Ca ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have UTh mass spectrometric ages of 8920 ± 60 yr and 7370 ± 50 yr, and δ 234U(t) values of 145 ± 2, similar to modern seawater. The Sr/Ca coral records provide 5-6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of ± 1°C, with occasional excursions of ± 2°C, which may indicate the more frequent recurrence of very strong ENSO (El Niño-Southern Oscillation) events. Mean annual Sr/Ca temperatures of 24.2 ± 1.1°C and 22.9 ± 0.8°C have been obtained, which are ˜ 2-3°C cooler than that exhibited by a modern Porites. These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (˜ 6°C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at ˜ 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at ˜ 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.

  14. Composition dependence of the structural chemistry and magnetism of Ca{sub 2.5}Sr{sub 0.5}(Ga,Co){sub 1+} {sub x} Mn{sub 2-} {sub x} O{sub 8}

    SciTech Connect

    Allix, Mathieu; Battle, Peter D. . E-mail: peter.battle@chem.ox.ac.uk; Frampton, Philip P.C.; Rosseinsky, Matthew J.; Ruiz-Bustos, Rocio

    2006-03-15

    Polycrystalline samples of bilayered brownmillerite-like Ca{sub 2.5}Sr{sub 0.5}GaCo{sub 0.15}Mn{sub 1.85}O{sub 8} and Ca{sub 2.5}Sr{sub 0.5}Ga{sub 1.2}Mn{sub 1.8}O{sub 8} have been prepared and characterised by magnetometry and neutron diffraction over a wide temperature range. The structural chemistry and magnetic properties are compared to those of Ca{sub 2.5}Sr{sub 0.5}GaMn{sub 2}O{sub 8}. Ga enrichment has a significant effect on the former but not on the latter, whereas changes in both occur when paramagnetic Co{sup 3+} cations enter the parent phase on the 4-coordinate sites. The coupling between the environment around the 4-coordinate cations and the transition to an antiferromagnetic ordered state that was observed in Ca{sub 2.5}Sr{sub 0.5}GaMn{sub 2}O{sub 8} is not apparent in the cation-substituted compositions, although both show long-range antiferromagnetic order at low temperatures.

  15. The Giant Pacific Oyster (Crassostrea gigas) as a modern analog for fossil ostreoids: Isotopic (Ca, O, C) and elemental (Mg/Ca, Sr/Ca, Mn/Ca) proxies

    NASA Astrophysics Data System (ADS)

    Ullmann, Clemens V.; Böhm, Florian; Rickaby, Rosalind E. M.; Wiechert, Uwe; Korte, Christoph

    2013-10-01

    Modern analogs are an essential part of palaeoclimate studies, because they provide the basis for the understanding of geochemical signatures of fossils. Ostreoids are common in many sedimentary sequences and because of their fast growth, high temporal resolution sampling of past seasonal variability is possible. Here, two shell structures of modern Giant Pacific Oysters (Crassostrea gigas), the chalky substance and foliate layers, have been sampled for trace element distributions (Mg, Sr, Mn) and stable isotope variability (C, O, Ca). Oxygen isotopes exhibit a clear seasonal signature. Mean carbon isotope values of different oysters agree within 0.1‰, but ontogenic variability is complicated by shell growth patterns and potential small vital effects. The calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of δ44/40Ca = 0.68 ± 0.16‰ (2 sd) SRM-915a which is consistent with other bivalve species. Calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios. Element/Ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high Sr/Ca and Mn/Ca ratios are observed for the first growth season of the oysters. Mg/Ca ratios in the chalky substance show a negative correlation with δ18O values, compatible with a temperature dependence, whereas this correlation is absent in the foliate layers. Seasonal changes of Sr/Ca are controlled by metabolic processes, whereas for Mn/Ca an additional environmental control is evident.

  16. Fluorescence kinetics of PSII crystals containing Ca(2+) or Sr(2+) in the oxygen evolving complex.

    PubMed

    van Oort, Bart; Kargul, Joanna; Maghlaoui, Karim; Barber, James; van Amerongen, Herbert

    2014-02-01

    Photosystem II (PSII) is the pigment-protein complex which converts sunlight energy into chemical energy by catalysing the process of light-driven oxidation of water into reducing equivalents in the form of protons and electrons. Three-dimensional structures from x-ray crystallography have been used extensively to model these processes. However, the crystal structures are not necessarily identical to those of the solubilised complexes. Here we compared picosecond fluorescence of solubilised and crystallised PSII core particles isolated from the thermophilic cyanobacterium Thermosynechococcus elongatus. The fluorescence of the crystals is sensitive to the presence of artificial electron acceptors (K3Fe(CN)3) and electron transport inhibitors (DCMU). In PSII with reaction centres in the open state, the picosecond fluorescence of PSII crystals and solubilised PSII is indistinguishable. Additionally we compared picosecond fluorescence of native PSII with PSII in which Ca(2) in the oxygen evolving complex (OEC) is biosynthetically replaced by Sr(2+). With the Sr(2+) replaced OEC the average fluorescence decay slows down slightly (81ps to 85ps), and reaction centres are less readily closed, indicating that both energy transfer/trapping and electron transfer are affected by the replacement.

  17. LFZ growth of (Bi,Pb)--Sr--Ca--Cu--O superconducting fibers

    SciTech Connect

    de la Fuente, G.F.; Navarro, R.; Lera, F.; Rillo, C.; Bartolome, J.; Badia, A. ); Beltran, D.; Ibanez, R.; Beltran, A. ); Sinn, E. )

    1991-04-01

    Powder x-ray diffraction, d.c. and a.c. susceptibilities, and SEM have been used to study (Bi{sub 1{minus}{ital x}}Pb{sub {ital x}}){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+{delta}} fibers grown by the Laser Floating Zone method. The well-oriented, long-grained superconductor fiber properties are shown to be highly dependent on the partial pressure of oxygen in the growth atmosphere, as well as on fiber pulling rate. Slowly grown fibers contain initially the 2212 (80 K) phase; the 2223 (110 K) phase also appears upon annealing in air. Faster growth rates result in fibers that contain a mixture of the 2212 and 2201 phases and, in this case, long annealing procedures are necessary to observe the 2223 phase.

  18. Enhanced Electrical Properties of La(CaSr) MnO Polycrystalline Composites with Ag Addition

    NASA Astrophysics Data System (ADS)

    Yue, Xuejiao; Zhan, Yanhong; Liu, Xiang; Gu, Gang; Wang, Qiangshen; Yin, Xuepeng

    2015-09-01

    La(CaSr)MnO:Ag(LCSMO:Ag, x = 0, 0.1, 0.2 and 0.3, mol%) polycrystalline composites were prepared by a solid-state reaction method. With the increasing of Ag addition, the temperature coefficient of resistance (TCR) and the metal-to-insulator transition temperature () reach the maximum values of 9.1 % K and 258 K for LCSMO:Ag ( x = 0.3) sample, which can be used as a candidate of bolometer or infrared detectors. The improvement of Mn concentration and grain connectivity by Ag addition is responsible for the enhancement of and TCR values. The fitting curves of electrical resistivity show that the low temperature region () is fitted with grain/domain boundary, electron-electron, and magnon scattering mechanisms, as well as the high temperature region () is fitted with adiabatic small-polaron hopping mechanism.

  19. Eu(2+) luminescence in SrCaP2 O7 pyrophosphate phosphor.

    PubMed

    Kohale, R L; Dhoble, S J

    2013-01-01

    A series of Eu(2+) activated SrCaP2 O7 pyrophosphate phosphors were synthesized by the modified solid-state reaction method. The X-ray diffraction (XRD) and photoluminescence (PL) properties of these phosphors were investigated at room temperature. The excitation spectra indicate that these phosphors can be effectively excited by Hg-free excitation. The emission spectra exhibit strong blue performance, which is due to the 4f(6) 5d(1) →4f(7) transition of Eu(2+) . The Fourier transform infrared spectrum at room temperature was investigated and surface morphology has been studied by scanning electron microscope. The prepared phosphor exhibited intense blue emission at the 427 nm owing to Eu(2+) ion by Hg-free excitation at 330 nm, that is, solid-state lighting excitation. Hence, the availability of such a phosphor will significantly help in the growth of blue-emitting solid-state lighting applications.

  20. Microstructure and flux pinning in superconducting Bi-Pb-Sr-Ca-Cu-O wires

    NASA Astrophysics Data System (ADS)

    Dou, S. X.; Liu, H. K.; Wang, J.; Apperley, M. H.; Sorrell, C. C.; Guo, S. J.; Loberg, B.; Easterling, K. E.

    1990-12-01

    The critical current density ( Jc) of Ag-clad Bi-Pb-Sr-Ca-Cu-O wire has been measured to be 1.2×10 4 A/cm 2 at 77 K in zero field. The high Jc is attributed to a combination of elimination of the poisoning effect of Ag on superconductivity, grain alignment, and enhancement of flux pinning. Jc- H dependence was significantly improved in the Ag-clad tape, which has a Jc of 1.0×10 3 A /cm 2 at 77 K and 4000 Oe, while the Jc of the sintered pellet drops two orders of magnitude at only 100 Oe. A pronounced anisotropy in Jc under high magnetic field is attributed to the grain alignment. Planar defects, such as heavy stacking faults parallel to the a- b plane in the rolled tape, are considered to be effective pinning centres.

  1. 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.

  2. 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.

  3. Cluster glass behaviour in Co-substituted double perovskite Ca{sub 2}FeMoO{sub 6}

    SciTech Connect

    Poddar, Asok; Mazumdar, Chandan

    2011-05-15

    Research highlights: {yields} We have presented the crystallographic, electrical transport and dc and ac magnetic measurements on double perovskite Ca{sub 2}Fe{sub 1-x}Co{sub x}MoO{sub 6} (0.1 {<=} x {<=} 0.4) system. {yields} Co exists in divalent state in these compounds. {yields} The substituted system exhibits cluster-glass like behaviour, close to that observed earlier in Sr{sub 2}Fe{sub 1-x}Co{sub x}MoO{sub 6} compatible with an electronic phase segregation scenario (Phys. Rev. B 73 (2006) 104417). -- Abstract: The transport and magnetic properties of the double perovskite compounds Ca{sub 2}Fe{sub 1-x}Co{sub x}MoO{sub 6} (0.1 {<=} x {<=} 0.4) have been explored through resistivity [{rho}(T)], dc magnetisation [M(H, T)] and ac susceptibility [{chi}(T, f)] measurements. Introduction of Co increases the lattice volume implying the divalent nature of cobalt in this system. For all the samples, {rho}(T) behaviour over the temperature range (25-273 K) can be adequately described by considering possible disorder-enhanced electron-electron interaction effect as well as spin-wave contribution. Our results reveal that with the increase of Co concentration, the ferromagnetic Curie temperatures (T{sub C}) gradually reduced due to the incorporation of antiferromagnetic Co{sup 2+}-Mo{sup 6+} pairs replacing ferromagnetic Fe{sup 3+}-Mo{sup 5+} pairs. A cluster-glass like behaviour is also observed in the system due to the presence of highly spin-disordered regions.

  4. Variation of Ca, Sr, Ba and Mg in the otolith of mudskipper in west coast of Peninsular Malaysia.

    PubMed

    Sarimin, A S; Ghaffar, M A; Mohamed, C A R

    2009-02-01

    A study on elemental composition in the otolith of giant mudskipper, Periophthalmodon schlosseri, was done from June to October 2003. Specimens were obtained from the mangrove areas of Kuala Selangor, Sepang and Melaka in the west coast of Peninsular Malaysia. A total of 70 sagitta otoliths were analyzed to detect variation of Sr, Ba and Mg, replacing the natural chemical composition of the otolith, which is the calcium carbonate (CaCO3). The average ratio of Sr:Ca was 0.11 x 10(-4), Ba:Ca was 5.7 x 10(-3) and Mg:Ca was 0.2 x 10(-3). Strong correlation (R > 0.8) between fish body size and otolith weight ofmudskipper (p < 0.01) also found during this study.

  5. FT-Raman and infrared spectroscopic study of aragonite-strontianite (Ca xSr 1 - xCO 3) solid solution

    NASA Astrophysics Data System (ADS)

    Alía, J. M.; de Mera, Y. Díaz; Edwards, H. G. M.; Martín, P. González; Andres, S. López

    1997-11-01

    Synthetic aragonite-strontianite solid-solution samples have been studied using dispersive IR and FT-Raman spectroscopy. In addition to the end-members, nine samples over a range of composition from Ca 0.9Sr 0.1CO 3 to Ca 0.1Sr 0.9CO 3 were analysed. Carbonate anion internal modes are examined in detail by means of band-shape analysis and component fitting procedures. Positional disorder induced by the random cationic substitution results in strong increase of the halfwidth in several vibrational bands. Results obtained for the doubly degenerate modes (antisymmetric stretching and bending, ν3 and ν4) reveal the presence of three components both in the IR antisymmetric stretching band as well as in the Raman antisymmetric bending band. These observations are interpreted in terms of an overtone 2 ν4 in possible Fermi resonance with the corresponding ν3 fundamental in the IR spectra, and the presence of Davidov (factor group) splitting in the FT-Raman ν4 band. Lattice modes in the FT-Raman spectra demonstrate weaker cohesion between the cation/carbonate/cation layers in aragonite ( synth) than in strontianite ( synth).

  6. Solid-Phase Equilibria for Metal-Silicon-Oxygen Ternary Systems I: Mg, Ca, Sr and Ba

    DTIC Science & Technology

    1990-07-01

    both Sr and Ba to their respective disilicides . An intermediate situation exists for the Ca oxides and silicates, in which excess Si can react with CaO...Si depends on their structural and electrical properties , and significant amounts of research would be required to grow such films and evaluate their... properties . The phase diagrams in Figs. 2-4 can also be used to estimate whether or not various forms of the new oxide superconductors are compatible

  7. 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

    2017-02-01

    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 ( ξ ), 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.

  8. 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.

  9. 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 Bi2Sr2CaCu2O8 (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO2). 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 PO2 range studied. The stability of these solid phases were found to be highly sensitive to PO2, 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 (Al2O3) and time resolved phase transformation studies (SrCO3). Finally, the Bi2212

  10. 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.

  11. Suppression of magnetic order in CaCo1.86As2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca(Co1–xFex)yAs2

    DOE PAGES

    Jayasekara, W. T.; Pandey, Abhishek; Kreyssig, A.; ...

    2017-02-23

    Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca(Co1–xFex)yAs2, 0 ≤ x ≤ 1, 1.86 ≤ y ≤ 2, are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲ 0.12(1). The antiferromagnetic order is smoothly suppressed with increasing x, with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤ 0.25, nor does ferromagnetic order for x up to at least x = 0.104, and a smooth crossover from the collapsed-tetragonal (cT) phase of CaCo1.86As2 tomore » the tetragonal (T) phase of CaFe2As2 occurs. Furthermore, these results suggest that hole doping CaCo1.86As2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.« less

  12. The effect of Na-bearing thermal solutions on Ca-Mg-bentonite sorption of Sr and Cs

    SciTech Connect

    Mukhamet-Galeyev, A.P.; Kudrin, A.V.; Nikonov, B.S.; Shikina, N.D.

    1995-12-31

    The sorption of Sr and Cs has been investigated on Ca-Mg-bentonite preliminary treated by 0.1--1.0 m NaCl solutions at 25, 170--250 C during 0.5--7 months. The bentonite remained stable in these conditions. Moreover, hydrothermal treatment has raised the sorption activity of the bentonite. The treated bentonite has shown a strong selectivity for Sr and less pronounced one for Cs. The sorption of the elements increased with temperature and decreased with NaCl content more significant for Sr, than for Cs. The distribution ratio R{sub d} was nearly independent on ion loading for Cs and strongly increased up to 10{sup 4.5} mL/g in 10{sup {minus}2.0}--10{sup {minus}0.5} meq/g ion loading interval for Sr, dropping sharply at more concentrations.

  13. Electrochemical performances of solid oxide fuel cells based on Y-substituted SrTiO 3 ceramic anode materials

    NASA Astrophysics Data System (ADS)

    Ma, Qianli; Tietz, Frank; Leonide, André; Ivers-Tiffée, Ellen

    Yttrium-substituted SrTiO 3 has been considered as anode material of solid oxide fuel cells (SOFCs) substituting of the state-of-the-art Ni cermet anodes. Sr 0.895Y 0.07TiO 3- δ (SYT) shows good electrical conductivity, compatible thermal expansion with yttria-stabilized ZrO 2 (YSZ) electrolyte and reliable stability during reduction and oxidation (redox) cycles. Single cells based on SYT anode substrates were fabricated in the dimension of 50 mm × 50 mm. The cell performances were over 1.0 A cm -2 at 0.7 V and 800 °C, which already reached the practical application level. Although Ti diffusion from SYT substrates to YSZ electrolytes was observed, it did not show apparent disadvantage to the cell performance. The cells survived 200 redox cycles without obvious OCV decrease and macroscopic damage, but performance decreased due to the electronic properties of the SYT material. The influence of water partial pressure on cell performance and coking tolerance of the cells are also discussed in this study.

  14. Metal-semiconductor-transition observed in Bi2Ca(Sr, Ba)2Co2O8+δ single crystals

    NASA Astrophysics Data System (ADS)

    Dong, Song-Tao; Zhang, Bin-Bin; Zhang, Lun-Yong; Chen, Y. B.; Yao, Shu-Hua; Zhou, Jian; Zhang, Shan-Tao; Gu, Zheng-Bin; Chen, Yan-Feng

    2014-07-01

    Electrical property evolution of Bi2AE2Co2O8+δ single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi2Ca2Co2O8+δ and Bi2Sr2Co2O8+δ demonstrates semiconductor-like properties. But Bi2Ba2Co2O8+δ shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi2Ba2Co2O8+δ to semiconductor-like Bi2Sr2Co2O8+δ can be attributed to Anderson localization. However the semiconductor behaviour of Bi2Sr2Co2O8+δ and Bi2Ca2Co2O8+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 Bi2Ba2Co2O8+δ compared with other two compounds. It suggests that Bi2Ba2Co2O8+δ is more apt to be metal in this material system.

  15. 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.

  16. New observations on the pressure dependence of luminescence from Eu2+-doped MF2 (M = Ca, Sr, Ba) fluorides.

    PubMed

    Su, Fu Hai; Chen, Wei; Ding, Kun; Li, Guo Hua

    2008-05-29

    The luminescence from Eu(2+) ions in MF2 (M = Ca, Sr, Ba) fluorides has been investigated under the pressure range of 0-8 GPa. The emission band originating from the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) ions in CaF2 and SrF2 shows the red-shift as increasing pressure with pressure coefficients of -17 meV/GPa for CaF2 and -18 meV/GPa for SrF2. At atmospheric pressure, the emission spectrum of BaF2:Eu(2+) comprises two peaks at 2.20 and 2.75 eV from the impurity trapped exciton (ITE) and the self-trapped exciton (STE), respectively. As the pressure is increased, both emission peaks shift to higher energies, and the shifting rate is slowed by the phase transition from the cubic to orthorhombic phase at 4 GPa. Due to the phase transition at 4-5 GPa pressure, the ITE emission disappears gradually, and the STE emission is gradually replaced by the 4f(6)5d(1) --> 4f(7) transition of Eu(2+). Above 5 GPa, the pressure behavior of the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) in BaF2:Eu(2+) is the same as the normal emission of Eu(2+) in CaF2 and SrF2 phosphors.

  17. 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.

  18. Growth of nucleation sites on Pb-doped Bi2Sr2Ca1Cu2O8 + delta

    NASA Astrophysics Data System (ADS)

    Finnemore, D. K.; Xu, Ming; Kouzoudis, D.; Bloomer, T.; Kramer, M. J.; McKernan, Stuart; Balachandran, U.; Haldar, Pradeep

    1996-01-01

    In the growth of Bi2Sr2Ca2Cu3O10+δ from mixed powders of Pb-doped Bi2Sr2Ca1Cu2O8+δ and other oxides, it has been discovered that a dense array of hillocks or mesas grow at the interface between a Ag overlay and Pb-doped Bi2Sr2Ca1Cu2O8+δ grains during the ramp up to the reaction temperature. As viewed in an environmental scanning electron microscope, the Ag coated grains develop a texture that looks like ``chicken pox'' growing on the grains at about 700 °C. These hillocks are about 100 nm across and are spaced at about 500 to 1000 nm. If there is no Ag, this texture does not develop. Preliminary measurements indicate that the hillocks are a recrystallization of (Bi,Pb)2Sr2Ca1Cu2O8+δ, and are definitely not a Pb rich phase.

  19. 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.

  20. Synthesis and Characterization of Alkaline-Earth Metal (Ca, Sr, and Ba) Doped Nanodimensional LaMnO3 Rare-Earth Manganites

    NASA Astrophysics Data System (ADS)

    Asma, Khalid; Saadat, Anwar Siddiqi; Affia, Aslam

    2013-07-01

    The substitution of divalent cations of alkaline-earth elements in nanodimensional structures of rare-earth manganites produces advanced materials with potential electrical and magnetic functionalities. A systematic investigation of La0.65A0.35MnO3 (A = Ca, Sr, Ba) materials synthesized with a modified citrate route adopting ethanol dehydration has been undertaken. The structural and morphological analyses are carried out by using x-ray diffraction and scanning electron microscopy, respectively. Resistivity measurements are performed in variation with temperature to study the electrical transport properties which are found to vary with the size of the A-site cationic radius. Room temperature magnetic measurements are carried out to investigate the type of magnetic phase present in materials. The stability of the magnetic phase and coercivity are found to be dependent on the size of nanocrystallites.

  1. 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.

  2. Temperature-dependent phonon Raman scattering and spectroscopic ellipsometry of pure and Ca-doped Sr x Ba1-x Nb2O6 ferroelectric ceramics across the phase transition region

    NASA Astrophysics Data System (ADS)

    Peng, Liang; Jiang, Kai; Zhang, Jinzhong; Hu, Zhigao; Wang, Genshui; Dong, Xianlin; Chu, Junhao

    2016-01-01

    Optical phonons and the phase transition of relaxor ferroelectric ceramics Sr x Ba1-x Nb2O6 (SBN) and Ca y (Sr0.5Ba0.5)1-y Nb2O6 (CSBN) with different composition (0.3≤slant x≤slant 0.5 , 0.1≤slant y≤slant 0.2 ) have been investigated by variable-temperature Raman scattering and spectroscopic ellipsometry. The anomalous temperature dependence of Tauc gap energy (E t ) is used to fit the phonon energy dependence of the permittivity, and the Raman intensity of some interesting optical phonons can be ascribed to the phase transition from a ferroelectric to a paraelectric structure. The Curie temperature of SBN decreases from 556 to 359 K with increasing Sr composition, which can be attributed to the substitution of smaller Sr2+ for Ba2+. On increasing the Ca composition, however, the phase transition temperature of CSBN remains nearly unchanged at about 350 K. This could be due to the fact that most doped Ca2+ ions move into the oxygen ion site and exhibit no obvious effect on the vibrational properties. Therefore, the general disorder which results from Sr2+ substituting Ba2+ , dominates the phase transition process for SBN-based ferroelectric oxides. Meanwhile, the dielectric functions from 200 to 600 K have been evaluated with the aid of the Tauc-Lorentz model. The electronic transition is located at about 5 eV and decreases with increasing temperature for all the samples. Moreover, the phase transition temperature range derived from the spectroscopic ellipsometry agrees well with that from the Raman scattering. It reveals that the variation of the fundamental energy gap may be associated with the phase transition of SBN ceramics. Both Raman scattering and spectroscopic ellipsometry are proven to be a effective method of exploring the phase transition of ferroelectric oxides.

  3. Fidelity of the Sr/Ca proxy in recording ocean temperature in the western Atlantic coral Siderastrea siderea

    USGS Publications Warehouse

    Kuffner, Ilsa B.; Roberts, Kelsey E.; Flannery, Jennifer A.; Morrison, Jennifer M.; Richey, Julie

    2017-01-01

    Massive corals provide a useful archive of environmental variability, but careful testing of geochemical proxies in corals is necessary to validate the relationship between each proxy and environmental parameter throughout the full range of conditions experienced by the recording organisms. Here we use samples from a coral-growth study to test the hypothesis that Sr/Ca in the coral Siderastrea siderea accurately records sea-surface temperature (SST) in the subtropics (Florida, USA) along 350 km of reef tract. We test calcification rate, measured via buoyant weight, and linear extension (LE) rate, estimated with Alizarin Red-S staining, as predictors of variance in the Sr/Ca records of 39 individual S. siderea corals grown at four outer-reef locations next to in-situ temperature loggers during two, year-long periods. We found that corals with calcification rates < 1.7 mg cm−2 d−1 or < 1.7 mm yr−1 LE returned spuriously high Sr/Ca values, leading to a cold-bias in Sr/Ca-based SST estimates. The threshold-type response curves suggest that extension rate can be used as a quality-control indicator during sample and drill-path selection when using long cores for SST paleoreconstruction. For our corals that passed this quality control step, the Sr/Ca-SST proxy performed well in estimating mean annual temperature across three sites spanning 350 km of the Florida reef tract. However, there was some evidence that extreme temperature stress in 2010 (cold snap) and 2011 (SST above coral-bleaching threshold) may have caused the corals not to record the temperature extremes. Known stress events could be avoided during modern calibrations of paleoproxies.

  4. 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.

  5. Growth and Characterization of High-Quality Single Crystals of Ni- and Zn-Doped Bi2Sr2Ca(Cu2-xMx)O8+δ (M = Ni or Zn) High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Liu, Shan-Yu; Zhang, Wen-Tao; Zhao, Lin; Liu, Hai-Yun; Wu, Yue; Liu, Guo-Dong; Dong, Xiao-Li; Zhou, Xing-Jiang

    2012-08-01

    High-quality large single crystals of Ni- and Zn-doped Bi2Sr2Ca(Cu2-xMx)O8+δ (M = Ni or Zn) have been successfully grown by the traveling solvent floating zone technique. The single crystals are characterized by compositional and structural analyses and their physical properties are investigated by magnetic susceptibility and resistivity measurements. A record high critical temperature with a Tc = 97.5 K has been achieved in the annealed pristine Bi2212 single crystal. Substitution of Cu by Ni or Zn reduces the superconducting transition temperature when compared with pristine Bi2Sr2CaCu2O8+δ (Bi2212) grown under similar conditions. The successful growth of such pristine Ni- and Zn-doped Bi2212 single crystals will facilitate studies of the relationship between the magnetism and superconductivity in high-temperature cuprate superconductors.

  6. Influence of oxygen on the structural stability and superconducting properties of ceramic (Bi,Pb) sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub. delta

    SciTech Connect

    Green, S.M.; Mei, Y.; Manzi, A.E.; Luo, H.L. )

    1989-10-15

    By post-annealing ceramic samples in various partial pressures of oxygen, the structural stability and superconducting properties of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {delta}} are demonstrated to be sensitive to {delta}. The small decrease of {ital T}{sub c} with increasing oxygen partial pressure is in agreement with previously reported results on Pb-free samples and may be connected to an optimization of the charge carrier concentration. The collapse of the 2223 phase when post-annealed above 700 {degree}C in pure argon is also documented. It is suggested that this decomposition and the stabilization of the 2223 phase by Pb substitution are both related to the amount of oxygen contained in the (Bi,Pb)-O layers which separate the Sr-Ca-Cu-O perovskite units.

  7. Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Punugupati, Sandhyarani; Prater, John T.; Narayan, Jagdish

    2016-04-01

    We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO3 (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba0.4Sr0.6TiO3 (BST). The epitaxial integration of BST (˜800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A1TO3 mode (at 521.27 cm-1) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.

  8. Erase-mode recording characteristics of photochromic CaF2, SrTiO3, and CaTiO3 crystals.

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.

    1972-01-01

    Erase-mode optical recording characteristics of photochromic crystal wafers of CaF2:La,Na; CaF2:Ce,Na; SrTiO3:Ni,Mo,Al; and CaTiO3:Ni,Mo have been measured. An argon laser operating at 5145 A was used for both optical recording and optical readout. Sensitometric curves of optical-density change versus logarithm of exposure are shown for a number of erase-beam intensities between 0.2 mW/sq cm and 2 W/sq cm. In this range, time-intensity reciprocity holds for the CaF2 materials but fails for the titanates, particularly at low intensities. The dependences of sensitivity, gamma, and maximum transmission contrast ratio on wafer thickness and material are discussed. Wafers of SrTiO3, CaTiO3, and CaF2 exhibiting approximately equal maximum contrast ratios have relative sensitivities approximately in the ratio 5:2:1, respectively, at an erase intensity of 1 W/sq cm.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Superconducting thin films of Bi-Sr-Ca-Cu-O by laser ablation

    SciTech Connect

    Bedekar, M.M.

    1992-01-01

    The discovery of a new class of copper oxide superconductors has led to the development of three major systems that exhibit superconducting properties. The Bi-Sr-Ca-Cu-O superconductors offer intrinsic advantages due to the high [Tc], chemical inertness and tolerance for a range of compositions. However, thin film research on these materials has progressed more slowly than the other cuprate systems. This dissertation examines the film growth, by laser ablation, of the Bi-Sr-Ca-Cu-O superconductors and the effect of the deposition parameters such as the laser target interaction, substrate temperature, target to substrate distance, deposition and cooling pressure, target type and processing and the substrate type. CO[sub 2] laser ablation was shown to give rise to a non-stoichiometric material transfer due to the low fluences and long pulse lengths. In situ superconducting thin films with T[sub c(0)]'s of 76 K could be deposited using the KrF laser at substrate temperatures of 5[degrees]C to 20[degrees]C below phases. Lower temperatures gave rise to a mixture of 2201 and glassy phases. An increase in the target to substrate distance led to a deterioration of the electrical and structural properties of the films due to a decrease in the energy for film formation. A maximum in T[sub c(0)] was observed at 450 mtorr as the deposition pressure was varied between 200 to 700 mtorr. Optimum oxygen incorporation could be achieved by cooling the films in high oxygen pressures and the best films were obtained with 700 torr cooling pressure. The oxygen deficiency of the hot pressed targets led to inferior properties compared to the conventionally sintered targets. The microwave surface resistance of the films measured at 35 GHz showed an onset at 80 K and dropped below that of copper at 30 K. The study of the laser ablation process in this system revealed the presence of a stoichiometric forward directed component and a diffuse evaporation component.

  14. 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.

  15. Prostate cancer metastatic to bone has higher expression of the calcium-sensing receptor (CaSR) than primary prostate cancer

    PubMed Central

    Feng, Jie; Xu, Xiaojun; Li, Bo; Brown, Edward; Farris, Alton B.; Sun, Shi-Yong; Yang, Jenny J.

    2015-01-01

    The calcium-sensing receptor (CaSR) is the principal regulator of the secretion of parathyroid hormone and plays key roles in extracellular calcium (Ca2+o) homeostasis. It is also thought to participate in the development of cancer, especially bony metastases of breast and prostate cancer. However, the expression of CaSR has not been systematically analyzed in prostate cancer from patients with or without bony metastases. By comparing human prostate cancer tissue sections in microarrays, we found that the CaSR was expressed in both normal prostate and primary prostate cancer as assessed by immunohistochemistry (IHC). We used two methods to analyze the expression level of CaSR. One was the pathological score read by a pathologist, the other was the positivity% obtained from the Aperio positive pixel count algorithm. Both of the methods gave consistent results. Metastatic prostate cancer tissue obtained from bone had higher CaSR expression than primary prostate cancer (P <0.05). The expression of CaSR in primary prostate cancers of patients with metastases to tissues other than bone was not different from that in primary prostate cancer of patients with or without bony metastases (P >0.05). The expression of CaSR in cancer tissue was not associated with the stage or status of differentiation of the cancer. These results suggest that CaSR may have a role in promoting bony metastasis of prostate cancer, hence raising the possibility of reducing the risk of such metastases with CaSR-based therapeutics. PMID:26065011

  16. Systematic study of compositional and synthetic control of vacancy and magnetic ordering in oxygen-deficient perovskites Ca2Fe(2-x)Mn(x)O(5+y)and CaSrFe(2-x)Mn(x)O(5+y) (x = 1/2, 2/3, and 1; y = 0-1/2).

    PubMed

    Ramezanipour, Farshid; Greedan, John E; Cranswick, Lachlan M D; Garlea, V Ovidiu; Donaberger, Ronald L; Siewenie, Joan

    2012-02-15

    Ten compounds belonging to the series of oxygen-deficient perovskite oxides Ca(2)Fe(2-x)Mn(x)O(5) and CaSrFe(2-x)Mn(x)O(5+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 T(d) chain (vacancy) disorder. In the special case of CaSrFeMnO(5) the neutron diffraction peaks broaden, indicating only short-range structural order on a length scale of ~160 Å. This reveals a systematic progression from Ca(2)FeMnO(5) (Pnma, well-ordered tetrahedral chains) to CaSrFeMnO(5) (Icmm, disordered tetrahedral chains, overall short-range order) to Sr(2)FeMnO(5) (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, T(c), decreases for the same x when Sr substitutes for one Ca. A review of the changes in T(c) for the series Ca(2)Fe(2-x)M(x)O(5), taking into account the tetrahedral/octahedral site preferences for the various M(3+) 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 Ca(2)Fe(2-x)Mn(x)O(5) and the CaSrFe(2-x)Mn(x)O(5) series. For the y > 0 phases, while a brownmillerite ordering of oxygen vacancies is preserved for the Ca(2) phases, a disordered Pm3m cubic

  17. 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

  18. Fidelity of the Sr/Ca proxy in recording ocean temperature in the western Atlantic coral Siderastrea siderea

    NASA Astrophysics Data System (ADS)

    Kuffner, Ilsa B.; Roberts, Kelsey E.; Flannery, Jennifer A.; Morrison, Jennifer M.; Richey, Julie N.

    2017-01-01

    Massive corals provide a useful archive of environmental variability, but careful testing of geochemical proxies in corals is necessary to validate the relationship between each proxy and environmental parameter throughout the full range of conditions experienced by the recording organisms. Here we use samples from a coral-growth study to test the hypothesis that Sr/Ca in the coral Siderastrea siderea accurately records sea-surface temperature (SST) in the subtropics (Florida, USA) along 350 km of reef tract. We test calcification rate, measured via buoyant weight, and linear extension (LE) rate, estimated with Alizarin Red-S staining, as predictors of variance in the Sr/Ca records of 39 individual S. siderea corals grown at four outer-reef locations next to in-situ temperature loggers during two, year-long periods. We found that corals with calcification rates < 1.7 mg cm-2 d-1 or < 1.7 mm yr-1 LE returned spuriously high Sr/Ca values, leading to a cold-bias in Sr/Ca-based SST estimates. The threshold-type response curves suggest that extension rate can be used as a quality-control indicator during sample and drill-path selection when using long cores for SST paleoreconstruction. For our corals that passed this quality control step, the Sr/Ca-SST proxy performed well in estimating mean annual temperature across three sites spanning 350 km of the Florida reef tract. However, there was some evidence that extreme temperature stress in 2010 (cold snap) and 2011 (SST above coral-bleaching threshold) may have caused the corals not to record the temperature extremes. Known stress events could be avoided during modern calibrations of paleoproxies.Plain Language SummaryCoral skeletons are used to decipher past environmental conditions in the ocean because they live for centuries and produce annual growth bands much like tree rings. Along with measuring coral growth rates in the past, coral skeletons can be chemically sampled to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23380208','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23380208"><span>In vitro and in vivo studies on biodegradable <span class="hlt">CaMgZnSr</span>Yb high-entropy bulk metallic glass.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, H F; Xie, X H; Zhao, K; Wang, Y B; Zheng, Y F; Wang, W H; Qin, L</p> <p>2013-11-01</p> <p>In order to enhance the corrosion resistance of the <span class="hlt">Ca</span>65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the <span class="hlt">Ca</span>20Mg20Zn20<span class="hlt">Sr</span>20Yb20 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 <span class="hlt">Ca</span>20Mg20Zn20<span class="hlt">Sr</span>20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the <span class="hlt">Ca</span>20Mg20Zn20<span class="hlt">Sr</span>20Yb20 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70178534','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70178534"><span>Multi-species coral <span class="hlt">Sr/Ca</span>-based sea-surface temperature reconstruction using Orbicella faveolata and Siderastrea siderea from the Florida Straits</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Flannery, Jennifer A.; Richey, Julie N.; Thirumalai, Kaustubh; Poore, Richard Z.; DeLong, Kristine L.</p> <p>2017-01-01</p> <p>We present new, monthly-resolved <span class="hlt">Sr/Ca</span>-based sea-surface temperature (SST) records from two species of massive coral, Orbicella faveolata and Siderastrea siderea, from the Dry Tortugas National Park, FL, USA (DTNP). We combine these new records with published data from three additional S. siderea coral colonies to generate a 278-year long multi-species stacked <span class="hlt">Sr/Ca</span>-SST record from DTNP. The composite record of mean annual <span class="hlt">Sr/Ca</span>-SST at DTNP shows pronounced decadal-scale variability with a range of 1 to 2°C. Notable cool intervals in the <span class="hlt">Sr/Ca</span>-derived SST lasting about a decade centered at ~1845, ~1935, and ~1965 are associated with reduced summer <span class="hlt">Sr/Ca</span>-SST (monthly maxima < 29°C), and imply a reduction in the spatial extent of the Atlantic Warm Pool (AWP). There is significant coherence between the composite DTNP <span class="hlt">Sr/Ca</span>-SST record and the Atlantic Multidecadal Oscillation (AMO) index, with the AMO lagging <span class="hlt">Sr/Ca</span>-SST at DTNP by 9 years. Low frequency variability in the Gulf Stream surface transport, which originates near DTNP, may provide a link for the lagged relationship between multidecadal variability at DTNP and the AMO.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010APS..MARZ36015H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010APS..MARZ36015H"><span>Magnetic Superstructure and Metal-Insulator Transition in Mn-<span class="hlt">Substituted</span> <span class="hlt">Sr</span>3Ru2O7</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hossain, M. A.; Bohnenbuck, B.; Chuang, Y.-D.; Geck, J.; Tokura, Y.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Sawatzky, G. A.; Damascelli, A.</p> <p>2010-03-01</p> <p>We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in <span class="hlt">Sr</span>3(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 <span class="hlt">substitution</span>. 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).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910050826&hterms=XRD+Measurement&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DXRD%2BMeasurement','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910050826&hterms=XRD+Measurement&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DXRD%2BMeasurement"><span>Preparation of 110K (Bi, Pb)-<span class="hlt">Sr-Ca</span>-Cu-O superconductor from glass precursor</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bansal, Narottam P.</p> <p>1990-01-01</p> <p>The Bi1.5Pb0.5<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900004792','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900004792"><span>Preparation of 110K (Bi, Pb)-<span class="hlt">Sr-Ca</span>-Cu-O superconductor from glass precursor</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bansal, Narottam P.</p> <p>1989-01-01</p> <p>The Bi1.5Pb0.5<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990STIA...9135449B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990STIA...9135449B"><span>Preparation of 110K (Bi, Pb)-<span class="hlt">Sr-Ca</span>-Cu-O superconductor from glass precursor</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bansal, Narottam P.</p> <p></p> <p>The Bi1.5Pb0.5<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989icst.cong.....B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989icst.cong.....B"><span>Preparation of 110K (Bi, Pb)-<span class="hlt">Sr-Ca</span>-Cu-O superconductor from glass precursor</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bansal, Narottam P.</p> <p>1989-10-01</p> <p>The Bi1.5Pb0.5<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995PhyC..253..182H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995PhyC..253..182H"><span>Isothermal melt processing of Bi 2<span class="hlt">Sr</span> 2<span class="hlt">Ca</span>Cu 2O y round wire</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Holesinger, T. G.; Johnson, J. M.; Coulter, J. Y.; Safar, H.; Phillips, D. S.; Bingert, J. F.; Bingham, B. L.; Maley, M. P.; Smith, J. L.; Peterson, D. E.</p> <p>1995-02-01</p> <p>Isothermal melt processing (IMP) has been used to process oxide-powder-in-tube (OPIT) Bi 2<span class="hlt">Sr</span> 2<span class="hlt">Ca</span>Cu 2O y (Bi-2212) round wire with high critical current densities. Isothermal melt processing is a process in which the melting and solidification steps are carried out at the same temperature by melting in an inert atmosphere and solidifying in a high oxygen partial pressure. For each particular oxidizing atmosphere used during IMP, the highest critical currents were found in wires processed in the temperature range between 790°C to 820°C. The highest critical current densities obtained in 1.0, 0.75, and 0.5 mm diameter wires at 4 K and self-field were 4.3 × 10 4, 6.0 × 10 4, and 6.0 × 10 4 A/cm 2, respectively. Transport measurements on a 0.75 mm wire revealed that critical current densities in excess of 3 × 10 4 A/cm 2 could be achieved at 4 K in applied magnetic fields of 9 T. Anisotropy measurements and SEM analysis were used to examine the radial alignment of the Bi-2212 grain colonies within the wires.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008MPLB...22.3241M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008MPLB...22.3241M"><span>Thermal Hysteresis in Resistivity and Magnetization of Pr<span class="hlt">Ca(Sr</span>)MnO</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mollah, S.</p> <p></p> <p>Thermal hysteresis in resistivity and magnetization of Pr0.65<span class="hlt">Ca</span>0.35-xSrxMnO3 (x = 0-0.35) manganites has been systematically studied to establish the interplay of their charge and spin-ordering. The increasing <span class="hlt">Sr</span> concentration (x) transforms the charge-ordered (CO)/antiferromagnetic (AFM) insulating system (for x = 0) into a mixed-phased one (for x = 0.1) with sharp metal-insulator (MI) transition and finally leads to a ferromagnetic (FM) metallic (for x = 0.35) system. It has been found that the interplay of charge and spin-ordering is higher in mixed-phased state and the thermal hysteresis loop area is bigger. It increases with the increase of sharpness of MI transition. Interplay of charge and spin-ordering decreases with the increase of either CO/AFM insulating or FM metallic phase and is almost absent in completely CO/AFM insulating (with x = 0) or FM metallic (with x = 0.35) states bringing about zero thermal hysteresis loop.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1812887G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1812887G"><span>Exploring the impact of temperature and fluid chemistry on <span class="hlt">Ca</span> and <span class="hlt">Sr</span> isotope composition of Arctica islandica shells via experimental alteration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goos, Manuela; Eisenhauer, Anton; Liebetrau, Volker; Böhm, Florian; Fietzke, Jan; Nehrke, Gernot; Buhl, Dieter; Mavromatis, Vasileios; Dietzel, Martin</p> <p>2016-04-01</p> <p>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 88/86<span class="hlt">Sr</span>SRM987= 0.391(1)‰ and 87<span class="hlt">Sr</span>/86<span class="hlt">Sr</span>= 0.70921(1) to δ 88/86<span class="hlt">Sr</span>SRM987= 0.179(1)‰ and 87<span class="hlt">Sr</span>/86<span class="hlt">Sr</span>= 0.70789(1) by sulfate extraction and <span class="hlt">Sr</span> 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 <span class="hlt">Sr</span> and <span class="hlt">Ca</span> concentrations increase (<span class="hlt">Sr</span>: 79 to 183 μ mol/l; <span class="hlt">Ca</span>: 8 to 30 mmol/l), while Mg concentration decreases (Mg: 42 to 22 mmol/l). A corresponding <span class="hlt">Sr</span> and <span class="hlt">Ca</span> depletion along with an increase of Mg occurred in the samples, especially in the dolomite rim. At 100r{ }C only minor increase of <span class="hlt">Sr</span>, <span class="hlt">Ca</span> and Mg</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFMPP31B0424H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFMPP31B0424H"><span>Tracing Environmental Variation Over The Past 130 Years In The Barents Sea: Mineral Ratio (Mg/<span class="hlt">Ca</span>, <span class="hlt">Sr/Ca</span>, Ba/<span class="hlt">Ca</span>, And Mn/<span class="hlt">Ca</span>) Evidence In Shells Of The Circumpolar Greenland Cockle, Serripes groenlandicus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Henkes, G. A.; Ambrose, W. G.; Johnson, B. J.; Carroll, M. L.; McMahon, K. W.; Denisenko, S. G.; Thorrold, S. R.</p> <p>2007-12-01</p> <p>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, <span class="hlt">Sr</span>, 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 <span class="hlt">Sr</span> show progressive change. On average for 9 individuals, Mg/<span class="hlt">Ca</span> was 10.6 percent greater and <span class="hlt">Sr/Ca</span> was 5.5 percent lower on the winter checks compared to other values, while Ba/<span class="hlt">Ca</span> and Mn/<span class="hlt">Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000PhyC..331...45T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000PhyC..331...45T"><span>Insulator-metal transition by the <span class="hlt">substitution</span> of Ho, Y or <span class="hlt">Ca</span> for Pr in PrBa 2Cu 3O 7- δ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tomkowicz, Z.; Lunkenheimer, P.; Knebel, G.; Bałanda, M.; Pacyna, A. W.; Zaleski, A. J.</p> <p></p> <p>Comparative studies of electrical transport in the non-superconducting part of the R 1- xPr xBa 2Cu 3O 7- δ system (R=Ho, Y; x>0.60) and in the Pr 1- x<span class="hlt">Ca</span> xBa 2Cu 3O 7- δ system ( x≤0.5) have been carried out for ceramic samples. Electrical conduction of all samples at low temperatures can be described by the formula σ= σ0+ axTn, where n≅1 for the Ho- and Y-systems and 1≤ n≤1.88 for the <span class="hlt">Ca</span>-system. For Ho 1- xPr xBa 2Cu 3O 7- δσ0≠0 and σ0→0 as x→1, but for Pr 1- x<span class="hlt">Ca</span> xBa 2Cu 3O 7- δσ0=0. Selected samples of the Ho 1- xPr xBa 2Cu 3O 7- δ system were <span class="hlt">substituted</span> with gold, which blocks the conduction of chains. For gold <span class="hlt">substituted</span> Ho 1- xPr xBa 2Cu 2.92Au 0.08O 7- δ samples σ0=0. We conclude that the suppression of superconductivity in the Ho 1- xPr xBa 2Cu 3O 7- δ system is connected with a metal-insulator (M-I) transition in planes (at x≈0.6), but chains are still conducting and become insulating only in the limit x=1. The electrical conduction of chains is dominated by tunneling, being possible due to the pronounced texture of samples. To get further insight into the mechanism of suppression, we studied also <span class="hlt">Sr</span>- and <span class="hlt">Ca-substituted</span>, oxygenated and deoxygenated samples. No superconductivity was obtained although it is known that Pr loses its anomalous properties in deoxygenated samples and <span class="hlt">Ca</span> induces superconductivity in the deoxygenated Y 1- x<span class="hlt">Ca</span> xBa 2Cu 3O 7- δ system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AIPC.1461..379M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AIPC.1461..379M"><span>Transition metal <span class="hlt">substituted</span> <span class="hlt">Sr</span>TiO3 perovskite oxides as promising functional materials for oxygen sensor</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Misra, Sunasira</p> <p>2012-07-01</p> <p>Modern industries employ several gases as process fluids. Leakage of these gases in the operating area could lead to undesirable consequences. Even in chemical industries, which use large quantities of inert gases in confined areas, accidental leakage of these process gases would result in the reduction of oxygen partial pressure in atmospheric air. For instance, large amounts of gaseous nitrogen and argon are used in pharmaceutical industries, gas filling/bottling plants, operating area of Fast Breeder reactors, etc. Fall of concentration of oxygen in air below 17% could lead to life risk (Asphyxiation) of the working personnel that has to be checked well in advance. Further, when the leaking gas is of explosive nature, its damage potential would be very high if its concentration level in air increases beyond its lower explosive limit. Surveillance of the ambient within these industries at the critical areas and also in the environment around them for oxygen therefore becomes highly essential. Sensitive and selective gas sensors made of advanced materials are required to meet this demand of monitoring environmental pollution. The perovskite class of oxides (ABO3) is chemically stable even at high temperatures and can tolerate large levels of dopants without phase transformations. The electronic properties of this parent functional material can be tailored by adding appropriate dopants that exhibit different valence states. Aliovalent transition metal <span class="hlt">substituted</span> <span class="hlt">Sr</span>TiO3 perovskites are good mixed ionic and electronic conductors and potential candidates for sensing oxygen at percentage level exploiting their oxygen pressure dependent electrical conductivity. This paper presents the preparation, study of electrical conductivity and oxygen-sensing characteristics of iron and cobalt <span class="hlt">substituted</span> <span class="hlt">Sr</span>TiO3.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70047273','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70047273"><span><span class="hlt">Sr/Ca</span> proxy sea-surface temperature reconstructions from modern and holocene Montastraea faveolata specimens from the Dry Tortugas National Park</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Flannery, Jennifer A.; Poore, Richard Z.</p> <p>2013-01-01</p> <p><span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> values from resulting powdered samples against a local SST record to obtain a calibration equation of <span class="hlt">Sr/Ca</span> = -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) <span class="hlt">Sr/Ca</span> subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr</span>/ <span class="hlt">Ca</span> 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 <span class="hlt">Sr/Ca</span> cycles with amplitudes ranging from ~0.3 to 0.6 mmol/mol. Absolute <span class="hlt">Sr/Ca</span> values and thus resulting SST estimates over the ~7-year long record are similar to those from the modern coral. We conclude that <span class="hlt">Sr/Ca</span> from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014IJMMM..21..720L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014IJMMM..21..720L"><span>Thermoelectric properties of Al <span class="hlt">substituted</span> misfit cobaltite <span class="hlt">Ca</span>3(Co1- x Al x )4O9 at low temperature</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Yi; Chen, Hong-mei; Hu, Jin-lian; Tang, Xu-bing; Li, Hai-jin; Wang, Wei</p> <p>2014-07-01</p> <p>Thermoelectric properties of Al <span class="hlt">substituted</span> compounds <span class="hlt">Ca</span>3(Co1- x Al x )4O9 ( x = 0, 0.03, 0.05), prepared by a sol-gel process, have been investigated in the temperature range 305-20 K. The results indicate that after Al <span class="hlt">substitution</span> for Co in <span class="hlt">Ca</span>3(Co1- x Al x )4O9, the direct current electrical resistivity and thermopower increase due to the reduction of carrier concentration. Experiments show that Al <span class="hlt">substitution</span> results in decreased lattice thermal conductivity. The figure of merit of temperature behavior suggests that <span class="hlt">Ca</span>3(Co0.97Al0.03)4O9 would be a promising candidate thermoelectric material for high-temperature thermoelectric application.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011APS..MAR.K1284H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011APS..MAR.K1284H"><span>Magnetic Superstructure and Metal-Insulator Transition in Mn-<span class="hlt">Substituted</span> <span class="hlt">Sr</span>3 Ru 2 O 7</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2011-03-01</p> <p>We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in <span class="hlt">Sr</span> 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 <span class="hlt">substitution</span>. Perhaps more important, our results suggest that the same checkerboard instability might be present already in the parent compound <span class="hlt">Sr</span> 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).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20382537','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20382537"><span>Antagonism of 4-<span class="hlt">substituted</span> 1,4-dihydropyridine-3,5-dicarboxylates toward voltage-dependent L-type <span class="hlt">Ca</span>2+ channels <span class="hlt">Ca</span> V 1.3 and <span class="hlt">Ca</span> V 1.2.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chang, Che-Chien; Cao, Song; Kang, Soosung; Kai, Li; Tian, Xinyong; Pandey, Prativa; Dunne, Sara Fernandez; Luan, Chi-Hao; Surmeier, D James; Silverman, Richard B</p> <p>2010-05-01</p> <p>L-type <span class="hlt">Ca</span>(2+) channels in mammalian brain neurons have either a <span class="hlt">Ca</span>(V)1.2 or <span class="hlt">Ca</span>(V)1.3 pore-forming subunit. Recently, it was shown that <span class="hlt">Ca</span>(V)1.3 <span class="hlt">Ca</span>(2+) channels underlie autonomous pacemaking in adult dopaminergic neurons in the substantia nigra pars compacta, and this reliance renders them sensitive to toxins used to create animal models of Parkinson's disease. Antagonism of these channels with the dihydropyridine antihypertensive drug isradipine diminishes the reliance on <span class="hlt">Ca</span>(2+) and the sensitivity of these neurons to toxins, pointing to a potential neuroprotective strategy. However, for neuroprotection without an antihypertensive side effect, selective <span class="hlt">Ca</span>(V)1.3 channel antagonists are required. In an attempt to identify potent and selective antagonists of <span class="hlt">Ca</span>(V)1.3 channels, 124 dihydropyridines (4-<span class="hlt">substituted</span>-1,4-dihydropyridine-3,5-dicarboxylic diesters) were synthesized. The antagonism of heterologously expressed <span class="hlt">Ca</span>(V)1.2 and <span class="hlt">Ca</span>(V)1.3 channels was then tested using electrophysiological approaches and the FLIPR Calcium 4 assay. Despite the large diversity in <span class="hlt">substitution</span> on the dihydropyridine scaffold, the most <span class="hlt">Ca</span>(V)1.3 selectivity was only about twofold. These results support a highly similar dihydropyridine binding site at both <span class="hlt">Ca</span>(V)1.2 and <span class="hlt">Ca</span>(V)1.3 channels and suggests that other classes of compounds need to be identified for <span class="hlt">Ca</span>(V)1.3 selectivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JCrGr.337....7C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JCrGr.337....7C"><span>Structural and dielectric behavior of pulsed laser ablated <span class="hlt">Sr</span> 0.6<span class="hlt">Ca</span> 0.4TiO 3 thin film and asymmetric multilayer of <span class="hlt">Sr</span>TiO 3 and <span class="hlt">Ca</span>TiO 3</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chakraborty, Pradip; Choudhury, Palash Roy; Krupanidhi, S. B.</p> <p>2011-12-01</p> <p>Homogeneous thin films of <span class="hlt">Sr</span> 0.6<span class="hlt">Ca</span> 0.4TiO 3 (SCT40) and asymmetric multilayer of <span class="hlt">Sr</span>TiO 3 (STO) and <span class="hlt">Ca</span>TiO 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 <span class="hlt">Sr</span> 0.6<span class="hlt">Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70048137','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70048137"><span><span class="hlt">Ca</span>, <span class="hlt">Sr</span>, O and D isotope approach to defining the chemical evolution of hydrothermal fluids: example from Long Valley, <span class="hlt">CA</span>, USA</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Brown, Shaun T.; Kennedy, B. Mack; DePaolo, Donald J.; Hurwitz, Shaul; Evans, William C.</p> <p>2013-01-01</p> <p>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, <span class="hlt">Sr</span>, and <span class="hlt">Ca</span>, 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. <span class="hlt">Sr</span> isotopes show subtle changes along the flow path, which requires rapid fluid flow and minimal reaction between the channelized fluids and the wallrocks. <span class="hlt">Sr</span> 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 <span class="hlt">Ca</span> suggest progressive fluid degassing (loss of CO2), which drives calcite precipitation as the fluid flows west-to-east and cools. The shifts in <span class="hlt">Ca</span> isotopes require that calcite precipitated at temperatures of 150–180 °C is fractionated by <span class="hlt">ca</span>. −0.3‰ to −0.5‰ relative to aqueous species. Our data are the first evidence that <span class="hlt">Ca</span> isotopes undergo kinetic fractionation at high temperatures (>100 °C) and can be used to trace calcite precipitation along hydrothermal fluid flow paths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSSCh.248..157C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSSCh.248..157C"><span>On the "alpha-phase" of <span class="hlt">Ca</span>2-xSrxMnO4 and extending the chemistry of <span class="hlt">Sr</span>7-yCayMn4O15 to y>1</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Craddock, Sarah; Senn, Mark S.</p> <p>2017-04-01</p> <p>There has been renewed interest in the Ruddlesden-Popper phase (n=2) of composition Can+1MnnO3 n+1 in the light of recent research that has highlighted the nature of the improper ferroelectric ground state, which arises due to the couplings between specific combinations of MnO6 octahedral rotations and tilts. A fruitful route to control these octahedral degrees of freedom, and hence such desired physical properties, is through chemical <span class="hlt">substitution</span> on the A-site cation i.e. <span class="hlt">Ca</span>2-xSrxMnO4 for n =1, and in light of this, we have reinvestigated the chemistry of this solid solution. Here we focus on a common impurity phase observed during this synthesis which has been termed the "alpha-phase" in the literature. We show that this impurity phase is actually comprised mainly of a structure related to <span class="hlt">Sr</span>7Mn4O15 but is found here with significantly higher <span class="hlt">Ca</span> <span class="hlt">substitution</span> than previously believed possible. <span class="hlt">Sr</span>7Mn4O15 is an interesting structural type in its own right, but has been mainly overlooked to date, exhibiting interesting physics related to low dimensional magnetic ordering and dimer interactions, and we show here that the structural type is a likely candidate for exhibiting a multiferroic ground state. The prospect of being able to tune the lattice and the exchange interactions through further chemical <span class="hlt">substitution</span> is likely to lead to a renewed interest in this material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26505461','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26505461"><span>New honeycomb iridium(V) oxides: NaIrO3 and <span class="hlt">Sr</span>3<span class="hlt">Ca</span>Ir2O9.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wallace, David C; McQueen, Tyrel M</p> <p>2015-12-21</p> <p>We report the structures and physical properties of two new iridates, NaIrO3 and <span class="hlt">Sr</span>3<span class="hlt">Ca</span>Ir2O9, both of which contain continuous two-dimensional honeycomb connectivity. NaIrO3 is produced by room temperature oxidative deintercalation of sodium from Na2IrO3, and contains edge-sharing IrO6 octahedra that form a planar honeycomb lattice. <span class="hlt">Sr</span>3<span class="hlt">Ca</span>Ir2O9, produced via conventional solid-state synthesis, hosts a buckled honeycomb lattice with novel corner-sharing connectivity between IrO6 octahedra. Both of these new compounds are comprised of Ir(5+) (5d(4)) and exhibit negligible magnetic susceptibility. They are thus platforms to investigate the origin of the nonmagnetic behavior exhibited by Ir(5+) oxides, and provide the first examples of a J = 0 state on a honeycomb lattice.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JMMM..346...26P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JMMM..346...26P"><span>Half metallic ferromagnetism in alkaline-earth metal nitrides XN (X=<span class="hlt">Ca</span>, <span class="hlt">Sr</span> and Ba): A first principles study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Palanichamy, R. Rajeswara; Priyanga, G. Sudha; Cinthia, A. Jemmy; Murugan, A.; Meenaatci, A. T. Asvini; Iyakutti, K.</p> <p>2013-11-01</p> <p>The structural, electronic, mechanical and magnetic properties of 3 alkaline-earth metal nitrides (XN: X=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) are investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation code. At ambient pressure all the 3 nitrides are stable in the ferromagnetic state with a cubic NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that these materials are half metallic ferromagnets at normal pressure. A pressure-induced structural phase transition from NaCl (B1) to CsCl (B2) phase is observed in <span class="hlt">Ca</span>N, <span class="hlt">Sr</span>N and BaN. On further increasing the pressure, a half metallic to metallic transition is also observed in these nitrides. Ferromagnetism is quenched in all the 3 nitrides at high pressures.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MPLB...3050379J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MPLB...3050379J"><span>Morphological, thermal and optical studies of jute-reinforced Pb<span class="hlt">SrCa</span>CuO-polypropylene composite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jacob, Reenu; Isac, Jayakumari</p> <p>2016-11-01</p> <p>New research with modern technologies has always grabbed substantial attention. Conservation of raw materials like natural fibers has helped composite world to explore eco-friendly components. The aim of this paper is to study the potential of jute fiber-reinforced ceramic polymers. Alkali-treated jute fiber has been incorporated in a polypropylene ceramic matrix at different volume fractions. The morphological, thermal and optical studies of jute-reinforced ceramic Pb2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O9 (Pb<span class="hlt">SrCa</span>CuO) are studied. Morphological results evidently demonstrate that when the polypropylene ceramic matrix is reinforced with jute fiber, interfacial interaction between the varying proportions of the jute fiber and ceramic composite takes place. TGA and DSC results confirm the enhancement in the thermal stability of ceramic composites reinforced with jute fiber. The UV analysis of the composite gives a good quality measure on the optical properties of the new composite prepared.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27877610','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27877610"><span>Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba, as thermoelectric materials.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Parker, David; Singh, David J</p> <p>2013-10-01</p> <p>We present a detailed theoretical study of three alkaline earth compounds <span class="hlt">Ca</span>2Pb, <span class="hlt">Sr</span>2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds <span class="hlt">Ca</span>2Sn, <span class="hlt">Sr</span>2Sn and Ba2Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli-roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1254797-strain-induced-topological-transition-srru2o6-caos2o6','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1254797-strain-induced-topological-transition-srru2o6-caos2o6"><span>Strain-induced topological transition in <span class="hlt">Sr</span>Ru2O6 and <span class="hlt">Ca</span>Os2O6</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Ochi, Masayuki; Arita, Ryotaro; Trivedi, Nandini; ...</p> <p>2016-05-24</p> <p>The topological property of <span class="hlt">Sr</span>Rumore » $$_2$$O$$_6$$ and isostructural <span class="hlt">Ca</span>Os$$_2$$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 <span class="hlt">Sr</span>Ru$$_2$$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 <span class="hlt">Ca</span>Os$$_2$$O$$_6$$, 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.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1093745','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1093745"><span>Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae=<span class="hlt">Ca,Sr</span>,Ba, as thermoelectric materials</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Parker, David S; Singh, David J</p> <p>2013-01-01</p> <p>We present a detailed theoretical study of three alkaline earth compounds <span class="hlt">Ca</span>2Pb, <span class="hlt">Sr</span>2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds <span class="hlt">Ca</span>2 Sn, <span class="hlt">Sr</span>2 Sn and Ba2 Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli - roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V44C..02H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V44C..02H"><span>40K-40<span class="hlt">Ca</span> and 87Rb-86<span class="hlt">Sr</span> Dating by SIMS: The Double-Plus Advantage</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harrison, T. M.; McKeegan, K. D.; Schmitt, A. K.</p> <p>2009-12-01</p> <p> retentivity of 40<span class="hlt">Ca</span>* relative to 40Ar* in white micas. This approach offers the potential to develop a branched-decay thermochronometer (K-<span class="hlt">Ca</span>-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-<span class="hlt">Sr</span> dating show promise. While resolving 87Rb+ from 87<span class="hlt">Sr</span>+ requires an MRP of ~290k, unattainable using any current SIMS instrument, 87Rb++ is so strongly suppressed that determination of 87<span class="hlt">Sr</span>++ is possible with minor peak stripping. 87Rb/86<span class="hlt">Sr</span> can be determined either from 85Rb+/88<span class="hlt">Sr</span>+ 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989AIPC..182..252T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989AIPC..182..252T"><span>Photoemission resonance study of sintered and single-crystal Bi4<span class="hlt">Ca</span>3<span class="hlt">Sr</span>3Cu4O16+x</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tang, Ming; Chang, Y.; Zanoni, R.; Onellion, M.; Joynt, Robert; Huber, D. L.; Margaritondo, G.; Morris, P. A.; Bonner, W. A.; Tarascon, J. M.; Stoffel, N. G.</p> <p>1989-02-01</p> <p>We present soft x-ray photoemission spectra that probe the valence and core electronic structure of the high-Tc superconductor Bi4<span class="hlt">Ca</span>3<span class="hlt">Sr</span>3Cu4O16+x. The identification of spectral features was helped by the observation of the resonant behavior of a Cu-related satellite feature. The resonance occurs at photon energies near the Cu3p optical absorption edge, and affects a peak 12.5 eV below the Fermi edge. We identified this feature as a correlation satellite characteristic of Cu in the 2+ valence state. Other features observed in the spectra more than 7 eV below the Fermi edge are due to several different core levels. In particular, we observed a strong Bi5d doublet. Other core level peaks are due to the <span class="hlt">Sr</span>4p and <span class="hlt">Ca</span>3p orbitals, and to Bi, <span class="hlt">Sr</span> and <span class="hlt">Ca</span> s-orbitals. Within 7 eV of the Fermi edge, the spectra are dominated by valence states. The most important feature is the Bi4<span class="hlt">Ca</span>3<span class="hlt">Sr</span>3Cu4O16+x Fermi edge itself, which we observed for the first time on this, and whose existence was subsequently confirmed by several other groups. On the contrary, no edge was observed in the photoemission spectra of materials in the YBa2Cu3O7-x family. The observation of the Fermi edge has important implications for the theoretical interpretation of high-Tc superconductivity. Furthermore, it enabled us to see near-edge changes associated with the superconducting transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PCE....32..559M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PCE....32..559M"><span>Adsorption of bivalent ions (<span class="hlt">Ca</span>(II), <span class="hlt">Sr</span>(II) and Co(II)) onto FEBEX bentonite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Missana, T.; García-Gutiérrez, M.</p> <p></p> <p>The sorption of the bivalent ions <span class="hlt">Ca</span>, <span class="hlt">Sr</span> 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 <span class="hlt">Ca</span> and <span class="hlt">Sr</span> is very similar both from a qualitative and quantitative point of view. The main sorption mechanism for <span class="hlt">Ca</span> and <span class="hlt">Sr</span> 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 <span class="hlt">Ca</span> and <span class="hlt">Sr</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6183510','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6183510"><span>Laser ablation deposition of superconducting Bi-<span class="hlt">Sr-Ca</span>-Cu-O thin films on zirconia-buffered crystalline quartz</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bohandy, J.; Agostinelli, E.; Kim, B.F.; Green, W.J.; Phillips, T.E.; Adrian, F.J.; Moorjani, K.</p> <p>1989-06-01</p> <p>Thin films of Bi-<span class="hlt">Sr-Ca</span>-Cu-O have been deposited on crystalline quartz substrates by laser ablation. Without a buffer layer, superconducting regions exist in the films as detected by magnetically modulated microwave absorption. However, with a 1000-A zirconia buffer layer, also deposited by laser ablation, continuous, superconducting thin films were obtained. It is shown that both annealing temperature and annealing time greatly affect the film quality.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015LaPhL..12i5001S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015LaPhL..12i5001S"><span><span class="hlt">Ca</span>F2, BaF2 and <span class="hlt">Sr</span>F2 crystals’ optical anisotropy parameters</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Snetkov, I. L.; Yakovlev, A. I.; Palashov, O. V.</p> <p>2015-09-01</p> <p>Using the original method, based on measurements of thermally induced depolarization, the optical anisotropy parameters of <span class="hlt">Ca</span>F2, BaF2 and <span class="hlt">Sr</span>F2 cubic crystals were measured and compared with what is known from the literature. Euler angles of crystallographic axis orientation [C], in which the thermally induced depolarization is minimal, were determined using experimental results for studied fluorides.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhRvB..90n4506J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhRvB..90n4506J"><span>Persistent Fe moments in the normal-state collapsed-tetragonal phase of the pressure-induced superconductor <span class="hlt">Ca</span>0.67<span class="hlt">Sr</span>0.33Fe2As2</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2014-10-01</p> <p>Using nonresonant Fe Kβ x-ray emission spectroscopy, we reveal that <span class="hlt">Sr</span> <span class="hlt">substitution</span> into <span class="hlt">Ca</span>Fe2As2 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940016290&hterms=Granite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DGranite','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940016290&hterms=Granite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DGranite"><span>Chronology of lunar granite 12033,576: Resetting of Rb-<span class="hlt">Sr</span> and K-<span class="hlt">Ca</span> isochrons</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Shih, C.-Y.; Wiesmann, H.; Garrison, D. H.; Nyquist, L. E.; Bogard, D. D.</p> <p>1993-01-01</p> <p>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-<span class="hlt">Ca</span>, Ar-39/Ar-40, and U-Pb zircon methods in previous studies and by the Rb-<span class="hlt">Sr</span> 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-<span class="hlt">Sr</span> and K-<span class="hlt">Ca</span> methods can be interpreted as reset by diffusion of the parent and daughter nuclides. The Rb-<span class="hlt">Sr</span> age is less resistant to resetting than the K-<span class="hlt">Ca</span> age, but more resistant that the Ar-39/Ar-40 age.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21612810','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21612810"><span>X-ray absorption investigation of the valence state and electronic structure of La{sub 1-x}<span class="hlt">Ca</span>{sub x}CoO{sub 3-{delta}} in comparison with La{sub 1-x}<span class="hlt">Sr</span>{sub x}CoO{sub 3-{delta}} and La{sub 1-x}<span class="hlt">Sr</span>{sub x}FeO{sub 3-{delta}</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Haas, O.; Ludwig, Chr.; Bergmann, U.; Singh, R.N.; Braun, A.; Graule, T.</p> <p>2011-12-15</p> <p>3d metal K-shell X-ray absorption spectra of perovskites with the composition La{sub 1-x}<span class="hlt">Ca</span>{sub x}CoO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La{sub 1-x}<span class="hlt">Sr</span>{sub x}CoO{sub 3-{delta}} (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La{sub 1-x}<span class="hlt">Sr</span>{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}<span class="hlt">Ca</span>{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}<span class="hlt">Ca</span>{sub x}CoO{sub 3-{delta}} and La{sub 1-x}<span class="hlt">Sr</span>{sub x}CoO{sub 3-{delta}} compounds and the Co-O distances are also not significantly reduced when La{sup 3+} is partially <span class="hlt">substituted</span> by <span class="hlt">Ca</span>{sup 2+} or <span class="hlt">Sr</span>{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 <span class="hlt">Ca</span> and <span class="hlt">Sr</span> <span class="hlt">substituted</span> 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}<span class="hlt">Sr</span>{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}<span class="hlt">Sr</span>{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}<span class="hlt">Ca</span>{sub x}CoO{sub 3-{delta}} and La{sub 1-x}<span class="hlt">Sr</span>{sub x}FeO{sub 3-{delta}} perovskites one of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22420632','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22420632"><span>Photoluminescence performance of thulium doped Li{sub 4}<span class="hlt">SrCa</span>(SiO{sub 4}){sub 2} under irradiation of ultraviolet and vacuum ultraviolet lights</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wang, Zhaofeng; Li, Yezhou; Liu, Xiong; Wei, Xingmin; Chen, Yueling; Zhou, Fei; Wang, Yuhua</p> <p>2014-11-15</p> <p>Highlights: • A novel blue-emitting phosphor Li{sub 4}<span class="hlt">SrCa</span>(SiO{sub 4}){sub 2}:Tm{sup 3+} was reported. • Li{sub 4}<span class="hlt">SrCa</span>(SiO{sub 4}){sub 2}:Tm{sup 3+} exhibited excellent thermal and irradiation stability. • Li{sub 4}<span class="hlt">SrCa</span>(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}<span class="hlt">SrCa</span>(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}<span class="hlt">SrCa</span>(SiO{sub 4}){sub 2} host by occupying the sites of <span class="hlt">Ca</span>{sup 2+} with the coordination number of 6. The luminescence results suggest that Li{sub 4}<span class="hlt">SrCa</span>(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}<span class="hlt">SrCa</span>(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}<span class="hlt">SrCa</span>(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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPSJ...85i4717O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPSJ...85i4717O"><span>Effects of Mn <span class="hlt">Substitution</span> on the Thermoelectric Properties and Thermal Excitations of the Electron-doped Perovskite <span class="hlt">Sr</span>1-xLaxTiO3</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Okuda, Tetsuji; Hata, Hiroto; Eto, Takahiro; Sobaru, Shogo; Oda, Ryosuke; Kaji, Hiroki; Nishina, Kousuke; Kuwahara, Hideki; Nakamura, Mitsutaka; Kajimoto, Ryoichi</p> <p>2016-09-01</p> <p>We studied how Mn <span class="hlt">substitution</span> affects the thermoelectric properties and thermal excitations of the electron-doped perovskite <span class="hlt">Sr</span>1-xLaxTiO3 by measuring its electrical and thermal transport properties, magnetization, specific heat, and inelastic neutron scattering. Slight Mn <span class="hlt">substitution</span> 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 <span class="hlt">substitution</span> increased the dimensionless thermoelectric figure of merit for <span class="hlt">Sr</span>1-xLaxTiO3 near room temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMMM..412...69A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMMM..412...69A"><span>Magnetic and dielectric properties of Bi3+ <span class="hlt">substituted</span> <span class="hlt">Sr</span>Fe12O19 hexaferrite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Auwal, I. A.; Erdemi, H.; Sözeri, H.; Güngüneş, H.; Baykal, A.</p> <p>2016-08-01</p> <p>In the present study, <span class="hlt">Sr</span>BixFe12-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, <span class="hlt">Sr</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvB..94s5142D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvB..94s5142D"><span>Optical properties of A Fe2As2 (A =<span class="hlt">Ca</span> , <span class="hlt">Sr</span>, and Ba) single crystals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dai, Y. M.; Akrap, Ana; Bud'ko, S. L.; Canfield, P. C.; Homes, C. C.</p> <p>2016-11-01</p> <p>The detailed optical properties have been determined for the iron-based materials A Fe2As2 , where A =<span class="hlt">Ca</span> , <span class="hlt">Sr</span>, and Ba, for light polarized in the iron-arsenic (a-b) planes over a wide frequency range, above and below the magnetic and structural transitions at TN=138 , 195, and 172 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above TN, the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below TN there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for T ≪TN may be related to the Dirac conelike dispersion of the electronic bands. Below TN new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at Δ1≃45 -80 meV, and Δ2≃110 -210 meV. The reduction in the spectral weight associated with the free carriers is captured by the gap structure; specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1342646-optical-properties-afe2as2-ca-sr-ba-single-crystals','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1342646-optical-properties-afe2as2-ca-sr-ba-single-crystals"><span>Optical properties of AFe2As2 ( A=<span class="hlt">Ca</span> , <span class="hlt">Sr</span>, and Ba) single crystals</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Dai, Y. M.; Akrap, Ana; Bud'ko, S. L.; ...</p> <p>2016-11-23</p> <p>The detailed optical properties have been determined for the iron-based materials A Fe2 As2 , where A = <span class="hlt">Ca</span> , <span class="hlt">Sr</span>, and Ba, for light polarized in the iron-arsenic (a-b) planes over a wide frequency range, above and below the magnetic and structural transitions at TN = 138 , 195, and 172 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above TN, the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below TN there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for Tmore » $$\\ll$$ TN may be related to the Dirac conelike dispersion of the electronic bands. Below TN new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at Δ1 ≃ 45 – 80 meV, and Δ2 ≃ 110 – 210 meV. In conclusion, the reduction in the spectral weight associated with the free carriers is captured by the gap structure; specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70026556','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70026556"><span>Mg/<span class="hlt">Ca</span>, <span class="hlt">Sr/Ca</span>, and stable isotopes in modern and Holocene Protothaca staminea shells from a northern California coastal upwelling region</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Takesue, R.K.; VanGeen, A.</p> <p>2004-01-01</p> <p>This study explores the potential of intertidal Protothaca staminea shells as high-resolution geochemical archives of environmental change in a coastal upwelling region. Mg/<span class="hlt">Ca</span> and <span class="hlt">Sr/Ca</span> 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/<span class="hlt">Ca</span> ratios appeared to be partly controlled by water temperature; the correlation coefficient between temperature and Mg/<span class="hlt">Ca</span> was r = 0.71 in one of four growth increments. Significant year-to-year differences in the sensitivity of Mg/<span class="hlt">Ca</span> to temperature in P. staminea could not be explained, however. <span class="hlt">Sr/Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APExp...6g2101T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APExp...6g2101T"><span>Eu2+-Activated <span class="hlt">CaSr</span>SiO4: a New Red-Emitting Oxide Phosphor for White-Light-Emitting Diodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tezuka, Satoko; Sato, Yasushi; Komukai, Tetsufumi; Takatsuka, Yuji; Kato, Hideki; Kakihana, Masato</p> <p>2013-07-01</p> <p><span class="hlt">Ca</span>1-x<span class="hlt">Sr</span>1-xEu2xSiO4 (<span class="hlt">CaSr</span>SiO4:Eu2+) phosphors were prepared by a novel aqueous solution technique using propylene glycol-modified silane (PGMS), combined with a freeze-drying process. The precursors were heat-treated under a reducing atmosphere with BaCl2 flux. X-ray diffraction indicated that the obtained phosphors exhibited an α'-<span class="hlt">CaSr</span>SiO4 structure. The wavelength at the phosphors' maximum emission was systematically shifted beyond 600 nm as the Eu2+ concentration was increased. The corresponding excitation spectra were extended to the visible light region (400-500 nm) with increasing Eu2+ concentration. These results implied that <span class="hlt">CaSr</span>SiO4:Eu2+ is a red-emitting phosphor excited by near-UV and blue-light-emitting diodes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15516874','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15516874"><span>Strontium <span class="hlt">substituted</span> calcium phosphate biphasic ceramics obtained by a powder precipitation method.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kim, Hae-Won; Koh, Young-Hag; Kong, Young-Min; Kang, Jun-Gu; Kim, Hyoun-Ee</p> <p>2004-10-01</p> <p>Strontium (<span class="hlt">Sr</span>) <span class="hlt">substituted</span> calcium phosphate ceramics were fabricated using a powder precipitation method. The <span class="hlt">Sr</span> ions were added up to 8 mol % to replace the <span class="hlt">Ca</span> ions during the powder preparation. Composition analysis showed that the added <span class="hlt">Sr</span> was not fully incorporated within the as-precipitated apatite structure, presumably being washed out during the powder preparation. After calcination, the <span class="hlt">Sr</span> containing powders were crystallized into apatite and tricalcium phosphate (TCP), that is, biphasic calcium phosphates were formed. The amount of TCP increased with increasing the <span class="hlt">Sr</span> addition. The lattice parameters of the calcined powders increased gradually with <span class="hlt">Sr</span> <span class="hlt">substitution</span> in both the a- and c-axis. However, the obtained values deviated slightly from the calculated ones at higher <span class="hlt">Sr</span> additions (>4%) due to the partial <span class="hlt">substitution</span> of <span class="hlt">Sr</span> ions. The microstructure of the sintered bodies changed with the <span class="hlt">Sr</span> addition due to the formation of TCP. The Vickers hardness increased slightly from 5.2 to 5.5 MPa with increasing <span class="hlt">Sr</span> addition, which was driven by the HA+TCP biphasic formation. The osteoblast-like cells cultured on the <span class="hlt">Sr-substituted</span> biphasic sample spread and grew actively. The proliferation rate of the cells was higher in the samples containing more <span class="hlt">Sr</span>. The alkaline phosphate activity of the cells was expressed to a higher degree with increasing <span class="hlt">Sr</span> addition. These observations confirmed the enhanced cell viability and differentiation of the <span class="hlt">Sr-substituted</span> biphasic calcium phosphate ceramics.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16403969','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16403969"><span>Antioxidants prevented oxidative injury of <span class="hlt">SR</span> induced by Fe2+/H2O2/ascorbate system but failed to prevent <span class="hlt">Ca</span>2+-ATPase activity decrease.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Horáková, Lubica; Strosová, Miriam; Skuciová, Mária</p> <p>2005-01-01</p> <p>Dysfunction of sarcoplasmic reticulum (<span class="hlt">SR</span>) <span class="hlt">Ca</span>2+-ATPase induced by oxidative stress may be a contributing factor to the development of serious age related diseases. Incubation of sarcoplasmic reticulum (<span class="hlt">SR</span>) vesicles of rabbit skeletal muscles with Fe2+/H2O2/ascorbate decreased the SH group content of <span class="hlt">SR</span> approximately to 35% and <span class="hlt">Ca</span>2+-ATPase activity to 50% of control not oxidized sample. Protein carbonyls increased twofold, lipid peroxidation was also significantly elevated. The antioxidant effects of trolox, the pyridoindole derivative stobadine and of the standardized extracts from bark of Pinus Pinaster PycnogenolR (Pyc) and from leaves of Ginkgo biloba (EGb 761) were studied on oxidatively injured <span class="hlt">SR</span>. All antioxidants exerted preventive effects against the oxidized lipids and protein SH groups of <span class="hlt">SR</span> vesicles. Trolox and stobadine did not influence protein carbonyl formation, while flavonoid extracts prevented carbonyl generation, probably by binding to protein. The preventive effects of the antioxidants studied on lipids and protein SH groups were however not associated with protection of <span class="hlt">Ca</span>2+-ATPase activity. Stobadine and trolox exerted no effect on enzyme activity, Pyc and EGb 761 enhanced the inhibitory effect of <span class="hlt">Ca</span>2+-ATPase activity in oxidatively injured <span class="hlt">SR</span>. Concluding, under the conditions of oxidative stress induced by Fe2+/H2O2/ascorbate against <span class="hlt">SR</span> of rabbit skeletal muscle, the agents studied demonstrated antioxidant effects yet failed to protect <span class="hlt">Ca</span>2+-ATPase activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27589858','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27589858"><span>Hypermethylation of the <span class="hlt">CaSR</span> and VDR genes in the parathyroid glands in chronic kidney disease rats with high-phosphate diet.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Uchiyama, Taketo; Tatsumi, Norifumi; Kamejima, Sahoko; Waku, Tsuyoshi; Ohkido, Ichiro; Yokoyama, Keitaro; Yokoo, Takashi; Okabe, Masataka</p> <p>2016-10-01</p> <p>Chronic kidney disease (CKD) disrupts mineral homeostasis and its representative pathosis is defined as secondary hyperparathyroidism (SHPT). SHPT occurs during the early course of progressive renal insufficiency, and is associated with mortality and cardiovascular events. SHPT results in reduction of calcium-sensing receptor (<span class="hlt">CaSR</span>) and vitamin D receptor (VDR) in the parathyroid glands during CKD. However, the precise mechanism of <span class="hlt">CaSR</span> and VDR reduction is largely unknown. CKD was induced through two-step 5/6 nephrectomy, and then CKD rats and sham-operated rats were maintained for 8 weeks on diets containing 0.7 % phosphorus (normal phosphate) or 1.2 % phosphorus (high phosphate). In gene expression analysis, TaqMan probes were used for quantitative real-time polymerase chain reaction. Finally, <span class="hlt">CaSR</span> and VDR protein expressions were analyzed using immunohistochemistry. DNA methylation analysis was performed using a restriction digestion and quantitative PCR. <span class="hlt">CaSR</span> and VDR mRNA were reduced only in CKD rats fed the high-phosphorus diets (CKD HP), then <span class="hlt">CaSR</span> and VDR immunohistochemical expressions were compatible with gene expression assay. SHPT was then confirmed only in CKD HP rats. Furthermore, sole CKD HP rats showed the hypermethylation in <span class="hlt">CaSR</span> and VDR genes; however, the percentage methylation of both genes was low. Although <span class="hlt">CaSR</span> and VDR hypermethylation was demonstrated in PTGs of CKD HP rats, the extent of hypermethylation was insufficient to support the relevance between hypermethylation and down-regulation of gene expression because of the low percentage of methylation. Consequently, our data suggest that mechanisms, other than DNA hypermethylation, were responsible for the reduction in mRNA and protein levels of <span class="hlt">CaSR</span> and VDR in PTGs of CKD HP rats.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21413756','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21413756"><span>Macrocyclic receptor showing extremely high <span class="hlt">Sr(II)/Ca</span>(II) and Pb(II)/<span class="hlt">Ca</span>(II) selectivities with potential application in chelation treatment of metal intoxication.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ferreirós-Martínez, Raquel; Esteban-Gómez, David; Tóth, Éva; de Blas, Andrés; Platas-Iglesias, Carlos; Rodríguez-Blas, Teresa</p> <p>2011-04-18</p> <p>Herein we report a detailed investigation of the complexation properties of the macrocyclic decadentate receptor N,N'-Bis[(6-carboxy-2-pyridil)methyl]-4,13-diaza-18-crown-6 (H(2)bp18c6) toward different divalent metal ions [Zn(II), Cd(II), Pb(II), <span class="hlt">Sr</span>(II), and <span class="hlt">Ca</span>(II)] in aqueous solution. We have found that this ligand is especially suited for the complexation of large metal ions such as <span class="hlt">Sr</span>(II) and Pb(II), which results in very high Pb(II)/<span class="hlt">Ca</span>(II) and Pb(II)/Zn(II) selectivities (in fact, higher than those found for ligands widely used for the treatment of lead poisoning such as ethylenediaminetetraacetic acid (edta)), as well as in the highest <span class="hlt">Sr(II)/Ca</span>(II) selectivity reported so far. These results have been rationalized on the basis of the structure of the complexes. X-ray crystal diffraction, (1)H and (13)C NMR spectroscopy, as well as theoretical calculations at the density functional theory (B3LYP) level have been performed. Our results indicate that for large metal ions such as Pb(II) and <span class="hlt">Sr</span>(II) the most stable conformation is Δ(δλδ)(δλδ), while for <span class="hlt">Ca</span>(II) our calculations predict the Δ(λδλ)(λδλ) form being the most stable one. The selectivity that bp18c6(2-) shows for <span class="hlt">Sr</span>(II) over <span class="hlt">Ca</span>(II) can be attributed to a better fit between the large <span class="hlt">Sr</span>(II) ions and the relatively large crown fragment of the ligand. The X-ray crystal structure of the Pb(II) complex shows that the Δ(δλδ)(δλδ) conformation observed in solution is also maintained in the solid state. The Pb(II) ion is endocyclically coordinated, being directly bound to the 10 donor atoms of the ligand. The bond distances to the donor atoms of the pendant arms (2.55-2.60 Å) are substantially shorter than those between the metal ion and the donor atoms of the crown moiety (2.92-3.04 Å). This is a typical situation observed for the so-called hemidirected compounds, in which the Pb(II) lone pair is stereochemically active. The X-ray structures of the Zn(II) and Cd(II) complexes show that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3321118','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3321118"><span>Voltage clamp methods for the study of membrane currents and <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ release in adult skeletal muscle fibres</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hernández-Ochoa, Erick O.; Schneider, Martin F.</p> <p>2012-01-01</p> <p>Skeletal muscle excitation-contraction (E-C)1 coupling is a process composed of multiple sequential stages, by which an action potential triggers sarcoplasmic reticulum (<span class="hlt">SR</span>)2 <span class="hlt">Ca</span>2+ release and subsequent contractile activation. The various steps in the E-C coupling process in skeletal muscle can be studied using different techniques. The simultaneous recordings of sarcolemmal electrical signals and the accompanying elevation in myoplasmic <span class="hlt">Ca</span>2+, due to depolarization-initiated <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ release in skeletal muscle fibres, have been useful to obtain a better understanding of muscle function. In studying the origin and mechanism of voltage dependency of E-C coupling a variety of different techniques have been used to control the voltage in adult skeletal fibres. Pioneering work in muscles isolated from amphibians or crustaceans used microelectrodes or ‘high resistance gap’ techniques to manipulate the voltage in the muscle fibres. The development of the patch clamp technique and its variant, the whole-cell clamp configuration that facilitates the manipulation of the intracellular environment, allowed the use of the voltage clamp techniques in different cell types, including skeletal muscle fibres. The aim of this article is to present an historical perspective of the voltage clamp methods used to study skeletal muscle E-C coupling as well as to describe the current status of using the whole-cell patch clamp technique in studies in which the electrical and <span class="hlt">Ca</span>2+ signalling properties of mouse skeletal muscle membranes are being investigated. PMID:22306655</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvB..94p1118Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvB..94p1118Z"><span>Compass impurity model of Tb <span class="hlt">substitution</span> in <span class="hlt">Sr</span>2IrO4</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Long; Wang, Fa; Lee, Dung-Hai</p> <p>2016-10-01</p> <p>We show that upon Tb <span class="hlt">substitution</span> the interaction between the magnetic moments on the impurity Tb4 + ion and its surrounding Ir4 + ions is described by a "compass" model, i.e., an Ising-like interaction favoring the magnetic moments across each bond to align along the bond direction. Such an interaction nucleates quenched magnetic vortices near the impurities and drives a reentrant transition out of the antiferromagnetic ordered phase at low temperatures, hence quickly suppressing the Néel temperature, consistent with the experiment [J. C. Wang et al., Phys. Rev. B 92, 214411 (2015), 10.1103/PhysRevB.92.214411]. As a by-product, we propose that the compass model can be realized in ordered double perovskites composed of spin-orbital-coupled d5 ions and half-closed-shell f7 ions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5308610','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5308610"><span><span class="hlt">Sr-substituted</span> bone cements direct mesenchymal stem cells, osteoblasts and osteoclasts fate</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Panseri, Silvia; Dapporto, Massimiliano; Tampieri, Anna; Sprio, Simone</p> <p>2017-01-01</p> <p>Strontium-<span class="hlt">substituted</span> apatitic bone cements enriched with sodium alginate were developed as a potential modulator of bone cells fate. The biological impact of the bone cement were investigated in vitro through the study of the effect of the nanostructured apatitic composition and the doping of strontium on mesenchymal stem cells, pre-osteoblasts and osteoclasts behaviours. Up to 14 days of culture the bone cells viability, proliferation, morphology and gene expression profiles were evaluated. The results showed that different concentrations of strontium were able to evoke a cell-specific response, in fact an inductive effect on mesenchymal stem cells differentiation and pre-osteoblasts proliferation and an inhibitory effect on osteoclasts activity were observed. Moreover, the apatitic structure of the cements provided a biomimetic environment suitable for bone cells growth. Therefore, the combination of biological features of this bone cement makes it as promising biomaterials for tissue regeneration. PMID:28196118</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4886260','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4886260"><span>Understanding cold bias: Variable response of skeletal <span class="hlt">Sr/Ca</span> to seawater pCO2 in acclimated massive Porites corals</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cole, Catherine; Finch, Adrian; Hintz, Christopher; Hintz, Kenneth; Allison, Nicola</p> <p>2016-01-01</p> <p>Coral skeletal <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal <span class="hlt">Sr/Ca</span> is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...626888C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...626888C"><span>Understanding cold bias: Variable response of skeletal <span class="hlt">Sr/Ca</span> to seawater pCO2 in acclimated massive Porites corals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cole, Catherine; Finch, Adrian; Hintz, Christopher; Hintz, Kenneth; Allison, Nicola</p> <p>2016-05-01</p> <p>Coral skeletal <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal <span class="hlt">Sr/Ca</span> is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1039342','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1039342"><span>The Effect of the CO32- to <span class="hlt">Ca</span>2+ Ion activity ratio on calcite precipitation kinetics and <span class="hlt">Sr</span>2+ partitioning</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tsigabu Gebrehiwet; Mikala S. Beig; George Redden; Yoshiko Fujita; Robert W. Smith</p> <p>2012-01-01</p> <p>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 <span class="hlt">Ca</span>CO{sub 3} precipitation kinetics and <span class="hlt">Sr</span>{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 <span class="hlt">Ca</span>{sup 2+}}) ranged from 0.003 to 4.15. Results: Under the chosen experimental conditions the <span class="hlt">Ca</span>CO{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 <span class="hlt">Sr</span>2+ (D{sup P}{sub <span class="hlt">Sr</span>}{sup 2+}) relative to the calcite precipitation rate (i.e. a positive correlation) indicate that increasing calcite precipitation rates increase the incorporation of <span class="hlt">Sr</span>{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}<span class="hlt">Sr</span>) and other toxic metals in engineered systems at contaminated sites. Extending our data plot range allowed us</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22475697','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22475697"><span>Influence of chemical <span class="hlt">substitution</span> on the photoluminescence of <span class="hlt">Sr</span>{sub (1−x)}Pb{sub x}WO{sub 4} solid solution</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hallaoui, A.; Taoufyq, A.; Arab, M.; Bakiz, B.; Benlhachemi, A.; Bazzi, L.; Villain, S.; Valmalette, J-C.; Guinneton, F.; Gavarri, J-R.</p> <p>2015-07-15</p> <p>The solid solution <span class="hlt">Sr</span>{sub 1−x}Pb{sub x}WO{sub 4} based on luminescent tungstates <span class="hlt">Sr</span>WO{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 <span class="hlt">substituted</span> 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 <span class="hlt">substitution</span> 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 <span class="hlt">substitution</span> rate. - Graphical abstract: Photoluminescence under X-ray excitation of <span class="hlt">Sr</span>{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 <span class="hlt">Sr</span>{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 <span class="hlt">substitution</span> of <span class="hlt">Sr</span> by Pb on two components, due to Pb–O–W interactions. • Enhancement of luminescence intensity in a specific composition range.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA359538','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA359538"><span>Heterostructures (<span class="hlt">CaSr</span>Ba)F2 on InP for Optoelectronics</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1995-01-01</p> <p>and <span class="hlt">Sr</span>F2 layers onto InP(100) have been grown at 350’C under ultra-high vacuum conditions using epitaxial and bulk substrates. MBE and Laser Vacuum... <span class="hlt">Sr</span>F2 /InP diodes prepared by sublimation of the fluoride under vacuum, an important modulation without hysteresis of the surface potential of the...grew the thin films of <span class="hlt">Sr</span>F2 by sublimation under a classical vacuum (10-7 Torr). They showed by Rutherford backscattering and by XPS measurements that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007NIMPA.580..293O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007NIMPA.580..293O"><span>Performance of thin <span class="hlt">Ca</span>SO4:Dy pellets for calibration of a <span class="hlt">Sr</span>90+Y90 source</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oliveira, M. L.; Caldas, L. V. E.</p> <p>2007-09-01</p> <p>Because of the radionuclide long half-life, <span class="hlt">Sr</span>90+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 <span class="hlt">Ca</span>SO4:Dy pellets are produced at IPEN specially for beta radiation detection. Previous works showed the feasibility of this material in the dosimetry of <span class="hlt">Sr</span>90+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 <span class="hlt">Sr</span>90+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 <span class="hlt">Sr</span>90+Y90 source, and the pellets were calibrated against a plane applicator; then they were utilized to calibrate the concave applicator.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1225418-high-tc-superconductivity-interface-between-cacuo2-srtio3-insulating-oxides','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1225418-high-tc-superconductivity-interface-between-cacuo2-srtio3-insulating-oxides"><span>High-Tc superconductivity at the interface between the <span class="hlt">Ca</span>CuO2 and <span class="hlt">Sr</span>TiO3 insulating oxides</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Di Castro, D.; Cantoni, C.; Ridolfi, F.; ...</p> <p>2015-09-28</p> <p>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 <span class="hlt">Ca</span>CuO2/<span class="hlt">Sr</span>TiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the <span class="hlt">Ca</span>CuO2/<span class="hlt">Sr</span>TiO3 interface must be realized between the <span class="hlt">Ca</span> plane of <span class="hlt">Ca</span>CuO2 and the TiO2 plane of <span class="hlt">Sr</span>TiO3. Only in this case can oxygen ions be incorporated in themore » interface <span class="hlt">Ca</span> 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 <span class="hlt">Ca</span>CuO2 unit cells close to the interface with <span class="hlt">Sr</span>TiO3. The results obtained for the <span class="hlt">Ca</span>CuO2/<span class="hlt">Sr</span>TiO3 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26551817','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26551817"><span>High-T(c) Superconductivity at the Interface between the <span class="hlt">Ca</span>CuO2 and <span class="hlt">Sr</span>TiO3 Insulating Oxides.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Di Castro, D; Cantoni, C; Ridolfi, F; Aruta, C; Tebano, A; Yang, N; Balestrino, G</p> <p>2015-10-02</p> <p>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 T(c). We report the occurrence of high T(c) superconductivity in the bilayer <span class="hlt">Ca</span>CuO(2)/<span class="hlt">Sr</span>TiO(3), where both the constituent oxides are insulating. In order to obtain a superconducting state, the <span class="hlt">Ca</span>CuO(2)/<span class="hlt">Sr</span>TiO(3) interface must be realized between the <span class="hlt">Ca</span> plane of <span class="hlt">Ca</span>CuO(2) and the TiO(2) plane of <span class="hlt">Sr</span>TiO(3). Only in this case can oxygen ions be incorporated in the interface <span class="hlt">Ca</span> plane, acting as apical oxygen for Cu and providing holes to the CuO(2) planes. 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 <span class="hlt">Ca</span>CuO(2) unit cells close to the interface with <span class="hlt">Sr</span>TiO(3). The results obtained for the <span class="hlt">Ca</span>CuO(2)/<span class="hlt">Sr</span>TiO(3) interface can be extended to multilayered high T(c) cuprates, contributing to explaining the dependence of T(c) on the number of CuO(2) planes in these systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21580014','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21580014"><span>M{sup II}Ge(PO{sub 4}){sub 2} (M=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba): Crystal structure, phase transitions and thermal expansion</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Popa, Karin; Wallez, Gilles; Bregiroux, Damien; Loiseau, Pascal</p> <p>2011-10-15</p> <p>Three earth alkali-germanium monophosphates M{sup II}Ge(PO{sub 4}){sub 2} (M=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO{sub 4}){sub 2} and high-temperature {beta}-<span class="hlt">Sr</span>Ge(PO{sub 4}){sub 2} (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas <span class="hlt">Ca</span>Ge(PO{sub 4}){sub 2} and low-temperature {alpha}-<span class="hlt">Sr</span>Ge(PO{sub 4}){sub 2} (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic. - Graphical abstract: The superstructure of <span class="hlt">Sr</span>Ge(PO{sub 4}){sub 2} at room temperature ({alpha}) results from the off-centering of cation <span class="hlt">Sr</span>{sup II}. Highlights: > Crystal structures of yavapaiite-type M{sup II}Ge(PO{sub 4}){sub 2} (M=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba) have been solved. > Distortion and superstructure result from <span class="hlt">Ca</span> and <span class="hlt">Sr</span> off-centering. > A global scheme for the polymorphism of yavapaiites is proposed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26027006','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26027006"><span>Tilting structures in inverse perovskites, M3TtO (M = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba, Eu; Tt = Si, Ge, Sn, Pb).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Nuss, Jürgen; Mühle, Claus; Hayama, Kyouhei; Abdolazimi, Vahideh; Takagi, Hidenori</p> <p>2015-06-01</p> <p>Single-crystal X-ray diffraction experiments were performed for a series of inverse perovskites, M3TtO (M = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba, Eu; Tt = tetrel element: Si, Ge, Sn, Pb) in the temperature range 500-50 K. For Tt = Sn, Pb, they crystallize as an 'ideal' perovskite-type structure (Pm3m, cP5); however, all of them show distinct anisotropies of the displacement ellipsoids of the M atoms at room temperature. This behavior vanishes on cooling for M = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Eu, and the structures can be regarded as `ideal' cubic perovskites at 50 K. The anisotropies of the displacement ellipsoids are much more enhanced in the case of the Ba compounds. Finally, their structures undergo a phase transition at ∼ 150 K. They change from cubic to orthorhombic (Ibmm, oI20) upon cooling, with slightly tilted OBa6 octahedra, and bonding angles O-Ba-O ≃ 174° (100 K). For the larger Ba(2+) cations, the structural changes are in agreement with smaller tolerance factors (t) as defined by Goldschmidt. Similar structural behavior is observed for <span class="hlt">Ca</span>3TtO. Smaller Tt(4-) anions (Si, Ge) introduce reduced tolerance factors. Both compounds <span class="hlt">Ca</span>3SiO and <span class="hlt">Ca</span>3GeO with cubic structures at 500 K, change into orthorhombic (Ibmm) at room temperature. Whereby, <span class="hlt">Ca</span>3SiO is the only representative within the M3TtO family where three polymorphs can be found within the temperature range 500-50 K: Pm3m-Ibmm-Pbnm. They show tiny differences in the tilting of the OCa6 octahedra, expressed by O-<span class="hlt">Ca</span>-O bond angles of 180° (500 K), ∼ 174° (295 K) and 170° (100 K). For larger M (<span class="hlt">Sr</span>, Eu, Ba), together with smaller Tt (Si, Ge) atoms, pronounced tilting of the OM6 octahedra, and bonding angles of O-M-O ≃ 160° (295 K) are observed. They crystallize in the anti-GdFeO3 type of structure (Pbnm, oP20), and no phase transitions occur between 500 and 50 K. The observed phase transitions are all accompanied by multiple twinning, in terms of pseudo-merohedry or reticular pseudo-merohedry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5958142','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5958142"><span>Characterization of hot isostatically pressed Bi-<span class="hlt">Sr-Ca</span>-Cu-O as a function of consolidation variables</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Goretta, K.C.; Miller, D.J.; Poeppel, R.B. ); Nash, A.S. )</p> <p>1991-11-01</p> <p>Fully dense, bulk Bi{sub 2}<span class="hlt">Sr</span>{sub 1.7}<span class="hlt">Ca</span>Cu{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}<span class="hlt">Sr</span>{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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1265814','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1265814"><span>Effects of chemical pressure on the magnetic ground states of the osmate double perovskites <span class="hlt">SrCa</span>CoOs<sub>6</sub> and <span class="hlt">Ca</span><sub>2</sub>CoOsO<sub>6</sub></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Morrow, Ryan; Yan, Jiaqiang; McGuire, Michael A.; Freeland, John W.; Haskel, Daniel; Woodward, Patrick M.</p> <p>2015-09-21</p> <p>The magnetic ground state in the double perovskite system <span class="hlt">Sr</span><sub>2-x</sub><span class="hlt">Ca</span><sub>x</sub>CoOsO<sub>6</sub> changes from an antiferromagnet (x=0), to a spin glass (x=1), to a ferrimagnet (x=2) as the <span class="hlt">Ca</span> content increases. Moreover, this crossover is driven by chemical pressure effects that control the relative strength of magnetic exchange interactions. The synthesis, crystal structure, and magnetism of <span class="hlt">SrCa</span>CoOsO<sub>6</sub> and <span class="hlt">Ca</span><sub>2</sub>CoOsO<sub>6</sub> are investigated and compared with <span class="hlt">Sr</span><sub>2</sub>CoOsO<sub>6</sub>. Both compounds adopt a monoclinic crystal structure with rock-salt ordering of Co<sup>2+</sup> and Os<sup>6+</sup> and a<sup>-</sup>a<sup>-</sup>b<sup>+</sup> octahedral tilting, but the average Co–O–Os bond angle evolves from 158.0(3) in <span class="hlt">SrCa</span>CoOsO<sub>6</sub> to 150.54(9)° in <span class="hlt">Ca</span><sub>2</sub>CoOsO<sub>6</sub> as the smaller <span class="hlt">Ca</span><sup>2</sup>+ ion replaces <span class="hlt">Sr</span><sup>2+</sup>. And while this change may seem minor, it has a profound effect on the magnetism, changing the magnetic ground state from antiferromagnetic in <span class="hlt">Sr</span><sub>2</sub>CoOsO<sub>6</sub> (TN1=108K, T<sub>N2</sub>=70K), to a spin glass in <span class="hlt">SrCa</span>CoOsO<sub>6</sub> (T<sub>f1</sub>=32K, T<sub>f2</sub>=13K), to ferrimagnetic in <span class="hlt">Ca</span><sub>2</sub>CoOsO<sub>6</sub> (T<sub>C</sub>=145K). Finally, in the first two compounds the observation of two transitions is consistent with weak coupling between the Co and Os sublattices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5307316','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5307316"><span>Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) and <span class="hlt">Sr</span>TiO3</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; Van Overmeere, Quentin; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Maran, Ronald; Anazawa, Toshihisa; Valanoor, Nagarajan; Imanaka, Yoshihiko</p> <p>2017-01-01</p> <p>The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for <span class="hlt">Sr</span>SnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices. PMID:28195149</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatSR...741725B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatSR...741725B"><span>Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) and <span class="hlt">Sr</span>TiO3</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; van Overmeere, Quentin; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Maran, Ronald; Anazawa, Toshihisa; Valanoor, Nagarajan; Imanaka, Yoshihiko</p> <p>2017-02-01</p> <p>The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for <span class="hlt">Sr</span>SnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JMMM..332..137A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JMMM..332..137A"><span>Characterization of <span class="hlt">Sr-substituted</span> W-type hexagonal ferrites synthesized by sol-gel autocombustion method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ahmad, Mukhtar; Grössinger, R.; Kriegisch, M.; Kubel, F.; Rana, M. U.</p> <p>2013-04-01</p> <p>The magnetic and microwave characterization of single phase hexaferrites of entirely new composition Ba1-xSrxCo2AlFe15O27 (x=0.2-1.0) for application in a microwave absorber, have been reported. The samples synthesized by sol-gel method were investigated by differential thermal analyzer, Fourier transform infrared spectroscope, X-ray diffractometer, field emission gun scanning electron microscope, vibrating sample magnetometer and vector network analyzer. Platelet grains exhibit well defined hexagonal shape which is a better shape for microwave absorption. M-H loops for a selected sample were measured for a temperature range of 4.2-400 K. Moreover M-H loops for all <span class="hlt">Sr-substituted</span> samples were also measured at room temperature up to a maximum applied field of 9 T. Saturation magnetization values were calculated by the law of approach to saturation. The room temperature coercivity for all the samples is found to be a few hundred oersteds which is necessary for electromagnetic materials and makes these ferrites ideal for microwave devices, security, switching and sensing applications. The complex permittivity, permeability and reflection losses of a selected ferrite-epoxy composite were also investigated over a frequency range of 0.5-13 GHz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23897245','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23897245"><span>Efficient red phosphor double-perovskite <span class="hlt">Ca</span>3WO6 with A-site <span class="hlt">substitution</span> of Eu3+.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhao, Xin; Wang, Jiajia; Fan, Li; Ding, Yufeng; Li, Zhaosheng; Yu, Tao; Zou, Zhigang</p> <p>2013-10-07</p> <p>Luminescent properties of Eu(3+) activated double perovskite structure <span class="hlt">Ca</span>3WO6 were investigated. It emits an ideal red color centered at the wavelength of 618 nm with suitable excitation from f-f transitions of Eu(3+) ions (360-550 nm) matching the near ultraviolet and blue LEDs. Charge compensation effect of Li(+), Na(+), and K(+) was investigated, and K(+) proved to be the best. The co-doping ion K(+) has a great effect on the lattice distortion of the host matrix <span class="hlt">Ca</span>3WO6, which facilitates the red emission of Eu(3+). The <span class="hlt">substitution</span> site for <span class="hlt">Ca</span> in <span class="hlt">Ca</span>3WO6 was analyzed in detail by Raman spectra and calculation results. A-site <span class="hlt">substitution</span> is responsible for the red emission of Eu(3+) activated <span class="hlt">Ca</span>3WO6. The integrated emission intensity of optimal <span class="hlt">Ca</span>3WO6:K(+),Eu(3+) excited at 395 nm is about 3.5 times greater than that of Y2O2S:Eu(3+) commercial phosphors, which makes it a promising red phosphor for white LEDs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MAR.T1173C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MAR.T1173C"><span>Structural and Magnetic Phase Coexistence in Oxygen Deficient Perovskites (<span class="hlt">Sr,Ca</span>)FeO 2 . 5 + δ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p></p> <p>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 (<span class="hlt">Sr,Ca</span>)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. <span class="hlt">Sr</span>FeO2 . 5 + δ exhibits cubic symmetry and paramagnetism at 300K, but <span class="hlt">Ca</span>FeO2 . 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 <span class="hlt">Ca</span> content. Financial support from the Villanova Undergraduate Research Fellowship program and the Research Corporation for Science Advancement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989JAP....66.5564O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989JAP....66.5564O"><span>White-light emitting thin film electroluminescent devices with stacked <span class="hlt">SrS:Ce/Ca</span>S:Eu active layers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ono, Yoshimasa A.; Fuyama, Moriaki; Onisawa, Ken-ichi; Tamura, Katsumi; Ando, Masahiko</p> <p>1989-12-01</p> <p>By stacking blue-green emitting <span class="hlt">Sr</span>S:Ce and red-emitting <span class="hlt">Ca</span>S:Eu active layers, white-light emitting electroluminescent (EL) devices were fabricated. Luminance improvement and EL characteristics of <span class="hlt">Sr</span>S:Ce and <span class="hlt">Ca</span>S:Eu EL devices were discussed. The electrooptical characteristics of white-light emitting EL devices with stacked <span class="hlt">SrS:Ce/Ca</span>S:Eu active layers were presented. Color changed from blue-green to white by changing the voltage or frequency. Finally, feasibility of multicolor EL devices by using the fabricated white-light emitting EL devices with color filters were discussed. UFpg5523,5527 UFid992922JAP UFttIn situ ac magnetic susceptibility of gadolinium thin films UFauF. H. SalasSUPa),b) and M. Mirabal-GarciaaSUPc) UFloInstitut fuur Atom- und Festkourperphysik, Freie Universitaut Berlin, D-1000 Berlin 33, ufquadFederal Republic of Germany UFsd(Received 27 April 1989; accepted for publication 3 August 1989) UFabWe report measurements of the ac magnetic susceptibility on Gd(0001)/W(110) thin films grown in ultrahigh vacuum. The measurements were made by using a pickup coil, in which the geometry and the number of turns were optimized. We applied an alternating magnetic field of about 2 Grms at frequencies of 180 and 340 Hz. The growth mode and the deposition rate of the Gd films were determined by performing conventional Auger electron spectroscopy during film growth. In films with thickness larger than 10 nm our technique is sensitive up to 1016 atoms/Grms , which allowed us to study the critical behavior of the magnetic susceptibility as the Curie temperature is approached from above, TT+C . A sharp maximum, which may be related to the Hopkinson effect, is observed at a temperature TH 289 K.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JPCS...79...23C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JPCS...79...23C"><span>Structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cinthia, A. Jemmy; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Iyakutti, K.</p> <p>2015-04-01</p> <p>The structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba) in the cubic (B1, B2 and B3) phases and in the wurtzite (B4) phase are investigated using density functional theory calculations as implemented in VASP code. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are computed. The calculated lattice parameters are in good agreement with the experimental and the other available theoretical results. Electronic structure reveals that all the five alkaline earth metal oxides exhibit semiconducting behavior at zero pressure. The estimated band gaps for the stable wurtzite phase of BeO is 7.2 eV and for the stable cubic NaCl phases of MgO, <span class="hlt">Ca</span>O, <span class="hlt">Sr</span>O and BaO are 4.436 eV, 4.166 eV, 4.013 eV, and 2.274 eV respectively. A pressure induced structural phase transition occurs from wurtzite (B4) to NaCl (B1) phase in BeO at 112.1 GPa and from NaCl (B1) to CsCl (B2) phase in MgO at 514.9 GPa, in <span class="hlt">Ca</span>O at 61.3 GPa, in <span class="hlt">Sr</span>O at 42 GPa and in BaO at 14.5 GPa. The elastic constants are computed at zero and elevated pressures for the B4 and B1 phases for BeO and for the B1 and B2 phases in the case of the other oxides in order to investigate their mechanical stability, anisotropy and hardness. The sound velocities and the Debye temperatures are calculated for all the oxides using the computed elastic constants.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Natur.532..343H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Natur.532..343H"><span>Detection of a Cooper-pair density wave in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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</p> <p>2016-04-01</p> <p>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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms and at the Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1341670-detection-cooper-pair-density-wave-bi2sr2cacu2o8','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1341670-detection-cooper-pair-density-wave-bi2sr2cacu2o8"><span>Detection of a Cooper-pair density wave in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Hamidian, M. H.; Edkins, S. D.; Joo, Sang Hyun; ...</p> <p>2016-04-13</p> <p>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. In this paper we report the use of nanometre-resolution scanned Josephson tunnelling microscopy to image Cooper pair tunnelling from a d-wave superconducting microscope tip to themore » condensate of the superconductor Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms and at the Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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. Finally, 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.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6683437','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6683437"><span>Hydrogen sites in A/sub 2/BH/sub y/ (A = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Eu; B = Ir, Rh, Ru)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Westlake, D.G.</p> <p>1984-06-01</p> <p>A geometric model has been applied to the A/sub 2/BH/sub y/ hydrides (deuterides), Eu/sub 2/IrD/sub 5/, <span class="hlt">Ca</span>/sub 2/IrH/sub 5/, <span class="hlt">Sr</span>/sub 2/IrD/sub 5/, <span class="hlt">Ca</span>/sub 2/RhH/sub 5/, <span class="hlt">Sr</span>/sub 2/RhH/sub 5/, <span class="hlt">Ca</span>/sub 2/RuH/sub 6/ and <span class="hlt">Sr</span>/sub 2/RuD/sub 6/, none of which can be synthesized directly by reaction of hydrogen (deuterium) gas with an A/sub 2/B compound. Hole radii and intersite distances were calculated for the two types of interstices in each compound. Ther are two very large cubical interstices per formula unit. These are coordinated by eight atoms of type A, but they must remain unoccupied in A/sub 2/BH/sub y/ with y = 5 (or 6), because of their proximity to the square pyramidal interstices, of which there are six per formula unit. The geometric model allows rationalization of the occupation of these pyramidal sites. Despite the very significant chemical differences between the compounds considered here and those for which the model was initially developed, the present results showed no inconsistency with geometric criteria requiring that occupied interstices in stable hydrides have minimum hole radii of 0.40 Angstrom and minimum hydrogen-hydrogen distances of 2.10 Angstrom. Published results indicate that the seemingly related compound Mg/sub 2/NiD/sub 4/ does not conform to these empirical rules, and this case is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SCPMA..6047011B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SCPMA..6047011B"><span>Optical spectroscopy study of charge density wave order in <span class="hlt">Sr</span>3Rh4Sn13 and (<span class="hlt">Sr</span>0.5<span class="hlt">Ca</span>0.5)3Rh4Sn13</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ban, W. J.; Wang, H. P.; Tseng, C. W.; Kuo, C. N.; Lue, C. S.; Wang, N. L.</p> <p>2017-04-01</p> <p>We perform optical spectroscopy measurement on single-crystal samples of <span class="hlt">Sr</span>3Rh4Sn13 and (<span class="hlt">Sr</span>0.5<span class="hlt">Ca</span>0.5)3Rh4Sn13. Formation of CDW energy gap was clearly observed for both single-crystal samples when they undergo the phase transitions. The existence of residual Drude components in σ 1( ω) below T CDW indicates that the Fermi surface is only partially gapped in the CDW state. The obtained value of 2Δ/ k B T CDW is roughly 13 for both <span class="hlt">Sr</span>3Rh4Sn13 and (<span class="hlt">Sr</span>0.5<span class="hlt">Ca</span>0.5)3Rh4Sn13 compounds, which is considerably larger than the mean-field value based on the weak-coupling BCS theory. The measurements provide optical evidence for the strong coupling characteristics of the CDW phase transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP43B1473O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP43B1473O"><span>Replicating and calibrating Haitian microatoll coral <span class="hlt">Sr/Ca</span> variations to build confidence in sea surface temperature reconstructions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ouellette, G., Jr.; DeLong, K. L.; Kilbourne, K. H.; Taylor, F. W.; Mann, P.; Jean, P.</p> <p>2014-12-01</p> <p>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 <span class="hlt">Sr/Ca</span> (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 <span class="hlt">Sr/Ca</span> (8.90 ±0.05 mmol/mol, 1σ for 10LEO1; and 8.83 ±0.06 mmol/mol, 1σ for 10BELOC4; n=100). Calibration of coral <span class="hlt">Sr/Ca</span> to OISST for the 1º grid including our study site results in a slope similar to previous studies using boulder-shaped S. siderea colonies (<span class="hlt">Sr/Ca</span>=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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002PhRvB..65v0501F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002PhRvB..65v0501F"><span>Electronic excitations near the Brillouin zone boundary of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Feng, D. L.; Kim, C.; Eisaki, H.; Lu, D. H.; Damascelli, A.; Shen, K. M.; Ronning, F.; Armitage, N. P.; Kaneko, N.; Greven, M.; Shimoyama, J.-I.; Kishio, K.; Yoshizaki, R.; Gu, G. D.; Shen, Z.-X.</p> <p>2002-06-01</p> <p>Based on angle resolved photoemission spectra measured on different systems at different dopings, momenta, and photon energies, we show that the anomalously large spectral linewidth in the (π,0) region of optimal doped and underdoped Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ has significant contributions from the bilayer band splitting, and that the scattering rate in this region is considerably smaller than previously estimated. This picture of the electronic excitation near (π,0) puts additional experimental constraints on various microscopic theories and data analyses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990JaJAP..29L.270A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990JaJAP..29L.270A"><span>Preparation of High-Quality Bi-Pb-<span class="hlt">Sr-Ca</span>-Cu Oxide Precursor by the Citrate Gel Process</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aoki, Aiko</p> <p>1990-02-01</p> <p>In order to achieve a high-Tc superconducting phase of Bi-Pb-<span class="hlt">Sr-Ca</span>-Cu oxide, we applied a highly reactive citrate gel process to yield a precursor powder. A citrate-nitrate solution was dehydrated and heated to form the desired compound. We applied a thermogravimetric analysis, scanning electron microscopy and X-ray diffraction to study thermal decomposition during the heat stage. Sintered sample showed good superconducting properties with Tc above 100 K. Chemical analyses revealed negligible loss of metals during the preparation procedure, indicating that the citrate gel process is an excellent and reliable method for this compound.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004ApPhL..85.3513P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004ApPhL..85.3513P"><span>Effects of high-intensity ultrasound on Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x superconductor</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Prozorov, Tanya; McCarty, Brett; Cai, Zhihua; Prozorov, Ruslan; Suslick, Kenneth S.</p> <p>2004-10-01</p> <p>Slurries of powdered Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x (BSCCO-2212) superconductor in high-boiling alkanes were irradiated with intense ultrasound. Significant enhancements of magnetic irreversibility as well as transport critical current are reported. The effects are dependent on the concentration of the slurry and are optimal for 1.5wt% slurry loading. Electron microscopy shows that ultrasonic treatment leads to a change in grain morphology and intergrain welding. The observed enhancement of superconducting properties is consistent with the limitations in critical currents in BSCCO superconductor being due to intergrain coupling rather than intragrain pinning strength.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5277976','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5277976"><span>Formation of the 110-K superconducting phase in Pb-doped Bi-<span class="hlt">Sr-Ca</span>-Cu-O thin films</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kula, W.; Sobolewski, R.; Gorecka, J.; Lewandowski, S.J. )</p> <p>1991-09-15</p> <p>Investigation of the 110-K Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>{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)-<span class="hlt">Sr-Ca</span>-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}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>{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 <span class="hlt">Ca</span>NdAlO{sub 4} and <span class="hlt">Sr</span>TiO{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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFMPP52A0954C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFMPP52A0954C"><span>280-year Long <span class="hlt">Sr/Ca</span> and δ 18O Records From Flinders Reef, Western Coral Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Calvo, E.; Marshall, J. F.; Pelejero, C.; McCulloch, M. T.; Lough, J.; Gagan, M. K.</p> <p>2003-12-01</p> <p>The combination of parallel <span class="hlt">Sr/Ca</span> and δ 18O records in corals allows reconstruction of past changes in sea surface temperature (SST) and seawater δ 18O composition (McCulloch et al., 1994). The latter provides climatic information related to changes in the hydrologic cycle and can be interpreted as a salinity proxy. Since the δ 18O signal is affected by both SST and seawater isotopic composition, a salinity record can be obtained by removing the temperature signal using a parallel <span class="hlt">Sr/Ca</span> record, a proxy for SST, obtained from the same coral. Low resolution (5-year intervals) <span class="hlt">Sr/Ca</span> and δ 18O analyses, going back to 1710 AD, have been performed on a Porites coral core collected from Flinders Reef, an offshore reef on the Queensland Plateau (17° S, 149° E), 250 km from the north-east coast of Australia. For the last 280 years, the preliminary <span class="hlt">Sr/Ca</span>-SST record shows an increasing long-term trend towards the warm temperatures recorded during 1990, when the coral was collected. An increasing trend towards more negative δ 18O values (warmer and/or less saline conditions) is also observed in the isotopic record, which also reflects the 20th century warming. Despite this general common trend, interdecadal variability differences between both records suggest that temperature alone cannot explain the δ 18O changes observed in this site of the Coral Sea. A freshening of surface waters after 1870 has recently been reported from coral cores collected from the inshore region in the Great Barrier Reef and interpreted as indicating a weakening in trade winds and ocean circulation (Hendy, 2002). In the Flinders coral, however, an apparent freshening occurs in the early 1800s, followed by a subsequent transition to more saline conditions during the first half of the 20th century. Our data will be compared to that from the GBR and elsewhere in the SW Pacific (Quinn, 1998). Hendy, E. J. et al. Science 295, 1511-1514 (2002) McCulloch, M.T. et al. Geochimica at Cosmochimica Acta</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004APS..MARP13001M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004APS..MARP13001M"><span>Electronic structure and unusual superconducting properties of of <span class="hlt">Ca</span>AlSi and <span class="hlt">Sr</span>AlSi</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mazin, Igor I.; Papaconstantopoulos, Dimitris</p> <p>2004-03-01</p> <p>We report full-potential LAPW calculations for <span class="hlt">Ca</span>AlSi and <span class="hlt">Sr</span>AlSi in ordered structures and in the virtual crystal approximation, at normal and elevated pressures. We also estimate the electron-phonon coupling using either frozen-phon calculations at the zone center, or the rigid muffin tin approximation. We conclude that there is no simple way to explain the recently reported qualitative disparity in the superconducting properties of the two compounds. An assumption of an ultrasoft phonon mode, on the other hand, allows to reconcile in a reasonable way the experimental findings with the theory.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000PhRvL..85.2569C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000PhRvL..85.2569C"><span>Nodal Quasiparticle Lifetime in the Superconducting State of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corson, J.; Orenstein, J.; Oh, Seongshik; O'Donnell, J.; Eckstein, J. N.</p> <p>2000-09-01</p> <p>We have measured the complex conductivity σ of a Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ thin film between 0.2 and 0.8 THz. We find σ in the superconducting state to be well described as the sum of contributions from quasiparticles, condensate, and order parameter fluctuations which draw 30% of the spectral weight from the condensate. An analysis based on this decomposition yields a quasiparticle scattering rate on the order of kBT/ħ for temperatures below Tc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21612877','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21612877"><span>Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, ({alpha}/{beta})-Ba)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Josse, M.; El-Ghozzi, M.; Avignant, D.; Andre, G.; Bouree, F.; Isnard, O.</p> <p>2012-01-15</p> <p>Neutron powder diffraction has been performed on the MTbF{sub 6} fluorides (M=Cd, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, ({alpha}/{beta})-Ba). Four of these fluorides (Cd, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, {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 (<span class="hlt">Ca</span>), 2.60 K (<span class="hlt">Sr</span>), 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=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23220722','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23220722"><span>Juxtaglomerular cell <span class="hlt">CaSR</span> stimulation decreases renin release via activation of the PLC/IP(3) pathway and the ryanodine receptor.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ortiz-Capisano, M Cecilia; Reddy, Mahendranath; Mendez, Mariela; Garvin, Jeffrey L; Beierwaltes, William H</p> <p>2013-02-01</p> <p>The calcium-sensing receptor (<span class="hlt">CaSR</span>) 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 <span class="hlt">CaSR</span> in JG cells is unknown. In parathyroids, <span class="hlt">CaSR</span> 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 <span class="hlt">CaSR</span> 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 <span class="hlt">CaSR</span> 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 <span class="hlt">CaSR</span>-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 <span class="hlt">CaSR</span> activates G(q), initiating the PLC/IP(3) pathway, activating RyR, increasing intracellular calcium, and resulting in calcium-mediated renin inhibition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP53C2358F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP53C2358F"><span>Multi-species Coral <span class="hlt">Sr/Ca</span>-Based Sea-Surface Temperature Reconstruction Using Orbicella faveolata and Siderastrea siderea from Dry Tortugas National Park, FL</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Flannery, J. A.; Richey, J. N.; Thirumalai, K.; Poore, R. Z.</p> <p>2015-12-01</p> <p>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 (<span class="hlt">Sr/Ca</span>) 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 <span class="hlt">Sr/Ca</span> determinations were made using ICP-OES. <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span>, 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 <span class="hlt">Sr/Ca</span>-based SST and <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span>-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.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26086277','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26086277"><span>Manganite based hetero-junction structure of La0.7<span class="hlt">Sr</span>(0.7-x)CaxMnO3 and <span class="hlt">Ca</span>MnO(3-δ) for cross-point arrays.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lee, Hong-Sub; Park, Hyung-Ho</p> <p>2015-07-10</p> <p>Resistive random access memory and the corresponding cross-point array (CPA) structure have received a great deal of attention for high-density next generation non-volatile memory. However, the cross-talk issue of CPA structure by sneak current should be overcome to realize the highest density integration. To accomplish this, the sneak current can be minimized by high, nonlinear characteristic behaviors of resistive switching (RS). Therefore this study fabricated pnp bipolar hetero-junction structure using the perovskite manganite family, such as La0.7<span class="hlt">Sr</span>(0.3-x)CaxMnO3 (LSCMO) and <span class="hlt">Ca</span>MnO(3-δ) (CMO), to obtain nonlinear RS behavior. The pnp structure not only shows nonlinear characteristics, but also a tunable characteristic with <span class="hlt">Ca</span> <span class="hlt">substitution</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPS...331..400Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPS...331..400Q"><span>The <span class="hlt">Ca</span> element effect on the enhancement performance of <span class="hlt">Sr</span>2Fe1.5Mo0.5O6-δ perovskite as cathode for intermediate-temperature solid oxide fuel cells</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Qiao, Jinshuo; Chen, Wenjun; Wang, Wenyi; Wang, Zhenhua; Sun, Wang; Zhang, Jing; Sun, Kening</p> <p>2016-11-01</p> <p>In this paper, the partial <span class="hlt">substitution</span> 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, <span class="hlt">Sr</span>2-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 <span class="hlt">Ca</span> content. X-ray photoelectron spectroscopy analysis suggests that <span class="hlt">Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhyC..486...32G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhyC..486...32G"><span>Preparation and characterization of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ thin films on MgO single crystal substrates by chemical solution deposition</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grivel, J.-C.; Kępa, K.; Hlásek, T.; Andersen, N. H.; Rubešová, K.</p> <p>2013-03-01</p> <p>Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8 thin films have been deposited on MgO single crystal substrates by spin-coating a solution based on 2-ethylhexanoate precursors. Pyrolysis takes place between 200 °C and 450 °C and is accompanied by the release of 2-ethylhexanoic acid, CO2 and H2O vapour. Highly c-axis oriented Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8 films were obtained after heat treatment at 840 °C in air. The highest Tc of 81 K was measured in a 10-layer film. Subsequent post-annealing in Ar and pure O2 did not improve the superconducting properties of the films and resulted in the appearance of Bi2<span class="hlt">Ca</span>CuO5 or Bi2(<span class="hlt">Sr</span>, <span class="hlt">Ca</span>)2CuO6 impurities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910012597','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910012597"><span>The series Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>(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</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Deguire, Mark R.; Bansal, Narottam P.; Farrell, David E.; Finan, Valerie; Kim, Cheol J.; Hills, Bethanie J.; Allen, Christopher J.</p> <p>1989-01-01</p> <p>Phase relations at 850 and 870 C, melting transitions in air, oxygen, and helium were studied for Bi(2.1)<span class="hlt">Sr</span>(1.9) CuO6 and for the Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>(n-1) Cu(n)O(2n+4) for n = 1, 2, 3, 4, 5, and infinity (<span class="hlt">Ca</span>CuO2). Up to 870 C, the n = 2 composition resides in the compatibility tetrahedron bounded by Bi(2+x)(<span class="hlt">Sr,Ca</span>)(3-y) Cu2O8, (<span class="hlt">Sr,Ca</span>)14 Cu24O41, <span class="hlt">Ca</span>2CuO3, and a Bi-<span class="hlt">Sr-Ca</span>-O phase. The n is greater than or equal to 3 compositions reside in the compatibility tetrahedron Bi(2+x)(<span class="hlt">Sr,Ca</span>)(3-y) Cu2O8 - (<span class="hlt">Sr,Ca</span>)14 Cu24O41 - <span class="hlt">Ca</span>2CuO3 - CuO up to 850 C. However, Bi(2+x)<span class="hlt">Sr</span>(4-y) Cu3O10 forms for n is greater than or equal to 3 after extended heating at 870 C. Bi(2+x)<span class="hlt">Sr</span>(2-y) CuO6 and Bi(2+x)(<span class="hlt">Sr,Ca</span>)(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)<span class="hlt">Sr</span>(2-y) CuO6, Bi(2+n)(<span class="hlt">Sr,Ca</span>)(3-y) Cu2O8, and Bi(2+x)(<span class="hlt">Sr,Ca</span>)(4-y) Cu3O10 exhibit crystallographic alignment in a magnetic field, with the c-axes orienting parallel to the field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21212097','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21212097"><span>High-pressure modifications of <span class="hlt">Ca</span>Zn{sub 2}, <span class="hlt">Sr</span>Zn{sub 2}, <span class="hlt">Sr</span>Al{sub 2}, and BaAl{sub 2}: Implications for Laves phase structural trends</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich</p> <p>2008-11-15</p> <p>High-pressure forms of intermetallic compounds with the composition <span class="hlt">Ca</span>Zn{sub 2}, <span class="hlt">Sr</span>Zn{sub 2}, <span class="hlt">Sr</span>Al{sub 2}, and BaAl{sub 2} were synthesized from CeCu{sub 2}-type precursors (<span class="hlt">Ca</span>Zn{sub 2}, <span class="hlt">Sr</span>Zn{sub 2}, <span class="hlt">Sr</span>Al{sub 2}) and Ba{sub 21}Al{sub 40} by multi-anvil techniques and investigated by X-ray powder diffraction (<span class="hlt">Sr</span>Al{sub 2} and BaAl{sub 2}), X-ray single-crystal diffraction (<span class="hlt">Ca</span>Zn{sub 2}), and electron microscopy (<span class="hlt">Sr</span>Zn{sub 2}). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu{sub 2} (C15) structure, the dizincides adopt the hexagonal MgZn{sub 2} (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu{sub 2}-type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27800684','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27800684"><span>First-Principles Prediction of Two-Dimensional Electron Gas Driven by Polarization Discontinuity in Nonpolar/Nonpolar AHfO3/<span class="hlt">Sr</span>TiO3 (A = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) Heterostructures.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cheng, Jianli; Nazir, Safdar; Yang, Kesong</p> <p>2016-11-23</p> <p>By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) in nonpolar/nonpolar AHfO3/<span class="hlt">Sr</span>TiO3 (A = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) heterostructures. Two types of nonpolar/nonpolar interfaces, (AO)(0)/(TiO2)(0) and (HfO2)(0)/(<span class="hlt">Sr</span>O)(0), each with AO and HfO2 surface terminations, are modeled, respectively. The polarization domain and resulting interfacial electronic property are found to be more sensitive to the surface termination of the film rather than the interface model. As film thickness increases, an insulator-to-metal transition is found in all the heterostructures with HfO2 surface termination: for (AO)(0)/(TiO2)(0) interfaces, predicted critical film thickness for an insulator-to-metal transition is about 7, 6, and 3 unit cells for <span class="hlt">Ca</span>HfO3/<span class="hlt">Sr</span>TiO3, <span class="hlt">Sr</span>HfO3/<span class="hlt">Sr</span>TiO3, and BaHfO3/<span class="hlt">Sr</span>TiO3, respectively; for (HfO2)(0)/(<span class="hlt">Sr</span>O)(0) interfaces, the critical film thickness is about 7.5, 5.5, and 4.5 unit cells, respectively. In contrast, for the heterostructures with AO surface termination, <span class="hlt">Ca</span>HfO3/<span class="hlt">Sr</span>TiO3 exhibits a much larger critical film thickness about 11-12 unit cells for an insulator-to-metal transition; while <span class="hlt">Sr</span>HfO3/<span class="hlt">Sr</span>TiO3 and BaHfO3/<span class="hlt">Sr</span>TiO3 do not show any polarization behavior even film thickness increases up to 20 unit cells. The strain-induced polarization behavior was well-elucidated from energy versus polarization profile. This work is expected to stimulate further experimental investigation to the interfacial conductivity in the nonpolar/nonpolar AHfO3/<span class="hlt">Sr</span>TiO3 HS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/959616','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/959616"><span>Elastic Anomalies Accompanying Phase Transitions in (<span class="hlt">CaSr</span>)TiO3 Perovskite III: Experimental Investigation of Polycrystalline Samples</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Carpenter,M.; Li, B.; Liebermann, R.</p> <p>2007-01-01</p> <p>Bulk and shear moduli of polycrystalline samples of perovskites with different compositions across the <span class="hlt">Ca</span>TiO3-<span class="hlt">Sr</span>TiO3 solid solution have been measured at ambient conditions and in-situ at high pressures by pulse-echo ultrasonic methods. The samples were prepared as dense pellets by hot pressing synthetic powders at {approx}7.5 GPa and {approx}1000 C. Any variations of bulk modulus due to phase transitions are small, but significant anomalies have been observed in the shear modulus at ambient conditions. These are associated with a sequence of symmetry changes PmFormulam -> I4/mcm -> Pbcm -> Pnma with increasing <span class="hlt">Ca</span>TiO3 content. Comparison with variations in elastic properties predicted using Landau theory suggests that a substantial part of the elastic softening observed in tetragonal samples could be due to anelastic contributions from transformation twin walls. This additional softening does not occur in orthorhombic samples, and the transition from tetragonal to orthorhombic symmetry results in a stiffening of the shear modulus. No overt evidence was found for a phase transition I4/mcm {leftrightarrow} Pnma at high pressures in <span class="hlt">Ca</span>0.35<span class="hlt">Sr</span>0.65TiO3 but small changes in the trends of both bulk and shear moduli in the range 2.5-3 GPa could be due either to a different transition or a change in compression mechanism. A PmFormulam {leftrightarrow} I4/mcm transition at {approx}2 GPa in <span class="hlt">Ca</span>0.05<span class="hlt">Sr</span>0.95TiO3 shows the same form of softening as observed for the transition as a function of composition. A simple model of twin wall contributions to the compliance of tetragonal samples failed to match the observed variations that, alternatively, seem to follow {Delta}G {proportional_to} q4 where {Delta}G is the change in shear modulus and q4 the driving order parameter for the PmFormulam {leftrightarrow} I4/mcm transition. Analogous elastic behavior is expected to occur in (Mg,Fe)SiO3 and <span class="hlt">Ca</span>SiO3 perovskites at high pressures and temperatures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.B21C0355F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.B21C0355F"><span>The effect of light on intrashell trace metal variability (Mg/<span class="hlt">Ca</span> and <span class="hlt">Sr/Ca</span>) in the planktic foraminifer Orbulina universa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fehrenbacher, J. S.; Spero, H. J.; Russell, A. D.; Gagnon, A. C.; Vetter, L.; Snyder, J.; Naumann, E.; Grimm, B. L.; Holland, K.</p> <p>2012-12-01</p> <p>The shell walls of many planktic foraminifers contain alternating bands of high and low Mg/<span class="hlt">Ca</span> calcite. These bands have been attributed to chamber formation, light-modulated (circadian-like) biological effects, and light (e.g. pH change in the calcifying environment driven by the photosynthesis/respiration of photosynthetic symbionts). Previous experiments on the living planktic foraminifer Orbulina universa confirm a diurnal nature in the banding of O. universa: a wide band of low-Mg calcite forms during the day (12-hour light) and a narrower band of high Mg calcite forms at night (12-hour dark) (Spero et al., in prep). During the summer of 2011, we explored the response of Mg banding to light by culturing foraminifera at constant temperature, salinity, and ambient seawater pH, but with different light schedules: reverse light cycles (day/night cycle shifted by 12 hours), constant (24-hour) light, and constant (24-hour) dark conditions. We used an artificial Ba spike to mark 12-hour intervals of growth, regardless of the imposed light regime. In specimens grown with a reversed day/night light/dark cycle, we observe an immediate shift in the timing of Mg/<span class="hlt">Ca</span> banding. The timing of high and low Mg/<span class="hlt">Ca</span> bands in these specimens is indistinguishable from specimens grown under a normal day/night light/dark cycle. Mg/<span class="hlt">Ca</span> bands are present in some of the specimens cultured in constant light and in all specimens grown in constant dark conditions. Banding in the constant light and constant dark specimens is not paced by a diurnal cycle. The amplitude of the banding in these specimens is diminished and the average Mg/<span class="hlt">Ca</span> ratios are 30% lower in comparison to those kept on a 12-hour light/dark cycle. Additionally, we find the <span class="hlt">Sr/Ca</span> ratios are similar in both the constant light and reverse light/dark specimens, but are statistically significantly lower in the constant dark specimens (8% lower, p-value << 0.05). These results indicate that changes in microenvironment pH due to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..MARA53007C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..MARA53007C"><span>Indications of a Quantum Critical Point in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ Using a Local Kondo Effect</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Calleja, Eduardo; Dai, Jixia; Arnold, Gerald; Gu, Genda; McElroy, Kyle</p> <p>2014-03-01</p> <p>A complete understanding of the complex phase diagrams that are present in high temperature superconductors remains elusive. While there is an overwhelming amount of experimental data on the existence and interplay of the phases present in high Tc superconductors from local probes, much of the existing data only looks at the charge degree of freedom of the material. By <span class="hlt">substituting</span> Fe atoms for Cu atoms in the CuO plane of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ (Bi2212), we gain the ability to access the spin degree of freedom since the Fe atoms retain their magnetization below the superconducting transition temperature. This leads to a local Kondo effect which can be observed using Spectroscopic-Imaging Scanning Tunneling Microscopy (SI-STM) and the local Kondo temperature can be extracted from spectra via a theoretical model. We show that the examination of this local Kondo temperature across local and sample average doping leads to the observation of a change in the quasiparticle spin degree of freedom at a quantum critical point (QCP) with a nominal hole doping of roughly 0.22, in agreement with other probes. The observation of the QCP in Bi2212 with this new method to access the spin degree of freedom helps to unravel some of the mystery behind the complex phase diagram of Bi2212.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22489716','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22489716"><span>Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped <span class="hlt">Ca</span>F{sub 2} and <span class="hlt">Sr</span>F{sub 2} crystals</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Barandiarán, Zoila Seijo, Luis</p> <p>2015-10-14</p> <p>Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/<span class="hlt">Ca</span> pairs in <span class="hlt">Ca</span>F{sub 2} and Yb/<span class="hlt">Sr</span> pairs in <span class="hlt">Sr</span>F{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+} + <span class="hlt">Ca</span>{sup 2+} (<span class="hlt">Sr</span>{sup 2+}) → Y b{sup 3+} + <span class="hlt">Ca</span>{sup +} (<span class="hlt">Sr</span>{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 <span class="hlt">Ca</span>F{sub 2}:Y b{sup 2+} because the Y b{sup 3+}–<span class="hlt">Ca</span>{sup +} states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in <span class="hlt">Sr</span>F{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-<span class="hlt">Sr</span> 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 <span class="hlt">Sr</span>F{sub 2} host, associated with the lowest 4f–5d band.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JChPh.143n4702B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JChPh.143n4702B"><span>Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped <span class="hlt">Ca</span>F2 and <span class="hlt">Sr</span>F2 crystals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barandiarán, Zoila; Seijo, Luis</p> <p>2015-10-01</p> <p>Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/<span class="hlt">Ca</span> pairs in <span class="hlt">Ca</span>F2 and Yb/<span class="hlt">Sr</span> pairs in <span class="hlt">Sr</span>F2 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 4fN-15d excited states of Y b2+: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b2+ + <span class="hlt">Ca</span>2+ (<span class="hlt">Sr</span>2+) → Y b3+ + <span class="hlt">Ca</span>+ (<span class="hlt">Sr</span>+) electron phototransfer. This mechanism applies to all the observed Y b2+ 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in <span class="hlt">Ca</span>F2:Y b2+ because the Y b3+-<span class="hlt">Ca</span>+ states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in <span class="hlt">Sr</span>F2:Y b2+ 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 b2+ active center, then, non-radiative Yb-to-<span class="hlt">Sr</span> 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 <span class="hlt">Sr</span>F2 host, associated with the lowest 4f-5d band.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26472390','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26472390"><span>Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped <span class="hlt">Ca</span>F2 and <span class="hlt">Sr</span>F2 crystals.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Barandiarán, Zoila; Seijo, Luis</p> <p>2015-10-14</p> <p>Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/<span class="hlt">Ca</span> pairs in <span class="hlt">Ca</span>F2 and Yb/<span class="hlt">Sr</span> pairs in <span class="hlt">Sr</span>F2 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+) + <span class="hlt">Ca</span>(2+) (<span class="hlt">Sr</span>(2+)) → Y b(3+) + <span class="hlt">Ca</span>(+) (<span class="hlt">Sr</span>(+)) 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 <span class="hlt">Ca</span>F2:Y b(2+) because the Y b(3+)-<span class="hlt">Ca</span>(+) states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in <span class="hlt">Sr</span>F2: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-<span class="hlt">Sr</span> 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 <span class="hlt">Sr</span>F2 host, associated with the lowest 4f-5d band.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21128479','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21128479"><span>Crystal structures and chemistry of double perovskites Ba{sub 2}M(II)M'(VI)O{sub 6} (M=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, M'=Te, W, U)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fu, W.T. Au, Y.S.; Akerboom, S.; IJdo, D.J.W.</p> <p>2008-09-15</p> <p>Structures of the double perovskites Ba{sub 2}M(II)M '(VI)O{sub 6} (M=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, M'=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=<span class="hlt">Sr</span>, the observed space groups are I2/m (M' =W) and R3-bar (M'=Te), respectively. In the case of M=<span class="hlt">Ca</span>, the space groups are either monoclinic P2{sub 1}/n (M'=U) or cubic Fm3-bar m (M'=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba{sub 2}<span class="hlt">Sr</span>TeO{sub 6} and Ba{sub 2}<span class="hlt">Ca</span>UO{sub 6}, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba{sub 2}<span class="hlt">Sr</span>WO{sub 6} and Ba{sub 2}<span class="hlt">Ca</span>WO{sub 6} in the temperature range between 80 and 723 K. It was found that the rhombohedral R3-bar structure exists in Ba{sub 2}<span class="hlt">Sr</span>WO{sub 6} above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba{sub 2}<span class="hlt">Ca</span>WO{sub 6} undergoes a structural phase transition at low temperature to the tetragonal I4/m structure. - Graphical abstract: Evolution of structures as function of temperature in Ba{sub 2}<span class="hlt">Sr</span>WO{sub 6} (left) and Ba{sub 2}<span class="hlt">Ca</span>WO{sub 6} (right). The existence of two phase region in Ba{sub 2}<span class="hlt">Sr</span>WO{sub 6} can be clearly seen by the progressive increase of the rhombohedral R3-bar phase marked by asterisk (*)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSSCh.238...46M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSSCh.238...46M"><span>The effect of chemical pressure on the structure and properties of A2CrOsO6 (A=<span class="hlt">Sr</span>, <span class="hlt">Ca</span>) ferrimagnetic double perovskite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2016-06-01</p> <p>The ordered double perovskites <span class="hlt">Sr</span>2CrOsO6 and <span class="hlt">Ca</span>2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. As reported previously <span class="hlt">Sr</span>2CrOsO6 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 <span class="hlt">Ca</span>2CrOsO6. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 μB. <span class="hlt">Sr</span>2CrOsO6 orders at 660 K while <span class="hlt">Ca</span>2CrOsO6 orders at 490 K. Variable temperature magnetization measurements suggest that the magnetization of the Cr3+ and Os3+ sublattices have different temperature dependences in <span class="hlt">Sr</span>2CrOsO6. This leads to a non-monotonic temperature evolution of the magnetic moment. Similar behavior is not seen in <span class="hlt">Ca</span>2CrOsO6. Both compounds have similar levels of Os/Cr antisite disorder, with order parameters of η=80.2(4)% for <span class="hlt">Sr</span>2CrOsO6 and η=76.2(5)% for <span class="hlt">Ca</span>2CrOsO6, where η=2θ-1 and θ is the occupancy of the osmium ion on the osmium-rich Wyckoff site.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25479002','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25479002"><span>Thermoelectric properties and electronic structure of the Zintl phase Sr₅In₂Sb₆ and the <span class="hlt">Ca</span>(5-x)<span class="hlt">Sr</span>(x)In₂Sb₆ solid solution.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zevalkink, Alex; Chanakian, Sevan; Aydemir, Umut; Ormeci, Alim; Pomrehn, Gregory; Bux, Sabah; Fleurial, Jean-Pierre; Snyder, G Jeffrey</p> <p>2015-01-14</p> <p>The Zintl phase <span class="hlt">Sr</span>5In2Sb6 is isostructural with <span class="hlt">Ca</span>5In2Sb6-a promising thermoelectric material with a peak zT of 0.7 when the carrier concentration is optimized by doping. Density functional calculations for <span class="hlt">Sr</span>5In2Sb6 reveal a decreased energy gap and decreased valence band effective mass relative to the <span class="hlt">Ca</span> analog. Chemical bonding analysis using the electron localizability indicator was found to support the Zintl bonding scheme for this structure type. High temperature transport measurements of the complete <span class="hlt">Ca</span>(5-x)<span class="hlt">Sr</span>(x)In2Sb6 solid solution were used to investigate the influence of the cation site on the electronic and thermal properties of A5In2Sb6 compounds. <span class="hlt">Sr</span> was shown to be fully miscible on the <span class="hlt">Ca</span> site. The higher density of the <span class="hlt">Sr</span> analog leads to a slight reduction in lattice thermal conductivity relative to <span class="hlt">Ca</span>5In2Sb6, and, as expected, the solid solution samples have significantly reduced lattice thermal conductivities relative to the end member compounds.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JETP..123..127E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JETP..123..127E"><span>Magnetic properties of (<span class="hlt">Sr</span>Fe12O19) x (<span class="hlt">Ca</span>Cu3Ti4O12)1- x composites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Eremina, R. M.; Sharipov, K. R.; Yatsyk, I. V.; Lyadov, N. M.; Gilmutdinov, I. F.; Kiiamov, A. G.; Kabirov, Yu. V.; Gavrilyachenko, V. G.; Chupakhina, T. I.</p> <p>2016-07-01</p> <p>New composite materials (<span class="hlt">Sr</span>Fe12O19) x (<span class="hlt">Ca</span>Cu3Ti4O12)1- x ( x = 0, 0.05, 1) have been synthesized. Their magnetic properties are studied in the temperature range 5-300 K using the magnetic resonance and magnetometry methods. It is found that strontium hexaferrite microinclusions in the (<span class="hlt">Sr</span>Fe12O19)0.05(<span class="hlt">Ca</span>Cu3Ti4O12)0.95 composite "magnetize" <span class="hlt">Ca</span>Cu3Ti4O12 at temperatures from 300 to 200 K, forming a ferrimagnetic particle near the <span class="hlt">Sr</span>Fe12O19 "core." The magnetic resonance line below 200 K splits into two lines corresponding to <span class="hlt">Sr</span>Fe12O19 and <span class="hlt">Ca</span>Cu3Ti4O12. The core effect decoration is manifested in the increase in the Curie-Weiss temperature from 25 K in <span class="hlt">Ca</span>Cu3Ti4O12 without the doping ceramics to 80 K in the composite with 5% of <span class="hlt">Sr</span>Fe12O19.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhLA..380.4075E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhLA..380.4075E"><span>Magnetism, hysteresis cycle, and Ir-<span class="hlt">substitution</span> doping of <span class="hlt">Sr</span>2CrIrO6 double perovskite: A Monte Carlo simulation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>El Rhazouani, O.; El Khatabi, M.; Zarhri, Z.; Slassi, A.; Benyoussef, A.; El Kenz, A.</p> <p>2016-12-01</p> <p>Iridium-based double perovskite (DP) <span class="hlt">Sr</span>2CrIrO6 is expected to have the highest Curie temperatures (Tc) among all DPs and a high spin-polarization at room temperature, thanks to the more extended 5d orbitals of Ir, which makes it potential candidate in spintronic applications. Several publications have appeared in recent years documenting Ir-based double perovskites, but very few have explored the promising compound <span class="hlt">Sr</span>2CrIrO6. In this paper, a Monte Carlo simulation has been carried out in the framework of Ising model to make an exploratory study of <span class="hlt">Sr</span>2CrIrO6. Thermal magnetization, magnetic susceptibility, internal energy and specific heat have been studied. Effect of crystal field of Ir on the magnetic properties has been explored. Magnetic hysteresis cycle has been studied in relation to the exchange coupling values. Effects of Ir-<span class="hlt">substitution</span> doping by Os "<span class="hlt">Sr</span>2CrIrxOs1 - xO6" and by Re "<span class="hlt">Sr</span>2CrIrxRe1 - xO6" (0.1 ≤ x ≤ 0.5) on the magnetic behavior have been investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998Natur.391..373F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998Natur.391..373F"><span>Transport properties governed by surface barriers in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fuchs, Dan T.; Zeldov, Eli; Rappaport, Michael; Tamegai, Tsuyoshi; Ooi, Shuuichi; Shtrikman, Hadas</p> <p>1998-01-01</p> <p>One of the most common investigation techniques of type-II superconductors is the transport measurement, in which an electrical current is applied to a sample and the corresponding resistance is measured as a function of temperature and magnetic field. At temperatures well below the critical temperature, Tc, the resistance of a superconductor is usually immeasurably low. But at elevated temperatures and fields, in the so-called vortex liquid phase, a substantial linear resistance is observed. In this dissipative state, which in anisotropic high-temperature superconductors like Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8 may occupy most of the mixed-state phase diagram, the transport current is usually assumed to flow uniformly across the sample as in a normal metal. To test this assumption, we have devised a measurement approach which allows determination of the flow pattern of the transport current across the sample. The surprising result is that, in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8 crystals, most of the current flows at the edges of the sample rather than in the bulk, even in the highly resistive state, due to the presence of strong surface barriers. This finding has significant implications for the interpretation of existing resistivity data and may be of importance for the development of high-temperature superconducting wires and tapes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995PhRvB..51.9180L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995PhRvB..51.9180L"><span>Superconducting fluctuations in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3Ox thin films: Paraconductivity, excess Hall effect, and magnetoconductivity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lang, W.; Heine, G.; Kula, W.; Sobolewski, Roman</p> <p>1995-04-01</p> <p>A detailed study of normal-state magnetotransport properties in (Bi,Pb)2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3Ox thin films with a zero-resistance critical temperature Tc0=105 K prepared by dc-magnetron sputtering on MgO substrates is reported. Measurements of the electrical resistivity, the magnetoresistance, and the Hall effect are analyzed with regard to contributions of the superconducting order-parameter thermodynamic fluctuations, using theories for two-dimensional, layered superconductors. We have obtained a consistent set of parameters, i.e., the in-plane coherence length ξab(0)=1.6 nm, the out-of-plane coherence length ξc(0)=0.14 nm, and the electron-hole asymmetry parameter β=-0.38. At temperatures below 118 K, we observe a remarkable enhancement (above theoretical predictions) of both the excess Hall effect and magnetoconductivity, whereas no such effect is detected for the zero-field paraconductivity. The above anomalies are attributed to a nonuniform critical temperature distribution inside our samples and can be well explained assuming a Gaussian distribution of Tc's with a standard deviation δTc=2.3 K. The excess Hall effect caused by superconducting fluctuations is negative in the entire accessible temperature range, which indicates, together with the paraconductivity and magnetoconductivity results that the indirect (Maki-Thompson) fluctuation process for (Bi,Pb)2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3Ox is vanishingly small at temperatures from Tc to 130 K.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19900028638&hterms=strontium+atomic+beam&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstrontium%2Batomic%2Bbeam','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19900028638&hterms=strontium+atomic+beam&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dstrontium%2Batomic%2Bbeam"><span>Electron beam flash evaporation for YBaCuO and Bi<span class="hlt">CaSr</span>CuO thin films</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Davis, Matthew F.; Wosik, Jaroslaw L.; Wolfe, J. C.</p> <p>1989-01-01</p> <p>An electron beam flash evaporation technique is described which reproduces the stoichiometry of superconducting YBa(2)Cu(3)O(x) (123), Bi(2)<span class="hlt">CaSr</span>(2)Cu(2)O(y) (2122), and Bi(2)<span class="hlt">Ca</span>(2)<span class="hlt">Sr</span>(2)Cu(3)O(z) (2223) source powders. Films of each material deposited with this technique exhibit zero resistance temperatures of 78 K or above when furnace annealed; 75 K zero temperatures are obtained for 123 films in situ annealed with atomic oxygen at 775 C. Transport critical current densities are 10,000 A/sq cm in 25-micron stripes patterned from 123 films, and 60,000 A/sq cm in 1-mm stripes of 2122 and 2223 films using a 1-microV/mm measurement criteria. Typical normal state resistivities are 700 micro-ohm cm for 2122 and 2223 films and 5 micro-ohm cm for 123 films. The 2122 films are highly textured with the c axis normal to the substrate. All results are for films deposited on MgO.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014LaPhy..24c5802L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014LaPhy..24c5802L"><span>Laser performance of diode-pumped Nd, Y-codoped <span class="hlt">Ca</span>F 2-<span class="hlt">Sr</span>F 2 mixed crystal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, J.; Fan, M. W.; Su, L. B.; Jiang, D. P.; Ma, F. K.; Zhang, Q.; Xu, J.</p> <p>2014-03-01</p> <p>A disordered Nd, Y-codoped <span class="hlt">Ca</span>F2-<span class="hlt">Sr</span>F2 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:<span class="hlt">Ca</span>F2-<span class="hlt">Sr</span>F2 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23883664','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23883664"><span>The k-space origins of scattering in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Alldredge, Jacob W; Calleja, Eduardo M; Dai, Jixia; Eisaki, H; Uchida, S; McElroy, Kyle</p> <p>2013-08-21</p> <p>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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP51C1143S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP51C1143S"><span>A Robust and Fully-Automated Chromatographic Method for the Quantitative Purification of <span class="hlt">Ca</span> and <span class="hlt">Sr</span> for Isotopic Analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, H. B.; Kim, H.; Romaniello, S. J.; Field, P.; Anbar, A. D.</p> <p>2014-12-01</p> <p>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 <span class="hlt">Ca</span> and <span class="hlt">Sr</span> 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, <span class="hlt">Ca</span>, Fe, Cu, Zn, <span class="hlt">Sr</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.166..189E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.166..189E"><span>Assessing the impact of diagenesis on δ11B, δ13C, δ18O, <span class="hlt">Sr/Ca</span> and B/<span class="hlt">Ca</span> values in fossil planktic foraminiferal calcite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Edgar, Kirsty M.; Anagnostou, Eleni; Pearson, Paul N.; Foster, Gavin L.</p> <p>2015-10-01</p> <p>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, <span class="hlt">Sr/Ca</span> and B/<span class="hlt">Ca</span> 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. <span class="hlt">Sr/Ca</span> and B/<span class="hlt">Ca</span> 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 <span class="hlt">Ca</span>CO3. Our finding may remove one potential source of uncertainty in δ11B based p</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910009655','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910009655"><span>Effects of antimony <span class="hlt">substitution</span> on bismuth based superconductors</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Barrientos, Alfonso</p> <p>1990-01-01</p> <p>The effect of Sb <span class="hlt">substitution</span> and simultaneous <span class="hlt">substitution</span> of Pb and Sb on the superconducting transition temperatures in the Bi<span class="hlt">SrCa</span>CuO 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 Bi<span class="hlt">SrCa</span>CuO system. After this preliminary attempt, four different families of samples were investigated. In the first family of samples, Bi was <span class="hlt">substituted</span> by Sb to form Bi(1.9)Sb(0.1)<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(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)<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(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)<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(y) and Bi(1.6)Sb(0.1)<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O(y). The results of these investigations are presented with a discussion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFMPP42A..01G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFMPP42A..01G"><span>The North Atlantic Oscillation Reconstructed at Bermuda for 220 Years Using <span class="hlt">Sr/Ca</span> Ratios in Diploria labyrinthiformis (brain coral)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goodkin, N. F.; Hughen, K. A.; Cohen, A. L.; Curry, W. B.; Doney, S. C.</p> <p>2006-12-01</p> <p>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 (<span class="hlt">Sr/Ca</span>) 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 <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/171697','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/171697"><span>Proton and hole conductivity of <span class="hlt">Sr</span>Y{sub 2-2x}<span class="hlt">Ca</span>{sub 2x}O{sub 4-{alpha}} in humid air</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Balakireva, V.B.; Gorelov, V.P.</p> <p>1995-05-01</p> <p>Previously, the authors studied the electrical conductivity of compounds <span class="hlt">Sr</span>R{sub 2}O{sub 4}(R=Y,Ho-Lu) doped with calcium: <span class="hlt">Sr</span>R{sub 1.98}<span class="hlt">Ca</span>{sub 0.02}O{sub 4-{alpha}}. In the presence of water vapor, high-temperature ionic transport in these materials was found to be associated with proton mobility. Among the compounds studied, the <span class="hlt">Sr</span>Y{sub 2}O{sub 4} ceramic showed the highest ionic conductivity. For this reason, the compounds <span class="hlt">Sr</span>Y{sub 2-2x}<span class="hlt">Ca</span>{sub 2x}O{sub 4-{alpha}} (x=0.01-09.1) were selected for further investigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25491955','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25491955"><span>Thermal exposure effects on the in vitro degradation and mechanical properties of Mg-<span class="hlt">Sr</span> and Mg-<span class="hlt">Ca-Sr</span> biodegradable implant alloys and the role of the microstructure.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bornapour, M; Celikin, M; Pekguleryuz, M</p> <p>2015-01-01</p> <p>Magnesium is an attractive biodegradable material for medical applications due to its non-toxicity, low density and good mechanical properties. The fast degradation rate of magnesium can be tailored using alloy design. The combined addition of <span class="hlt">Sr</span> and <span class="hlt">Ca</span> results in a good combination of mechanical and corrosion properties; the alloy compositions with the best performance are Mg-0.5<span class="hlt">Sr</span> and Mg-0.3<span class="hlt">Sr</span>-0.3<span class="hlt">Ca</span>. In this study, we investigated an important effect, namely thermal treatment (at 400 °C), on alloy properties. The bio-corrosion of the alloys was analyzed via in vitro corrosion tests in simulated body fluid (SBF); the mechanical properties were studied through tensile, compression and three-point bending tests in two alloy conditions, as-cast and heat-treated. We showed that 8h of heat treatment increases the corrosion rate of Mg-0.5<span class="hlt">Sr</span> very rapidly and decreases its mechanical strength. The same treatment does not significantly change the properties of Mg-0.3<span class="hlt">Sr</span>-0.3<span class="hlt">Ca</span>. An in-depth microstructural investigation via transmission electron microscopy, scanning electron microscopy, electron probe micro-analysis and X-ray diffraction elucidated the effects of the thermal exposure. Microstructural characterization revealed that Mg-0.3<span class="hlt">Sr</span>-0.3<span class="hlt">Ca</span> has a new intermetallic phase that is stable after 8h of thermal treatment. Longer thermal exposure (24h) leads to the dissolution of this phase and to its gradual transformation to the equilibrium phase Mg17<span class="hlt">Sr</span>2, as well as to a loss of mechanical and corrosion properties. The ternary alloy shows better thermal stability than the binary alloy, but the manufacturing processes should aim to not exceed exposure to high temperatures (400 °C) for prolonged periods (over 24 h).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.3236S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.3236S"><span><span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Mo and U isotopes evidence ocean acidification and deoxygenation during the Late Permian mass extinction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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</p> <p>2014-05-01</p> <p>The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, <span class="hlt">ca</span>. 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 - <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, 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 δ44/40<span class="hlt">Ca</span> 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 δ88/86<span class="hlt">Sr</span> 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 δ44/40<span class="hlt">Ca</span> and δ88/86<span class="hlt">Sr</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22499372','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22499372"><span>Enhancement of redox- and phase-stability of thermoelectric <span class="hlt">Ca</span>MnO{sub 3−δ} by <span class="hlt">substitution</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Thiel, Philipp; Populoh, Sascha; Yoon, Songhak; Weidenkaff, Anke</p> <p>2015-09-15</p> <p>Redox Reactivity and structural phase transitions have a major impact on transport and me-chemical properties of thermoelectric <span class="hlt">Ca</span>MnO{sub 3−δ}. In this study series of <span class="hlt">Ca</span>{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+}) <span class="hlt">substitution</span>, 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 <span class="hlt">substitution</span> 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 <span class="hlt">substitution</span> level and substituents inducing a high orthorhombic distortion. - Graphical abstract: Thermoelectric n-type <span class="hlt">Ca</span>Mn{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 <span class="hlt">Ca</span>{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 <span class="hlt">substitution</span>. • <span class="hlt">Substitution</span> increases orthorhombicity of <span class="hlt">Ca</span>{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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22309042','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22309042"><span>Synthesis, structure and chemical bonding of <span class="hlt">Ca</span>Fe{sub 2−x}Rh{sub x}Si{sub 2} (x=0, 1.32, and 2) and <span class="hlt">Sr</span>Co{sub 2}Si{sub 2}</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hlukhyy, Viktor Hoffmann, Andrea V.; Fässler, Thomas F.</p> <p>2013-07-15</p> <p>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 <span class="hlt">Ca</span>Fe{sub 2}Si{sub 2}, <span class="hlt">Ca</span>Fe{sub 0.68(6)}Rh{sub 1.32(6)}Si{sub 2}, <span class="hlt">Ca</span>Rh{sub 2}Si{sub 2} and <span class="hlt">Sr</span>Co{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 <span class="hlt">Ca</span>Fe{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 <span class="hlt">Ca</span>Fe{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 <span class="hlt">Ca</span>Rh{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 <span class="hlt">Sr</span>Co{sub 2}Si{sub 2}. The structure of <span class="hlt">Sr</span>Co{sub 2}Si{sub 2} contains isolated [Co{sub 2}Si{sub 2}]{sup 2−} 2D-layers in the ab-plane whereas in <span class="hlt">Ca</span>Fe{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 <span class="hlt">Sr</span>Co{sub 2}Si{sub 2} and <span class="hlt">Ca</span>Rh{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 <span class="hlt">Ca</span>Fe{sub 2}Si{sub 2} is a full <span class="hlt">substituted</span> variant (As/Si) of <span class="hlt">Ca</span>Fe{sub 2}As{sub 2</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22489621','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22489621"><span>Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-<span class="hlt">substituted</span> (La,<span class="hlt">Sr</span>)MnO{sub 3}</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tsekouras, George Boudoire, Florent; Braun, Artur; Pal, Banabir; Sarma, D. D.; Vondráček, Martin; Prince, Kevin C.</p> <p>2015-09-21</p> <p>The electronic structure of the (La{sub 0.8}<span class="hlt">Sr</span>{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 <span class="hlt">substitution</span> of (La,<span class="hlt">Sr</span>)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 <span class="hlt">substitution</span>. 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 <span class="hlt">substitution</span> 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 <span class="hlt">substitution</span> on the B-site of (La,<span class="hlt">Sr</span>)MnO{sub 3} is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1909275','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1909275"><span>Alterations in the force-frequency relationship by tert-butylbenzohydroquinone, a putative <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ pump inhibitor, in rabbit and rat ventricular muscle.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Baudet, S.; Do, E.; Noireaud, J.; Le Marec, H.</p> <p>1996-01-01</p> <p>1. The effects of 2,5 di-(tert-butyl)-1,4-benzohydroquinone (TBQ), a putative inhibitor of the sarcoplasmic reticulum (<span class="hlt">SR</span>) <span class="hlt">Ca</span>2+ pump, on twitch tension, time course and <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ content have been studied at different stimulation frequencies (0.5-3 Hz) in isolated preparations from the rabbit and rat right ventricle, at 37 degrees C. 2. At 0.5Hz, 30 microM TBQ induced a marked negative inotropic effect in both species (-57% in the rabbit and -68% in the rat) and decreased the rate of rise and fall of twitch tension. In parallel, <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ content (assessed by rapid cooling contractures) was depressed in the rabbit by 42%. The force-frequency relationship (positive for the rabbit and negative for the rat) was significantly attenuated. In the rabbit, this alteration was shown to rely on insufficient <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ reloading with increasing frequencies. 3. Exposure of TBQ-treated preparations to 8 mM extracellular <span class="hlt">Ca</span>2+ or 5 microM isoprenaline were effective in reloading the <span class="hlt">SR</span> with <span class="hlt">Ca</span>2+ whereas 20 mM caffeine emptied this compartment. 4. In the rabbit ventricle, increase in stimulation frequency shortened control twitch time course by decreasing both the time to peak tension (TTP) and the time to half relaxation (t1/2). TBQ did not differentially affect the pattern for t1/2 but significantly attenuated the frequency-induced decrease of TTP. 5. In rabbit ventricular muscle, the action potential duration increased between 0.5 and 3 Hz whether or not TBQ was present. However, TBQ induced a small but significant additional action potential shortening. 6. TBQ decreased twitch tension in the rat ventricle between 0.5 and 3 Hz but the negative staircase was not differentially affected by the <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ pump inhibitor. In control conditions and in the presence of 30 microM TBQ, t1/2 was frequency-independent but TBQ consistently increased this parameter (by approximately 29%). 7. These data argue in favour of a specific and partial inhibition of the <span class="hlt">SR</span> <span class="hlt">Ca</span>2+ pump by 30 microM TBQ in the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhRvL.107a7203H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhRvL.107a7203H"><span>Spin Gap in the Zigzag Spin-1/2 Chain Cuprate <span class="hlt">Sr</span>0.9<span class="hlt">Ca</span>0.1CuO2</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hammerath, F.; Nishimoto, S.; Grafe, H.-J.; Wolter, A. U. B.; Kataev, V.; Ribeiro, P.; Hess, C.; Drechsler, S.-L.; Büchner, B.</p> <p>2011-07-01</p> <p>We report a comparative study of Cu63 nuclear magnetic resonance spin lattice relaxation rates T1-1 on undoped <span class="hlt">Sr</span>CuO2 and <span class="hlt">Ca</span>-doped <span class="hlt">Sr</span>0.9<span class="hlt">Ca</span>0.1CuO2 spin chain compounds. A temperature independent T1-1 is observed for <span class="hlt">Sr</span>CuO2 as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T1-1 for T<90K in the <span class="hlt">Ca</span>-doped sample evidencing the opening of a spin gap. The data analysis within the J1-J2 Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J2-exchange coupling as a possible cause of the spin gap.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19475338','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19475338"><span>The effect of composition on ion release from <span class="hlt">Ca-Sr</span>-Na-Zn-Si glass bone grafts.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Murphy, S; Boyd, D; Moane, S; Bennett, M</p> <p>2009-11-01</p> <p>Controlled delivery of active ions from biomaterials has become critical in bone regeneration. Some silica-based materials, in particular bioactive glasses, have received much attention due to the ability of their dissolution products to promote cell proliferation, cell differentiation and activate gene expression. However, many of these materials offer little therapeutic potential for diseased tissue. Incorporating trace elements, such as zinc and strontium, known to have beneficial and therapeutic effects on bone may provide a more viable bone graft option for those suffering from metabolic bone diseases such as osteoporosis. Rational compositional design may also allow for controlled release of these active ions at desirable dose levels in order to enhance therapeutic efficacy. In this study, six differing compositions of calcium-strontium-sodium-zinc-silicate (<span class="hlt">Ca-Sr</span>-Na-Zn-Si) glass bone grafts were immersed in pH 7.4 and pH 3 solutions to study the effect of glass composition on zinc and strontium release in a normal and extreme physiological environment. The zinc release levels over 30 days for all zinc-containing glasses in the pH 7.4 solution were 3.0-7.65 ppm. In the more acidic pH 3 environment, the zinc levels were higher (89-750 ppm) than those reported to be beneficial and may produce cytotoxic or negative effects on bone tissue. Strontium levels released from all examined glasses in both pH environments similarly fell within apparent beneficial ranges--7.5-3500 ppm. Glass compositions with identical <span class="hlt">Sr</span>O content but lower ZnO:Na(2)O ratios, showed higher levels of <span class="hlt">Sr</span>(2+) release. Whereas, zinc release from zinc-containing glasses appeared related to ZnO compositional content. Sustainable strontium and zinc release was seen in the pH 7.4 environment up to day 7. These results indicate that the examined <span class="hlt">Ca-Sr</span>-Na-Zn-Si glass compositions show good potential as therapeutic bone grafts, and that the graft composition can be tailored to allow therapeutic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992PhyC..200...31W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992PhyC..200...31W"><span>Characteristics of Bi-Pb-<span class="hlt">Sr-Ca</span>-Cu-O powders produced by aerosol decomposition and their rapid conversion to the high-T c phase</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ward, Timothy L.; Lyons, Shirley W.; Kodas, Toivo T.; Brynestad, Jorulf; Kroeger, Donald M.; Hsu, Huey</p> <p>1992-09-01</p> <p>Bi-Pb-<span class="hlt">Sr-Ca</span>-Cu-O powders were produced by aerosol decomposition of nitrate solutions. The effects of reactor temperature and residence time on particle morphology and evaporative Pb loss from particles were demonstrated, and conditions necessary to control Pb loss established. Pb loss was roughly proportional to residence time, and minimal loss occurred with short residence times (3s) and T≤800°C. Particles produced at 700°C typically contained significant porosity, while those produced at T≥800°C were solid. Mixtures of the Bi 2<span class="hlt">Sr</span> 2CuO y (2201) and Bi 2<span class="hlt">Sr</span> 2<span class="hlt">Ca</span>Cu 2O y (2212) phases were produced at 700-900°C in nitrogen and air. However, after hearing in air for 16 h at 850°C, pellets of powder produced at 700°C with nominal composition Pb 0.44Bi 1.8<span class="hlt">Sr</span> 2<span class="hlt">Ca</span> 2.2Cu 3O y converted to approximately 79 vol.% of the Bi 2<span class="hlt">Sr</span> 2<span class="hlt">Ca</span> 2Cu 3O y (2223) phase and displayed a Tc (onset) of 110 K. Rapid conversion to 2223 was promoted by powder synthesis conditions, leading to controlled Pb loss and a homogeneous fine-grained dispersion of mixed-oxide precursor phases within particles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARL19006L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARL19006L"><span>DFT+ U study of electronic structure and Curie temperature of A2 B ReO6 (A=<span class="hlt">Sr</span>, <span class="hlt">Ca</span> and B=Cr, Fe)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Alex; Marianetti, Chris</p> <p></p> <p>Re-based double perovskites (DPs) have attracted much attention due to their high Curie temperature (TC) and colossal magneto resistance with large potential for spintronic applications. Here we investigate the electronic and magnetic properties of the Re-based DPs A2 B ReO6 (A=<span class="hlt">Sr</span>, <span class="hlt">Ca</span> and B=Cr, Fe) using density functional theory + U (DFT+ U) calculations. While monoclinic <span class="hlt">Ca</span>2CrReO6 and <span class="hlt">Ca</span>2FeReO6 (monoclinic) are insulating within GGA+ U, tetragonal <span class="hlt">Sr</span>2CrReO6 (a0a0c0) and <span class="hlt">Sr</span>2FeReO6 (a0a0c-) remain metallic. We show that both on-site interaction U and octahedral tilting are critical to obtain the insulating phases. The a0a0c- -phase of <span class="hlt">Sr</span>2CrReO6 is most stable and insulating with nonzero U, suggesting that the high quality <span class="hlt">Sr</span>2CrReO6 film on STO substrate can be a semiconductor as reported in recent experiments. We explain that the insulator-to-metal transition (MIT) of <span class="hlt">Ca</span>2FeReO6 at 140K is predominantly due to a structural phase transition which drives the insulating state. Curie temperatures of Re-based DPs are calculated using the classical Monte Carlo simulations based on the Heisenberg model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1095139','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1095139"><span>Overcoming phase instability of RBaCo2O5+ (R = Y and Ho) by <span class="hlt">Sr</span> <span class="hlt">substitution</span> for application as cathodes in solid oxide fuel cells</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kim, Jung-Hyun; Young Nam, Kim; Bi, Zhonghe; Manthiram, Arumugam; Paranthaman, Mariappan Parans; Huq, Ashfia</p> <p>2013-01-01</p> <p>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 <span class="hlt">Sr</span> <span class="hlt">substitution</span> ( 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 <span class="hlt">Sr</span> <span class="hlt">substitution</span> (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(Ba0.3<span class="hlt">Sr</span>0.7)Co2O5+ + GDC composite cathode delivered the optimum electrochemical performances with a stable phase demonstrating the potential as a cathode in SOFC.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989JaJAP..28L1175T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989JaJAP..28L1175T"><span>Direct Preparation of Fine Powders of the 80 K Superconducting Phase in the Bi-<span class="hlt">Ca-Sr</span>-Cu-O System by Spray Pyrolysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tohge, Noboru; Tatsumisago, Masahiro; Minami, Tsutomu; Okuyama, Kikuo; Arai, Kouji; Kousaka, Yasuo</p> <p>1989-07-01</p> <p>Submicron powders of the 80 K superconducting phase in the Bi-<span class="hlt">Ca-Sr</span>-Cu-O system have been directly prepared by the spray pyrolysis of aqueous solutions of corresponding metal nitrates, Bi:<span class="hlt">Ca:Sr</span>:Cu=1:1:1:2. The powders obtained were spheres with uniformly distributed diameters below 1 μm. The crystalline phase of these powders was found to greatly depend on the oxygen partial pressure in the carrier gas as well as the decomposition temperature. The preparation conditions for the 80 K superconducting phase were examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001JaJAP..40..669O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001JaJAP..40..669O"><span>Temperature Dependence of the Surface Resistance of a Bi-<span class="hlt">Sr-Ca</span>-Cu-O Whisker Measured by the Probe-Coupled Microstrip Resonator Method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Okai, Daisuke; Ohshima, Shigetoshi; Kishida, Satoru; Hatano, Takeshi</p> <p>2001-07-01</p> <p>The temperature dependence of the surface resistance of Bi-<span class="hlt">Sr-Ca</span>-Cu-O whiskers measured by the probe-coupled microstrip resonator method was examined. Two kinds of whiskers were measured: plate-like and wire-like. The surface resistances of the plate-like and wire-like whiskers were 0.65 mΩ and 1.6 mΩ at 53 K and 6.9 GHz, respectively. These values were approximately 4 ˜ 10 times larger than that of a high-quality Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2Ox (Bi-2212) single crystal.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013LaPhL..10j5806L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013LaPhL..10j5806L"><span>Characteristics of a diode-pumped Yb:<span class="hlt">Ca</span>F2-<span class="hlt">Sr</span>F2 mode-locked laser using a carbon nanotube absorber</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, J.; Feng, C.; Su, L. B.; Jiang, D. P.; Zheng, L. H.; Qian, X. B.; Wang, J. Y.; Xu, J.; Wang, Y. G.</p> <p>2013-10-01</p> <p>Yb:<span class="hlt">Ca</span>F2-<span class="hlt">Sr</span>F2 disordered crystals are successfully grown by the TGT method. By using a double-walled carbon nanotube saturable absorber (DWCNT-SA), the continuous-wave mode-locked (CWML) laser properties of Yb:<span class="hlt">Ca</span>F2-<span class="hlt">Sr</span>F2 crystals are demonstrated under diode pumping for the first time. The mode-locked laser delivers pulses as short as 5 ps at a center wavelength of 1045.5 nm without any dispersion compensation. The oscillator operating at a repetition rate of ˜87 MHz delivers 292 mW average output power.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6653187','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6653187"><span>A high-resolution <span class="hlt">Sr/Ca</span> and [delta][sup 18]O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Nino</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>McCulloch, M.T.; Gagan, M.K.; Mortimer, G.E.; Chivas, A.R. ); Isdale, P.J. )</p> <p>1994-06-01</p> <p>A high-resolution (near weekly) <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> temperature calibration of De Villiers et al., the <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/CA</span> 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 <span class="hlt">Sr/Ca</span> 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]) <span class="hlt">Sr</span> and <span class="hlt">Ca</span> contents of river runoff relative to seawater, it is possible to use the <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> and [delta][sup 18]O systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFMPP44A..08G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFMPP44A..08G"><span>Growth-Dependent Calibration of Coral <span class="hlt">Sr/Ca</span>-SST From Multiple Colonies Provides Potential for Long SST Records from Fossil Corals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Goodkin, N. F.</p> <p>2005-12-01</p> <p>Extended reconstructions of sea surface temperature (SST) are critical to examining long-term climate variability not captured in instrumental records. Coral skeleton, which continuously accretes in annual density bands, preserves unique, multi-century archives of sub-annual resolution SST. Despite the promise of coral proxies, however, SSTs derived from corals are often several degrees cooler than those derived from other archives. Here we present strontium to calcium ratios (<span class="hlt">Sr/Ca</span>) for four brain corals (Diploria labyrinthiformis) collected from the south shore of Bermuda that are strongly correlated with both instrumental SST (Hydrostation S, 30km southeast) and annual skeletal extension rate. High <span class="hlt">Sr/Ca</span> ratios correspond with cold SSTs and slow skeletal growth rate, and vice versa. Over a ~25 year calibration period, the four corals have distinct average growth rates (2.57, 2.68, 3.55 and 4.03 mm/yr). For each colony, we provide a quantitative calibration of annual <span class="hlt">Sr/Ca</span> to annual extension rate and annual SST along the axis of maximum growth and derive an individual growth dependent <span class="hlt">Sr/Ca</span>-SST calibration equation: <span class="hlt">Sr/Ca</span> = m*(SST) + n*(annual growth rate)*(SST) + b The slopes and intercepts of the four equations are found to be linearly related to the average growth-rate during the calibration periods of each colony, and a final multi-variant regression is performed to establish one final <span class="hlt">Sr/Ca</span>-Growth Rate-SST calibration, in the form: <span class="hlt">Sr/Ca</span> = m*(SST) + n*(annual growth rate)*(SST) + o*(average colony growth rate)*(SST) + b This growth-dependent calibration is shown to be applicable to a fossil coral of the same species in order to reconstruct SSTs at Bermuda for 223 years. A reconstruction excluding the influence of growth yields SSTs that exaggerate both cool and warm periods. SST anomalies near the end of the Little Ice Age (~1850) that are derived using a non-growth dependent calibration are exaggerated by a factor of two relative to those from a growth</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1263913-electronic-structure-ingredient-planes-cuprate-superconductor-bi2sr2cuo6-comparison-study-bi2sr2cacu2o8','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1263913-electronic-structure-ingredient-planes-cuprate-superconductor-bi2sr2cuo6-comparison-study-bi2sr2cacu2o8"><span>Electronic structure of the ingredient planes of the cuprate superconductor Bi2<span class="hlt">Sr</span>2CuO6+δ: A comparison study with Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Yan -Feng Lv; Gu, G. D.; Wang, Wen -Lin; ...</p> <p>2016-04-15</p> <p>By means of low-temperature scanning tunneling microscopy, we report on the electronic structures of the BiO and <span class="hlt">Sr</span>O planes of the Bi2<span class="hlt">Sr</span>2CuO6+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 <span class="hlt">Sr</span>O is always characteristic of a PG-like feature. This contrasts with the Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ (Bi-2212) superconductor where vHS occurs solely on the <span class="hlt">Sr</span>O 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 <span class="hlt">Sr</span>O planes, respectively, in Bi-2201 and Bi-2212. This is supported by the contrasting structural buckling amplitude of the BiO and <span class="hlt">Sr</span>O 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009PhyB..404.2495I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009PhyB..404.2495I"><span>Giant magneto-caloric effect around room temperature at moderate low field variation in La 0.7(<span class="hlt">Ca</span> 1-x<span class="hlt">Sr</span> x) 0.3MnO 3 perovskites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Islam, M. S.; Hanh, D. T.; Khan, F. A.; Hakim, M. A.; Minh, D. L.; Hoang, N. N.; Hai, N. H.; Chau, N.</p> <p>2009-08-01</p> <p>Among the perovskite manganites, a series of La 1-x<span class="hlt">Ca</span> xMnO 3 has the largest magneto-caloric effect (MCE) (|Δ Sm| max=3.2-6.7 J/kg K at Δ H=13.5 kOe), but the Curie temperatures, TC, are quite low (165-270 K). The system of La<span class="hlt">Sr</span>MnO 3 has quite high TC but its MCE is not so large. The manganites La 0.7(<span class="hlt">Ca</span> 1-x<span class="hlt">Sr</span> x) 0.3MnO 3 ( x=0, 0.05, 0.10, 0.15, 0.20, 0.25) have been prepared by solid state reaction technique with an expectation of large MCE at room temperature region. The samples are of single phase with orthorhombic structure. The lattice parameters as well as the volume of unit cell are continuously increased with the increase of x due to large <span class="hlt">Sr</span> 2+ ions <span class="hlt">substituted</span> for smaller <span class="hlt">Ca</span> 2+ ions. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic measurements at low field and low temperatures indicate that there is a spin-glass like (or cluster glass) state occurred. The Curie temperature TC increases continuously from 258 K (for x=0) to 293 K (for x=0.25). A large MCE of 5 J/kg K has been observed around 293 K at the magnetic field change Δ H=13.5 kOe for the sample x=0.25. The studied samples can be considered as giant magneto-caloric materials, which is an excellent candidate for magnetic refrigeration at room temperature region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AIPC.1728b0355A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AIPC.1728b0355A"><span>Effect of sintering temperature on structural and dielectric properties of Bi and Li co-<span class="hlt">substituted</span> <span class="hlt">Sr</span>TiO3</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alkathy, Mahmoud S.; Goud, J. Pundareekam; Raju, K. C. James</p> <p>2016-05-01</p> <p>Sintering is an important factor that affects the microstructure development in ceramics. In this work, Bi and Li co-<span class="hlt">substituted</span> Strontium Titanate (ST) ceramics samples sintered at different temperatures are prepared and analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD was used to detect phase structure of the sintered samples and SEM was used for microstructure analysis. Dielectric properties of Bi and Li co-<span class="hlt">substituted</span> <span class="hlt">Sr</span>TiO3 samples were measured using Agilent 4294A Impedance analyzer in the frequency range 40 Hz to 5 MHz at room temperature. The result reveals that the dielectric constant of Bi and Li co-<span class="hlt">substituted</span> <span class="hlt">Sr</span>TiO3 ceramics increases with increasing sintering temperature up to 1250°C and then decreases beyond that. The highest value of dielectric constant obtained is 860 at 1KHz frequency and lowest dielectric loss observed is 0.04 at the same frequency for samples sintered at 1250°C. Also the grain size increases with increase of sintering temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ChPhB..23l8701F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ChPhB..23l8701F"><span>Effects of A1 site occupation on dielectric and ferroelectric properties of <span class="hlt">Sr</span>4<span class="hlt">Ca</span>RTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fang, Yu-Jiao; Gong, Gao-Shang; Gebru, Zerihun; Yuan, Song-Liu</p> <p>2014-12-01</p> <p><span class="hlt">Sr</span>4<span class="hlt">Ca</span>RTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of <span class="hlt">Sr</span>4<span class="hlt">Ca</span>RTi3Nb7O30 (R = Ce, Eu) tetragonal tungsten bronzes are investigated. The <span class="hlt">Sr</span>4<span class="hlt">Ca</span>CeTi3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. <span class="hlt">Sr</span>4<span class="hlt">Ca</span>EuTi3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between <span class="hlt">Ca</span>2+ and Eu3+ could lead to the uneven distribution of <span class="hlt">Ca</span>2+ and Eu3+ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization—electric field (P—E) curves are evaluated at room temperature and both of them show hysteresis loops. <span class="hlt">Sr</span>4<span class="hlt">Ca</span>CeTi3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density—electric field (J—E) curves are measured at room temperature with a largest leakage current density of ~ 10-6 A/cm2, indicating that their leakage currents are rather low.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016CP....474....7C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016CP....474....7C"><span>Theoretical survey on M@C80 (M = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba): Behavior of different alkaline earth metal impacting the chemical stability and electronic properties</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cui, Jin-Bo; Guo, Yi-Jun; Li, Qiao-Zhi; Zhao, Pei; Zhao, Xiang</p> <p>2016-08-01</p> <p>Structures of mono-metallofullerenes M@C80 (M = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba) that separated in early experiment are determined owning the C2v(31920)-C80 cage. The change rule of properties for M@C80 (M = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, 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 <span class="hlt">Ca</span>@C2v(31920)-C80 and <span class="hlt">Ca</span>@D5h(31923)-C80 are mostly located on the trapped metal, whereas reduction reactions of <span class="hlt">Ca</span>@C2v(31920)-C80 and <span class="hlt">Ca</span>@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 = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba) are in perfect accord with the spectra obtained experimentally.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22581618','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22581618"><span>Synthesis and characterization of <span class="hlt">Ca</span>{sup 2+} <span class="hlt">substituted</span> barium niobate nanopaticles for photocatalytic and luminescence applications</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dudhe, C.M.; Nagdeote, S.B.; Palikundwar, U.A.</p> <p>2016-09-15</p> <p>Highlights: • Nanoparticles of <span class="hlt">Ca</span>{sup 2+} (30 mol%) <span class="hlt">substituted</span> BaNb{sub 2}O{sub 6} were synthesized. • <span class="hlt">Ca</span>{sup 2+} ions occupy newer 8d Wyckoff positions rather than 4c. • Self-activated photoluminescence was observed. • Excellent H{sub 2} generation tendency from pure water under UV light was also observed. - Abstract: <span class="hlt">Ca</span>{sup 2+} <span class="hlt">substituted</span> barium niobate i.e. <span class="hlt">Ca</span>{sub x}Ba{sub 1-x}Nb{sub 2}O{sub 6} (x = 0.3) compound in nanoparticles form was synthesized by a simple co-precipitation method for the first time and its structural characterization has been done by using powder X-ray diffraction data. Other characterizations were done by using transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. It was found that the <span class="hlt">Ca</span>{sub x}Ba{sub 1-x}Nb{sub 2}O{sub 6} (x = 0.3) compound stabilizes in the orthorhombic phase (Pbcn space group) with the lattice parameters a = 14.984 Å, b = 5.761 Å and c = 5.216 Å. A representative TEM image shows the irregular sphere like morphology of the synthesized particles with the size ranging from 70 to 120 nm. The optical band gap energy was found to be 3.74 eV. It was observed that the synthesized nanoparticles exhibit excellent H{sub 2} evolution tendency and self–activated photoluminescence under the excitation of UV light. These activities were assigned to the nanocrystalline nature of the synthesized material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA461292','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA461292"><span>Partial Melt Processing of Solid-Solution Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+delta Thick-Film Conductors with Nanophase Al2O3 Additions</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2006-04-01</p> <p>range of partial-melt temperatures. Results were compared to Al2O3-free films with compositions lying within the single-phase solid - solution 2212 region...Nanophase Al2O3 reacted with 2212-type precursors to form a composite of micron size or smaller particles of solid - solution (<span class="hlt">Sr,Ca</span>)3Al2O6 in a solid ... solution 2212 superconducting matrix. The <span class="hlt">Ca</span> content of the (<span class="hlt">Sr,Ca</span>)3Al2O6 in a solid - solution 2212 superconducting matrix. The <span class="hlt">Ca</span> content of the (<span class="hlt">Sr,Ca</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26460605','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26460605"><span>Improved conductivity of NdFeO₃ through partial <span class="hlt">substitution</span> of Nd by <span class="hlt">Ca</span>: a theoretical study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, You; Wang, Yun; Ren, Wei; Liu, Porun; Zhao, Huijun; Chen, Jun; Deng, Jinxia; Xing, Xianran</p> <p>2015-11-21</p> <p>NdFeO3 is an important candidate material for gas sensors and intermediate-temperature solid oxide fuel cells (IT-SOFC). However, its low conductivity prohibits its applications. In this study, we report that the doping of <span class="hlt">Ca</span> by partially replacing Nd can effectively increase its conductivity. Through the electronic structure analysis of Nd(1-x)<span class="hlt">Ca</span>(x)FeO3 (x = 0.00, 0.25, 0.50, 0.75 or 1.00) based on the first-principles density functional theory calculations, it is found that the hole states introduced by <span class="hlt">Ca</span> <span class="hlt">substitution</span> appear just above the Fermi level, which implies a high mobility of electrons/holes along the Fe-O-Fe bonding network. Specifically, it becomes easier to form O vacancies after <span class="hlt">Ca</span> doping. Since the diffusion of O anions occurs through a vacancy hopping mechanism, the ion conductivity is also improved. These findings help us to gain an in-depth understanding of the colossally increased conductivity of <span class="hlt">Ca</span> doped NdFeO3 and turn the electronic conduction for its practical application in gas sensors and IT-SOFC.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006PhRvB..74q2509E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006PhRvB..74q2509E"><span>Unadulterated spectral function of low-energy quasiparticles in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>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.</p> <p>2006-11-01</p> <p>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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ApSS..292..570Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ApSS..292..570Z"><span>The photo-catalytic activities of MP (M = Ba, <span class="hlt">Ca</span>, Cu, <span class="hlt">Sr</span>, Ag; P = PO43-, HPO42-) microparticles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Fan; Shi, Yuanji; Zhao, Zongshan; Song, Weijie; Cheng, Yang</p> <p>2014-02-01</p> <p>For the good performance of apatite-based materials in the removal of dyes and their environment-friendly advantage, five kinds of apatite microparticles of MP (M = Ba, <span class="hlt">Ca</span>, Cu, <span class="hlt">Sr</span>, Ag; P = PO43-, HPO42-) were synthesized by a simple precipitation method and their photo-catalytic properties were invested. Better performance in the decolorization of methyl orange (MO) under the assistance of H2O2 than that of TiO2 were obtained for all the MPs. The photo-catalytic activity was mainly affected by surface area, energy band, impurity, crystallinity and crystal structure. The DFT calculation results demonstrated that the 2p of O and 3p of P in PO43- played the main role in the photo-catalytic process. This work would be helpful to design and synthesize low cost apatite materials with good photo-catalytic performance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005PhyC..424..133D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005PhyC..424..133D"><span>Possible structural phase transitions on Bi 2<span class="hlt">Sr</span> 2<span class="hlt">Ca</span>Cu 2O y measured by anelastic spectroscopy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Albuquerque Gimenez, Juliana Maria; Grandini, Carlos Roberto; dos Santos, Dayse Iara</p> <p>2005-08-01</p> <p>Anelastic spectroscopy measurements (internal friction) are sensitive tools for the study of defects in solids, in particular the mobility of interstitial oxygen. Samples of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2Oy were analyzed after being submitted to two thermal treatments in vacuum, one at 973 K and another at 673 K. Anelastic spectroscopy measurements were performed using a torsion pendulum operating at around 38 Hz and at a temperature range of 88 and 700 K with heating rate of 1 K/min and vacuum better than 10-5 Torr. Complex relaxation structures reversible with new thermal treatments were observed. These relaxation structures were attributed to O-M structural phase transitions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JEMat..45.3059U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JEMat..45.3059U"><span>Structural and Optoelectronic Properties of X3ZN (X = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.</p> <p>2016-06-01</p> <p>We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JAP...113m3902B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JAP...113m3902B"><span>Direct imaging of hot spots in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ mesa terahertz sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Benseman, T. M.; Koshelev, A. E.; Kwok, W.-K.; Welp, U.; Vlasko-Vlasov, V. K.; Kadowaki, K.; Minami, H.; Watanabe, C.</p> <p>2013-04-01</p> <p>Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ (Bi-2212) (BSCCO) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs, hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power. Here, we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612 nm fluorescence line of Eu3+ in a europium chelate. The images directly reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1048940','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1048940"><span>Numerical Investigation of the Quench Behavior of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2Ox Wire</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Arbelaez, D.; Prestemon, S. O.; Dietderich, D. R.; Godeke, A.; Ye, L.; Hunte, F.; Schwartz, J.</p> <p>2010-08-01</p> <p>The quench behavior of Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub x} (Bi2212) wire is investigated through numerical simulations. This work is part of the U.S. Very High Field Superconducting Magnet Collaboration (VHFSMC). Numerical simulations are carried out using a one-dimensional computational model of thermal transport in Bi2212 composite wires. A quench is simulated by introducing heat in a section of the wire, and the voltage and temperature are monitored as function of time and position. The quench energy, normal zone propagation velocity, and spatial distribution of temperature are calculated for varying transport current and applied magnetic field. The relevance of these simulations in defining criteria for experimental measurements is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997APS..MAR..I909K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997APS..MAR..I909K"><span>Plastic Flow of the Vortex Solid in Bi_2<span class="hlt">Sr</span>_2<span class="hlt">Ca</span>Cu_2O_8+δ Crystals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keener, C. D.; Ammirata, S. M.; Trawick, M. L.; Hebboul, S. E.; Garland, J. C.</p> <p>1997-03-01</p> <p>We have recently presented evidence in electrical transport data for a first order vortex lattice melting transition in Bi_2<span class="hlt">Sr</span>_2<span class="hlt">Ca</span>Cu_2O_8+δ single crystals. Below the melting temperature T_m, current-induced motion of the vortex solid causes dissipation for sufficiently high currents. We have measured resistance vs. temperature curves in magnetic fields 50 Oe < H < 500 Oe and high currents (I >= 1 mA). Below Tm (≈ 80 K at 100 Oe), we find large temporal resistance fluctuations which are characteristic of vortex plastic flow. This vortex motion seems to be well described as ``intermittently flowing rivers" of vortices.(F. Nori, Science 271, 1373 (1996).)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994AnP...506..215G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994AnP...506..215G"><span>Peltier-effect in the mixed state of (Bi, Pb)2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Galffy, M.; Hohn, Ch.; Freimuth, A.</p> <p></p> <p>We present measurements of the Peltier-effect in the mixed state of Bi1.76Pb0.24<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O. The Peltier-coefficient broadens in a magnetic field quite similar to the resistivity and the thermopower. Comparison with the thermopower shows that Onsagers relation holds well. The occurrence of the Peltier-heat in the mixed state well below Tc implies that the electric current is accompanied by a large heat current. We show that the vortex contribution to the Peltier-heat is negligibly small. Therefore the heat current has to be attributed to normal quasiparticle excitations. Our results indicate that this quasiparticle contribution to the heat current remains large even at temperatures far below Tc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ApPhL.104z1908W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ApPhL.104z1908W"><span>Correlation between upconversion photoluminescence and dielectric response in Ba-<span class="hlt">substituted</span> (<span class="hlt">Sr</span>1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wei, T.; Wang, X. D.; Zhao, C. Z.; Liu, M. F.; Liu, J. M.</p> <p>2014-06-01</p> <p>The filled tetragonal tungsten bronze (<span class="hlt">Sr</span>1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30 (SBLTNx: Ho-Yb) ceramics with different Ba <span class="hlt">substitution</span> levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The <span class="hlt">substitution</span> of <span class="hlt">Sr</span>2+ ions at the A2-sites by larger Ba2+ ions results in substantial variation of the UC-PL intensity as a function of <span class="hlt">substitution</span> level x. Furthermore, the dielectric response to the <span class="hlt">substitution</span> of <span class="hlt">Sr</span>2+ by Ba2+ suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/15014254','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/15014254"><span>San Francisco Estuary Striped Bass Migration History Determined by Electron-microprobe Analysis of Otolith <span class="hlt">Sr/Ca</span> Ratio</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ostrach, D J; Phillis, C C; Weber, P K; Ingram, B L; Zinkl, J G</p> <p>2004-09-17</p> <p>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 (<span class="hlt">Sr/Ca</span>) 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 <span class="hlt">Sr/Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1989PhyC..161..567P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1989PhyC..161..567P"><span>Electrical resistivity, magnetoresistance, magnetisation, hall coefficient and excess conductivity in Pb-doped Bi-<span class="hlt">Sr-Ca</span>-Cu oxides</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Poddar, A.; Mandal, P.; Das, A. N.; Ghosh, B.; Choudhury, P.</p> <p>1989-12-01</p> <p>The electrical resistance, Meissner signal, magnetoresistance and Hall coefficient of Bi 1.75Pb 0.25<span class="hlt">Sr</span> 2<span class="hlt">Ca</span> 2Cu 3O x and Bi 1.5Pb 0.5<span class="hlt">Sr</span> 2<span class="hlt">Ca</span> 2Cu 3O x (nominal compositions) have been measured. Resistance of the Bi 1.75Pb 0.25 sample becomes zero for T≤106 K while the Bi 1.5Pb 0.5 sample shows a 65% drop in the resistance around 106 K and TR = 0 c ≈ 73 K. Powder X-ray diffraction analysis reveals that the major phase in the Bi 1.75Pb 0.25 sample is the high-T c phase and in the Bi 1.5 Pb 0.5 sample the low-T c phase. The Hall coefficients (R H) of both samples are positive with R-1H> linear in temperature. The temperature dependence of R H is stronger in the Bi 1.75Pb 0.25 sample than in the Bi 1.5Pb 0.5 sample. The carrier concentration determined R-1H for the Bi 1.75Pb 0.25 and the Bi 1.5Pb 0.5 samples at 300 K are 1.59 × 10 21 cm -3 and 3.66 × 10 21 cm -3, respectively. The excess conductivity of both samples is analyzed using the Aslamazov-Larkin expression. The critical exponent λ obtained for the Bi 1.75Pb 0.25 sample is 0.78 and that for the Bi 1.5Pb 0.5 sample, in the temperature region where the high- Tc phase contributes only, is 0.77.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AIPC.1528..292L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AIPC.1528..292L"><span>Nanosized Cr2O3 as pinning center in (Bi,Pb)-<span class="hlt">Sr-Ca</span>-Cu-O superconductor tapes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, G. H.; Abd-Shukor, R.</p> <p>2013-05-01</p> <p>Nanosized Cr2O3 (6 nm) has been introduced into (Bi,Pb)-<span class="hlt">Sr-Ca</span>-Cu-O/Ag tapes fabricated by the powderin-tube method. The starting powder with composition (Bi,Pb)2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>2Cu3O10(Cr2O3)0.05 was prepared by the solid state reaction method. The superconductor tapes with thickness of about 0.3 mm and length about 2 cm were heated at 845°C for 96, 144, 192 and 240 h. The samples were characterized by the four point probe electrical measurements, X-ray powder diffraction method and scanning electron microscopy. The transport critical current density, Jc was measured from 30 to 65 K using the 1 μ/cm criterion. The highest Jc was obtained for the tape heated for 240 h with Jc = 1700 A/cm2 at 30 K. XRD patterns showed that the samples consisted of the 2212 and 2223 phase. SEM micrographs showed the plat-like structure. The role of nano-Cr2O3 in the superconductor system is discussed. The size of the nanoparticle (R) was larger than the coherence length, ξ but smaller than the penetration depth, λ(ξ< R <λ). The temperature dependent Jc from 30 to 65 K showed a linear relation for all except for the tapes heated at 240 h. Using the self-field approximation together with the Jc dependence on temperature, it was observed that between 30 and 65 K the characteristic length (Lc) associated with the pinning force Fp is approximately the same as the average grain size (Rg) in all samples except for the tapes heated for 240 h where Rg < Lc. This shows that a change in the flux pinning mechanism occurred in the tapes when the heating time was prolonged.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3329419','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3329419"><span>The Effect of the CO32- to <span class="hlt">Ca</span>2+ Ion activity ratio on calcite precipitation kinetics and <span class="hlt">Sr</span>2+ partitioning</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2012-01-01</p> <p>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-/a<span class="hlt">Ca</span>2+). To better understand the effect of ion activity ratios on <span class="hlt">Ca</span>CO3 precipitation kinetics and <span class="hlt">Sr</span>2+ 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-/a<span class="hlt">Ca</span>2+) 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-/a<span class="hlt">Ca</span>2+ ratios did not affect the distribution coefficient for <span class="hlt">Sr</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28197823','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28197823"><span>The deposition of strontium and zinc Co-<span class="hlt">substituted</span> hydroxyapatite coatings.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Robinson, L; Salma-Ancane, K; Stipniece, L; Meenan, B J; Boyd, A R</p> <p>2017-03-01</p> <p>The in vitro and in vivo performance of hydroxyapatite (HAp) coatings can be modified by the addition of different trace ions, such as silicon (Si), lithium (Li), magnesium (Mg), zinc (Zn) or strontium (<span class="hlt">Sr</span>) into the HAp lattice, to more closely mirror the complex chemistry of human bone. To date, most of the work in the literature has considered single ion-<span class="hlt">substituted</span> materials and coatings, with limited reports on co-<span class="hlt">substituted</span> calcium phosphate systems. The aim of this study was to investigate the potential of radio frequency magnetron sputtering to deposit <span class="hlt">Sr</span> and Zn co-<span class="hlt">substituted</span> HAp coatings using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The FTIR and XPS results highlight that all of the <span class="hlt">Sr</span>, Zn and <span class="hlt">Sr</span>-Zn co-<span class="hlt">substituted</span> surfaces produced are all dehydroxylated and are calcium deficient. All of the coatings contained HPO4(2-) groups, however; only the pure HAp coating and the <span class="hlt">Sr</span> <span class="hlt">substituted</span> HAp coating contained additional CO3(2-) groups. The XRD results highlight that none of the coatings produced in this study contain any other impurity <span class="hlt">Ca</span>P phases, showing peaks corresponding to that of ICDD file #01-072-1243 for HAp, albeit shifted to lower 2θ values due to the incorporation of <span class="hlt">Sr</span> into the HAp lattice for <span class="hlt">Ca</span> (in the <span class="hlt">Sr</span> and <span class="hlt">Sr</span>-Zn co-<span class="hlt">substituted</span> surfaces only). Therefore, the results here clearly show that RF magnetron sputtering offers a simple means to deliver <span class="hlt">Sr</span> and Zn co-<span class="hlt">substituted</span> HAp coatings with enhanced surface properties. (a) XRD patterns for RF magnetron sputter deposited hydroxyapatite coatings and (b)-(d) for <span class="hlt">Sr</span>, Zn and <span class="hlt">Sr</span>-Zn co-<span class="hlt">substituted</span> coatings, respectively. The XPS spectra in (b) confirms the presence of a HA sputter deposited coating as opposed to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000PhRvB..61..778J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000PhRvB..61..778J"><span>High-pressure synthesis and superconducting properties of the oxychloride superconductor (<span class="hlt">Sr,Ca</span>)3Cu2O4+δCl2-y</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jin, C.-Q.; Puzniak, R.; Zhao, Z.-X.; Wu, X.-J.; Tatsuski, T.; Tamura, T.; Adachi, S.; Tanabe, K.; Yamauchi, H.; Tanaka, S.</p> <p>2000-01-01</p> <p>Chlorine-containing (<span class="hlt">Sr,Ca</span>)3Cu2O4+δCl2-y superconductors have been synthesized at 5.0 GPa and ~1000 °C. The double-[CuO2] layered compound crystallizes into (La,<span class="hlt">Sr</span>)2<span class="hlt">Ca</span>Cu2O6 structure with Cl residing at the apical anion site relative to the [CuO2] plane. The critical transition temperature Tc 80 K has been achieved in these superconductors. The <span class="hlt">Sr</span>2.3<span class="hlt">Ca</span>0.7Cu2O4+δCl1.3 superconductor was studied in terms of irreversibility field Hirr and intragrain critical current density Ic. It is found that the irreversibility field of the superconductor can be described by the power law dependence (1-T/Tc)n, with n~2. The reduced Hirr(T/Tc) line is positioned between those of YBa2Cu3O7 and Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8 in the H-T plane, close to HgBa2<span class="hlt">Ca</span>Cu2O6+δ. The critical current density Jc(T) was extracted from the Bean critical-state model and showed a smooth temperature dependence. No significant difference was found for the general behavior of Hirr(T) and Jc(T) of (<span class="hlt">Sr,Ca</span>)3Cu2O4+δCl2-y from those of oxide high-Tc superconducting cuprates (HTSC). The off-plane space remains the important parameter to evaluate interlayer coupling of the oxyhalide HTSC, which is consistent with oxide HTSC. The results suggest the potential application capability of the oxyhalide superconductors even though the off-plane block is composed of oxyhalide instead of the routine oxides.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26245750','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26245750"><span>Red/blue-shift dual-directional regulation of α-(<span class="hlt">Ca</span>, <span class="hlt">Sr</span>)2SiO4:Eu(2+) phosphors resulting from the incorporation content of Eu(2+)/<span class="hlt">Sr</span>(2+) ions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lu, Zhijuan; Mao, Zhiyong; Chen, Jingjing; Wang, Dajian</p> <p>2015-09-21</p> <p>In this work, tunable emission from green to red and the inverse tuning from red to green in α-(<span class="hlt">Ca</span>, <span class="hlt">Sr</span>)2SiO4:Eu(2+) phosphors were demonstrated magically by varying the incorporation content of Eu(2+) and <span class="hlt">Sr</span>(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 <span class="hlt">Sr</span>(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 <span class="hlt">Sr</span>(2+). The excellent tuning characteristics for α-(<span class="hlt">Ca</span>, <span class="hlt">Sr</span>)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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ApPhL..86p2504M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ApPhL..86p2504M"><span>Effects of cation disorder and size on metamagnetism in A-site <span class="hlt">substituted</span> Pr0.5<span class="hlt">Ca</span>0.5MnO3 system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mavani, K. R.; Paulose, P. L.</p> <p>2005-04-01</p> <p>The effects of A-site cation disorder and size on metamagnetism of ABO3 type charge and orbital ordered Pr0.5<span class="hlt">Ca</span>0.5MnO3 system have been studied by <span class="hlt">substituting</span> Ba+2 for <span class="hlt">Ca</span>+2 or La+3 for Pr+3. <span class="hlt">Substitution</span> of 5% Ba+2 or 5% La+3 drastically reduces the critical magnetic field (Hc) for metamagnetism and induces successive steplike metamagnetic transitions at low temperatures. Interestingly, with further increase in <span class="hlt">substitution</span>, Hc rises. We find that there is a sharp decrease in electrical resistivity corresponding to the metamagnetic transitions, which is indicative of strongly correlated magnetic and electronic transitions in these manganites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JAP...111j3709H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JAP...111j3709H"><span>Enhanced thermoelectric figure-of-merit ZT for hole-doped Bi2<span class="hlt">Sr</span>2Co2Oy through Pb <span class="hlt">substitution</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hsu, H. C.; Lee, W. L.; Wu, K. K.; Kuo, Y. K.; Chen, B. H.; Chou, F. C.</p> <p>2012-05-01</p> <p>Single crystals of Bi2-xPbx<span class="hlt">Sr</span>2Co2Oy (0 ≤ x ≤ 0.55) have been grown using optical floating-zone method. The chemical compositions were determined using combined electron probe microanalysis and iodometric titration. Physical properties including electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were measured using single crystal specimens. Successful hole doping through Pb <span class="hlt">substitution</span> is confirmed through combined iodometry titration, electrical transport, and Seebeck coefficient measurements. Significant reduction on both in-plane resistivity and thermal conductivity was found as a result of Pb <span class="hlt">substitution</span> to the Bi site. The thermoelectric figure-of-merit ZT for x ˜ 0.55 is raised 20 folds from the undoped sample at room temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22299800','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22299800"><span>Crystal structure and magnetic properties of Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Rangi, Manisha; Agarwal, Ashish Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.</p> <p>2014-08-15</p> <p>Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, 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 <span class="hlt">substituted</span> 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 <span class="hlt">Ca</span>-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 <span class="hlt">substitution</span> 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 <span class="hlt">substitution</span> 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 <span class="hlt">substituted</span> samples revealing a strong correlation between ionic radii and magnetization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20050501','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20050501"><span>Creep of polycrystalline (Bi,Pb){sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>{sub 2}Cu{sub 3}O{sub x}</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Martinez-Fernandez, J.; Dominguez-Rodriguez, A.; Routbort, J.L.; Goretta, K.C.</p> <p>2000-04-14</p> <p>Plastic deformation has proved to be essential to the manufacture of bulk (Bi,Pb){sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>{sub 2}Cu{sub 3}O{sub x} (Bi-2223) superconductors. Compressive creep of dense, forged Bi-2223, Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub x} (Bi-2212), and Bi{sub 2}<span class="hlt">Sr</span>{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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://fishbull.noaa.gov/1013/1013toc.htm','USGSPUBS'); return false;" href="http://fishbull.noaa.gov/1013/1013toc.htm"><span>Effect of analytical conditions in wavelength dispersive electron microprobe analysis on the measurement of strontium-to-calcium (<span class="hlt">Sr/Ca</span>) ratios in otoliths of anadromous salmonids</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Zimmerman, Christian E.; Nielsen, Roger L.</p> <p>2003-01-01</p> <p>The use of strontium-to-calcium (<span class="hlt">Sr/Ca</span>) ratios in otoliths is becoming a standard method to describe life history type and the chronology of migrations between freshwater and seawater habitats in teleosts (e.g. Kalish, 1990; Radtke et al., 1990; Secor, 1992; Rieman et al., 1994; Radtke, 1995; Limburg, 1995; Tzeng et al. 1997; Volk et al., 2000; Zimmerman, 2000; Zimmerman and Reeves, 2000, 2002). This method provides critical information concerning the relationship and ecology of species exhibiting phenotypic variation in migratory behavior (Kalish, 1990; Secor, 1999). Methods and procedures, however, vary among laboratories because a standard method or protocol for measurement of <span class="hlt">Sr</span> in otoliths does not exist. In this note, we examine the variations in analytical conditions in an effort to increase precision of <span class="hlt">Sr/Ca</span> measurements. From these findings we argue that precision can be maximized with higher beam current (although there is specimen damage) than previously recommended by Gunn et al. (1992).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JCrGr.452..117E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JCrGr.452..117E"><span>Influence of Co-<span class="hlt">substitution</span> on the structural and magnetic properties of nanocrystalline Ba0.5<span class="hlt">Sr</span>0.5Fe12O19</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ezhil Vizhi, R.; Harikrishnan, V.; Saravanan, P.; Rajan Babu, D.</p> <p>2016-10-01</p> <p>One-step citrate gel combustion method followed by annealing (800 °C/2 h) was employed to synthesize cobalt <span class="hlt">substituted</span> barium strontium hexaferrite with a chemical composition of Ba0.5<span class="hlt">Sr</span>0.5Fe12-xCoxO19 (x=0, 0.5, 0.7, and 0.9). A combination of thermo-gravimetric analysis and differential scanning calorimetry was employed to understand the thermo-chemical behavior of Ba0.5<span class="hlt">Sr</span>0.5Fe12O19. X-ray diffraction (XRD) was used to evaluate the hexagonal phase evolution for the barium strontium ferrite nanopowders and a formation of secondary phase: α-Fe2O3 is evident for the Ba0.5<span class="hlt">Sr</span>0.5Fe12O19. Raman spectroscopy confirmed the presence of different sublattices of Fe3+ present in the hexaferrite structure. Fourier transform infrared spectroscopy demonstrated the usual stretching vibrations of tetrahedral and octahedral M-O bands. The morphology and chemical composition of the samples were analyzed by transmission electron microscopy and field emission scanning electron microscopy attached with energy dispersive X-ray analysis, respectively. Selected area electron diffraction studies showed the nanocrystalline nature of the samples. The magnetic parameters such as saturation magnetization MS, coercivity, HC and remanent magnetization, MR were estimated from the hysteresis loops. Maximum value of MS (70.5 emu/g) was obtained for the Ba0.5<span class="hlt">Sr</span>0.5Fe11.5Co0.5O19 nanoparticles. A possible growth mechanism on the crystallization of Ba0.5<span class="hlt">Sr</span>0.5Fe12O19 hexagonal platelets during the citrate gel combustion synthesis is highlighted.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhyB..407..218M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhyB..407..218M"><span>Comparison of the structural and magnetic properties of ground-state <span class="hlt">Sr</span>TcO 3 and <span class="hlt">Ca</span>TcO 3 from first principles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Chun-Lan; Zhou, Tong</p> <p>2012-01-01</p> <p>The generalized gradient approximation (GGA) plus on-site Coulomb interaction corrections (GGA+ U) method is employed for the total energies and electronic structure calculations of <span class="hlt">Sr</span>TcO 3 and <span class="hlt">Ca</span>TcO 3. G-type antiferromagnetic (G-AFM) is found to be ground state for both compounds, in consistence with the previous experimental results. The mechanism of Neel temperature of <span class="hlt">Sr</span>TcO 3 being higher than that of <span class="hlt">Ca</span>TcO 3 is explored. The insulating band gaps of <span class="hlt">Sr</span>TcO 3 and <span class="hlt">Ca</span>TcO 3 are found to be 1.71 eV and 1.74 eV, respectively. The magnetic moment of Tc1 is found to be 2.237μB in <span class="hlt">Sr</span>TcO 3 unit cell and 2.266μB in <span class="hlt">Ca</span>TcO 3 unit cell. Structural parameters and electronic structure of the two compounds are examined to explore the origin of their different electrical and magnetic characters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997PhRvB..55.2678G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997PhRvB..55.2678G"><span>Comment on ``Electrical and dielectric propertiesof the Bi4<span class="hlt">Sr</span>3<span class="hlt">Ca</span>3Cu4Ox (4:3:3:4) glassy semiconductor''</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ghosh, A.</p> <p>1997-01-01</p> <p>A recent paper from Som and Chaudhuri [Phys. Rev. B 41, 1581 (1990)], regarding the electrical and dielectric properties of Bi4<span class="hlt">Sr</span>3<span class="hlt">Ca</span>3Cu4Ox glass is reanalyzed. It is shown that the theoretical analysis for the ac conductivity and its frequency exponent performed by the authors is incorrect.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70177928','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70177928"><span>Multi-species coral <span class="hlt">Sr/Ca</span> based sea-surface temperature reconstruction data using Orbicella faveolata and Siderastrea siderea from Dry Tortugas National Park, Florida</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Flannery, Jennifer A.; Richey, Julie N.; Thirumalai, Kaustubh; Poore, Richard Z.; Delong, Kristine</p> <p>2016-01-01</p> <p>New sub annual and mean annual <span class="hlt">Sr/Ca</span> records from two species of massive coral, Orbicella faveolata (coral B3) and Siderastrea siderea (coral CG2), from the Dry Tortugas National Park, FL (DRTO). Both corals have well-constrained chronologies, with coral B3 ranging from 1893-2008 and coral CG2 ranging from 1837-2012. We combine these new records with published <span class="hlt">Sr/Ca</span> data from three additional S. siderea coral colonies (DeLong et al., 2014) to generate a 278-year-long multi-species composite <span class="hlt">Sr/Ca</span>-SST record from DRTO. This new record from a region sensitive to the Atlantic Multidecadal Oscillation (AMO) and Atlantic Meridional Overturning Circulation (AMOC) variations provides insight into the link between the two systems. Also included are new annual linear extension rates for each species. The coral samples and derived data were collected under the National Park Service Scientific Research and Collecting permits DRTO-2008-SCI-0015 and DRT0-2012-SCI-0001; accession numbers DRTO-241 and DRTO-353. For further information regarding data collection and/or processing methods refer to Flannery, J. A., J. N. Richey, K. Thirumalai, R. Z. Poore, and K. L. DeLong, 2016, Multi-species coral <span class="hlt">Sr/Ca</span> based sea-surface temperature reconstruction using Orbicella faveolata and Siderastrea siderea from the Florida Straits, Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, http://dx.doi.org/10.1016/j.palaeo.2016.10.022.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP43B1472H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP43B1472H"><span>Assessing the accuracy of oxygen isotopes and <span class="hlt">Sr/Ca</span> as proxies of sea surface temperature at the extreme latitudinal limits of Porites corals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hirabayashi, S.; Yokoyama, Y.; Suzuki, A.; Kawakubo, Y.; Miyairi, Y.; Okai, T.; Nojima, S.</p> <p>2014-12-01</p> <p>Oxygen isotope and <span class="hlt">Sr/Ca</span> ratios in harmatypic coral skeletons are widely employed as proxies of sea-surface temperature (SST) in paleoclimatology, yet they are considered to be influenced from growth rate of corals. Corals in temperate regions have lower skeletal growth rate because of relatively stressful environment, in particular lower SST than those in the tropics or subtropics. Dependency on SST proxies from those effects are required to be validated to better understand paleo-environment using temperate corals. This study reports <span class="hlt">Sr/Ca</span>-based SST reconstructions for three temperate Porites coral colonies (USB93, USB12-01, USB12-03) collected from Kyushu, Japan, near the northern latitudinal limits of Porites. Results clearly indicated that <span class="hlt">Sr/Ca</span> reliably reproduced SST variation, independent from growth rate variations, in contrast to δ18O-based reconstruction (Hirabayashi et al., 2013, Geochemical Journal). The inter-colony variation of skeletal <span class="hlt">Sr/Ca</span> of two Porites corals (USB12-01, USB12-03) were observed. This is attributed to the difference in calcification processes between so called "smooth type" and "sharp type" proposed by Gagan et al. (2012) as is defined by the ratio of tissue thickness/extension rate. According to these observations, summer SST reconstruction can be achieved by a limited number of coral specimens in a temperate region with comparable accuracy to tropical and subtropical corals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.161...36C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.161...36C"><span>In vitro synthesis of amorphous Mg-, <span class="hlt">Ca</span>-, <span class="hlt">Sr</span>- and Ba-carbonates: What do we learn about intracellular calcification by cyanobacteria?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cam, N.; Georgelin, T.; Jaber, M.; Lambert, J.-F.; Benzerara, K.</p> <p>2015-07-01</p> <p>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 <span class="hlt">Sr/Ca</span> and Ba/<span class="hlt">Ca</span> 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-, <span class="hlt">Ca</span>-, <span class="hlt">Sr</span>- 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 <span class="hlt">Sr</span> and Ba can favor stabilization of poorly crystalline carbonates. In contrast, the differential partitioning of <span class="hlt">Sr</span>, Ba and <span class="hlt">Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27181035','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27181035"><span>Coral <span class="hlt">Sr/Ca</span>-based sea surface temperature and air temperature variability from the inshore and offshore corals in the Seribu Islands, Indonesia.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cahyarini, Sri Yudawati; Zinke, Jens; Troelstra, Simon; Suharsono; Aldrian, Edvin; Hoeksema, B W</p> <p>2016-09-30</p> <p>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 <span class="hlt">Sr/Ca</span> variation. The results show that <span class="hlt">Sr/Ca</span> of the offshore coral tracked SST, while <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017OptMa..66....1Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017OptMa..66....1Z"><span>Site occupation and photoluminescence properties of Ce3+ in <span class="hlt">Sr</span>4<span class="hlt">Ca</span>4La2 (PO4)6O2: Experiments and ab initio calculations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhou, Rongfu; Ning, Lixin; Zhou, Weijie; Lin, Litian; Shi, Rui; Liang, Hongbin</p> <p>2017-04-01</p> <p>Cerium-doped oxyapatite phosphors, <span class="hlt">Sr</span>4<span class="hlt">Ca</span>4La2(PO4)6O2: Ce3+, are prepared by a traditional solid-state reaction method. X-ray diffraction (XRD) refinement reveals that the hexagonal <span class="hlt">Sr</span>4<span class="hlt">Ca</span>4La2(PO4)6O2 structure is characterized by a random distribution of <span class="hlt">Sr</span> and <span class="hlt">Ca</span> atoms on the nine-coordinated cationic 4f sites and of <span class="hlt">Sr</span>, <span class="hlt">Ca</span>, and La atoms on the seven-coordinated cationic 6 h sites. Photoluminescence properties of Ce-doped samples are then studied with excitation energies in the vacuum-ultraviolet (VUV) to ultraviolet (UV) range at low temperature. Three main types of occupation sites for Ce3+ are identified based on analysis of emission and excitation spectra and of luminescence decay behaviors. The Ce3+ occupation on the seven-coordinated La (6 h) site is found to be dominant, which is supported by wave function-based CASSCF/CASPT2 embedded cluster calculations on Ce3+ 4f → 5d transition energies at the spin-orbit level. The role of the coordinated oxygen ion that is not bonded with P5+ in the 5d centroid shift of CeLa(6h)3+ is emphasized. The thermal stability and doping concentration dependence of the 5d luminescence are also investigated and discussed in association with the coordination structures of Ce3+.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JLum..133...81S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JLum..133...81S"><span>Impurity-trapped excitons and electron traps in <span class="hlt">Ca</span>F2:Yb2+ and <span class="hlt">Sr</span>F2:Yb2+ probed by transient photoluminescence enhancement</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Senanayake, P. S.; Wells, J. P. R.; Reid, M. F.; Berden, G.; Meijerink, A.; Reeves, R. J.</p> <p>2013-01-01</p> <p><span class="hlt">Ca</span>F$_2$:Yb$^{2+}$ and <span class="hlt">Sr</span>F$_2$:Yb$^{2+}$ crystals have been investigated by a two-color UV + IR transient photoluminescence enhancement technique. The enhancement gives information about both changes in internal energy levels of the excitons and liberation of electrons from traps in the crystals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26192245','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26192245"><span>Electronic, Dielectric, and Plasmonic Properties of Two-Dimensional Electride Materials X2N (X=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>): A First-Principles Study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Guan, Shan; Yang, Shengyuan A; Zhu, Liyan; Hu, Junping; Yao, Yugui</p> <p>2015-07-20</p> <p>Based on first-principles calculations, we systematically study the electronic, dielectric, and plasmonic properties of two-dimensional (2D) electride materials X2N (X=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>). We show that both <span class="hlt">Ca</span>2N and <span class="hlt">Sr</span>2N are stable down to monolayer thickness. For thicknesses larger than 1-monolayer (1-ML), there are 2D anionic electron layers confined in the regions between the [X2N](+) layers. These electron layers are strongly trapped and have weak coupling between each other. As a result, for the thickness dependence of many properties such as the surface energy, work function, and dielectric function, the most dramatic change occurs when going from 1-ML to 2-ML. For both bulk and few-layer <span class="hlt">Ca</span>2N and <span class="hlt">Sr</span>2N, the in-plane and out-of-plane real components of their dielectric functions have different signs in an extended frequency range covering the near infrared, indicating their potential applications as indefinite media. We find that bulk <span class="hlt">Ca</span>2N and <span class="hlt">Sr</span>2N could support surface plasmon modes in the near infrared range. Moreover, tightly-bounded plasmon modes could exist in their few-layer structures. These modes have significantly shorter wavelengths (few tens of nanometers) compared with that of conventional noble metal materials, suggesting their great potential for plasmonic devices with much smaller dimensions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70017191','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70017191"><span>Dissolution of aragonite-strontianite solid solutions in nonstoichiometric <span class="hlt">Sr</span> (HCO3)2-<span class="hlt">Ca</span> (HCO3)2-CO2-H2O solutions</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Plummer, L.N.; Busenberg, E.; Glynn, P.D.; Blum, A.E.</p> <p>1992-01-01</p> <p>Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated non-stoichiometric solutions of <span class="hlt">Sr</span>(HCO3)2 and <span class="hlt">Ca</span>(HCO3)2 at 25??C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in <span class="hlt">Ca</span>(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In <span class="hlt">Sr</span>(HCO3)2 solutions the reactions usually become incongruent, precipitating a <span class="hlt">Sr</span>-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 <span class="hlt">Sr</span>(HCO3)2 solutions and 0-4 layers thick in <span class="hlt">Ca</span>(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 <span class="hlt">Sr</span>-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 <span class="hlt">Sr</span>(HCO3)2 and <span class="hlt">Ca</span>(HCO3)2 solutions, respectively. In <span class="hlt">Sr</span>(HCO3)2 solutions, the XPS signal from the outer ~ 60 A?? on aragonite indicates a composition of 16 mol% <span class="hlt">Sr</span>CO3 after only 2 min of contact, and 14-18 mol% <span class="hlt">Sr</span>CO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% <span class="hlt">Ca</span>CO3 after 2 min of contact with <span class="hlt">Ca</span>(HCO3)2 solution, and is 34-39 mol% <span class="hlt">Ca</span>CO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer ~25</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFM.V21C..06R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFM.V21C..06R"><span>Constraining Open-System Processes in the Generation of Basaltic Magma Using 87<span class="hlt">Sr</span>/86<span class="hlt">Sr</span> of Individual Minerals and Melt Inclusions, Pisgah Crater, <span class="hlt">Ca</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ramos, F. C.; Wolff, J. A.</p> <p>2002-12-01</p> <p>Basaltic magmas have been extensively used to infer the geochemical nature of mantle sources. Studies which make such inferences typically focus on basalts that are characterized by assumed primary magma characteristics such as high MgO contents. Such characteristics are typically used as justification to discount or suggest only a minimal influence of open-system modifications, such as those resulting from crustal assimilation. Often, very little effort is made to more thoroughly eliminate this possibility because it is very difficult to identify and constrain such effects especially if the assimilated crust is mafic in character. Alkali basalts and hawaiities erupted at Pisgah Crater in the Mojave Desert of California result from open-system processes yet still retain high MgO (6-8%) contents. The specific processes responsible for extensive trace element and isotopic variations in these basalts, however, are in dispute. Glazner et al. (1991) suggest that Pisgah Crater trace element and isotopic variations originate from assimilation of mafic crust while Reiners (2002) suggests that such variations result from mixing of mantle-derived garnet peridotite and garnet pyroxenite magmas. Large 87<span class="hlt">Sr</span>/86<span class="hlt">Sr</span> variations among and within individual plagioclase, clinopyroxene, amphibole, groundmass, and melt inclusions in olivine attest to the effects of open-system processes and indicate a complex mixing process (i.e., not two-component mixing) that occurred up to the time of eruption (Ramos et al, in prep). 87<span class="hlt">Sr</span>/86<span class="hlt">Sr</span> of minerals indicate that early and intermediate erupted lavas retain relatively uncontaminated signatures while the latest erupted lavas reflect much higher 87<span class="hlt">Sr</span>/86<span class="hlt">Sr</span>, consistent with contamination at crustal pressures (i.e., within the plagioclase stability field). Major element compositions of melt inclusions hosted in olivine confirm the presence of highly evolved magmas (e.g., MgO: 0.5 to 3%, SiO2: 52-57%) in later erupted lavas. Whole grain olivine</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ECSS..133..293J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ECSS..133..293J"><span>Methods for estimating a critical value for determining the freshwater/estuarine habitat residence of American eels from otolith <span class="hlt">Sr:Ca</span> data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jessop, B. M.; Shiao, J. C.; Iizuka, Y.</p> <p>2013-11-01</p> <p>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 <span class="hlt">Sr:Ca</span> data. The LDA process requires <span class="hlt">Sr:Ca</span> 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 (<span class="hlt">Sr:Ca</span>) case, the LDA process defaults to Fisher's linear discriminant where the HDCV equals the average of the group mean <span class="hlt">Sr:Ca</span> values. The difference between freshwater and estuarine resident eel mean otolith <span class="hlt">Sr:Ca</span> 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 <span class="hlt">Sr:Ca</span> 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 <span class="hlt">Sr:Ca</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP42A..07B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP42A..07B"><span>A Modern <span class="hlt">Sr/Ca</span>-δ18O-Sea Surface Temperature Calibration for Isopora Corals in the Great Barrier Reef</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brenner, L. D.; Linsley, B. K.; Potts, D. C.</p> <p>2014-12-01</p> <p>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 <span class="hlt">Sr/Ca</span>-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 <span class="hlt">Sr/Ca</span> record with monthly SST yielded an average relationship of SST=-11.48×(<span class="hlt">Sr/Ca</span>)+131.1 (r2 = 0.42-0.78). The <span class="hlt">Sr/Ca</span> 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 <span class="hlt">Sr/Ca</span>-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 <span class="hlt">Sr/Ca</span>-SST calibration will expand the paleoceanographic utility of Isopora and, by assisting interpretation of <span class="hlt">Sr/Ca</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9726E..1CS','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9726E..1CS"><span>Effect of cryogenic temperature on spectroscopic and laser properties of Er,La:<span class="hlt">Sr</span>F2-<span class="hlt">Ca</span>F2 crystal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Švejkar, Richard; Šulc, Jan; Němec, Michal; Jelínková, Helena; Doroshenko, Maxim E.; Nakladov, Andrei N.; Osiko, Vjatcheslav V.</p> <p>2016-03-01</p> <p>The laser and spectroscopic properties of crystal Er,La:<span class="hlt">Sr</span>F2-<span class="hlt">Ca</span>F2 at temperature range 80 - 300 K, which is appropriate for generation of radiation around 2.7 um is presented. The sample of Er,La:<span class="hlt">Sr</span>F2-<span class="hlt">Ca</span>F2 (concentration Er(0.04), La(0.12):<span class="hlt">Ca</span>(0.77)<span class="hlt">Sr</span>(0.07)) had plan-parallel face-polished faces without anti-reflection coatings (thickness 8.2 mm). During spectroscopy and laser experiments the Er,La:<span class="hlt">Sr</span>F2-<span class="hlt">Ca</span>F2 was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra of Er,La:<span class="hlt">Sr</span>F2-<span class="hlt">Ca</span>F2 together with the fluorescence decay time were measured in dependence on temperature. The excitation of Er,La:<span class="hlt">Sr</span>F2-<span class="hlt">Ca</span>F2 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:<span class="hlt">Sr</span>F2-<span class="hlt">Ca</span>F2 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20784926','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20784926"><span>Synthesis, structure, and properties of four ternary compounds: <span class="hlt">CaSr</span>Tt, Tt=Si, Ge, Sn, Pb</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Liu Shengfeng; Corbett, John D. . E-mail: jcorbett@iastate.edu</p> <p>2006-03-15</p> <p>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 <span class="hlt">Sr</span> and <span class="hlt">Ca</span> atoms in which the smaller <span class="hlt">Ca</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMPP41B1503W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMPP41B1503W"><span>A new calibration for the <span class="hlt">Sr/Ca</span>-temperature relationship in sclerosponges reveals synchronous changes in Caribbean specimens indicative of warming and multi-decadal climate variability</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Waite, A. J.; Swart, P. K.; Rosenheim, B. E.</p> <p>2009-12-01</p> <p>Previous work defined the calibration between the skeletal <span class="hlt">Sr/Ca</span> ratio of the sclerosponge Ceratoporella nicholsoni and the ambient seawater temperature. However, application of this calibration to records throughout the Caribbean reveals a nearly 4°C warming over the last 150 years, in excess of what one might expect from global climate averages. As the original C. nicholsoni <span class="hlt">Sr/Ca</span>-temperature relationship was calibrated between 26 and 30°C, it is possible that the relationship differed outside of the examined temperature window. This suspicion is confirmed by the measurement of <span class="hlt">Sr/Ca</span> ratios from additional specimens of the same species. These show a significantly different slope between <span class="hlt">Sr/Ca</span> and temperature at lower temperatures (21 to 26°C). Using this information, the calibration equation has been refined and the subsequent reconstructions of temperature are much more realistic, indicating a warming of approximately 1°C over the last 150 years. Applying this new calibration to additional published sclerosponge records of <span class="hlt">Sr/Ca</span> reveals remarkable agreements between records from the Bahamas and Jamaica, both in amplitude of warming and smaller scale variability. In addition, the depth versus temperature relationship associated with these specimens is preserved. The refined temperature reconstruction of a 600 year record from Exuma Sound, Bahamas, demonstrates the cyclic nature of its variability (~15 and 28 year periodicities). Further use of these data and stable oxygen isotopes to calculate salinity reveals variability on multi-decadal timescales. This includes an approximately 20 year periodicity between 1400 and 1790. From 1790 to 2000, the dominant mode appears to switch to a roughly 60 year periodicity, consistent with that of the Atlantic Multi-decadal Oscillation (AMO).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PalOc..31.1315F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PalOc..31.1315F"><span>Intrareef variations in Li/Mg and <span class="hlt">Sr/Ca</span> sea surface temperature proxies in the Caribbean reef-building coral Siderastrea siderea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fowell, Sara E.; Sandford, Kate; Stewart, Joseph A.; Castillo, Karl D.; Ries, Justin B.; Foster, Gavin L.</p> <p>2016-10-01</p> <p>Caribbean sea surface temperatures (SSTs) have increased at a rate of 0.2°C per decade since 1971, a rate double that of the mean global change. Recent investigations of the coral Siderastrea siderea on the Belize Mesoamerican Barrier Reef System (MBRS) have demonstrated that warming over the last 30 years has had a detrimental impact on calcification. Instrumental temperature records in this region are sparse, making it necessary to reconstruct longer SST records indirectly through geochemical temperature proxies. Here we investigate the skeletal <span class="hlt">Sr/Ca</span> and Li/Mg ratios of S. siderea from two distinct reef zones (forereef and backreef) of the MBRS. Our field calibrations of S. siderea show that Li/Mg and <span class="hlt">Sr/Ca</span> ratios are well correlated with temperature, although both ratios are 3 times more sensitive to temperature change in the forereef than in the backreef. These differences suggest that a secondary parameter also influences these SST proxies, highlighting the importance for site- and species-specific SST calibrations. Application of these paleothermometers to downcore samples reveals highly uncertain reconstructed temperatures in backreef coral, but well-matched reconstructed temperatures in forereef coral, both between <span class="hlt">Sr/Ca</span>-SSTs and Li/Mg-SSTs, and in comparison to the Hadley Centre Sea Ice and Sea Surface Temperature record. Reconstructions generated from a combined <span class="hlt">Sr/Ca</span> and Li/Mg multiproxy calibration improve the precision of these SST reconstructions. This result confirms that there are circumstances in which both Li/Mg and <span class="hlt">Sr/Ca</span> are reliable as stand-alone and combined proxies of sea surface temperature. However, the results also highlight that high-precision, site-specific calibrations remain critical for reconstructing accurate SSTs from coral-based elemental proxies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JSSCh.203..232H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JSSCh.203..232H"><span>Synthesis, structure and chemical bonding of <span class="hlt">Ca</span>Fe2-xRhxSi2 (x=0, 1.32, and 2) and <span class="hlt">Sr</span>Co2Si2</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hlukhyy, Viktor; Hoffmann, Andrea V.; Fässler, Thomas F.</p> <p>2013-07-01</p> <p>The finding of superconductivity in Ba0.6K0.4Fe2As2 put the attention on the investigation of compounds that crystallize with ThCr2Si2 structure type such as AT2X2 (A=alkali/alkaline earth/rare earth element; T=transition metal and X=element of the 13-15th group). In this context the silicides <span class="hlt">Ca</span>Fe2Si2, <span class="hlt">Ca</span>Fe0.68(6)Rh1.32(6)Si2, <span class="hlt">Ca</span>Rh2Si2 and <span class="hlt">Sr</span>Co2Si2 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 ThCr2Si2-type structure with space group I4/mmm (No. 139): a=3.939(1) Å, c=10.185(1) Å, R1=0.045, 85 F2 values, 8 variable parameters for <span class="hlt">Ca</span>Fe2Si2; a=4.0590(2) Å, c=9.9390(8) Å, R1=0.030, 90 F2 values, 10 variable parameters for <span class="hlt">Ca</span>Fe0.68(6)Rh1.32(6)Si2; a=4.0695(1) Å, c=9.9841(3) Å, R1=0.031, 114 F2 values, 9 variable parameters for <span class="hlt">Ca</span>Rh2Si2; and a=3.974(1) Å, c=10.395(1) Å, R1=0.036, 95 F2 values, 8 variable parameters for <span class="hlt">Sr</span>Co2Si2. The structure of <span class="hlt">Sr</span>Co2Si2 contains isolated [Co2Si2]2- 2D-layers in the ab-plane whereas in <span class="hlt">Ca</span>Fe2-xRhxSi2 the [T2Si2] layers (T=Fe and Rh) are interconnected along the c-axis via Si3Si bonds resulting in a three-dimentional (3D) [T2Si2]2- polyanions and therefore belong to the so-called collapsed form of the ThCr2Si2-type structure. The <span class="hlt">Sr</span>Co2Si2 and <span class="hlt">Ca</span>Rh2Si2 are isoelectronic to the parent 122 iron-pnictide superconductors AeFe2As2 (Ae=alkaline earth elements), whereas <span class="hlt">Ca</span>Fe2Si2 is a full <span class="hlt">substituted</span> variant (As/Si) of <span class="hlt">Ca</span>Fe2As2. The crystal chemistry and chemical bonding in the title compounds are discussed in terms of LMTO band structure calculations and a topological analysis using the Electron Localization Function (ELF).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25377924','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25377924"><span>Towards a high thermoelectric performance in rare-earth <span class="hlt">substituted</span> <span class="hlt">Sr</span>TiO3: effects provided by strongly-reducing sintering conditions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kovalevsky, A V; Yaremchenko, A A; Populoh, S; Thiel, P; Fagg, D P; Weidenkaff, A; Frade, J R</p> <p>2014-12-28</p> <p>Donor-<span class="hlt">substituted</span> strontium titanate ceramics demonstrate one of the most promising performances among n-type oxide thermoelectrics. Here we report a marked improvement of the thermoelectric properties in rare-earth <span class="hlt">substituted</span> titanates <span class="hlt">Sr</span>0.9R0.1TiO3±δ (R = La, Ce, Pr, Nd, Sm, Gd, Dy, Y) to achieve maximal ZT values of as high as 0.42 at 1190 K < T < 1225 K, prepared via a conventional solid state route followed by sintering under strongly reducing conditions (10%H2-90%N2, 1773 K). As a result of complex defect chemistry, both electrical and thermal properties were found to be dependent on the nature of the rare-earth cation and exhibit an apparent correlation with the unit cell size. High power factors of 1350-1550 μW m(-1) K(-2) at 400-550 K were observed for R = Nd, Sm, Pr and Y, being among the largest reported so far for n-type conducting bulk-ceramic <span class="hlt">Sr</span>TiO3-based materials. Attractive ZT values at high temperatures arise primarily from low thermal conductivity, which, in turn, stem from effective phonon scattering in oxygen-deficient perovskite layers formed upon reduction. The results suggest that highly-reducing conditions are essential and should be employed, whenever possible, in other related micro/nanostructural engineering approaches to suppress the thermal conductivity in target titanate-based ceramics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARX30012M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARX30012M"><span>Aberration Corrected Scanning Transmission Electron Microscopy of (<span class="hlt">Ca</span> , <span class="hlt">Sr</span>)Fe2O5 Brownmillerite superlattices</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mukherjee, Debangshu; Stone, Greg; Moon, Eun Ju; Young, Joshua; Gopalan, Venkatraman; Rondinelli, James; May, Steven; Alem, Nasim</p> <p></p> <p>The brownmillerite phase A2B2O5 consists of ordered oxygen vacancies in alternate perovskite layers forming chiral tetrahedral chains. The handedness of these tetrahedral chains control the polarization of the structure. The current study focuses on 1-1 brownmillerite superlattices grown on a <span class="hlt">Sr</span>TiO3 substrates using molecular beam epitaxy. The B-site in this structure is iron throughout the superlattice film, while the A-site alternates between calcium and strontium in the superlattice layers. In this study, we use atomic resolution aberration corrected scanning transmission electron microscopy (STEM) to investigate the structure and chemistry of the film-substrate interface as well as the chemical structure of the superlattice. Atom positions are determined to measure displacement vectors of A-site cations in the superlattice structure. D.M., G.A.S., V.G. and N.A. were supported by the National Science Foundation under Grant No. DMR-1420620. E.J.M. and S.J.M. were supported by the National Science Foundation under Grant No. DMR-1151649.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JPS...249..483Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JPS...249..483Y"><span>Mixed conductivity, thermochemical expansion and electrochemical activity of Fe-<span class="hlt">substituted</span> (La,<span class="hlt">Sr</span>)(Cr,Mg)O3-δ for solid oxide fuel cell anodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yaremchenko, A. A.; Kharton, V. V.; Kolotygin, V. A.; Patrakeev, M. V.; Tsipis, E. V.; Waerenborgh, J. C.</p> <p>2014-03-01</p> <p>The effect of iron <span class="hlt">substitution</span> in perovskite-type (La0.9<span class="hlt">Sr</span>0.1)0.98Cr0.9-xFexMg0.1O3-δ (x = 0-0.3) is evaluated with emphasis on the properties relevant for solid oxide fuel cell anode application including the phase stability, oxygen nonstoichiometry, mixed ionic-electronic transport, thermochemical expansion and electrochemical activity. Thermogravimetric analysis, Mössbauer spectroscopy and electrical measurements in combination with X-ray diffraction confirm the stability of perovskite phase for x = 0.3 down to p(O2) as low as 10-19 atm at 1223 K. Mössbauer spectroscopy results indicate also that iron cations <span class="hlt">substitute</span> in 3+ oxidation state in both oxidized and reduced material. The total conductivity is predominantly p-type electronic, with negligible contribution of ionic transport under oxidizing conditions. <span class="hlt">Substitution</span> with iron decreases electronic transport, but also leads to higher oxygen deficiency and ionic conductivity under reducing conditions. The oxygen nonstoichiometry variations, determined by coulometric titration, and defect chemistry of (La0.9<span class="hlt">Sr</span>0.1)0.98Cr0.6Fe0.3Mg0.1O3-δ can be described by non-ideal solution model and site-exclusion effects. The materials exhibit moderate thermal expansion coefficients (10.1-11.5) × 10-6 K-1 in air, nearly independent of iron content and p(O2), and favorably small chemical expansion on reduction. Porous (La0.9<span class="hlt">Sr</span>0.1)0.98Cr0.6Fe0.3Mg0.1O3-δ anodes applied onto LaGaO3-based solid electrolyte with thin Ce0.8Gd0.2O2-δ interlayers show a better electrochemical performance compared to (La0.75<span class="hlt">Sr</span>0.25)0.95Cr0.5Mn0.5O3-δ under identical conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhyB..507..147L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhyB..507..147L"><span>Structural, elastic and electronic properties of C14-type Al2M (M=Mg, <span class="hlt">Ca</span>, <span class="hlt">Sr</span> and Ba) Laves phases</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lishi, Ma; Yonghua, Duan; Runyue, Li</p> <p>2017-02-01</p> <p>The structural and mechanical properties, Debye temperatures and anisotropic sound velocities of the Laves phases Al2M (M=Mg, <span class="hlt">Ca</span>, <span class="hlt">Sr</span> and Ba) with C14-type structure were investigated using the first-principles corresponding calculations. The corresponding calculated structural parameters and formation enthalpies are in good agreement with the available theoretical values, and Al2<span class="hlt">Ca</span> has the best phase stability. The mechanical properties, including elastic constants, bulk modulus B, shear modulus G, Young's modulus E, and Poisson ratio ν, were deduced within the Voigt-Reuss-Hill approximation. The brittleness and ductility were estimated by the values of Poisson ratio, B/G and Cauchy pressure. Moreover, the elastic anisotropy was investigated by calculating and discussing several anisotropy indexes. Finally, the electronic structures were used to illustrate the bonding characteristics of C14-Al2M (M=Mg, <span class="hlt">Ca</span>, <span class="hlt">Sr</span> and Ba) phases.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22415272','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22415272"><span>Fabrication of (111)-oriented <span class="hlt">Ca</span>{sub 0.5}<span class="hlt">Sr</span>{sub 0.5}IrO{sub 3}/<span class="hlt">Sr</span>TiO{sub 3} superlattices—A designed playground for honeycomb physics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori</p> <p>2015-04-01</p> <p>We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of <span class="hlt">Ca</span>{sub 0.5}<span class="hlt">Sr</span>{sub 0.5}IrO{sub 3} perovskite and two layers of <span class="hlt">Sr</span>TiO{sub 3} perovskite on <span class="hlt">Sr</span>TiO{sub 3}(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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28379230','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28379230"><span>Understanding how cAMP-dependent protein kinase can catalyze phosphoryl transfer in the presence of <span class="hlt">Ca</span>(2+) and <span class="hlt">Sr</span>(2+): a QM/MM study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pérez-Gallegos, Ayax; Garcia-Viloca, Mireia; González-Lafont, Àngels; Lluch, José M</p> <p>2017-04-05</p> <p>Recent experimental results have challenged conventional views on the role metals play in the chemistry of protein kinases because it has been shown that (cAMP)-dependent protein kinase (PKA) is active in the presence of other divalent alkaline earth metal cations besides physiological Mg(2+) ions. This has raised the important possibility that <span class="hlt">Ca</span>(2+) may also be a physiological cofactor of protein kinases. In this work, QM/MM calculations, at the DFT and MP2 levels for the QM part, on complete solvated models of PKAc-M2ATP-substrate ternary complexes, with PKAc as the catalytic subunit of PKA, M denoting <span class="hlt">Ca</span>(2+) or <span class="hlt">Sr</span>(2+) and substrate denoting SP20 or Kemptide, have been carried out for the overall phosphoryl transfer reaction. In accordance with the experimental data, our theoretical results show for the first time at the molecular level how the overall PKAc-catalyzed phosphorylation of SP20, via a dissociative mechanism, is plausible with <span class="hlt">Ca</span>(2+) and <span class="hlt">Sr</span>(2+). The viability of the catalytic reaction with Kemptide and <span class="hlt">Ca</span>(2+) is also verified here. The energy barrier of the rate-limiting phosphoryl-transfer step does not depend on different coordination environments of the alkaline earth metal cations whereas the proton-transfer step region is metal dependent making the global chemical process more exoergic on going from Mg(2+) to <span class="hlt">Sr</span>(2+). This trend is in agreement with the less effective release of the phosphorylated product observed experimentally in the presence of <span class="hlt">Ca</span>(2+)versus Mg(2+), and would explain also the lower activity of PKAc with <span class="hlt">Ca</span>(2+), since phospho-substrate and ADP releases are rate limiting for catalytic turnover. For the same reason, we predict an even lower activity of PKAc with <span class="hlt">Sr</span>(2+). Moreover, the active sites of the in silico reactant and product complexes and the available X-ray crystallographic structures show good agreement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004JSSCh.177.3610Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004JSSCh.177.3610Z"><span>On the characterization of Bi MO 2NO 3 ( M=Pb, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba) materials related with the Sillén X 1 structure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ziegler, Peter; Grigoraviciute, Inga; Gibson, Katharina; Glaser, Jochen; Kareiva, Aivaras; Meyer, H.-Jürgen</p> <p>2004-10-01</p> <p>The compounds BiMO2NO3, with M=Pb, <span class="hlt">Ca</span>, <span class="hlt">Sr</span>, and Ba, were obtained as single-phase products from solid-state reactions in an atmosphere of nitrous gases. The oxide nitrates with Pb and <span class="hlt">Ca</span> crystallize in the tetragonal space group I4/mmm with two formula units per unit cell; the oxide nitrates with <span class="hlt">Sr</span> and Ba crystallize in the orthorhombic space group Cmmm with four formula units per unit cell. Lattice parameters at room temperature are a=397.199(4), c=1482.57(2) pm for M=Pb; a=396.337(5), c=1412.83(3) pm for M=<span class="hlt">Ca</span>; a=1448.76(3), b=567.62(1), c=582.40(1) pm for M=<span class="hlt">Sr</span> and a=1536.50(8), b=571.67(3), c=597.55(3) pm for M=Ba. The structures, which were refined by powder X-ray diffraction, consist of alternating [BiMO2]+ and [NO3]- layers stacked along the direction of the long axis. IR and thermogravimetric data are also given. The various M2+ cations in BiMO2NO3 are compatible with each other; therefore and because of their layer-type structure, these compounds are interesting precursors for oxide materials, e.g., the HTSC compounds (Bi,Pb)2<span class="hlt">Sr</span>2Can-1CunOx.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26934836','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26934836"><span>Upconversion-luminescent/magnetic dual-functional sub-20 nm core-shell <span class="hlt">Sr</span>F2:Yb,Tm@<span class="hlt">Ca</span>F2:Gd heteronanoparticles.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Ai-Hua; Lü, Mengyun; Yang, Jun; Chen, Lin; Cui, Xiaohong; Sun, Zhijun</p> <p>2016-04-07</p> <p>Sub-20 nm core-shell and water-soluble <span class="hlt">Sr</span>F2:Yb,Tm@<span class="hlt">Ca</span>F2:Gd heteronanoparticles with both upconversion luminescence (UCL) and magnetic resonance imaging (MRI) capabilities were designed and synthesized via a two-step hydrothermal method. In the design of the heteronanoparticles, <span class="hlt">Sr</span>F2:Yb,Tm nanoparticles with high UCL efficiency are chosen as the core material for strong UCL output; and by epitaxially coating the <span class="hlt">Sr</span>F2:Yb,Tm core particles with inert and biocompatible shells of <span class="hlt">Ca</span>F2:Gd, the core-shell heteronanoparticles are endowed with a magnetic capability (longitudinal relaxivity of 2.4 mM(-1) s(-1)) for MRI, as well as an enhancement of the near infrared (NIR) UCL by 9.2 times. The aqueous dispersion of <span class="hlt">Sr</span>F2:Yb,Tm@<span class="hlt">Ca</span>F2:Gd heteronanoparticles with a concentration of 2.6 wt% can emit NIR UCL so as to be easily detected with a fiber optical spectrometer under illumination of a 975 nm laser diode with a power density of 8.8 W cm(-2). Such a dispersion with a Gd(3+) concentration of 0.0143 mM in the shell region of the heteronanoparticles can also generate the detectable quickening of longitudinal relaxation. The results promise the strong potential of this nanomaterial for applications in bioimaging as a dual-functional probe.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6948567','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6948567"><span>New photocathode materials for hydrogen evolution: <span class="hlt">Ca</span>Fe/sub 2/O/sub 4/ and <span class="hlt">Sr</span>/sub 7/Fe/sub 10/O/sub 22/</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Matsumoto, Y.; Omae, M.; Sugiyama, K.; Sato, E.</p> <p>1987-01-29</p> <p>The photoelectrochemical properties of p-type <span class="hlt">Ca</span>Fe/sub 2/O/sub 4/ and <span class="hlt">Sr</span>/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 <span class="hlt">Sr</span>/sub 7/Fe/sub 10/O/sub 22/ and <span class="hlt">Ca</span>Fe/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 <span class="hlt">Sr</span>/sub 7/Fe/sub 10/O/sub 22/ and <span class="hlt">Ca</span>Fe/sub 2/O/sub 4/, respectively. The flatband potential of <span class="hlt">Sr</span>/sub 7/Fe/sub 10/O/sub 22/ is 0.1 V vs. SCE, but that of <span class="hlt">Ca</span>Fe/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. <span class="hlt">Ca</span>Fe/sub 2/O/sub 4/ is more stable than <span class="hlt">Sr</span>/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 <span class="hlt">Ca</span>Fe/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 <span class="hlt">Sr</span>/sub 7/Fe/sub 10/O/sub 22/ and <span class="hlt">Ca</span>Fe/sub 2/O/sub 4/ and their photoelectrochemical processes are also discussed.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhRvB..87i4411J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhRvB..87i4411J"><span>Stabilization of the spin density wave structure with rare-earth <span class="hlt">substitution</span> in <span class="hlt">Ca</span>3Co2O6</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jain, Anil; Yusuf, S. M.; Meena, S. S.; Ritter, Clemens</p> <p>2013-03-01</p> <p>We report the structural and magnetic properties of rare-earth <span class="hlt">substituted</span> spin-chain compounds <span class="hlt">Ca</span>2.75R0.25Co2O6 (R = Dy and Lu). The Rietveld refinement of neutron and x-ray powder diffraction patterns confirms the single-phase formation of both compounds in the rhombohedral structure (space group R3¯c). The derived values (from the analysis of the neutron diffraction patterns at 50 K) of the bond-valence sum indicate a reduction in the oxidation state of the cobalt ions at the trigonal prism (TP) site (6a) with R <span class="hlt">substitution</span>, which is further supported by low temperature neutron diffraction [where a zero value of the ordered moment at the 6b site and a reduction in the values of the maximum ordered moment at the TP site have been observed] and dc magnetization studies. In the neutron diffraction patterns, additional Bragg peaks appear for both compounds below Néel temperature (TN) of ˜16 K, indicating the onset of an antiferromagnetic ordering of cobalt spin chains on the triangular lattice. The magnetic structure corresponds to a spin density wave (SDW) structure [with a propagation vector k={0,0,1.02}], having c axis as a direction of both moment and modulation. For both compounds, the refined values of the ordered moment at the 18e, 6b, and 6a sites are ˜0.03(2),0.02(2), and 4.2 (2) μB, respectively. Unlike the parent compound <span class="hlt">Ca</span>3Co2O6, no temperature dependence as well as no time dependence in the intensity of the strongest antiferromagnetic reflection (10 τ), corresponding to the propagation vector k = {0, 0, 1.02}, has been observed down to 1.5 K confirming that the SDW structure is stabilized by the <span class="hlt">substitution</span> with rare-earth ions. The stabilization of the SDW structure and the observed decrease in the values of TN could be due to a decrease in the value of positive FM intrachain exchange interaction J with the rare-earth <span class="hlt">substitution</span> in a system with competing intrachain and interchain exchange interactions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AIPC.1731m0041T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AIPC.1731m0041T"><span>Effect of trivalent <span class="hlt">substitution</span> on the magnetic and dielectric properties of Z-type hexaferrite, <span class="hlt">Sr</span>3Co2Fe24O41</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tiwari, Shivangi; Vitta, Satish</p> <p>2016-05-01</p> <p>Magnetic and dielectric properties of polycrystalline Z type hexaferrite <span class="hlt">Sr</span>3Co2Fe24-xAlxO41 (x = 0, 0.45) have been studied. In the unsubstituted (x = 0) compound a single hump was observed in the magnetization curve at ~ 370 K while the <span class="hlt">substituted</span> compound (x = 0.45) exhibits additional peaks at lower temperatures at 100, 500 and 1000 Oe magnetic fields. The room temperature hysteresis shows that the x = 0 compound has a simple ferrimagnetic behavior while the <span class="hlt">substituted</span> compound exhibits discontinuities - a step like M variation indicative of successive evolution of the magnetic structure at different fields. In both the compounds, permittivity and resistivity decreases with increasing frequency. The permittivity of unsubstituted compound however is higher compare to the <span class="hlt">substituted</span> compound at low frequency. The resistivity of x = 0 compound decreases from 106 Ωm to 6×104 Ωm while for x = 0.45, it decreases from 107 Ωm to 6×104 Ωm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/83945','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/83945"><span>Electron-spectroscopy investigation of the Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub 8} and Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub 8+{ital y}} single-crystal cleaved surfaces</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ori, D.M.; Goldoni, A. |; del Pennino, U.</p> <p>1995-08-01</p> <p>This paper presents spectroscopic investigations of the normal-state properties of Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub 8} and Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeCoA.105..240G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeCoA.105..240G"><span><span class="hlt">Sr/Ca</span> sensitivity to aragonite saturation state in cultured subsamples from a single colony of coral: Mechanism of biomineralization during ocean acidification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gagnon, Alexander C.; Adkins, Jess F.; Erez, Jonathan; Eiler, John M.; Guan, Yunbin</p> <p>2013-03-01</p> <p>Using a new and rapid NanoSIMS-based method, we quantified the sensitivity of skeletal <span class="hlt">Sr/Ca</span> in coral to the aragonite saturation state of seawater (ΩSW). Skeletal <span class="hlt">Sr/Ca</span> is a common proxy for temperature while ΩSW is a parameter that varied in the past ocean and is predicted to change with continued ocean acidification. Five adult branches of the surface coral Stylophora pistillata were grown at different ΩSW from 2.7 to 4.9 (pH of 7.9-8.5) but at a constant temperature of 25 °C. Despite a large range of growth parameters and a twofold range in calcification rates, the average skeletal <span class="hlt">Sr/Ca</span> of coral exposed to each condition are within 1.2% of each other (2σ std. dev. of the 5 means). Furthermore, the average skeletal <span class="hlt">Sr/Ca</span> measured in this study agrees with the results of two previous coral culture experiments conducted at the same temperature but where ΩSW was not controlled. These results suggest that aragonite saturation has little or no influence on <span class="hlt">Sr/Ca</span> paleothermometry over the range of ΩSW investigated. Combined with existing data for low ΩSW conditions, our results were used to elucidate the mechanisms controlling calcifying fluid acid-base chemistry during coral biomineralization. Assuming that coral drive precipitation through alkalinity pumping, our data suggest that this pumping occurs until the calcifying fluid reaches a target pH. Below a threshold ΩSW bounded by 1 < ΩSW < 2.4, however, coral do not pump enough alkalinity to reach the target pH and instead pump a maximal but finite amount of alkalinity. In this low ΩSW regime, calcifying fluid pH is expected to decrease with ΩSW. The interplay between these two alkalinity pumping regimes and external seawater composition explain the full range of observed <span class="hlt">Sr/Ca</span> sensitivity to ΩSW and suggest that surface coral may become increasingly sensitive to ocean acidification below a threshold ΩSW bounded by 1 < ΩSW < 2.4.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7115609','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7115609"><span>Effect of cations on methane adsorption by NaY, MgY, <span class="hlt">Ca</span>Y, <span class="hlt">Sr</span>Y, and BaY zeolites</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Talu, O.; Zhang, S.Y.; Hayhurst, D.T. )</p> <p>1993-12-09</p> <p>Methane isotherms on NaY, MgY, <span class="hlt">Ca</span>Y, <span class="hlt">Sr</span>Y, and BaY zeolites are measured between 25 and 70[degree]C and upto 6760 kPa. All isotherms are of type I. The initial heat of adsorption for divalent cationic forms decreased with decreasing charge density (<span class="hlt">Ca</span>Y > MgY > <span class="hlt">Sr</span>Y > BaY) except for MgY. Similar anamoly was observed for methane adsorption on MgX (Zhang, S. Y.; Talu, O.; Hayhurst, D. T. J. Phys. Chem. 1991, 95, 1722) and it is attributed to incomplete dehydration (activation) at normal activation temperatures. The cation type significantly affected adsorption properties even at loadings as high as 7.5 molecules/cavity. <span class="hlt">Ca</span>Y has the largest capacity per weight, but the methane pore density decreased in order of decreasing cationic size (BaY > <span class="hlt">Sr</span>Y > <span class="hlt">Ca</span>Y > MgY > NaY) at 25[degrees]C and 5200 kPa fugacity. This unexpected result is attributed to possible differences in molecular packing around the cations at high loadings. The data were satisfactorily correlated by the virial isotherm model. 29 refs., 6 figs., 3 tabs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10105999','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10105999"><span>Melt processing of the Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub y} superconductor in oxygen and argon atmospheres</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Holesinger, T.G.; Miller, D.J.; Chumbley, L.S.</p> <p>1992-08-01</p> <p>Solidification and subsequent annealing of Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{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}<span class="hlt">Sr</span>{sub 3-x}<span class="hlt">Ca</span>{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 <span class="hlt">Ca</span>O segregation in the melt may be minimized with an overall composition such as Bi{sub 2.15}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>{sub 0.85}Cu{sub 2}O{sub y}.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/7134578','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/7134578"><span>Melt processing of the Bi[sub 2]<span class="hlt">Sr</span>[sub 2]<span class="hlt">Ca</span>Cu[sub 2]O[sub y] superconductor in oxygen and argon atmospheres</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Holesinger, T.G.; Miller, D.J. ); Chumbley, L.S. )</p> <p>1992-08-01</p> <p>Solidification and subsequent annealing of Bi[sub 2]<span class="hlt">Sr</span>[sub 2]<span class="hlt">Ca</span>Cu[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]<span class="hlt">Sr</span>[sub 3-x]<span class="hlt">Ca</span>[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 <span class="hlt">Ca</span>O segregation in the melt may be minimized with an overall composition such as Bi[sub 2.15]<span class="hlt">Sr</span>[sub 2]<span class="hlt">Ca</span>[sub 0.85]Cu[sub 2]O[sub y].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005APS..MAR.V1001S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005APS..MAR.V1001S"><span>Fourier Transform Inelastic Tunneling Spectroscopy of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+x</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Seamus Davis, J. C.</p> <p>2005-03-01</p> <p>Jinho Lee^1, K. McElroy^1,2, James Slezak^1, H. Eisaki^3, & S. Uchida^4 Inelastic electron tunneling spectroscopy (IETS) played a central role in determining that phonons were responsible for conventional superconductivity[1]. Since STM-based IETS can reveal local vibrational modes[2], and STM-based Fourier transform scanning tunneling spectroscopy (FT-STS) [3] can reveal momentum-space structure of elastic scattering processes[4], a combination of these techniques might be used to elucidate the momentum-space structure of electron-boson inelastic processes in cuprates[5]. Here we introduce this new STM technique, FT-IETS, in which we map the derivative of the differential conductance, d^2I/dV^2, with atomic resolution in the high-Tc superconductor Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δg. Fourier analysis is then used to search for the momentum-space structure of electron-boson interactions in this system [6]. 1. J.R. Schrieffer, D.J. Scalapino & J. Wilkins, Phys. Rev. Lett . 10, 336 (1963); W.L. McMillan & J.M. Rowell Phys. Rev. Lett. 14, 108 (1965). 2. B.C. Stipe et al Science 280, 1732 (1998) 3. J.E. Hoffman et al Science 266, 455 (2002) ; J.E. Hoffman et al Science 297, 1148 (2002). 4. K. McElroy et al Nature 422, 520 (2003). 5. J.-X. Zhu, J. Sun, Q. Si, and A. V. Balatsky Phys. Rev. Lett. 92, 017002 (2004) 6. Jinho Lee et al, Submitted. ^1 Department of Physics, Cornell University, Ithaca NY 14850, USA.^ 2Department of Physics, University of California, Berkeley, <span class="hlt">CA</span> 94720-7300, USA. ^3AIST, 1-1-1 Central 2, Umezono, Tsukuba, Ibaraki, 305-8568 Japan. ^4Department of Physics, University of Tokyo, Tokyo, 113-8656 Japan.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22451142','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22451142"><span>Monoclinic distortion and magnetic coupling in the double perovskite <span class="hlt">Sr</span>{sub 2−x}<span class="hlt">Ca</span>{sub x}YRuO{sub 6}</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bernardo, P.L.; Ghivelder, L.; Eslava, G.G.; Amorim, H.S.; Felner, I.; Garcia, S.</p> <p>2014-12-15</p> <p>Abstracts: This work investigates in the insulating double perovskites <span class="hlt">Sr</span>{sub 2−x}<span class="hlt">Ca</span>{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 <span class="hlt">Ca</span> 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 T<T{sub M}. - Graphical abstract: Tilting of the oxygen octahedra in <span class="hlt">Sr</span>{sub 2−x}<span class="hlt">Ca</span>{sub x}YRuO{sub 6} due to strong monoclinic distortions. - Highlights: • Neel temperatures in <span class="hlt">SrCa</span>YRuO were correlated quantitatively with lattice distortions. • Bending of Ru–O–Y planes plays a major role in the magnetic properties of <span class="hlt">SrCa</span>YRuO. • The structural–magnetic correlation is due to π–σ mixing of the magnetic orbitals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22803718','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22803718"><span>Regional variation in otolith <span class="hlt">Sr:Ca</span> ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lin, Y-J; Jessop, B M; Weyl, O L F; Iizuka, Y; Lin, S-H; Tzeng, W-N; Sun, C-L</p> <p>2012-07-01</p> <p>Otolith <span class="hlt">Sr:Ca</span> 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 <span class="hlt">Sr:Ca</span> ratios in the otolith edge differed significantly among rivers and had large effect sizes, but did not differ among sites within a river. Otolith <span class="hlt">Sr:Ca</span> ratios did not differ among rivers for A. marmorata. When rivers were pooled, the edge <span class="hlt">Sr:Ca</span> ratios of A. mossambica were not significantly different from those of A. marmorata. According to the river-specific critical <span class="hlt">Sr:Ca</span> 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 <span class="hlt">Sr:Ca</span> ratios affect the critical <span class="hlt">Sr:Ca</span> value and are a challenge for the reconstruction of migratory life histories that should be explicitly considered to avoid bias and uncertainty.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARP25007H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARP25007H"><span>Artificially induced hotspots in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8 mesa terahertz sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hao, Yang; Welp, Ulrich; Koshelev, Alexei; Vlasko-Vlasov, Vitalii; Kwok, Wai-Kwong; Kadowaki, Kazuo; Benseman, Timothy</p> <p></p> <p>Mesa-shaped devices comprising stacked Intrinsic Josephson Junctions (IJJs) in the high-temperature superconductor Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27982036','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27982036"><span>Interplay of Dirac electrons and magnetism in <span class="hlt">Ca</span>MnBi2 and <span class="hlt">Sr</span>MnBi2.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhang, Anmin; Liu, Changle; Yi, Changjiang; Zhao, Guihua; Xia, Tian-Long; Ji, Jianting; Shi, Youguo; Yu, Rong; Wang, Xiaoqun; Chen, Changfeng; Zhang, Qingming</p> <p>2016-12-16</p> <p>Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin-Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPhCS.667a2007M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.667a2007M"><span>Tilted vortex lattice in irradiate Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ single crystals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mirkovic, J.; Kakeya, I.; Savel'ev, S.; Kashiwagi, T.; Markovic, B.; Kadowaki, K.</p> <p>2016-01-01</p> <p>In order to enlighten the structure of vortex matter in irradiated layered Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ single crystals, the interaction of Josephson vortices and pancake vortices in was investigated by means of the local ac-magnetic permeability measurements by using the miniature local coils, while vortex matter in pristine crystals was studied by in-plane resistivity measurements. The transition anomaly, separating the strong pinning phase and the weak pinning vortex phase was found by both techniques deep in the vortex solid phase solid near ab-plane, indicating crossover from the vortex chains + lattice phase to tilted vortex chains phase. While the columnar defects affect strongly the first-order vortex-lattice melting transition, the magnetic permeability anomaly, associated with the crossover from vortex chains + lattice phase to tilted lattice, is surprisingly still clear, deep in the vortex solid phase. However, the stronger columnar defects eventually affect the crossover anomaly that it disappears too.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996PhyC..270..107O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996PhyC..270..107O"><span>AC transport losses in Ag sheathed (Bi,Pb) 2<span class="hlt">Sr</span> 2<span class="hlt">Ca</span> 2Cu 3O x tapes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oota, A.; Fukunaga, T.; Ito, T.</p> <p>1996-02-01</p> <p>The AC transport losses under self-fields have been investigated at 77 K on the Ag sheathed (Bi,Pb) 2<span class="hlt">Sr</span> 2<span class="hlt">Ca</span> 2Cu 3O x 19-filamentary untwisted and twisted (with a pitch of 13 mm) tapes, in comparison with the monofilamentary tape. The resistive voltages on the untwisted and twisted tapes show a dependence on the voltage-taps configuration, which is found in the monofilamentary tape. The AC transport losses per cycle for the tapes are nearly independent of frequency between 10 and 100 Hz, so that the main contribution to the losses comes from the hysteresis loss of superconductor in the same way as the monofilamentary tape. The twist of superconductor filaments causes no notable influence on the loss behaviors, and the results are explained by the theory of Norris for an elliptical superconductor with the same critical current, independent of whether or not the filaments are twisted. It is suggested that the distribution of transport currents in the filaments is not equalized in the twisted tape.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4895017','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4895017"><span>Bipartite electronic superstructures in the vortex core of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Machida, T.; Kohsaka, Y.; Matsuoka, K.; Iwaya, K.; Hanaguri, T.; Tamegai, T.</p> <p>2016-01-01</p> <p>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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900018478','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900018478"><span>Flux creep in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8(sub +x) single crystals</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Agostinelli, E.; Balestrino, G.; Fiorani, D.; Muzi, R.; Paroli, P.; Tejada, J.; Testa, A. M.</p> <p>1990-01-01</p> <p>The results of a magnetic study on a Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O(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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920012380','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920012380"><span>Composite superconducting wires obtained by high-rate tinning in molten Bi-Pb-<span class="hlt">Sr-Ca</span>-Cu-O system</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grosav, A. D.; Konopko, L. A.; Leporda, N. I.</p> <p>1991-01-01</p> <p>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(<span class="hlt">Sr,Ca</span>)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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatCo...713833Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatCo...713833Z"><span>Interplay of Dirac electrons and magnetism in <span class="hlt">Ca</span>MnBi2 and <span class="hlt">Sr</span>MnBi2</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Anmin; Liu, Changle; Yi, Changjiang; Zhao, Guihua; Xia, Tian-Long; Ji, Jianting; Shi, Youguo; Yu, Rong; Wang, Xiaoqun; Chen, Changfeng; Zhang, Qingming</p> <p>2016-12-01</p> <p>Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin-Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT........92Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT........92Y"><span>Quench Behavior and Degradation Limit of Ag-sheathed Bi 2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2Ox Round Wires</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ye, Liyang</p> <p></p> <p>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 Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2Ox (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.).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5172363','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5172363"><span>Interplay of Dirac electrons and magnetism in <span class="hlt">Ca</span>MnBi2 and <span class="hlt">Sr</span>MnBi2</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zhang, Anmin; Liu, Changle; Yi, Changjiang; Zhao, Guihua; Xia, Tian-long; Ji, Jianting; Shi, Youguo; Yu, Rong; Wang, Xiaoqun; Chen, Changfeng; Zhang, Qingming</p> <p>2016-01-01</p> <p>Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin–Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices. PMID:27982036</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/898547','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/898547"><span>Vanishing of phase coherence in underdopedBi_2<span class="hlt">Sr</span>_2<span class="hlt">Ca</span>Cu_2O_8+d</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Corson, John; Mallozzi, R.; Orenstein, J.; Eckstein, N.; Bozovic,I.</p> <p>1998-10-21</p> <p>Although the binding of electrons into Cooper pairs is essential in forming the superconducting state, its remarkable properties--zero resistance and perfect diamagnetism--require phase coherence among the pairs as well. When coherence is lost at the transition temperature Tc, pairing remains, together with phase correlations which are finite in space and time. In conventional metals, Cooper pairs with short-range phase coherence survive no more than 1 K above Tc. In underdoped high-Tc copper oxides, spectroscopic evidence for some form of pairing is found up to a temperature T*, which is roughly 100 K above Tc (refs 1,2,3). How this pairing and Cooper-pair formation are related is a central problem in high-Tc superconductivity. The nature of this relationship hinges on the extent to which phase correlations accompany pairing in the normal state4. Here we report measurements of high-frequency conductivity that track the phase-correlation time tau in the normal state of the Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+delta family of underdoped copper oxide superconductors. Just above Tc, we find that tau reflects the motion of thermally generated topological defects in the phase, or vortices5,6. However, vortex proliferation reduces tau to a value indistinguishable from the lifetime of normal-state electrons at 100 K, well below T*.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999Natur.398..221C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999Natur.398..221C"><span>Vanishing of phase coherence in underdoped Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corson, J.; Mallozzi, R.; Orenstein, J.; Eckstein, J. N.; Bozovic, I.</p> <p>1999-03-01</p> <p>Although the binding of electrons into Cooper pairs is essential in forming the superconducting state, its remarkable properties-zero resistance and perfect diamagnetism-require phase coherence among the pairs as well. When coherence is lost at the transition temperature T c, pairing remains, together with phase correlations which are finite in space and time. In conventional metals, Cooper pairs with short-range phase coherence survive no more than 1K above T c. In underdoped high-T c copper oxides, spectroscopic evidence for some form of pairing is found up to a temperature T *, which is roughly 100K above T c (refs 1,2,3). How this pairing and Cooper-pair formation are related is a central problem in high-T c superconductivity. The nature of this relationship hinges on the extent to which phase correlations accompany pairing in the normal state. Here we report measurements of high-frequency conductivity that track the phase-correlation timeτ in the normal state of the Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ family of underdoped copper oxide superconductors. Just above T c, we find that τ reflects the motion of thermally generated topological defects in the phase, or vortices,. However, vortex proliferation reduces τ to a value indistinguishable from the lifetime of normal-state electrons at 100K, well below T *.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/979041','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/979041"><span>A momentum-dependent perspective on quasiparticleinterference in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O_8+delta</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Vishik, I. M.</p> <p>2010-04-29</p> <p>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}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18502710','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18502710"><span>Structural analysis of a series of strontium-<span class="hlt">substituted</span> apatites.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>O'Donnell, M D; Fredholm, Y; de Rouffignac, A; Hill, R G</p> <p>2008-09-01</p> <p>A series of <span class="hlt">Sr-substituted</span> hydroxyapatites, (<span class="hlt">Sr(x)Ca</span>(1-)(x))(5)(PO(4))(3)OH, where x=0.00, 0.25, 0.50, 0.75 and 1.00, were made by a standard wet chemical route and investigated using X-ray diffraction (XRD), Rietveld refinement and Raman spectroscopy. We report apatites manufactured by two synthesis routes under 90 degrees C, and only the fully <span class="hlt">Sr-substituted</span> sample had a small amount of an impurity phase, which is believed to be strontium pyrophosphate. Lattice parameters (a and c), unit cell volume and density were shown to increase linearly with strontium addition and were consistent with the addition of a slightly larger and heavier ion (<span class="hlt">Sr</span>) in place of <span class="hlt">Ca</span>. XRD Lorentzian peak widths increased to a maximum at x=0.50, then decreased with increasing <span class="hlt">Sr</span> content. This indicated an increase in crystallite size when moving away from the x=0.50 composition (d approximately 9.4nm). There was a slight preference for strontium to enter the <span class="hlt">Ca</span>(II) site in the mixed apatites (6 to 12% depending on composition). The position of the Raman band attributed to v(1)PO(4)(3-) at around 963cm(-1) in hydroxyapatite decreased linearly to 949cm(-1) at full <span class="hlt">Sr-substitution</span>. The full width at half maximum of this peak also correlated well and increased linearly with increasing crystallite size calculated from XRD.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17149548','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17149548"><span>Shrinking of anionic polyacrylate coils induced by <span class="hlt">Ca</span>2+, <span class="hlt">Sr</span>2+ and Ba2+: a combined light scattering and ASAXS study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schweins, R; Goerigk, G; Huber, K</p> <p>2006-10-01</p> <p>Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations <span class="hlt">Ca</span>(2+), <span class="hlt">Sr</span>(2+) and Ba(2+). Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl(2)]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations <span class="hlt">Ca</span>(2+), <span class="hlt">Sr</span>(2+) and Ba(2+). Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected intermediates close to the precipitation threshold of <span class="hlt">Sr</span>PA were performed. The distribution of <span class="hlt">Sr</span> counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The <span class="hlt">Sr</span>(2+) scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [ <span class="hlt">Sr</span>Cl(2)]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22131138','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22131138"><span>Ternary <span class="hlt">Ca</span>Cu{sub 4}P{sub 2}-type pnictides AAg{sub 4}Pn{sub 2} (A=<span class="hlt">Sr</span>, Eu; Pn=As, Sb)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Stoyko, Stanislav S.; Khatun, Mansura; Scott Mullen, C.; Mar, Arthur</p> <p>2012-08-15</p> <p>Four ternary pnictides AAg{sub 4}Pn{sub 2} (A=<span class="hlt">Sr</span>, 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 <span class="hlt">Ca</span>Cu{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 <span class="hlt">Sr</span>Ag{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 <span class="hlt">Sr</span>Ag{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 <span class="hlt">Ca</span>Al{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 <span class="hlt">Sr</span>Ag{sub 4}As{sub 2} and <span class="hlt">Sr</span>Ag{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: <span class="hlt">Sr</span>Ag{sub 4}As{sub 2} and related pnictides adopt a <span class="hlt">Ca</span>Cu{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 <span class="hlt">Ca</span>Cu{sub 4}P{sub 2}-type structure. Black-Right-Pointing-Pointer Ag atoms are stuffed in trigonal planar sites within <span class="hlt">Ca</span>Al{sub 2}Si{sub 2}-type slabs. Black-Right-Pointing-Pointer Ag-Ag bonding develops through attractive d{sup 10}-d{sup 10} interactions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25765825','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25765825"><span>Luminescent nitridophosphates <span class="hlt">Ca</span>P2 N4 :Eu(2+) , <span class="hlt">Sr</span>P2 N4 :Eu(2+) , BaP2 N4 :Eu(2+) , and Ba<span class="hlt">Sr</span>2 P6 N12 :Eu(2.).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pucher, Florian J; Marchuk, Alexey; Schmidt, Peter J; Wiechert, Detlef; Schnick, Wolfgang</p> <p>2015-04-20</p> <p>Nitridophosphates MP2 N4 :Eu(2+) (M=<span class="hlt">Ca</span>, <span class="hlt">Sr</span>, Ba) and Ba<span class="hlt">Sr</span>2 P6 N12 :Eu(2+) have been synthesized at elevated pressures and 1100-1300 °C starting from the corresponding azides and P3 N5 with EuCl2 as dopant. Addition of NH4 Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single-crystal X-ray diffraction data (<span class="hlt">Ca</span>P2 N4 :Eu(2+) (P63 , no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) Å(3) , Z=24, 2033 observed reflections, 176 refined parameters, wR2 =0.096). Upon excitation by UV light, luminescence due to parity-allowed 4f(6) ((7) F)5d(1) →4f(7) ((8) S7/2 ) transition was observed in the orange (<span class="hlt">Ca</span>P2 N4 :Eu(2+) , λmax =575 nm), green (<span class="hlt">Sr</span>P2 N4 :Eu(2+) , λmax =529 nm), and blue regions of the visible spectrum (Ba<span class="hlt">Sr</span>2 P6 N12 :Eu(2+) and BaP2 N4 :Eu(2+) , λmax =450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline-earth ions. The corresponding full width at half maximum values (2240-2460 cm(-1) ) are comparable to those of other known Eu(2+) -doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba3 P5 N10 Br:Eu(2+) , this investigation represents the first report on the luminescence of Eu(2+) -doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu(2+) -doped nitridophosphates may have the potential to be further developed into efficient light-emitting diode phosphors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAP...118u3106Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAP...118u3106Y"><span>Improving γ-ray energy resolution, non-proportionality, and decay time of NaI:Tl+ with <span class="hlt">Sr</span>2+ and <span class="hlt">Ca</span>2+ co-doping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, K.; Menge, P. R.</p> <p>2015-12-01</p> <p>Commercially available thallium activated sodium iodide scintillators are typically characterized by a γ-ray energy resolution of 6.5% at 662 keV and a scintillation decay time constant of 230 ns. Energy resolution, non-proportionality, and scintillation decay time are improved when the crystal is co-doped with alkaline earth metals (<span class="hlt">Sr</span>2+ and <span class="hlt">Ca</span>2+). The energy resolution of NaI:Tl+ is improved to 5.3%, and the decay time is simultaneously reduced to 170 ns with <span class="hlt">Sr</span>2+ and <span class="hlt">Ca</span>2+ co-doping. The improvement in energy resolution, non-proportionality, and decay time are likely due to the suppression of the slow scintillation processes in NaI:Tl+.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhyC..484...77M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhyC..484...77M"><span>Crossover from crossing to tilted vortex phase in Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ single crystals near ab-plane</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mirkovic, Jovan; Buzdin, Alexandre; Kashiwagi, Takanari; Yamamoto, Takashi; Kadowaki, Kazuo</p> <p>2013-01-01</p> <p>In extremely anisotropic layered superconductors of Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ the stacks of vortex pancakes (PV) and the Josephson vortex (JV) interpenetrate, and due to PV-JV mutual pinning energy, weakly interact and form various tilted and crossing lattice structures including vortex chains, stripes, mixed chain + lattice phases, etc. In order to study these phenomena, it is decisive to have excellent quality of samples and the ideal experimental techniques. The vortex phases in high-quality Bi2<span class="hlt">Sr</span>2<span class="hlt">Ca</span>Cu2O8+δ single crystals were studied by in-plane resistivity measurement and local ac magnetic permeability. The sharp crossover was shown by both techniques, deep in the vortex solid state separating the Abrikosov dominant ‘strong pinning’ phase from the Josephson dominant ‘weak pinning’ phase. Those two vortex states were recognized as the mixed chain + lattice vortex phase and chains (tilted) vortex phase, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994PhyC..229..361I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994PhyC..229..361I"><span>Oxygen nonstoichiometry and Tc of the La 2- xM xM‧Cu 2O y (M, M‧ = <span class="hlt">Sr</span>, <span class="hlt">Ca</span>) superconductor</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Idemoto, Yasushi; Ohara, Mitsuo; Fueki, Kazuo</p> <p>1994-08-01</p> <p>The 326 superconducting oxide La x- xM xM‧Cu 2O y (M, M‧ = <span class="hlt">Sr</span>, <span class="hlt">Ca</span>) was annealed under various conditions and the copper valence was determined by chemical analysis. It was found that the copper valence of LSSCO is twice as high as that of LSCCO and LCCCO for the same composition x and oxygen annealing condition. Both Tc on and Tc zero of LSCCO increased with increasing copper valence, while LSSCO did not exhibit superconduction. The site preference parameter S indicated that <span class="hlt">Ca</span> strongly prefers the 2a site but that <span class="hlt">Sr</span> prefers both 2a and 4e sites almost equally. The high copper valence of LSSCO was interpreted in terms of S.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ApSS..378..136Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApSS..378..136Z"><span>Micro-oxidation treatment to improve bonding strength of <span class="hlt">Sr</span> and Na co-<span class="hlt">substituted</span> hydroxyapatite coatings for carbon/carbon composites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Leilei; Li, Hejun; Li, Kezhi; Zhang, Yulei; Liu, Shoujie; Guo, Qian; Li, Shaoxian</p> <p>2016-08-01</p> <p>To improve the bonding strength of <span class="hlt">Sr</span> and Na co-<span class="hlt">substituted</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1163907','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1163907"><span>Combined effects of transition metal (Ni and Rh) <span class="hlt">substitution</span> and annealing/quenching on the physical properties of <span class="hlt">Ca</span>Fe2As2</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ran, S; Bud'ko, S L; Straszheim, W E; Canfield, P C</p> <p>2014-08-01</p> <p>We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T=Ni, Rh <span class="hlt">substitution</span> (x) on the physical properties of <span class="hlt">Ca</span>(Fe1-xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both <span class="hlt">substitutions</span> to map out the relations between ground states and compared them with that of Co <span class="hlt">substitution</span>. Ni <span class="hlt">substitution</span>, which brings one more extra electron per <span class="hlt">substituted</span> atom and suppresses the c-lattice parameter at roughly the same rate as Co <span class="hlt">substitution</span>, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as that found for Co <span class="hlt">substitution</span>, 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-<span class="hlt">substituted</span> BaFe2As2 are compared. On the other hand, Rh <span class="hlt">substitution</span>, which brings the same amount of extra electrons as does Co <span class="hlt">substitution</span>, 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 <span class="hlt">substitution</span> there was no difference between phase diagrams for samples annealed for 1 or 7 days, for Ni and Rh <span class="hlt">substitutions</span> a second, reversible effect of annealing was revealed by 7-day anneals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880041646&hterms=superconductivity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsuperconductivity','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880041646&hterms=superconductivity&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dsuperconductivity"><span>Superconductivity up to 114 K in the Bi-Al-<span class="hlt">Ca-Sr</span>-Cu-O compound system without rare-earth elements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chu, C. W.; Bechtold, J.; Gao, L.; Hor, P. H.; Huang, Z. J.</p> <p>1988-01-01</p> <p>Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-<span class="hlt">Ca-Sr</span>-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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26979077','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26979077"><span>Potential roles for calcium-sensing receptor (<span class="hlt">CaSR</span>) and transient receptor potential ankyrin-1 (TRPA1) in murine anorectic response to deoxynivalenol (vomitoxin).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wu, Wenda; Zhou, Hui-Ren; Pestka, James J</p> <p>2017-01-01</p> <p>Food contamination by the trichothecene mycotoxin deoxynivalenol (DON, vomitoxin) has the potential to adversely affect animal and human health by suppressing food intake and impairing growth. In mice, the DON-induced anorectic response results from aberrant satiety hormone secretion by enteroendocrine cells (EECs) of the gastrointestinal tract. Recent in vitro studies in the murine STC-1 EEC model have linked DON-induced satiety hormone secretion to activation of calcium-sensing receptor (<span class="hlt">CaSR</span>), a G-coupled protein receptor, and transient receptor potential ankyrin-1 (TRPA1), a TRP channel. However, it is unknown whether similar mechanisms mediate DON's anorectic effects in vivo. Here, we tested the hypothesis that DON-induced food refusal and satiety hormone release in the mouse are linked to activation of <span class="hlt">CaSR</span> and TRPA1. Oral treatment with selective agonists for <span class="hlt">CaSR</span> (R-568) or TRPA1 (allyl isothiocyanate (AITC)) suppressed food intake in mice, and the agonist's effects were suppressed by pretreatment with corresponding antagonists NPS-2143 or ruthenium red (RR), respectively. Importantly, NPS-2143 or RR inhibited both DON-induced food refusal and plasma elevations of the satiety hormones cholecystokinin (CCK) and peptide YY3-36 (PYY3-36); cotreatment with both antagonists additively suppressed both anorectic and hormone responses to DON. Taken together, these in vivo data along with prior in vitro findings support the contention that activation of <span class="hlt">CaSR</span> and TRPA1 contributes to DON-induced food refusal by mediating satiety hormone exocytosis from EEC.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10161064','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10161064"><span>Vortex line pinning in Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub 8} single crystals with columnar defects</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>van der Beek, C.J.; Vinokur, V.M.; Crabtree, G.W.; Schmidt, B.; Konczykowski, M.</p> <p>1994-05-01</p> <p>The ac transmittivity of heavy-ion irradiated Bi{sub 2}<span class="hlt">Sr</span>{sub 2}<span class="hlt">Ca</span>Cu{sub 2}O{sub 8} single crystals shows a sharp cusp as function of the dc field orientation with respect to the columnar defects. This unambiguously demonstrates the connected nature of vortices in these samples. In contrast, the irreversibility line does not reveal a cusp.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1326842-strong-magnetic-correlations-single-crystals-trigonal-antiferromagnetic-insulators-srmn2as2-camn2as2','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1326842-strong-magnetic-correlations-single-crystals-trigonal-antiferromagnetic-insulators-srmn2as2-camn2as2"><span>Strong magnetic correlations to 900 K in single crystals of the trigonal antiferromagnetic insulators <span class="hlt">Sr</span>Mn2As2 and <span class="hlt">Ca</span>Mn2As2</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; ...</p> <p>2016-09-15</p> <p>Crystallographic, electronic transport, thermal, and magnetic properties are reported for <span class="hlt">Sr</span>Mn2As2 and <span class="hlt">Ca</span>Mn2As2 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 <span class="hlt">Ca</span>Al2Si2-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 <span class="hlt">Sr</span>Mn2As2 and 61 meV for <span class="hlt">Ca</span>Mn2As2. 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 <span class="hlt">Sr</span>Mn2As2 and <span class="hlt">Ca</span>Mn2As2, 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 <span class="hlt">Sr</span>Mn2As2 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GGG....17..846V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GGG....17..846V"><span>Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral <span class="hlt">Sr/Ca</span> records</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>von R