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1

Evolution of normal-state magnetic fluctuations by Ca and Ti substitutions in Sr2RuO4: 87Sr-NMR study  

NASA Astrophysics Data System (ADS)

We report magnetic properties of (Sr2-xCax)RuO4 and Sr2(Ru1-yTiy)O4 investigated by 87Sr nuclear magnetic resonance NMR to shed light on the effect of multibands on the magnetic character in the spin-triplet superconductor Sr2RuO4. In (Sr2-xCax)RuO4, the Knight shift (87K) at 1.4 K increases progressively up to x=1.5. The Korringa relation between K and the nuclear-spin-lattice-relaxation rate 1/T1 divided by temperature (1/T1T) reveals that ferromagnetic (FM) fluctuations develop with the increasing Ca content. In Sr2(Ru1-yTiy)O4, in contrast, it is found that anisotropic incommensurate (IC) antiferromagnetic (AFM) fluctuations present in the y=0 material are enhanced by a small amount of Ti substitution: 1/T1T is enhanced with the magnetic field parallel to the RuO2 plane, whereas it is unchanged for the field along the c axis in 3% Ti-doped Sr2RuO4. We demonstrate that Ca substitution affects the two-dimensional (2D) ? band by enhancing the FM fluctuations, and that the Ti-substitution affects the 1D ? and ? bands by enhancing the IC-AFM fluctuations. The unique substitution effects would relate with the multiband character in Sr2RuO4.

Ishida, K.; Minami, Y.; Kitaoka, Y.; Nakatsuji, S.; Kikugawa, N.; Maeno, Y.

2003-06-01

2

Chemistry and valence of Sb-substitution for Bi in high Tc Bi1-xSbxSrCaCu2Oy and Bi2-xSbxSr2CaCu2Oy superconductors  

Microsoft Academic Search

The effect of Sb-substitution for Bi has been studied in the high Tc superconducting materials Bi1-xSbxSrCaCu2Oy (Tc ~ 70 K) and Bi2-xSbxSr2CaCu2Oy (Tc ~ 100 K). For materials synthesized in an oxidizing atmosphere the solubility o f Sb is quite low and its substitution for Bi leads to a complex chemistry which results in the depression of Tc with increasing

W. Peng; R. H. Hannon; H. Lee; A. P. Genis; V. J. Melim; C. W. Kimball; B. Dabrowski; D. G. Hinks

1989-01-01

3

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

SciTech Connect

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

Yamauchi, Hisao [Laboratory of Inorganic Chemistry, Department of Chemistry, Aalto University, FI-00076 AALTO (Finland); Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Karvonen, Lassi [Laboratory of Inorganic Chemistry, Department of Chemistry, Aalto University, FI-00076 AALTO (Finland); Egashira, Takayuki; Tanaka, Yoshiaki [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Karppinen, Maarit, E-mail: maarit.karppinen@tkk.f [Laboratory of Inorganic Chemistry, Department of Chemistry, Aalto University, FI-00076 AALTO (Finland); Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan)

2011-01-15

4

Superconducting order parameter in partially substituted Bi2Sr2CaCu2O8+x single crystals as measured by the tunneling effect  

NASA Astrophysics Data System (ADS)

Tunneling-spectroscopy measurements have been performed on pure and Ni- and Zn-substituted Bi2Sr2CaCu2O8+x single crystals using a scanning tunneling microscope and a break-junction setup. The superconducting energy gap for the Ni-doped samples was found to be larger with respect to the pure samples. Anomalies have also been found in the temperature dependence of the gap for the Ni-substituted samples.

Hancotte, H.; Deltour, R.; Davydov, D. N.; Jansen, A. G. M.; Wyder, P.

1997-02-01

5

Substitution sites of Pb and Y in Bi2Sr2Ca1Cu2O8+delta: X-ray photoelectron diffraction as fingerprinting tool  

Microsoft Academic Search

The substitution site of Y and Pb in the cuprate-type high temperature superconductor Bi2Sr2Ca1Cu2O8+delta is determined in a very direct and unambiguous way by means of angle-scanned x-ray photoelectron diffraction (XPD). Using XPD as a fingerprinting tool, we conclude that Y occupies the Ca sites and Pb the Bi sites, respectively. Furthermore, low-energy electron diffraction data unequivocally show the presence

Th. Pillo; J. Hayoz; P. Schwaller; H. Berger; P. Aebi; L. Schlapbach

1999-01-01

6

Fingerprinting substitution sites in Pb,Dy-Bi_2Sr_2Ca_1Cu_2O8+delta using X-ray Photoelectron Diffraction  

Microsoft Academic Search

The substitution sites of Pb and Dy dopants in the cuprate-type high temperature superconductor Bi2Sr2Ca1Cu2O{8+delta} are determined by a direct comparison of the angle-scanned X-ray photoelectron diffraction (XPD) patterns. We demonstrate the power of XPD as a fingerprinting tool and conclude that Pb occupies Bi sites and Dy the Ca sites. The presence of the incommensurate lattice modulation is not

D. Popovic; M. Bovet; H. Berger; P. Aebi

2005-01-01

7

Relaxation of substitutive atoms in manganites La2/3A1/3MnO3, with A=Ca, Sr and Ba  

NASA Astrophysics Data System (ADS)

We have studied an internal friction (IF) peak at 400 K which appears when site A in manganite type ABO3 is partially substituted by Ca, Sr and Ba atoms. In the case of total substitution in CaMnO3, the 400 K peak is absent. The appearance and the increase of this peak measured in La1-xCaxMnO3 manganites with x= 0, 0.1, 0.2 and 0.33, reported in Salva et al. Physica B 384 (2006) 62], was associated to a Zener relaxation of the cations occupying equivalent crystallographic sites. In La2/3Sr1/3MnO3 and La2/3Ba1/3MnO3 compounds, the 400 K peak is also observed [S.S. Seiro, A.A. Ghilarducci, H.R. Salva, M. Vasquez Mansilla, M. Saint-Paul, P. Lejay, P. Monceau, J. Magn. Magn. Mater. 226 230 (2001) 988; H.R. Salva, P. Monceau, A. Ghilarducci, S. Seiro, M. Saint Paul, P. Lejay. Physica B 320 (2002) 97] [2,3], with activation enthalpies between 4 and 6 eV. We analyse both the increase of IF maxima and relaxation strength with the increase of the substitutional atom size (1.26, 1.39 and 1.56 Å for Ca, Sr and Ba atoms, respectively); and with the increase of the Goldschmidt tolerance factor. This behaviour is comprehensible because the intensity of the Zener relaxation depends on the distortions introduced by pairs of substitutional atoms.

Salva, H. R.; Seiro, S. S.; Ghilarducci, A. A.

2007-09-01

8

Structure and conductivity investigations of alkaline earth substituted uranium oxide, U 1 ? x M x O 2 ± ? (M = Mg, Ca, Sr) for solid oxide fuel cell applications  

Microsoft Academic Search

Alkaline earth substituted UO2 (U1?xMxO2±?; M=Mg, Ca, Sr; 0.1?x?0.525) with fluorite structure was synthesized in reducing atmosphere. Structure and conductivity properties of U1?xMxO2±? fluorites were investigated for possible application in solid oxide fuel cells (SOFC). At room temperature and ambient atmosphere the materials are stable; however they decompose at an oxygen partial pressure pO2>10?4 atm and temperatures higher than 600

H. Runge; M. Greenblatt

2006-01-01

9

Study of the yttrium and zinc substitutions effects in Bi2Sr2CaCu2O8+? compounds by transport measurements  

NASA Astrophysics Data System (ADS)

The effects of yttrium Y and zinc Zn substitution on calcium Ca and cupper Cu sites in Bi2Sr2CaCu2O8+? compounds have been investigated by resistivity measurements. At high temperature, after a superconducting transition, the electrical behaviour evolves from a metallic state in compounds with a weak Y concentration into a semi-conducting state (hopping conduction) in compounds with a large Y concentration. Similarly, the Zn substitution modifies the electrical behaviour from metallic to insulating with a much lower concentration comparatively to Y. In the two cases, the semi-conducting behaviour is described by hopping between localised states in the conduction band. This localization is explained by the random distribution of the doping elements which originates from the Y/Zn and Cu wave-functions overlap. The obtained results show the localization is improved in the case of Zn. Consequently, it is suggested that the direct substitution of Zn into the planes leads to a greater overlap. Moreover, the superconducting transition (critical temperature: TC) shows an irregular depression when Zn is substituted. According to an X-Ray diffraction study, this result can be interpreted by internal micro-strains in the structure.

Pignon, B.; Autret-Lambert, C.; Ruyter, A.; Decourt, R.; Bassat, J. M.; Monot-Laffez, I.; Ammor, L.

2008-06-01

10

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

SciTech Connect

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

Seshadri, R.; Maignan, A.; Hervieu, M. [ISMRA et Universite de Caen (France)] [and others

1996-11-15

11

Sr-substituted hydroxyapatites for osteoporotic bone replacement.  

PubMed

Porous apatites, which during resorption can release in situ Sr ions, were prepared to associate an anti-osteoporotic action with the peculiar features of the inorganic phase constituting the bone. Sr-substituted hydroxyapatite (SrHA) powder was directly synthesized using the classical neutralization route, but including Sr ions, and characterized. The higher solubility of SrHA granules of 400-600 microm size, potentially usable as a bone filler, was assessed compared with that of analogous stoichiometric HA granules. The Sr released in synthetic body fluid became constant after 1 week. The Ca release is improved for SrHA compared with stoichiometric HA, due to the higher solubility of the first material. Porous scaffolds with micro-macro interconnected porosity, which mimic the morphology of the spongy bone, were prepared by the impregnation of cellulose sponges with suspensions of the powder and a specific sintering process. A compressive strength of 4.52+/-1.40 MPa was obtained for SrHA scaffolds characterized with 45 vol.% of porosity. Promising biomedical applications, such as resorbable bone filler or bone substitute releasing in situ Sr ions for a prolonged time, can be hypothesized for the SrHA materials when pathologies related with Sr deficiency are present. PMID:17618844

Landi, Elena; Tampieri, Anna; Celotti, Giancarlo; Sprio, Simone; Sandri, Monica; Logroscino, Giandomenico

2007-06-19

12

Superconducting order parameter in partially substituted Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} single crystals as measured by the tunneling effect  

SciTech Connect

Tunneling-spectroscopy measurements have been performed on pure and Ni- and Zn-substituted Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} single crystals using a scanning tunneling microscope and a break-junction setup. The superconducting energy gap for the Ni-doped samples was found to be larger with respect to the pure samples. Anomalies have also been found in the temperature dependence of the gap for the Ni-substituted samples. {copyright} {ital 1997} {ital The American Physical Society}

Hancotte, H.; Deltour, R. [Universite Libre de Bruxelles, Service de Physique des Solides, CP233, Boulevard du Triomphe, B-1050 Brussels (Belgium); Davydov, D.N.; Jansen, A.G.; Wyder, P. [Grenoble High Magnetic Field Laboratory, Max-Planck-Institut fuer Festkoerperforschung and Centre National de la Recherche Scientifique, Boite Postale 166, F38042 Grenoble Cedex 9 (France)

1997-02-01

13

Structure-microwave property relations of Ca and Sr titanates  

Microsoft Academic Search

The microwave dielectric properties of the SrxCa1?xTiO3, Srn+1TinO3n+1 and (SrxCa1?x)3Ti2O7 series have been measured. TCF decreases from +1647 to +859 MK?1 as Ca content increases in the SrxCa1?xTiO3 series, due to the onset of octahedral tilt transitions. Additions of excess SrO to SrTiO3 form the Srn+1TinO3n+1 series with Q a maximum for Sr3Ti2O7. Ca substitutions to Sr3Ti2O7 result in a

P. L Wise; I. M Reaney; W. E Lee; T. J Price; D. M Iddles; D. S Cannell

2001-01-01

14

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

SciTech Connect

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.

Menassel, S.; Mosbah, M-F.; Altintas, S. P.; Varilci, A.; Bouaicha, F. [Universite Mentouri. Laboratoire Couches Minces et Interfaces. Route de Ain el Bey - 25017 Constantine (Algeria); Abant Izzet Baysal University. Department of Physics. 14280 Bolu. (Turkey)

2012-09-06

15

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

NASA Astrophysics Data System (ADS)

Superconducting Bi2Sr2Ca1-xYxCu2O8 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.

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

2012-09-01

16

Superconductivity in Bi-Sr-Ca-Mg-Cu-oxide  

SciTech Connect

This paper reports on a Mg-substituted material with nominal composition Bi{sub 2}Sr{sub 2}Ca{sub 3}Mg{sub 2}Cu{sub 6}O{sub x}, prepared by partial substitution of Ca by isovalent Mg in the 2256 composition of Bi-Sr-Ca-Cu-O, studied by the measurements of electrical resistance, magnetic susceptibility and x-ray diffraction pattern. Results show the existence of a superconducting phase with onset T{sub c} at 112l.5 {plus minus} 1 K along with a minor phase with onset T{sub c} = 88 K. The material retained superconducting characteristics (Meissner effect and T{sub c}{sup onset}) even after a period of six months.

Khan, A.Y.; Mohammad, M.; Shahnaz, M. (Dept. of Chemistry, Quaid-i-Azam Univ., Islamabad (PK)); Hasnain, S.K. (Dept. of Physics, Quaid-i-Azam Univ., Islamabad (PK))

1991-05-10

17

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

SciTech Connect

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.

Patapis, S.K.; Sideridis, L.; Apostolopoulos, G. (Athens Univ. (Greece). Dept. of Physics); Ausloos, M. (Liege Univ. (Belgium). Inst. de Physique); Luo, H.L. (California Univ., San Diego, La Jolla, CA (United States). Dept. of Electrical and Computer Engineering); Politis, C. (Kernforschungszentrum Karlsruhe GmbH (Germany). Inst. fuer Nukleare Festkoerperphysik); Puig, T.; Pont, M.; Munoz, J.S. (Univ

1991-01-01

18

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

SciTech Connect

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.

Patapis, S.K.; Sideridis, L.; Apostolopoulos, G. [Athens Univ. (Greece). Dept. of Physics; Ausloos, M. [Liege Univ. (Belgium). Inst. de Physique; Luo, H.L. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Electrical and Computer Engineering; Politis, C. [Kernforschungszentrum Karlsruhe GmbH (Germany). Inst. fuer Nukleare Festkoerperphysik; Puig, T.; Pont, M.; Munoz, J.S. [Universidad Autonoma de Barcelona (Spain). Dept. of Physics; Balachadran, U. [Argonne National Lab., IL (United States)

1991-12-31

19

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

NASA Astrophysics Data System (ADS)

Coral skeletal Sr/Ca is a commonly used palaeothermometer and has been used to estimate past sea surface temperatures. However the processes controlling Sr incorporation in coral aragonite are poorly understood. The Sr/Ca chemistry of the massive Porites spp. corals typically used for palaeoenvironmental reconstruction is dominated by short-term (weekly-monthly) oscillations of ~10% which do not reflect seawater temperature. This heterogeneity may reflect variations in the composition of the fluid used for calcification. Coral skeletons precipitate from an extracellular calcifying fluid enclosed in a semi-isolated space between the skeleton and the calicoblastic epithelium (the tissue layer at the base of the coral organism). Seawater diffuses directly to the calcification site and the calcification fluid has a composition derived from that of seawater but modified by other transport processes. In zooxanthellate corals, Ca2+ is transported transcellularly to the calcification site by both calcium channels and by the carrier protein Ca-ATPase. Sr2+ has a similar ionic radius to Ca2+, but it is not clear if Sr2+ can substitute for Ca2+ in these transport mechanisms. Variations in the relative contributions of each of the transport mechanisms to the calcification fluid and the efficiencies with which each process transports Sr2+ and Ca2+ could explain the Sr/Ca heterogeneity observed in coral skeletons. To test the impact of transcellular Ca transport processes on skeletal Sr/Ca and Mg/Ca we cultured Pocillopora damicornis corals in the presence of inhibitors of Ca-ATPase (ruthenium red) and Ca channels (verapamil). The photosynthesis, respiration and calcification rates of the colonies were monitored throughout the experiment. The skeleton subsequently deposited was identified (by 42Ca spike) and analysed by secondary ion mass spectrometry. The Sr/Ca and Mg/Ca of the aragonite deposited in the presence of either of the inhibitors was not significantly different from that of the control, although the coral calcification rate was reduced by up to 66 and 73% in the ruthenium red and verapamil treatments respectively. The typical precision (95% confidence limits) of mean Sr/Ca determinations within any one treatment was ±0.8% and differences in mean Sr/Ca between treatments were correspondingly small. Either Ca-ATPase and Ca channels transport Sr2+ and Ca2+ in virtually the same ratio in which they are present in seawater or any preferential transport of Ca2+ by these processes is so limited as to be insignificant i.e. transcellularly transported Ca contributes little to the total Ca at the calcification site. This suggests that variations in the activities of Ca-ATPase and Ca-channels are not responsible for the short term Sr/Ca heterogeneity observed in coral skeletons or for the differences in mean Sr/Ca which are observed between colonies growing at different rates.

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

2010-12-01

20

The effect of Ca substitution on the structural and electrical properties of La0.7Sr0.3-xCaxMnO3 perovskite manganite films  

NASA Astrophysics Data System (ADS)

This study demonstrates the effect of a Ca substituent for Sr on the structural, chemical, and electrical properties in La0.7Sr0.3-xCaxMnO3 perovskite manganite films. The structural modification of films was found to be affected by the amount of Ca substituent. Raman spectroscopy analysis reveals a decrease of bond angle and an increase of Jahn-Teller type distortion in MnO6 octahedra with increasing Ca. The resistance value of high resistance state, switching voltage and resistive switching ratio of La0.7Sr0.3-xCaxMnO3 films decreased with increasing amounts of Ca substituent. The relationships among structural, interfacial, and electrical properties including resistive switching behaviour of La0.7Sr0.3-xCaxMnO3 were examined.

Choi, Sun Gyu; Lee, Hong-Sub; Choi, Hyejung; Chung, Sung-Woong; Park, Hyung-Ho

2013-10-01

21

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

PubMed

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. PMID:23674327

Singh, Navneet; Chakrabarty, Subhas

2013-06-08

22

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

PubMed

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 of metals on avian reproduction in regions with high Sr deposits in rock and soil, Sr concentrations in the eggshell also should be measured to evaluate additional effects on thickness and reproduction. PMID:21660600

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

2011-06-10

23

Allometric constraints on Sr\\/Ca and Ba\\/Ca partitioning in terrestrial mammalian trophic chains  

Microsoft Academic Search

In biological systems, strontium (Sr) and barium (Ba) are two non-essential elements, in comparison to calcium (Ca) which is essential. The Sr\\/Ca and Ba\\/Ca ratios tend to decrease in biochemical pathways which include Ca as an essential element, and these processes are termed biopurification of Ca. The quantitative pathway of the biopurification of Ca in relation to Sr and Ba

Vincent Balter

2004-01-01

24

Are seawater Sr/Ca variations preserved in Quaternary foraminifera?  

SciTech Connect

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.

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

1999-11-01

25

Structural and Magnetic Characterisation of the Double Perovskites AA?MnWO 6 (AA? = Ba 2 , SrBa, Sr 2 , SrCa and Ca 2 )  

Microsoft Academic Search

The double perovskites AA' MnWO 6 (AA' = Ba 2 , SrBa, Sr 2 , SrCa and Ca 2 ) have been prepared as pure powders by a conventional solid-state reaction process. Stoichiometric amounts of BaCO 3 , SrCO 3 , CaCO 3 , MnO and WO 3 were mixed, ground and calcined in a nitrogen atmosphere. The materials have

A. K. Azad; S.-G. Eriksson; S. A. Ivanov; H. Rundlöf; J. Eriksen; R. Mathieu; P. Svedlindh

2002-01-01

26

Interstitial and substitutional Zr in SrTiO3  

NASA Astrophysics Data System (ADS)

We investigate Zr in SrTiO3 (STO) as an electronic dopant and as a model for nuclear waste forms in which radioactive Sr decays to Y and then to stable Zr through beta emission. Density functional theory (DFT) within the supercell model is used to predict the thermodynamic stability and electronic states of interstitial and Sr- or Ti-substituted Zr atoms in the STO lattice. Native point defects such as vacancies and antisites are also considered. When Zr replaces Sr, its most stable configuration is to simply occupy the Sr site (instead of, for example, replacing a Ti and displacing the Ti to the Sr site.) For Zr added to the lattice, its most stable configuration is to replace a Ti, making a ZrTi impurity plus a Ti interstitial (as opposed to the Zr just remaining as an interstitial atom.) ZrSr is predicted to be a double electron donor, ZrTi is electrically inactive and interstitial Zr and Ti are predicted to be quadruple donors, with all donor levels in the conduction band. ZrSr and the tetravalent interstitials are all predicted to increase the crystal volume, and the interstitials also are predicted to lead to a tetragonal distortion of the lattice. Experiments with injection of Zr atoms into STO qualitatively confirm these predictions of crystal structural changes.

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

2011-03-01

27

Interstitial and substitutional zirconium in SrTiO3  

SciTech Connect

We investigate Zr in SrTiO3 (STO) as a model for nuclear waste forms in which the fission product Sr90 eventually decays to stable Zr through beta emission. The transformation of a divalent into a tetravalent constituent is expected to affect the long-term structural and chemical stability of this solid. Computational methods of electronic structure theory, specifically the density functional theory (DFT) within the supercell model, are used to predict the thermodynamic stability and electronic states of interstitial and Sr- or Ti-substituted Zr atoms in the STO lattice. Native defects such as vacancies and antisites are also considered. When Zr replaces Sr, its most stable configuration is to simply occupy the Sr site (instead of, for example, replacing a Ti and displacing the Ti to the Sr site.) For Zr added to the lattice, its most stable configuration is to replace a Ti, making a ZrTi impurity plus a Ti interstitial (as opposed to the Zr just remaining as an interstitial atom.) ZrSr is predicted to be a double electron donor, ZrTi is electrically inactive and interstitial Zr and Ti are predicted to be quadruple donors, with all donor levels in the conduction band. ZrSr and the tetravalent interstitials are all predicted to increase the crystal volume, and the interstitials also are predicted to lead to a tetragonal distortion of the lattice. Experiments with injection of Zr atoms into STO qualitatively confirm these predictions of crystal structural changes.

Jaffe, John E.; Van Ginhoven, Renee M.; Jiang, Weilin

2012-02-22

28

Temperature Dependent Sr-Isotope (? 88Sr) and Ca-Isotope (? 44Ca) Fractionation in Carbonate Precipitates and Corals  

NASA Astrophysics Data System (ADS)

The knowledge of the influence of temperature and other environmental factors on isotope fractionation of divalent cations like Ca2+ and Sr2+ during inorganic and biogenic controlled precipitation of calcium carbonate is crucial for their interpretation as paleo proxies. In order to extend our earlier studies on Ca-isotope fractionation (e.g. Gussone et al., 2003), we determined ? 88Sr isotope ratios on seawater and on corals. We define the stable Sr isotope ratio as ? 88Sr=((88Sr/86Sr)Sample/(88Sr/86Sr)Standard -1)*1000; Sr Standard is NBS 987. First measurements of the IAPSO seawater standard result in ? 88Sr of 0.38+/-0.02 ‰ . Coral CaCO3 precipitated from seawater in a temperature range from about 22° C to about 27° C correspond to ? 88Sr-values ranging from 0.17 ‰ to about 0.32 ‰ indicating that carbonate precipitated from seawater is isotopically lighter than seawater itself. The slope of 0.027 ‰ /° C for the temperature-? 88Sr relationship in corals is about a factor of 1.7 larger than the slope of ? 44Ca ratios in inorganically precipitated aragonite. However, the fractionation ? (T)=((88Sr/86Sr)CaCO3)/(88Sr/86Sr)Seawater) at a given temperature is about one order of magnitude less for Sr-isotopes relative to Ca-isotopes. The larger temperature-? 88Sr gradient in comparison to the Ca-isotopes is interpreted to reflect the smaller ion potential and the correspondingly smaller mass of the associated Sr2+-aquocomplex. The observation that ? 88Sr and ? 44Ca are positively correlated with temperature points to the likelihood that kinetic or equilibrium fractionation effects and the mass of the associated acquocomplex control the degree of divalent cation isotope fractionation during CaCO3-precipitation. Reference: Gussone N., Eisenhauer A., Heuser A., Dietzel M., Bock B., Böhm F., Spero H., Lea D. W., Bijma J., and Nägler T. F. (2003) Model for Kinetic Effects on Calcium Isotope Fractionation (? 44Ca) in Inorganic Aragonite and Cultured Planktonic Foraminifera. Geochim Cosmochim Acta 67(7), 1375-1382.

Eisenhauer, A.; Fietzke, J.; Gussone, N.; Böhm, F.; Bock, B.; Nägler, T.

2003-12-01

29

Metabolism controls Sr/Ca ratios in fossil aragonitic mollusks  

NASA Astrophysics Data System (ADS)

Sr/Ca and Mg/Ca ratios in biomineral CaCO3 have recently been regarded as more reliable than ?18O values as proxy for paleotemperature because they are less affected by salinity or polar ice volume. We argue, however, that vital effects can exert a greater control than paleotemperature over fossil Sr/Ca. Seasonal perturbations in isotopic data from the Eocene bivalve Venericardia planicosta reveal a gradually decreasing annual growth rate through ontogeny. High-resolution Sr/Ca ratios, analyzed with a new proton-microbe technique, increase markedly through ontogeny, however, suggesting that more Sr was incorporated as growth rate slowed rather than as a result of changing paleotemperature. Comparative ?18O and Sr/Ca data from the broadly coeval marine gastropod Clavilithes macrospira, which exhibits a linear growth rate through ontogeny, also shows a significant increase in Sr concentration with age as well as seasonal, possibly temperature-related variations. Our observations show that neither growth, calcification rate, nor temperature can be the sole factor controlling Sr incorporation into molluscan aragonite. Metabolic activity, related to factors such as temperature, salinity, age, and growth rate, is likely to exert the primary control over Sr/Ca ratios in aragonitic mollusks.

Purton, Louise M. A.; Shields, Graham A.; Brasier, Martin D.; Grime, Geoff W.

1999-12-01

30

Enhanced dielectric properties and sinterability of CaCu3Ti4O12 ceramics by Sr2+ doping  

NASA Astrophysics Data System (ADS)

CaCu3Ti4O12 ceramics substituted by Sr2+ for Ca2+ were prepared by the solid state reaction method. It was found that Sr2+ substitution increased the lattice constant of CaCu3Ti4O12 in a consistent manner. The dielectric properties, sinterability, and microstructures of the Ca1-xSrxCu3Ti4O12 ceramics were investigated. Large enhancement of dielectric properties (increase in dielectric constants and decrease in dielectric losses) was observed in the Ca1-xSrxCu3Ti4O12 ceramics at x=0.2 within the frequency range between 0.2 and 20 kHz. It was found that the doping of Sr2+ greatly improved the sinterability of Ca1-xSrxCu3Ti4O12 ceramics by largely reducing sintering temperature and promoting densification and grain growth during sintering.

Li, Wang; Qiu, Shen-Yu; Chen, Nan; Liu, Bing-Fa; Du, Guo-Ping

2010-02-01

31

Fermi surface topology of Ca1.5Sr0.5RuO4 determined by ARPES  

Microsoft Academic Search

We report ARPES results of the Fermi surface of Ca1.5Sr0.5RuO4, which is at the boundary of magnetic\\/orbital instability in the phase diagram of the Ca-substituted Sr ruthenates. Three t2g energy bands and the corresponding Fermi surface sheets are observed, which are also present in the Ca-free Sr2RuO4. We find that while the Fermi surface topology of the ?, ? (dyz,zx)

S.-C. Wang; H.-B. Yang; A. K. P. Sekharan; S. Souma; H. Matsui; T. Sato; T. Takahashi; Chenxi Lu; Jiandi Zhang; R. Jin; D. Mandrus; E. W. Plummer; Z. Wang; H. Ding

32

Newly developed Sr-substituted alpha-TCP bone cements.  

PubMed

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. PMID:19733700

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

2009-09-04

33

Correlation of Bone Ba\\/Ca and Sr\\/Ca due to Biological Purification of Calcium  

Microsoft Academic Search

Analyses of more than 1000 samples of soils, plants and bones of many species from a temperate woodland environment confirm the ubiquity of biopurification processes in which Ba\\/Ca and Sr\\/Ca decrease with increasing trophic position. This study reveals that differences among Ba\\/Ca and Sr\\/Ca ratios in soils and plants themselves are comparable to or greater than differences due to biopurification

James H. Burton; T. Douglas Price; William D. Middleton

1999-01-01

34

Ferromagnetism in Cr substituted SrMoO3 system  

NASA Astrophysics Data System (ADS)

Systematic studies of structural, magnetic, electric transport, and specific heat properties have been performed on lightly Cr-doped molybdates SrMo1-xCrxO3 (0<=x<=0.10). Based on the analysis of structural parameter variations, the valence state of the doped Cr ions in SrMo1-xCrxO3 system is suggested to be +2. Cr substitution as low as x=0.025 is sufficient to drive SrMo1-xCrxO3 system from the Pauli-paramagnetic state to a ferromagnetic state. The Curie temperature TC increases monotonically with increasing Cr-doping content. All samples exhibit metalliclike transport behavior in the whole studied temperature range except for the x=0.10 sample. The magnitude of the resistivity increases monotonically with increasing Cr-doping level. The evolution of the magnetic and resistive properties with Cr-doping content x may be related to the narrowed d-band width due to Cr substitution. In addition, the temperature dependence of specific heat for all samples has also been studied.

Zhao, B. C.; Sun, Y. P.; Zhang, S. B.; Song, W. H.; Dai, J. M.

2007-12-01

35

Use of foliar Ca\\/Sr discrimination and 87 Sr\\/ 86 Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest  

Microsoft Academic Search

Calcium\\/strontium and 87Sr\\/86Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the\\u000a discrimination of Ca\\/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage\\u000a of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at

Joel D. Blum; Amanda A. Dasch; Steven P. Hamburg; Ruth D. Yanai; Mary A. Arthur

2008-01-01

36

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

SciTech Connect

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.

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

2007-12-19

37

Sr / Ca and Mg / Ca ratios in polygenetic carbonate allochems from a Michigan marl lake  

NASA Astrophysics Data System (ADS)

Rapid accumulation of CaCO 3 is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO 3 , primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota . Gyraulus deflectus and Amnicola integra . and the dominant aragonitic pelecypod Sphaerium partumeium . Samples of each of these groups were analyzed for Ca, Sr and Mg. Molar Mg / Ca ratios are primarily controlled by allochem mineralogy, with calcitic forms having Mg / Ca ratios 5-10 times larger than aragonitic (shelled) forms. The Sr / Ca ratios are primarily controlled by biochemical fractionation, and are significantly lower than Sr / Ca ratios of inorganically precipitated aragonite from other settings. Partition coefficients were determined for both Sr and Mg for each carbonate allochem group and, based on comparisons with results reported by other workers, the partition coefficients determined here are generally considered `typical' or representative values for biogeneous freshwater carbonates. An analysis of variance of the data indicates that most genera and species of carbonate-secreting organisms in marl lakes have highly characteristic Sr / Ca and Mg / Ca ratios. These ratios can potentially serve as geochemical tracers in future investigations of lacustrine carbonate diagenesis. Both Sr and Mg are influenced by grain size and/or surface area, probably due to the presence of these elements in non-lattice-held (exchangeable) positions.

Treese, Thomas N.; Owen, Robert M.; Wilkinson, Bruce H.

1981-03-01

38

'Eventless' InsP3-dependent SR-Ca2+ release affecting atrial Ca2+ sparks.  

PubMed

Augmented inositol 1,4,5-trisphosphate receptor (InsP3R) function has been linked to a variety of cardiac pathologies, including cardiac arrhythmia. The contribution of inositol 1,4,5-trisphosphate-induced Ca(2+) release (IP3ICR) in excitation-contraction coupling (ECC) under physiological conditions, as well as under cellular remodelling, remains controversial. Here we test the hypothesis that local IP3ICR directly affects ryanodine receptor (RyR) function and subsequent Ca(2+)-induced Ca(2+) release in atrial myocytes. IP3ICR was evoked by UV-flash photolysis of caged InsP3 under whole-cell configuration of the voltage-clamp technique in atrial myocytes isolated from C57/BL6 mice. Photolytic release of InsP3 was accompanied by a significant increase in the Ca(2+) release event frequency (4.14 ± 0.72 vs. 6.20 ± 0.76 events (100 ?m)(-1) s(-1)). These individual photolytically triggered Ca(2+) release events were identified as Ca(2+) sparks, which originated from RyR openings. This was verified by Ca(2+) spark analysis and pharmacological separation between RyR and InsP3R-dependent sarcoplasmic reticulum (SR)-Ca(2+) release (2-aminoethoxydiphenyl borate, xestospongin C, tetracaine). Significant SR-Ca(2+) flux but eventless SR-Ca(2+) release through InsP3R were characterized using SR-Ca(2+) leak/SR-Ca(2+) load measurements. These results strongly support the idea that IP3ICR can effectively modulate RyR openings and Ca(2+) spark probability. We conclude that eventless and highly efficient InsP3-dependent SR-Ca(2+) flux is the main mechanism of functional cross-talk between InsP3Rs and RyRs, which may be an important factor in the modulation of ECC sensitivity. PMID:23381902

Horn, Tamara; Ullrich, Nina D; Egger, Marcel

2013-02-04

39

Mesures conjointes des rapports Sr/Ca et ? 18O effectuées sur Acropora nobilis et Pontes lutea: le paléothermomètre Sr/Ca est-il toujours fiable?  

NASA Astrophysics Data System (ADS)

We measured the Sr/Ca and 18O/ 16O ratios in Acropora nobilis and Porites lutea, from the Mayotte lagoon. As the variations of ? 18O seawater are negligible, coral ? 18O aragonite reflects only seasonal temperature variations. While there is a good agreement between the Sr/Ca ratio and ? 18O for Acropora nobilis, it is not the case for Porites lutea. Coral biological and environmental parameters cannot explain the discrepancies between Sr/Ca ratios and isotopic measurements. However, transport mechanisms of Sr 2+ and Ca 2+ and the presence of two mineralogical structures of strontium may affect the Sr/Ca ratio.

Boiseau, Muriel; Cornu, Hélène; Turpin, Laurent; Juillet-Leclerc, Anne

1997-11-01

40

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

41

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

PubMed Central

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

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

2011-01-01

42

Phonon Dispersion in the Fcc Metals Ca, Sr and Yb  

NASA Astrophysics Data System (ADS)

Within the harmonic approximation and adiabatic approximation, the expressions of atomic force constants have been derived. Phonon dispersion curves along four major symmetry directions and four off-symmetry directions have been simulated for alkaline-earth metals Ca, Sr and the rare-earth metal Yb by combining the modified analytic embedded atom method with the theory of lattice dynamics. The simulated phonon dispersion curves for the fcc metals Ca, Sr and Yb along four major symmetry directions have been compared to the corresponding experimental data. The results show that the simulated results are general consistent with available experimental results, with a maximum deviation of approximately 14 %. The simulated phonon frequencies of the fcc metals Ca, Sr and Yb lay a significant foundation for guiding and judging relative experiment results, especially for the phonon dispersion relation along off-symmetry directions.

Zhang, Xiao-Jun; Chen, Chang-Le

2012-10-01

43

Sr/Ca and early hominin diets revisited: new data from modern and fossil tooth enamel.  

PubMed

A previous study of strontium/calcium (Sr/Ca) ratios in Paranthropus suggested that it consumed more animal foods than was previously believed. However, that study looked at Sr/Ca in fossil bone, which is known to be highly susceptible to diagenesis. Enamel, in contrast, is resistant to post-mortem alteration making it a more appropriate material for Sr/Ca analysis of Plio-Pleistocene fossils. Yet, we know virtually nothing about Sr/Ca in the enamel of modern African mammals, much less fossil taxa. To address this gap, we studied Sr/Ca in tooth enamel from modern mammals in the greater Kruger National Park, South Africa, as well as fossil fauna from the Sterkfontein Valley. Grazing herbivores have the highest Sr/Ca, followed by browsers and carnivores in both modern and fossil fauna. This similarity in ecological Sr/Ca patterning between modern and fossil fauna shows that diagenesis has not obscured the primary dietary signals. Australopithecus has significantly higher Sr/Ca than Paranthropus, and higher Sr/Ca than fossil papionins, browsers, and carnivores. Paranthropus has lower Sr/Ca than grazers, but its Sr/Ca is higher or equal to that of fossil papionins, browsers, and carnivores. Thus, Sr/Ca for both hominins is relatively high, and provides no direct evidence for omnivory in either taxon. The consumption of underground resources or insects are among the possible explanations for the highly elevated Sr/Ca in Australopithecus. PMID:15701528

Sponheimer, Matt; de Ruiter, Darryl; Lee-Thorp, Julia; Späth, Andreas

2004-12-21

44

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

NASA Astrophysics Data System (ADS)

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

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

2002-12-01

45

Energetics of La1-xAxCrO3-? perovskites (A=Ca or Sr)  

NASA Astrophysics Data System (ADS)

A series of perovskites with the general formula La1-xAxCrO3-? (A=Ca or Sr) have been synthesized in the solid solution range 0.0Ca-doped samples, and from -440±150 to -290±50 kJ/mol O2 for Sr-doped ones. This dependence of enthalpy of oxidation on composition suggests oxygen vacancies are increasingly short-range ordered in reduced samples. The higher oxidation state of chromium is stabilized by the substitution of alkaline earth ions, but with increasing doping, the enthalpy of formation of the fully oxidized sample in both Ca and Sr-doped systems becomes more endothermic. This destabilization effect is attributed to the large endothermic enthalpy of oxygen vacancy formation (395±30 kJ/mol of VO··) for the reaction AAx+OOx=ALa'+0.5VO··+0.5O2(A=Ca or Sr) that over-rides the exothermic enthalpies of oxidation. At a given composition, Sr-doped LaCrO3 is more stable than its Ca-doped counterpart, which is consistent with basicity arguments.

Cheng, Jihong; Navrotsky, Alexandra

2005-01-01

46

Synthesis of BiPbSrCaCuO superconductor  

DOEpatents

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.

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

1994-04-05

47

Structures and self-activating photoluminescent properties of Sr3-xAxGaO4F (A=Ba, Ca) materials  

NASA Astrophysics Data System (ADS)

The synthesis, structures and photoluminescent properties of mixed oxyfluorides of the type Sr3-xAxGaO4F are compared to Sr3-xAxAlO4F (A=Ca, Ba) materials. In these compounds the F- and O2- ions are ordered and located on two distinct crystallographic sites. When substituting Sr2+ by Ba2+ and Ca2+, we find in Sr3-xAxGaO4F materials an ordering of the alkaline earth cations over the two crystallographic sites. The amount of Ba2+ ions that can be substituted into Sr3-xAxGaO4F is x?1.2, which is slightly more than can be incorporated into the previously reported Al-analog Sr3-xAxAlO4F (x=1.0). Conversely, the amount of Ca2+ ions that can be substituted into Sr3-xCaxGaO4F (x=0.3) is significantly less than in Sr3-xCaxAlO4F (x=1.0). A post-synthesis reduction step causes these materials to exhibit self-activating broad band photoluminescence where the emitted colors vary with the amount of ions substituted into the host lattice.

Green, Robert; Vogt, Thomas

2012-10-01

48

Occurrence of interactions between individual Sr(2+)- and Ca(2+)-effects on maize root and shoot growth and Sr(2+), Ca(2+) and Mg(2+) contents, and membrane potential: Consequences on predicting Sr(2+)-impact.  

PubMed

Occurrence of functional interactions between Sr(2+) and Ca(2+) were investigated on maize plants grown under hydroponic conditions in presence of various mixtures of SrCl2 [0-0.01-1-10mM] and CaCl2 [0-0.2-2-20mM]. External [Ca(2+)] modulated the effect of Sr(2+) on the plant dry weight, and on the Sr(2+), Ca(2+) and Mg(2+) contents of roots and shoots. An intermediary functional step between external [Sr(2+)] and [Ca(2+)], and organ ion content, occurred at the plasma membrane of cortical root cells where Sr(2+) and Ca(2+) could influence ion uptake by acting on membrane potential. The decrease of the Sr(2+)-evoked membrane depolarization induced by Ca(2+) could not solely be attributed to the Ca(2+)-effect on the resting membrane potential. Most of the time the individual effects of Sr(2+) and Ca(2+) were not additive, as these two ions clearly interacted with each other to jointly affect the plant physiology. In spite of these interactions, both [Sr(2+)]ext or [Sr(2+)]ext/[Ca(2+)]ext ratio values seemed to enable a correct prediction of the Sr(2+)-effects on the plant. However using the [Sr(2+)]ext/[Ca(2+)]ext ratio improved significantly the adequacy of prediction compared to the use of [Sr(2+)]ext alone, as it increased up to 25% the proportion of variability accounted for by the model. PMID:23850941

Moyen, Christelle; Roblin, Gabriel

2013-06-21

49

Fermi Surface Topology of Ca1.5Sr0.5RuO4 Determined by Angle-Resolved Photoelectron Spectroscopy  

Microsoft Academic Search

We report angle-resolved photoelectron spectroscopy results of the Fermi surface of Ca1.5Sr0.5RuO4, which is at the boundary of magnetic\\/orbital instability in the phase diagram of the Ca-substituted Sr ruthenates. Three t2g energy bands and the corresponding Fermi surface sheets are observed, which are also present in the Ca-free Sr2RuO4. We find that while the Fermi surface topology of the alpha,beta

S.-C. Wang; H.-B. Yang; A. K. Sekharan; S. Souma; H. Matsui; T. Sato; T. Takahashi; Chenxi Lu; Jiandi Zhang; R. Jin; D. Mandrus; E. W. Plummer; Z. Wang; H. Ding

2004-01-01

50

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

NASA Astrophysics Data System (ADS)

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.

Peek, Stephanie; Clementz, Mark T.

2012-10-01

51

Phase Transformation and Temperature Dependence of Relative Permittivity for A-site Substituted Sr(Y 0.5 Ta 0.5 )O 3 Perovskites  

Microsoft Academic Search

A-site cation substitution with Ba2+ or Ca2+ ions was made for the ordered complex perovskite Sr(Y0.5Ta0.5)O3 to correlate the structure evolution and the change in the temperature coefficient of relative permittivity (TCer) with the cation substitution. The crystal symmetry of the solid solutions at room temperature changed as monoclinic ? rhombohedral ? cubic with the corresponding A-site cation species of

T. Fujii; J. Takahashi; S. Shimada; K. Kageyama

1999-01-01

52

Tracer diffusion of Mg, Ca, Sr, and Ba in Na-aluminosilicate melts  

NASA Astrophysics Data System (ADS)

We employed the thin source technique to investigate tracer diffusion of Mg, Ca, Sr, and Ba in glasses and supercooled melts of albite (NaAlSi 3O 8) and jadeite (NaAlSi 2O 6) compositions. The experiments were conducted at 1 bar and at temperatures between 645 and 1025°C. Typical run durations ranged between 30 min and 35 days. The analysis of the diffusion profiles was performed with the electron microprobe. Diffusivities of Ca, Sr, and Ba were found to be independent of either duration t of the experiment or tracer concentration M, initially introduced into the sample. Mg exhibits a diffusivity depending on run time and concentration and tracer diffusivity is derived by extrapolation to M/?t = 0. Temperature dependence of the diffusivity D can be represented by an Arrhenius equation D = D o exp(-E a/RT), yielding the following least-squares fit parameters (with D in m 2/s and E a in kJ/mol): D Mg = 1.8 · 10 -5 exp(-234 ± 20/RT), D Ca = 3.5 · 10 -6 exp(-159 ± 6/RT), D Sr = 3.6 · 10 -6 exp(-160 ± 6/RT), and D Ba = 6.0 · 10 -6 exp(-188 ± 12/RT) for albite; and D Mg = 8.3 · 10 -6 exp(-207 ± 18/RT), D Ca = 3.8 · 10 -6 exp(-153 ± 4/RT), D Sr = 2.3 · 10 -6 exp(-150 ± 4/RT), and D Ba = 3.7 · 10 -5 exp(-198 ± 4/RT) for jadeite composition. Ca and Sr diffusivities agree within error in both compositions and exhibit the fastest diffusivities, whereas Mg reveals the lowest diffusivity. The relationship between activation energy and radius shows a minimum at Ca and Sr for albite and jadeite compositions extending the relationship already observed elsewhere for alkalies. With increasing substitution of Si by (Na + Al), diffusivities increase, whereas activation energies decrease. Furthermore, a simple model modified from that of Anderson and Stuart (Anderson O. L. and Stuart D. A., "Calculation of activation energy of ionic conductivity in silica glasses by classical methods," J. Am. Ceram. Soc.37, 573-580, 1954) is discussed for calculating the activation energies.

Roselieb, Knut; Jambon, Albert

2002-01-01

53

Trace element proxies (Sr\\/Ca, Ba\\/Ca and Pb\\/Ca) in Bivalve shells: environmental signals or not?  

Microsoft Academic Search

Coral and sclerosponge skeletons have both been used as recorders of their environment. Sr\\/Ca, Ba\\/Ca and Pb\\/Ca have all shown to be useful in these substrates, giving insight into the past environment in which the skeleton grew (e.g., Lea et al., 1989, Nature 340, 373-376; Beck et al., 1992, Science 257, 644-647; Lazareth et al., 2000, Geology 28, 515-518; Rosenheim

D. P. Gillikin; F. Dehairs; D. Steenmans; L. Meng; T. Haifeng; J. Navez; L. Andre; W. Baeyens; E. Keppens

2004-01-01

54

A novel CaSR mutation presenting as a severe case of neonatal familial hypocalciuric hypercalcemia  

PubMed Central

Background Familial Hypocalciuric Hypercalcemia (FHH) is a generally benign disorder caused by heterozygous inactivating mutations in the Calcium-Sensing Receptor (CaSR) gene resulting in altered calcium metabolism. Objective We report a case of unusually severe neonatal FHH due to a novel CaSR gene mutation that presented with perinatal fractures and moderate hypercalcemia. Case overview A female infant was admitted at 2?weeks of age for suspected non-accidental trauma (NAT). Laboratory testing revealed hypercalcemia (3.08?mmol/L), elevated iPTH (20.4 pmol/L) and low urinary calcium clearance (0.0004). Radiographs demonstrated multiple healing metaphyseal and rib fractures and bilateral femoral bowing. The femoral deformity and stage of healing were consistent with prenatal injuries rather than non-accidental trauma (NAT). Treatment was initiated with cholecalciferol, 400?IU/day, and by 6?weeks of age, iPTH levels had decreased into the high-normal range. Follow up radiographs demonstrated marked improvement of bone lesions by 3?months. A CaSR gene mutation study showed heterozygosity for a T>C nucleotide substitution at c.1664 in exon 6, resulting in amino acid change I555T in the extracellular domain consistent with a missense mutation. Her mother does not carry the mutation and the father is unknown. At 18?months of age, the child continues to have relative hyperparathyroidism and moderate hypercalcemia but is otherwise normal. Conclusion This neonate with intrauterine fractures and demineralization, moderate hypercalcemia and hyperparathyroidism was found to have a novel inactivating missense mutation of the CaSR not detected in her mother. Resolution of bone lesions and reduction of hyperparathyroidism was likely attributable to the natural evolution of the disorder in infancy as well as the mitigating effect of cholecalciferol treatment.

2012-01-01

55

Chemical diffusion in the Bi, Sr, Ca, Cu\\/O system  

Microsoft Academic Search

Monodimensional diffusion measurements have been used to characterise the solid state reactivity in the Ca, Sr, Cu, Bi\\/O system at 750°C under pure oxygen flux (1 atm). The investigated couples are: (1) Bi2O3-CaCO3; (2) CaCO3-CuO; (3) CaCO3-SrCO3; (4) Sr2Bi2O5-CaCO3; (5) CaBi2O4-SrCO3; (6) CaBi2O4-CuO; (7) CaBi2O4-CaCO3; (8) CaBi2O4-SrCuO2. The paper reports the phase nature and composition of the solid products formed

G. Spinolo; U. Anselmi-Tamburini; P. Ghigna; G. Flor

1993-01-01

56

87Sr/86Sr and Sr/Ca in speleothems for paleoclimate reconstruction in Central China between 70 and 280 kyr ago  

NASA Astrophysics Data System (ADS)

Limestone cave deposits (speleothems) provide archives for past changes in regional climates over a range of timescales. While ?18O and ?13C in speleothem calcite have been commonly used for reconstruction of paleoclimates, we report here further efforts in the use of 87Sr/86Sr and Sr/Ca signals in speleothem calcite to deduce paleomonsoon variability near the Loess Plateau of central China. A two end-member mass-balance model of concentration and isotopic composition of strontium in a cave system is used to estimate variation of the 87Sr/86Sr ratio in sediments overlying a limestone cave. We show that this ratio reflects climate-driven variations in the provenance and the extent of chemical weathering of the epikarstic sediments. The measurements of 87Sr/86Sr made on a well-dated stalagmite, SFL, from Buddha Cave (33o40N? 109o05?E) show ratios of 0.71092 to 0.71133 (±0.00001 as 2?) during relatively cold periods (e.g., Marine Isotope Stage (MIS) 5b, 5d, and 8), lower than ratios of 0.71133 to 0.71194 during relatively warm periods (e.g., MIS 5a, 5c, 5e, and 7). As changes in the Sr/Ca ratio may affect speleothem 87Sr/86Sr, we show that the direct use of speleothem 87Sr/86Sr is less ideal than our modeled 87Sr/86Sr for the exogenic Sr source above the cave as a paleomonsoon proxy. Using the ?18O, ?13C, Sr/Ca, and 87Sr/86Sr records of the stalagmite, we reconstruct the variability of the East Asian monsoon for the time period between 70 and 280 kyr ago. The results show that summer monsoons were more intense during interglacial periods than during glacial periods.

Li, Hong-Chun; Ku, Teh-Lung; You, Chen-Feng; Cheng, Hai; Edwards, R. Lawrence; Ma, Zhi-Bang; Tsai, Wang-Sheng; Li, Mung-Dar

2005-08-01

57

The muSR-study of the London penetration depth in the high-Tc compounds Bi2Sr2Ca1-xYxCu2O8+delta  

Microsoft Academic Search

The substitution of the trivalent Y for the bivalent Ca in Bi2Sr2Ca1-xYxCu2O8+delta changes the charge carrier density in this compound. We have performed the muon spin rotation measurements of the London penetration depth lambda(T) in the high-Tc superconductor Bi2Sr2Ca1-xYxCu2O8+delta for x=0.0-0.45. The yttrium doping leads to a decrease in Tc and to an increase in lambda(0). In all investigated samples

M. Weber; A. Amato; V. N. Duginov; V. G. Grebinnik; I. I. Gurevich; F. N. Gygax; S. Kapusta; B. F. Kirillov; A. B. Lazarev; H. Maletta; B. A. Nikolsky; V. G. Olshevsky; A. V. Pirogov; V. Yu. Pomjakushin; A. N. Ponomarev; A. Schenck; S. N. Shilov; V. G. Storchak; V. A. Suetin; V. A. Zhukov

1991-01-01

58

Ontogenetic variations in Sr/Ca and Ba/Ca ratios of dental bioapatites from Bos taurus and Odocoileus virginianus.  

PubMed

Sr/Ca and Ba/Ca ratios of bone are commonly used as biochemical indicators of trophic level in modern and fossil mammals. Concerns over the effects of diagenesis on Sr/Ca and Ba/Ca ratios of bone led archaeologists and paleontologists to favor tooth enamel, which is less prone to alteration. Sr/Ca and Ba/Ca ratios of bone, enamel, and dentin from three farm-raised steers (Bos taurus) and five wild white-tailed deer (Odocoileus virginianus) from central Missouri were compared. Our results show that changes in diet, discrimination, and growth rate during ontogeny can lead to significant differences in Sr/Ca and Ba/Ca ratios of different bioapatite types as well as significant differences within the same bioapatite forming at different times. Early- and late-forming tooth enamel can have significant differences in Sr/Ca and Ba/Ca ratios equivalent to almost one full trophic step. Although differences between early- and late-forming dentin are typically not significant, dentin Sr/Ca and Ba/Ca ratios are significantly greater than enamel values. This difference in Sr/Ca or Ba/Ca ratios between enamel and dentin from the same tooth can be greater than one full trophic step. These results have profound implications for the use of dental bioapatites in trophic level reconstructions. They highlight the importance of consistency in bioapatite selection, tooth selection, and relative location of sampling within the enamel cap. Furthermore, this expected difference in Sr/Ca and Ba/Ca ratios could be used as another means of checking for diagenetic alteration in ancient samples. PMID:22677541

Peek, Stephanie; Clementz, Mark T

2012-06-06

59

Mg/Ca and Sr/Ca in living benthic foraminiferal tests from the northeastern Atlantic  

NASA Astrophysics Data System (ADS)

Mg/Ca in benthic foraminiferal tests has been recently used as an indicator of bottom water temperature (BWT). We analysed Mg/Ca and Sr/Ca in living (Rose Bengal stained) and dead foraminifera collected at five stations in the Bay of Biscay in NE Atlantic (43˜44^oN, 2^oW) at interval of 3 to 4 months (1997--2000). Four species with different microhabitat were studied: Cibicidoides pachydermus, Uvigerina peregrina, Melonis barleeanus and Globobulimina affinis. Water depth of the studied stations varies from 550 m to 2755 m, which corresponds to a BWT range of 12--2^oC. Foraminiferal tests were cleaned with ultrasonic bath, oxidative cleaning and diluted acid leaching. Results show that there is no systematic bias between living and dead specimens. Mg/Ca of C. pachydermus varies with water depth and BWT. Mg/Ca of G. affinis is ˜ four times higher than Mg/Ca of C. pachydermus and varies with BWT. In contrast, Mg/Ca of U. peregrina and M. barleeanus show poor relationships with BWT. The largest scatter is observed for living foraminifera collected at the shallowest station. Seasonal variability in BWT and salinity does not account for this dispersion. Some duplicate cores from this station differs significantly, suggesting that spatial heterogeneity of sediments may be a cause of the scatter. This heterogeneity is also observed for taxonomic assemblage (FONTANIER et al., 2002). At the studied sites, Sr/Ca of U. peregrina varies linearly with BWT. The observed temperature dependency is not totally negligible comparing to seawater Sr/Ca variability due to glacial-interglacial sea level change.

Tachikawa, K.; Fontanier, C.; Jorissen, F.; Bard, E.

2003-04-01

60

Trace element proxies (Sr/Ca, Ba/Ca and Pb/Ca) in Bivalve shells: environmental signals or not?  

NASA Astrophysics Data System (ADS)

Coral and sclerosponge skeletons have both been used as recorders of their environment. Sr/Ca, Ba/Ca and Pb/Ca have all shown to be useful in these substrates, giving insight into the past environment in which the skeleton grew (e.g., Lea et al., 1989, Nature 340, 373-376; Beck et al., 1992, Science 257, 644-647; Lazareth et al., 2000, Geology 28, 515-518; Rosenheim et al., 2004, Geology 32, 145-148). Although bivalves have not been studied as extensively as corals, these proxies are apparently not as reliable in bivalves (e.g., Vander Putten et al., 2000, GCA 64, 997-1011). We therefore investigate Sr/Ca and Pb/Ca in two species of aragonitic clams (Mercenaria mercenaria and Saxidomus giganteus) and Ba/Ca in the calcite layer of the mussel Mytilus edulis. Results indicate that Sr/Ca is primarily controlled by growth rate in S. giganteus whereas there was no relationship between these parameters in M. mercenaria. Pb/Ca is somewhat reproducible between specimens of S. giganteus, however long-term Pb/Ca records (1949-2003) in the shell of M. mercenaria did not show the expected curve of anthropogenically introduced lead, indicating that they are not recording environmental Pb concentrations. Therefore, Sr/Ca and Pb/Ca incorporation seem to be regulated by biological processes and not directly by environmental parameters. Ba/Ca in M. edulis shells on the other hand, does seem to be directly linked to the environment. Shells grown under laboratory and natural conditions both show the same linear relationship between dissolved Ba/Ca and shell Ba/Ca. Experiments involving manipulations of dissolved and particulate (i.e. food) Ba/Ca, suggest that the dominant pathway of barium into the shell is from the dissolved phase via the hemolymph. We were unable to explain the large peaks noted in the Ba/Ca profiles, however, they did not seem linked to phytoplankton blooms as has been previously suggested (Stecher et al., 1996, GCA 60, 3445-3456; Vander Putten et al., 2000; Lazareth et al., 2003, Est. Coast. Shelf Sci. 17, 1461-1470).

Gillikin, D. P.; Dehairs, F.; Steenmans, D.; Meng, L.; Haifeng, T.; Navez, J.; Andre, L.; Baeyens, W.; Keppens, E.; Calmars Group,.

2004-12-01

61

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

NASA Astrophysics Data System (ADS)

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.

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

2012-09-01

62

Strong kinetic effects on Sr\\/Ca ratios in the calcitic bivalve Pecten maximus  

Microsoft Academic Search

Although Sr\\/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report Sr\\/Ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve Pecten maximus (age class I). Ratios of Sr\\/Ca were found to be variable among individuals that

Anne Lorrain; David P. Gillikin; Yves-Marie Paulet; Laurent Chauvaud; Alain Le Mercier; Jacques Navez; Luc André

2005-01-01

63

A study of the magnetic properties of hydrothermally synthesised Sr hexaferrite with Sm substitution  

NASA Astrophysics Data System (ADS)

Sm doped Sr hexaferrite particles were synthesised hydrothermally. Post-synthesised calcination with the aim of improving the magnetic properties of as-synthesised particles was conducted at temperatures ranging from 900°C to 1150°C for 2h in air. The effects of the Sm/Sr ratio and the calcination temperature on the crystallography, particle morphology and magnetic properties of Sm doped Sr hexaferrite were investigated by an X-ray diffractometer, scanning electron microscope and vibrating sample magnetometer. It was found that, unlike transition metal element substitution, Sm substitution does not decrease the hexaferrite particle size. The intrinsic coercivities of Sm doped Sr hexaferrite are significantly higher than those of Sr hexaferrite. It has been observed that Sm substitution can increase the intrinsic coercivity of Sr hexaferrite without causing any deterioration of the saturation magnetisation and remanence. In the Sm/Sr range 1/8-1/2 inclusively, there is little change in the coercivity but a slight fall in both the magnetisation and the remanence.

Wang, J. F.; Ponton, C. B.; Harris, I. R.

2001-09-01

64

Controls on Mg/Ca and Sr/Ca in Planktonic Foraminifera: Results From Culturing Experiments  

NASA Astrophysics Data System (ADS)

Culturing experiments were carried out on Globigerinoides ruber (white) and Globigerinella siphonifera, collected from the Gulf of Eilat and grown in seawater (i) at constant salinity but varying temperatures of 18 to 31 degC, (ii) at constant temperature but varying salinities of 32 to 44 psu, (iii) at constant salinity, temperature and dissolved inorganic carbon but varying pH of 7.9 to 8.4. Temperature response of Mg/Ca in cultured G. ruber (with an exponential constant of 11 +/- 2% per degC) agrees well with previous calibrations from core tops and net catches. Mg/Ca in G. ruber shows secondary dependence on salinity (6 +/- 2% per salinity unit). This compares well with the salinity response of Mg/Ca in cultured G. sacculifer (approx. 7% per salinity unit; Nuernberg et al., 1996), implying a similar salinity effect for shallow dwelling species. Mg/Ca in G. ruber shows no dependence on pH at ambient seawater range (8.1 to 8.3; NBS scale), but demonstrates considerable variation below and above the normal range of seawater pH. We observe no significant control of seawater temperature or pH on Sr/Ca in G. ruber. However, there is a significant correlation between Sr/Ca ratios and salinity (approx. 0.016 mmol/mol per salinity unit). Multiple regression analysis on Mg/Ca data of cultured G. ruber gives a calibration equation as a function of temperature and salinity [Mg/Ca = 0.29(+/-0.13)Sal + 0.46(+/- 0.13)Temp - 17.0(+/-5.9), R2=0.96, p=0.05]. Salinity can be independently derived from the regression for Sr/Ca [Sr/Ca = 0.016(+/-0.015)Sal + 0.72(+/-0.55), R2=0.91, p<0.05]. Nuernberg, D. et al., 1996. Assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures. Geochimica et Cosmochimica Acta, 60: 803-814.

Kisakurek, B.; Eisenhauer, A.; Erez, J.; Boehm, F.; Garbe-Schoenberg, D.

2007-12-01

65

Cation and anion ordering in the layered oxyfluorides Sr3-xAxAlO4F (A=Ba, Ca)  

Microsoft Academic Search

The synthesis and structural characterization of mixed oxyfluorides of the type Sr3-xAxAlO4F is reported, where A is either calcium or barium. In these compounds the fluoride and oxide ions are ordered onto two distinct crystallographic sites. There is also an ordering of the alkaline earth cations over two crystallographic sites upon substitution of Ba2+ or Ca2+ for Sr2+. The solid

A. K. Prodjosantoso; B. J. Kennedy; T. Vogt; P. M. Woodward

2003-01-01

66

Cation and anion ordering in the layered oxyfluorides Sr 3? x A x AlO 4F ( A=Ba, Ca)  

Microsoft Academic Search

The synthesis and structural characterization of mixed oxyfluorides of the type Sr3?xAxAlO4F is reported, where A is either calcium or barium. In these compounds the fluoride and oxide ions are ordered onto two distinct crystallographic sites. There is also an ordering of the alkaline earth cations over two crystallographic sites upon substitution of Ba2+ or Ca2+ for Sr2+. The solid

A. K Prodjosantoso; B. J Kennedy; T Vogt; P. M Woodward

2003-01-01

67

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)

We use Sr and Ca isotopes to constrain solute sources in small tropical catchments. We look at Ca isotope fractionation in streams and groundwater. We discuss source-specific and biogeochemical isotope fractionation effects. Possibilities and limitations of Ca isotopes as tracer in hydrological systems.

Wiegand, B. A.; Schwendenmann, L.

2013-04-01

68

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

SciTech Connect

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.

de Villiers, S.; Shen, G.T.; Nelson, B.K. (Univ. of Washington, Seattle, WA (United States))

1994-01-01

69

Sr heterogeneity in textit{Arctica islandica} shells and the potential use of Sr/Ca ratios as paleotemperature proxies  

NASA Astrophysics Data System (ADS)

Quantifiable paleotemperature data can help to verify predictions made by numerical climate models. Traditionally, paleotemperature estimates are based on ?18O values of biogenic hard parts. However, oxygen isotope values not only reflect changes in ambient temperature, but also changes in ?18Owater, i.e. driven by freshwater influx, evaporation etc. Information regarding the ?18Owater value of past environments is limited for the geological past. The validity of published ?18O paleotemperature data can be tested using element-to-calcium ratios of bivalve shells such as the long-lived ocean quahog, Arctica islandica. Preliminary investigations suggest that Sr/Ca ratios of this species may provide more reliable paleotemperature data. However, contemporaneously deposited shell portions within the outer shell layer demonstrate at least a 30% variability in the Sr/Ca value. This study presents Sr/Ca ratios measured by ICP-OES wet-chemical analyses. Significantly different distributions of Sr/Ca ratios were recorded from the shell surface (over 1330 ppm), through the interior (850 ppm) and to the inner shell surface (1860 ppm). Furthermore, this study showed that different shell crystal fabrics incorporate different amounts of Sr into the CaCO3 lattice of the A. islandica shell. Disparate Sr distribution could potentially be explained either by postdepositional diagenetic processes or syndepositional processes during biomineralization (i.e. different amounts of Sr incorporated into the shell). Understanding the mechanism of the observed Sr heterogeneity is essential if Sr/Ca ratios are to be used confidently in paleotemperature reconstructions.

Radermacher, Pascal; Schöne, Bernd R.; Nunn, Elizabeth V.; Zengjie, Zhang

2010-05-01

70

Migration and Rearing Histories of Chinook Salmon (Oncorhynchus tshawytscha) Determined by Ion Microprobe Sr Isotope and Sr/Ca Transects of Otoliths  

NASA Astrophysics Data System (ADS)

With the goal of monitoring fish habitat during the first year of life, we used the Stanford-USGS SHRIMP RG ion microprobe to determine 87Sr/86Sr and Sr/Ca ratios in 25 × 35 ? m areas along radial transects of otoliths from juvenile Chinook salmon (Oncorhynchus tshawytscha) native to four watersheds of markedly different geology. Otoliths from ocean-type Chinook salmon from the Skagit River estuary, Washington, have pre-hatch regions with 87Sr/86Sr ratios (~0.709) suggesting a marine signature inherited maternally, extensive freshwater growth zones with 87Sr/86Sr ratios similar that of the Skagit River (~0.705), and marine-like 87Sr/86Sr ratios near edges. Otoliths from stream-type Chinook salmon from three watersheds in central Idaho have pre-hatch 87Sr/86Sr ratios >0.711, indicating that a maternal marine Sr isotopic signature is not preserved after the ~1000-1400 km migration from the Pacific Ocean. The 87Sr/86Sr ratios in the outer portions of these otoliths are similar to those of their respective streams (~0.708-0.722). For the Skagit juveniles, freshwater growth is marked by a small decrease in otolith Sr/Ca ratio, with an increase in Sr/Ca corresponding to the observed increase in 87Sr/86Sr with migration into salt water. Otoliths from the Idaho fish have similar Sr/Ca radial variation patterns that appear to record seasonal fluctuation in ambient water Sr/Ca ratio documented by our water analyses and USGS NASQAN time series data. The ability of the ion microprobe to measure both 87Sr/86Sr and Sr/Ca ratios of otolith aragonite at high spatial resolution in situ provides a new dimension in studies of fish rearing and migration.

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

2004-05-01

71

A review of high-temperature superconductivity and the effect of chemical modifications on Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10  

NASA Astrophysics Data System (ADS)

The aim was to 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 are two sets of samples. One set was based on the structure Bi2Sr2CaCu2O8 and the other on Bi2-Sr2Ca2Cu3O10. 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. percent 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). The effect of the substitutions on the crystal structure was determined.

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

1991-08-01

72

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

SciTech Connect

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.

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

1991-08-01

73

Study of the Superconducting Properties of the Bi-Ca-Sr-Cu-O System. (Abstract Only).  

National Technical Information Service (NTIS)

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 report...

M. H. Khan A. A. Qidwai S. M. Zia-ul-haq R. Binsaif

1990-01-01

74

Study of the Superconducting Properties of the Bi-Ca-Sr-Cu-O System.  

National Technical Information Service (NTIS)

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 report...

M. H. Khan S. M. M. R. Naqvi S. M. Zia-ul-haq

1991-01-01

75

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

Microsoft Academic Search

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

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

2004-01-01

76

Single Crystal X-Ray Structure Analysis of Bi2(Sr, Ca)2CuOx and Bi2(Sr, Ca)3Cu2Ox Superconductors  

NASA Astrophysics Data System (ADS)

Average crystal structures of Bi2(Sr, Ca)2CuOx and Bi2(Sr, Ca)3Cu2Ox were analyzed using single crystal X-ray intensity data applying anisotropic temperature factors. Crystal data: Bi2Sr1.60Ca0.40CuO6, Bbmb, a{=}5.3826(8)Å, b{=}5.3761(11), c{=}24.384(7), Rw{=}0.108 for 282 reflections; Bi2.06Sr1.70Ca1.24Cu2O8, Bbmb, a{=}5.3946(8), b{=}5.3895(13), c{=}30.649(12), Rw{=}0.064 for 354 reflections. Precession photographs show that Bi2Sr1.60Ca0.40CuO6 has a monoclinic modulated structure and Bi2.06Sr1.70Ca1.24Cu2O8 has an orthorombic one. The incommensurate modulated structures were qualitatively illustrated by using a modulation wave model.

Imai, Katsuhiro; Nakai, Izumi; Kawashima, Takuji; Sueno, Shigeho; Ono, Akira

1988-09-01

77

Signaling through the extracellular calcium-sensing receptor (CaSR).  

PubMed

The extracellular calcium ([Formula: see text])-sensing receptor (CaSR) was the first GPCR identified whose principal physiological ligand is an ion, namely extracellular Ca(2+). It maintains the near constancy of [Formula: see text] that complex organisms require to ensure normal cellular function. A wealth of information has accumulated over the past two decades about the CaSR's structure and function, its role in diseases and CaSR-based therapeutics. This review briefly describes the CaSR and key features of its structure and function, then discusses the extracellular signals modulating its activity, provides an overview of the intracellular signaling pathways that it controls, and, finally, briefly describes CaSR signaling both in tissues participating in [Formula: see text] homeostasis as well as those that do not. Factors controlling CaSR signaling include various factors affecting the expression of the CaSR gene as well as modulation of its trafficking to and from the cell surface. The dimeric cell surface CaSR, in turn, links to various heterotrimeric and small molecular weight G proteins to regulate intracellular second messengers, lipid kinases, various protein kinases, and transcription factors that are part of the machinery enabling the receptor to modulate the functions of the wide variety of cells in which it is expressed. CaSR signaling is impacted by its interactions with several binding partners in addition to signaling elements per se (i.e., G proteins), including filamin-A and caveolin-1. These latter two proteins act as scaffolds that bind signaling components and other key cellular elements (e.g., the cytoskeleton). Thus CaSR signaling likely does not take place randomly throughout the cell, but is compartmentalized and organized so as to facilitate the interaction of the receptor with its various signaling pathways. PMID:22453940

Chakravarti, Bandana; Chattopadhyay, Naibedya; Brown, Edward M

2012-01-01

78

Structural and superconducting properties of Bi-Sr-Ca-Cu superconductors studied by Fe doping  

SciTech Connect

1.5% of Fe has been substituted for Cu in several 2212'' and 2223'' Bi-Sr-Ca-Cu superconductors. All of the samples show a reduction of {ital T}{sub {ital c}} by about 13 K due to the Fe impurities. Moessbauer measurements at room temperature reveal structural characteristics such as stacking faults and intergrowth of different phases in these Bi-based compounds on the microscopic scale. The suppression of {ital T}{sub {ital c}} due to Fe doping in the Bi 2212'' or 2223'' system is comparable to that of the 123'' system, but much smaller than that of the 214'' system. The interplanar correlation existing in the 123'' and the Bi 2212'' and 2223''systems seems to play an important role in sustaining the high-temperature superconductivity and weakening the detrimental effect of impurity elements on superconductivity in these two systems.

Tang, H.; Qiu, Z.Q.; Du, Y.W.; Walker, J.C. (Department of Physics Department of Astronomy, The John Hopkins University, Baltimore, Maryland 21218 (USA))

1990-05-01

79

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

NASA Astrophysics Data System (ADS)

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 on the other hand, also does not have an easily discernable periodicity in the Sr signal, but Mg does seem to be more in sync with d18O. Also, both Sr and Mg are higher in the more recently formed shell section (when the clam is older) indicating that this may be due to the ontogenic change in physiology and hence, again, suggests a physiological control on the incorporation of both these elements. If there is an effect of temperature on the incorporation of these elements in these three species, the signal is masked by the larger signal produced by vital effects.

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

2003-12-01

80

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

SciTech Connect

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.

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

2009-06-03

81

The relative uptake of Ca and Sr into tree foliage using a whole-watershed calcium addition  

Microsoft Academic Search

The use of strontium isotopes and ratios of alkaline earth elements (i.e., 87Sr\\/86Sr and Ca\\/Sr) to trace Ca sources to plants has become common in ecosystem studies. Here we examine the relative uptake of\\u000a Ca and Sr in trees and subsequent accumulation in foliage. Using a whole-watershed Ca addition experiment at the Hubbard Brook\\u000a Experimental Forest in N.H., we measured

Amanda Ash Dasch; Joel D. Blum; Christopher Eagar; Timothy J. Fahey; Charles T. Driscoll; Thomas G. Siccama

2006-01-01

82

Calcium-sensing receptor (CaSR): pharmacological properties and signaling pathways.  

PubMed

In this article we consider the mechanisms by which the calcium-sensing receptor (CaSR) induces its cellular responses via the control (activation or inhibition) of signaling pathways. We consider key features of CaSR-mediated signaling including its control of the heterotrimeric G-proteins Gq/11, Gi/o and G12/13 and the downstream consequences recognizing that very few CaSR-mediated cell phenomena have been fully described. We also consider the manner in which the CaSR contributes to the formation of specific signaling scaffolds via peptide recognition sequences in its intracellular C-terminal along with the origins of its high level of cooperativity, particularly for Ca(2+)o, and its remarkable resistance to desensitization. We also consider the nature of the mechanisms by which the CaSR controls oscillatory and sustained Ca(2+)i mobilizing responses and inhibits or elevates cyclic adenosine monophosphate (cAMP) levels dependent on the cellular and signaling context. Finally, we consider the diversity of the receptor's ligands, ligand binding sites and broader compartment-dependent physiological roles leading to the identification of pronounced ligand-biased signaling for agonists including Sr(2+) and modulators including l-amino acids and the clinically effective calcimimetic cinacalcet. We note the implications of these findings for the development of new designer drugs that might target the CaSR in pathophysiological contexts beyond those established for the treatment of disorders of calcium metabolism. PMID:23856262

Conigrave, Arthur D; Ward, Donald T

2013-06-17

83

Re-examination of the structural properties of solid solutions Sr {sub x}Ca{sub 1-x}CO{sub 3}  

SciTech Connect

We have re-examined the evolution of orthorhombic cell parameters as a function of the substitution parameter x in solid solutions Sr {sub x}Ca{sub 1-x}CO{sub 3} in order to clarify contradictory results found in the literature. Calcium carbonate has been synthesized in the presence of Sr{sup 2+} ions (Sr/Ca molar ratio ranging from 10{sup -2} to 1), using experimental conditions that previously allowed us to obtain monophasic aragonite. The precipitates obtained have been analysed using powder X-ray diffractometry (XRD) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The powder XRD data confirm the occurrence of purely monophasic strontian-aragonites. Moreover, the cell parameters as well as the substitution parameter x have been refined for 0 < x < 0.5 against powder XRD data through Rietveld refinement. On the other hand, x was deduced from chemical analysis by ICP-AES. The agreement between both techniques is very satisfactory. The evolution of the cell parameters as a function of x is found to be linear within the studied range, this feature being confirmed for the overall domain (0 {<=} x {<=} 1) if one takes into account the cell parameters of aragonite CaCO{sub 3} and strontionite SrCO{sub 3}. This result, that is consistent with the existence of continuous solid solutions obeying the Vegard's law in the Sr {sub x}Ca{sub 1-x}CO{sub 3} system, contradicts previously published assertions.

Lucas-Girot, Anita [UMR 6226 CNRS-Universite de Rennes 1, Sciences Chimiques de Rennes, Bat. 10B, Campus de Beaulieu, Avenue du General Leclerc, F-35042 Rennes (France)]. E-mail: anita.lucas@univ-rennes1.fr; Hernandez, Olivier [UMR 6226 CNRS-Universite de Rennes 1, Sciences Chimiques de Rennes, Bat. 10B, Campus de Beaulieu, Avenue du General Leclerc, F-35042 Rennes (France); Oudadesse, Hassane [UMR 6226 CNRS-Universite de Rennes 1, Sciences Chimiques de Rennes, Bat. 10B, Campus de Beaulieu, Avenue du General Leclerc, F-35042 Rennes (France)

2007-06-05

84

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

NASA Astrophysics Data System (ADS)

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

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

1995-05-01

85

Synthesis of CxSr2Ca2Cu3Oz Superconductor from Sr2Ca2Cu3Oy Precursor  

NASA Astrophysics Data System (ADS)

A novel compound was derived by annealing a high-pressure-synthesized sample of Sr2Ca2Cu3Oy at 350 °C for 30 min in air. Energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy indicated that the composition of Sr, Ca, and Cu was not changed from the original material, and the C-K edge energy-loss near-edge structure was similar to that of CaCO3. Structure analysis revealed that this compound has a primitive tetragonal unit cell with a=3.88(3) and c=14.13(2) Å. It is likely that carbonate is incorporated either from air or secondary-phase grains into the pristine structure and forms the CxSr2Ca2Cu3Oz compound during annealing. Magnetization measurements revealed superconductivity with Tc,onset=89 K.

Aoba, Tomoya; Suzuki, Tsuneo; Nakayama, Tadachika; Suematsu, Hisayuki; Niihara, Koichi

2013-07-01

86

Oxygen nonstoichiometry and phase instability of Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

Oxygen nonstoichiometry, ? , of Bi2Sr2CaCu2O8+? was determined by thermogravimetric measurement as functions of temperature and partial pressure of oxygen (PO2). Dependencies of thermodynamic quantities, lattice constant and critical temperature on ? show anomalous behaviors at same oxygen content of ? =0.235. A quite sluggish and a large amount of weight increase observed at about 600°C under PO2=1 atm was found to correspond to the decomposition of Bi2Sr2CaCu2O8+? phase to Bi-Sr-Ca-O, Bi2Sr2CuOy and CuO. This suggests that the Bi2Sr2CaCu2O8+? phase is unstable at low temperature under high PO2.

Shimoyama, J.; Kase, J.; Morimoto, T.; Mizusaki, J.; Tagawa, H.

1991-12-01

87

Formation of Bi-2212-based composites with submicrometre-grained (Sr, Ca)SnO3  

NASA Astrophysics Data System (ADS)

Phase assemblage was investigated in the Bi-Sr-Ca-Cu-Sn-O system at temperatures of Bi-2212 phase crystallization. It is found that the Sr1-x Cax SnO3 phase (x = 0.1-0.2) is compatible with Bi-2212 as well as with Bi-2201, CuO, alkaline-earth metal cuprates and bismuthates. The solubility of Sn in Bi-2212 is limited to low values. The superconducting composites Bi-2212-(Sr, Ca)SnO3 were prepared by melt crystallization using single precursor and mixed precursor routes. The materials consisted of Bi-2212 matrix with submicron (Sr, Ca)SnO3 grains included in Bi-2212 lamellas and agglomerated in between. The composites exhibited enhanced flux pinning at T = 60 K, while at 5 K the effect of (Sr, Ca)SnO3 addition was not revealed.

Kazin, P. E.; Shuba, R. A.; Tretyakov, Yu D.; Knotko, A. V.; Jansen, M.; Freitag, B.

2000-02-01

88

A field-based study on variation in Mg/Ca and Sr/Ca in larger benthic foraminifera  

NASA Astrophysics Data System (ADS)

The Mg/Ca and Sr/Ca ratios of foraminifera are used as proxies of paleotemperature. Although the Mg/Ca is found to be related with temperature in planktonic foraminifera, the reliability of this proxy in benthic foraminifera has yet to be established. It is essential therefore to understand the minor elements' composition and their relation to ambient water parameters in different benthic foraminiferal species. In this study, a systematic field-based study was carried out on larger benthic foraminifera (LBF) of Okinawa (Japan) to assess if Mg/Ca and Sr/Ca in their tests could be used as proxies of seawater temperature. Five seasonal samples were collected from the reef flat to pick live specimens of Amphistegina lessonii, Neorotalia calcar, Calcarina hispida, Calcarina gaudichaudii, Baculogypsina sphaerulata, and Marginopora kudakajimaensis. The Mg/Ca in A. lessonii was ˜60 mmol/mol, while in the remaining five species the values were >200 mmol/mol, substantially higher than that recorded in planktonic and smaller benthic foraminifera. Interspecies and intraspecies Mg/Ca variations were fairly large even in samples of the same season. The Sr/Ca were quite uniform (˜2 mmol/mol) across the species and seasons. The correlations between test Mg/Ca and Sr/Ca and ambient water temperature and salinity were found to be poor. The possible reasons are (1) the influence of biological activities, particularly the photosynthesis-respiration cycle of algal symbionts, and (2) masking of the true relationship due to an "averaging" effect in whole-test analysis of species having longer a life span. In view of this it is suggested that the whole-shell Mg/Ca and Sr/Ca of LBF is not an apt proxy of paleotemperature.

Raja, Ramalingam; Saraswati, Pratul Kumar; Iwao, Kenji

2007-10-01

89

Electric quadrupole transition probabilities for the lowest 1D metastable state in Ca and Sr  

Microsoft Academic Search

FOTOS many-electron calculations have yielded electric quadrupole transition probabilities for the important Ca I 4s3d 1D to 4s21S (4575 AA) and Sr I 5s4d 1D to 5s21S (4961 AA) lines. In the length formulation, A(Ca)-60.2 s-1, A(Sr)=60.0 s-1. The existing discrepancy between theory and experiment in Ca is reduced but not eliminated. There are no previous results for Sr.

D. R. Beck; C. A. Nicolaides

1983-01-01

90

The effect of lead doping and grain alignment on Bi-Sr-Ca-Cu-O superconductors  

Microsoft Academic Search

The influence of composition on the properties of both untextured and textured Bi-Pb-Sr-Ca-Cu-O superconducting ceramics is reported. Samples have been prepared at the compositions Bi(2-x)PbxSr2Ca2Cu3O1 ('2223') and Bi1,6Pb0.4Sr2Ca3Cu4O2 ('2234'). The variation in the diamagnetic response and Jc with lead content, x, of the '2223' composition is shown. In untextured, sintered wires a maximum Jc of 300 A cm-2 at 77

F. Wellhofer; C. E. Gough; D. A. O'Connor; T. W. Button; N. McN Alford

1990-01-01

91

Magnetoelastic Coupling Across the Metamagnetic Transition in Ca 2- x Sr x RuO 4  

Microsoft Academic Search

The magnetoelastic coupling in Ca1.8Sr0.2RuO4 and in Ca1.5Sr0.5RuO4 has been studied combining high-resolution dilatometer and diffraction techniques. Both compounds exhibit strong anomalies\\u000a in the thermal-expansion coefficient at zero and at high-magnetic field as well as an exceptionally large magnetostriction.\\u000a All these structural effects, which are strongest in Ca1.8Sr0.2 RuO4, point to a redistribution of electrons between the different t2g orbitals tuned by

J. Baier; P. Steffens; O. Schumann; M. Kriener; S. Stark; H. Hartmann; O. Friedt; A. Revcolevschi; P. G. Radaelli; S. Nakatsuji; Y. Maeno; J. A. Mydosh; T. Lorenz; M. Braden

2007-01-01

92

Impact of zn Substitution on Phase Formation and Superconductivity of Bi1.6Pb0.4Sr2Ca2Cu3-xZnxO10-? with x = 0.0, 0.015, 0.03, 0.06, 0.09 and 0.12  

NASA Astrophysics Data System (ADS)

Samples of series Bi1.6Pb0.4Sr2Ca2Cu3-xZnxO10-? with x = 0.0, 0.015, 0.03, 0.06, 0.09 and 0.12 are synthesized by solid-state reaction route. All the samples crystallize in tetragonal structure with majority (> 90%) of Bi-2223 (Bi2Sr2Ca2Cu3O10) phase (c-lattice parameter ~ 36 Å). The proportion of Bi-2223 phase decreases slightly with an increase in x. The lattice parameters a and c of main phase (Bi-2223) do not change significantly with increasing x. Superconducting critical transition temperature (Tc) decreases with x as evidenced by both resistivity [?(T)] and ac magnetic susceptibility [?(T)] measurements. Interestingly the decrement of Tc is not monotonic and the same saturates at around 96 K for x > 0.06. In fact Tc decreases fast (~ 10 K/at%) for x = 0.015 and 0.03 samples and later nearly saturates for higher x values. Present results of Zn doping in Bi-2223 system are compared with other Zn-doped HTSC (high temperature superconducting) systems, namely the RE-123 (REBa2Cu3O7) and La-214 ((La, Sr)2CuO4).

Saxena, R. B.; Giri, Rajiv; Awana, V. P. S.; Singh, H. K.; Ansari, M. A.; Kumaraswamy, B. V.; Gupta, Anurag; Nigam, Rashmi; Singh, K. P.; Kishan, H.; Srivastava, O. N.

93

Relationship between cation substitution and stability of perovskite structure in SrCoO 3– ? -based mixed conductors  

Microsoft Academic Search

In SrCoO3–? (SC)-based mixed conductors, cation substitution is necessary to stabilize the high-oxygen permeable perovskite structure, but the dose of the substitution should be minimized to avoid degradation of permeability. To clarify the relation between the substitutional cation and the perovskite stability of the mixed conductor, SC-based oxides, (La0.1Sr0.9)CoO3–? and Sr(Co0.9X0.1)O3–? where X was Ni, Cu, Zn, Cr, Fe, Al,

T. Nagai; W. Ito; T. Sakon

2007-01-01

94

Synthesis of Bi-Ca-Sr-Cu-O superconductive material  

SciTech Connect

This patent describes a process for making a sinterable superconductive composition in powder form having the formula Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub x} where x is from about 7.5 to about 8.5. It comprises forming an admixture comprising an alkali metal chloride solvent material selected from the group consisting of sodium chloride and potassium chloride and mixtures thereof, and the oxide or oxide precursors of bismuth, calcium, strontium, and copper in amounts sufficient to form the composition by reaction, heating the admixture to a temperature sufficient to melt the alkali metal chloride, dissolve the oxides of bismuth, calcium, strontium and copper and form the superconductive composition, maintaining the temperature to continuously dissolve reactant oxides or oxide precursors until substantially consumed by formation and precipitation of the composition from the reactant-saturated solvent material; cooling the molten mass to a solid; separating and recovering the superconductive composition by dissolving the alkali metal chloride solvent material in water; and comminuting the superconductive composition to produce powder.

Arendt, R.H.

1992-03-17

95

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

PubMed Central

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

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

2003-01-01

96

Electrical transport and magnetoresistive properties of nanophasic La1-XAXMnO3 (A = Ca, Sr and Na) manganites  

NASA Astrophysics Data System (ADS)

With a view to understand the electrical transport and magnetoresistance behavior of divalent (Ca & Sr) and monovalent (Na) substituted nanophasic lanthanum manganites, a series of materials were prepared using co-precipitation route by sintering at 800 °C. The effect of doping has been investigated in terms of structural, grain size, metal-insulator transition and variation in magnetoresistance properties for La0.7Ca0.3MnO3 (LCMO), La0.7Sr0.3MnO3 (LSMO) and La0.8Na0.2MnO3 (LNMO) samples. The X-ray diffraction data were analyzed using Rietveld refinement technique. It has been found that the samples doped with Sr and Na having rhombohedral structure with R-3c space group. The sample with Ca doping crystallizes into orthorhombic structure with Pnma space group. From resistivity measurements, it is found that all the samples exhibit metal-insulator transition (TMI) in the range of 201-261 K, which is low as compared to the samples prepared by ceramic route. The electrical resistivity data were analyzed using various theoretical models.

Mankadia, S. R.; Bhalodia, J. A.

2013-06-01

97

Piezoelectric Properties of V and Ba Substituted SrBi2Nb2O9 Ceramics  

Microsoft Academic Search

Piezoelectric properties of vanadium and barium-substituted strontium bismuth niobate, Sr1?xBaxBi2Nb2?yVyO9 [SBBNV-x (x = 0.0?0.2, y = 0.05)] ceramics synthesized by a low-temperature ceramic fabrication process were investigated. Grain orientation effects on their piezoelectric properties were also investigated using a hot-forging (HF) method. SBBNV-x ceramics were sintered at 950?1050°C. This sintering temperature is about 200°C lower than that of non-V-substituted SBBN-x.

Shinya Inai; Jyunpei Sato; Rintaro Aoyagi; Yuji Hiruma; Muneyasu Suzuki; Hajime Nagata; Tadashi Takenaka

2007-01-01

98

Regulation of systolic [Ca2+]i and cellular Ca2+ flux balance in rat ventricular myocytes by SR Ca2+, L-type Ca2+ current and diastolic [Ca2+]i  

PubMed Central

The force–frequency response is an important physiological mechanism regulating cardiac output changes and is accompanied in vivo by ?-adrenergic stimulation. We sought to determine the role of sarcoplasmic reticulum (SR) Ca2+ content and L-type current (ICa-L) in the frequency response of the systolic Ca2+ transient alone and during ?-adrenergic stimulation. Experiments (on single rat ventricular myocytes) were designed to be as physiological as possible. Under current clamp stimulation SR Ca2+ content increased in line with stimulation frequency (1–8 Hz) but the systolic Ca2+ transient was maximal at 6 Hz. Under voltage clamp, increasing frequency decreased both systolic Ca2+ transient and ICa-L. Normalizing peak ICa-L by altering the test potential decreased the Ca2+ transient amplitude less than an equivalent reduction achieved through changes in frequency. This suggests that, in addition to SR Ca2+ content and ICa-L, another factor, possibly refractoriness of Ca2+ release from the SR contributes. Under current clamp, ?-adrenergic stimulation (isoprenaline, 30 nm) increased both the Ca2+ transient and the SR Ca2+ content and removed the dependence of both on frequency. In voltage clamp experiments, ?-adrenergic stimulation still increased SR Ca2+ content yet there was an inverse relation between frequency and Ca2+ transient amplitude and ICa-L. Diastolic [Ca2+]i increased with stimulation frequency and this contributed substantially (69.3 ± 6% at 8 Hz) to the total Ca2+ efflux from the cell. We conclude that Ca2+ flux balance is maintained by the combination of increased efflux due to elevated diastolic [Ca2+]i and a decrease of influx on ICa-L on each pulse.

Dibb, K M; Eisner, D A; Trafford, A W

2007-01-01

99

Effects of amino acid substitutions at glycine 420 on SR-BI cholesterol transport function.  

PubMed

Scavenger receptor class B type I (SR-BI) facilitates the uptake of HDL cholesteryl esters (CEs) in a two-step process involving binding of HDL to its extracellular domain and transfer of HDL core CEs to a metabolically active membrane pool, where they are subsequently hydrolyzed by a neutral CE hydrolase. Recently, we characterized a mutant, G420H, which replaced glycine 420 in the extracellular domain of SR-BI with a histidine residue and had a profound effect on SR-BI function. The G420H mutant receptor exhibited a reduced ability to mediate selective HDL CE uptake and was unable to deliver HDL CE for hydrolysis, despite the fact that it retained the ability to bind HDL. This did not hold true if glycine 420 was replaced with an alanine residue; G420A maintained wild-type HDL binding and cholesterol transport activity. To further understand the role that glycine 420 plays in SR-BI function and why there was a disparity between replacing glycine 420 with a histidine versus an alanine, we generated a battery of point mutants by substituting glycine 420 with amino acids possessing side chains that were charged, hydrophobic, polar, or bulky and tested the resulting mutants for their ability to support HDL binding, HDL cholesterol transport, and delivery for hydrolysis. The results indicated that substitution with a negatively charged residue or a proline impaired cell surface expression of SR-BI or its interaction with HDL, respectively. Furthermore, substitution of glycine 420 with a positively charged residue reduced HDL CE uptake as well as its subsequent hydrolysis. PMID:17372332

Parathath, Saj; Darlington, Yolanda F; de la Llera Moya, Margarita; Drazul-Schrader, Denise; Williams, David L; Phillips, Michael C; Rothblat, George H; Connelly, Margery A

2007-03-19

100

Interlaboratory comparison study of Mg\\/Ca and Sr\\/Ca measurements in planktonic foraminifera for paleoceanographic research  

Microsoft Academic Search

Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg\\/Ca and Sr\\/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg\\/Ca

Yair Rosenthal; Suzanne Perron-Cashman; Caroline H. Lear; Edouard Bard; Stephen Barker; Katharina Billups; Martha Bryan; Margaret L. Delaney; Peter B. deMenocal; Gary S. Dwyer; Henry Elderfield; Chris R. German; Mervyn Greaves; David W. Lea; Thomas M. Marchitto; Dorothy K. Pak; Georges L. Paradis; Ann D. Russell; Ralph R. Schneider; Kathleen Scheiderich; Lowell Stott; Kazuyo Tachikawa; Eric Tappa; Robert Thunell; Michael Wara; Syee Weldeab; Paul A. Wilson

2004-01-01

101

Magnetic order changes in Al substituted Sr 2FeMoO 6 double perovskites  

Microsoft Academic Search

We have studied the effect of Al substituting for Fe in Sr2(Fe1?xAlx)MoO6 (x?0.3) double perovskites. X-ray diffraction, magnetic measurements at low and room temperature and Mössbauer spectroscopy have been used to determine the structural and magnetic properties of these compounds. The main observed effect is an increase with respect to the undoped composition, of the cationic order with Al doping

J. Gutiérrez; L. M Rodr??guez-Mart??nez; J. M Barandiarán; T. Hernández; T. Rojo

2003-01-01

102

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

NASA Astrophysics Data System (ADS)

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.

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

2009-12-01

103

Composite microstructures in the Bi-Sr-Ca-Cu-O system  

Microsoft Academic Search

We report a detailed microstructural study of red phases obtained in the crystal growth of the 2212 superconductor from Bi-Sr-Ca-Cu-O\\u000a melts (Bi : Sr : Ca : Cu = 4 : 3 : 3 : 4 or 2 : 2 : 2 : 4) during cooling from 1000–1050°C. Crystallization from temperatures\\u000a well above 1000°C leads to quantitative formation of red

M. Yu. Kameneva; L. P. Kozeeva; N. V. Podberezskaya; D. Yu. Naumov; N. V. Kurat’eva; V. E. Fedorov

2007-01-01

104

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

Microsoft Academic Search

We propose a method of using two tracers, water Sr\\/Ca ratio (with a precision of better one per mil), and salinity, to differentiate the freshwater and marine sources of oceanic water for coastal areas with strong upwelling. In general, water column Sr\\/Ca ratios increase from a surface value of 8.50 mmol\\/mol to 8.64 mmol\\/mol, found below 1000 m in the

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

2002-01-01

105

Characteristic of IR absorption of 110K Bi(Pb)-Sr-Ca-Cu-O superconductor  

NASA Astrophysics Data System (ADS)

We used the co-decomposition method to prepare Bi(Pb)-Sr-Ca-Cu-O superconductor under partial oxygen pressure. The oxygen dependence of the high Tc phase was studied. The IR absorption of (Bi1-x Pbx)2Sr2Ca2Cu3O10+b superconductor was measured at various temperatures from 98K to 290K. An absorption peak was observed at wave number 1265cm-1 below 217K.

Ze, Xianyu; Quanli, Hu; Yubo; Cunjuan, Li; Sundi; Dingzhan, Sun

1991-12-01

106

Zero-phonon lines in CaF2 and SrF2  

Microsoft Academic Search

A number of prominent zero-phonon lines have been investigated in additively coloured CaF2 and SrF2 using uniaxial stress. Stark effect and magneto-optical techniques. It is tentatively suggested that a line at 598.8 nm in CaF2 may be a transition of a square planar F4 complex. There is a corresponding centre in SrF2. Other lines investigated appear to be associated with

J. H. Beaumont; A. L. Harmer; W. Hayes; A. R. L. Spray

1972-01-01

107

Infiltration and Injection of a Ca-Citrate-PO4 Solution to Form Apatite In Situ for Sr-90 Remediation at the Hanford 100N Area – An Update  

SciTech Connect

Sr-90 present in groundwater and the vadose zone at the Hanford 100N area due to past waste disposal practices has reached the nearby Columbia River, as evidenced by Sr-90 concentrations in near river wells and aquifer tubes and near shore sediments. Sr-90 is currently being remediated by adsorption onto apatite (55 times stronger than Sr-90 adsorption to sediment), followed by incorporation of the Sr-90 into the apatite structure. If the Sr-90 can remain immobilized for 300 years (~ten 29.1-yr half-lives of Sr-90 decay), it will have decayed below regulatory limits to Y-90 and to stable Zr-90. Apatite [Ca10(PO4)6(OH)2] is being precipitated in situ in saturated zone sediments by injection of a aqueous solution of Ca-citrate and Na-phosphate through a series of 16 wells. For the treatability study, field scale demonstration of the technology was implemented through injection of a low-concentration, apatite-forming solution, followed by high concentration solution injections as required to emplace sufficient treatment capacity to meet treatability test objectives. Analysis of field cores collected after the low concentration injections indicates that targeted apatite contents were achieved and that ~25% of the Sr-90 associated with the sediment was incorporated in the apatite structure. Aqueous Sr-90 monitoring in four compliance monitoring wells over a year following the high concentration injections indicates 84% to 95% decrease in Sr-90 concentrations (relative to the low and high end of the baseline range, respectively). Cores are currently being analyzed to confirm the apatite mass and Sr-90 substitution in apatite after these high concentration injections.

Szecsody, James E.; Fruchter, Jonathan S.; Vermeul, Vincent R.; Williams, Mark D.; Fritz, Brad G.; Mendoza, Donaldo P.; McKinley, James P.

2010-03-11

108

Decomposition products of superconducting (Bi,Pb)2Sr2Ca2Cu3O(10 + delta)  

NASA Astrophysics Data System (ADS)

High-temperature in situ x-ray studies of Pb-doped Bi2Sr2Ca2Cu3O(10 + delta) have been carried out in a variety of different environments in order to determine the range of stability and the decomposition products that appear as this material transforms into phases. In air at 840 C, a combination of Bi2Sr2Ca0Cu1O(6 + delta) Ca2PbO4, (Sr,Ca)2Cu1O3, and some liquid phase coexists with Bi2Sr2Ca2Cu3(10 + delta) as it gradually decomposes. When the Bi2Sr2Ca2Cu3O(10 + delta) is completely gone the Bi2Sr2Ca0Cu1O(6 + delta) Ca2PbO4, and (Sr,Ca)2Cu1O3 transform to a liquid with CaO and other phases floating on the liquid. If Ag is micromilled with the Bi2Sr2Ca2Cu3O(10 + delta) the decomposition process similar, but all of the temperatures are lowered substantially. If the partial pressure of O2 is reduced to 10 kPa over the BiSr2Ca2Cu3O(10 + delta)/Ag sample, the decomposition temperatures and products are similar to the 20 kPa case.

Xu, Ming; Finnemore, D. K.

1994-07-01

109

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

SciTech Connect

The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2#2;y)O(7-j,) (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2#2;x)SrxRhyZr(2#2;y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had significantly less carbon (0.17 gcarbon/gcatalyst). It is speculated that improved oxygen ion mobility in the LSRZ material, which resulted from Sr substitution, was responsible for the reduction in carbon formation on the surface.

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

2008-01-01

110

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

SciTech Connect

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, and PO4 solutions show greater Sr and Sr-90 incorporation during initial precipitation and less initial mobilization with solutions with low Ca2+ concentration. While all solutions showed nearly the same Sr uptake into apatite (14 to 17% by 2 weeks, 21% to 30% by 5 weeks), the incorporation efficiency (i.e., mM Sr incorporated per mM PO4 injected) was higher for solutions containing citrate. The Sr incorporation rate into apatite during initial precipitation (by 1 month) averaged 4.64 ± 1.9 x 10-4 h-1 (half-life 1500 ± 430 h, 8.85 x 10-7 mg Sr/day/mg apatite). The injection solution used in field injections #3 to #18 (10 mM PO4, 1 mM Ca, 2.5 mM citrate), which is deficient in Ca (a total of 16.7 mM needed to form apatite with 10 mM of PO4), resulted in the initial Sr and Ca peak (24 h) at 4.7x groundwater. By 30 days, the aqueous Sr concentration was 0.28x groundwater and Ca 0.43x groundwater, as both Sr and Ca are used to form initial apatite precipitates. Reactive transport simulation of the complex ion exchange, biodegradation, and precipitation processes showed that the initial Sr groundwater increase mobilized only 1.5% of the Sr mass in sediments. Citrate biodegradation, a necessary step in Ca-citrate-PO4 solutions forming apatite, had an average half-life of 50 h (at aquifer sediment/water ratio and temperature), and decreased an order of magnitude with sediment depth as the microbial biomass decreased five orders of magnitude. The rate of citrate biodegradation was relatively invariant with biomass and water saturation (50% to 100%, for vadose zone infiltration) possibly due to significant microbial injection using river water and subsurface microbial mobilization.

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

111

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

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

112

High precision measurement of Mg/Ca and Sr/Ca ratios in carbonates by cool plasma quadrupole inductively coupled plasma mass spectrometry  

NASA Astrophysics Data System (ADS)

We have developed a high-precision analytical technique using an quadrupole inductively coupled plasma mass spectrometer Agilent 7500s, for simultaneously measuring Mg/Ca and Sr/Ca ratios in carbonates, which are broadly used as environmental and climatic proxies in the Earth Sciences. Cool plasma technique with 650-W RF power was employed to diminish spectral interference. A desolvation introduction system was used to enhance sensitivity, improve detection limit and reduce sample size. Intensities of isotopes, including 24Mg, 43Ca and 86Sr, were all detected in pulse-counting mode. Mg/Ca and Sr/Ca ratios were calculated directly from intensity ratios, 24Mg/43Ca and 86Sr/43Ca, using external matrix-matched standards to correct for instrumental mass discrimination and low-frequency ratio drift. For Mg/Ca analysis, matrix effect of Ca level is 0.018 Mg/Ca (mmol/mol) / [Ca] (ppm). This problem can be overcome by holding [Ca] from 6-8 ppm in sample solution or correcting measured ratio with an empirical formula. Different Sr/Ca also slightly affects Mg/Ca determination with a slope of 0.017 Mg/Ca (mmol/mol) / Sr/Ca (mmol/mol). It is mainly caused by the formation of doubly-charge ion of 86Sr, which biases intensity measurement of 43Ca+ ion beam. This effect brings about only a trivial offset less than 0.1% on Mg/Ca determination for Quaternary foraminiferal and coral samples. Internal precision given by our method ranges 0.1-0.2% (2sd). Replicate measurements made on standards and samples show that external uncertainties of 0.5% and 0.4% (2sd) can be achieved for Mg/Ca and Sr/Ca, respectively. Requirement of a small sample size of only 3.5 microgram carbonate even allows investigating characteristics of single foraminiferal chamber.

Shen, C.; Chui, H.; Chu, M.; Chen, M.; Wei, K.; Steinke, S.

2004-12-01

113

Preparation, crystal structure and superconductivity of (C, Cu)(Sr, Ca)2(Y, Ca, Sr)Cu2O7  

NASA Astrophysics Data System (ADS)

A series of solid solutioins containing CO3 groups, (cycu1-y)(Sr1-z/2Caz/2)2(Y1-xCax-zSrz)Cu2 Odd with 0.30<=x<=0.70, was prepared at 1313 K under the atmosphere of O2-CO2. 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 (Tc 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 CO3 groups and by the introduction of oxygen atoms into the vacant ``apical'' oxygen site, where the CO3 group is not present.

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

1994-09-01

114

In-plane orientation of Bi2Sr2CaCu2Ox thin films on (110) SrTiO3 vicinal surfaces  

Microsoft Academic Search

Crystal structures of Bi2Sr2CaCu2Ox thin films of which the c axes are tilted about 45° against substrate surfaces were investigated with x-ray-diffraction, x-ray asymmetric reflection, x-ray topography, and cross-sectional high-resolution transmission-electron microscopy. The following substrates were used: (110), 2° off (110), 5° off (110), and 10° off (110) SrTiO3. Bi2Sr2CaCu2Ox films were epitaxially grown with the (117) Bi2Sr2CaCu2Ox vicinal surface

M. Kataoka; J. Tanimura; O. Wada; T. Ogama; K. Kuroda; T. Takami; K. Kojima

1993-01-01

115

Amounts of Sr and Ca eluted from deciduous enamel to artificial saliva related to dental caries.  

PubMed

This study was performed to elucidate the relationship between dental caries and the levels of Sr and Ca eluted from enamel, and to examine whether these elements are useful as factors to assess caries risk. The available 103 (Sr) and 108 (Ca) samples were obtained among 111 collected deciduous teeth. The healthy regions of enamel were decalcified in artificial saliva at pH 6.2 and 5.5. The eluted levels of these elements from enamel were determined using atomic absorption spectrophotometry. Sr and Ca levels were not affected by the sex nor tooth type. Sr levels of the caries-experienced tooth (CE) group were 2.6-fold (pH 6.2) and 2.2-fold (pH 5.5) higher than those of the sound tooth (ST) group, respectively. Furthermore, the Sr levels were significantly higher in the teeth with treated than in those with untreated caries. Only at pH 6.2 was a significant difference found in Ca levels between the ST and CE groups. In the ST group, at pH 5.5, both the Sr and Ca levels significantly increased when the children had six or more carious teeth. The Sr and Ca elution levels were significantly inhibited in the teeth receiving fluoride application every 3 or 4 months compared to those that were not. These findings indicate that Sr can be an indicator of the acid resistance of teeth, and a useful factor to assess future caries risk. PMID:22391794

Enomoto, Ayaka; Tanaka, Toshiko; Kawagishi, Shigenori; Nakashima, Hideaki; Watanabe, Koji; Maki, Kenshi

2012-03-06

116

A skeletal Sr/Ca record preserved in Dipsastraea (Favia) speciosa and implications for coral Sr/Ca thermometry in mid-latitude regions  

NASA Astrophysics Data System (ADS)

A core (900 mm long) of the scleractinian coral Dipsastraea (Favia) speciosa was collected from Iki Island (˜33°48'N), Japan, one of the highest latitude coral reefs known to exist at present, where winter monthly mean sea surface temperature (SST) drops to 13°C. The Sr/Ca profile was constructed using a bulk sampling method for the uppermost 280 mm interval of the core, which grew between 1966 and 2007, to test whether it could act as a suitable proxy for SST in a harsh environmental setting where reef-building coral do not usually survive. The Sr/Ca-SST relationship derived from the annual Sr/Ca and SST extremes predicted the observed monthly averaged summer SST extremes within an error range of ±1.1°C (1 s.d., n = 40). The obtained Sr/Ca-SST calibration was also found to be valid for subtropical Dipsastraea (Favia) corals, proving its broad applicability. However, low-amplitude winter peaks were observed in the slow-growing intervals, which we confirmed (using individual spot analysis along a continuous growth line) result from the mixing of theca grown at different times. Our bulk sampling approach, across multiple growth lines in the skeleton of D. (F.) speciosa, led to the mixing of asynchronous skeletal part. At the study site, D. (F.) speciosa grows continuously, even during the cold season, suggesting that the skeletal Sr/Ca obtained from specimens of D. (F.) speciosa can be used as an SST proxy in the northwest Pacific marginal seas.

Seo, Inah; Lee, Yong Il; Watanabe, Tsuyoshi; Yamano, Hiroya; Shimamura, Michiyo; Yoo, Chan Min; Hyeong, Kiseong

2013-08-01

117

Large Magnetothermopower Effect in Dirac Materials (Sr/Ca)MnBi2  

SciTech Connect

We report temperature and magnetic field dependence of the thermal transport properties in single crystals of (Sr/Ca)MnBi2 with linear energy dispersion. In SrMnBi2 thermopower is positive, indicating hole-type carriers and the magnetic field enhances the thermopower significantly. The maximum change of thermopower is about 1600% in 9 T field and at 10 K. A negative thermopower is observed in CaMnBi2 with dominant electron-type carriers, and, in contrast, the magnetic field suppresses the absolute value of thermopower. First-principle band structure shows that the chemical potential is close to the Dirac-cone-like points in linear bands. The magnetic field suppresses the apparent Hall carrier density of CaMnBi2 below 50 K. The large magnetothermopower effect in (Sr/Ca)MnBi2 is attributed to the magnetic field shift of chemical potential.

Petrovic C.; Wang, K.; Wang, L.

2012-03-12

118

The Extracellular Calcium-Sensing Receptor (CaSR) Is a Critical Modulator of Skeletal Development  

PubMed Central

The extracellular Ca2+-sensing receptor (CaSR) plays a nonredundant role in the functions of the parathyroid gland (PTG) and the kidney. Severe hyperparathyroidism, premature death, and incomplete gene excision in Casr?/? mice have precluded the assessment of CaSR function in other tissues. We generated mice with tissue-specific deletion of Casr in the PTG, bone, or cartilage. Deletion of Casr in the PTG or bone resulted in profound bone defects, whereas deletion of Casr in chondrocytes (cartilage-producing cells) resulted in death before embryonic day 13 (E13). Mice in which chondrocyte-specific deletion of Casr was induced between E16 and E18 were viable but showed delayed growth plate development. Our data show a critical role for the CaSR in early embryogenesis and skeletal development.

Chang, Wenhan; Tu, Chialing; Chen, Tsui-Hua; Bikle, Daniel; Shoback, Dolores

2012-01-01

119

The effects of La–Zn substitution on the magnetic properties of Sr-magnetoplumbite ferrite nano-particles  

Microsoft Academic Search

The La–Zn substituted Sr-Magnetoplumbite ferrite LaxSr1?xZnxFe12?xO19 (x=0–0.6) fine particles were prepared to investigate the effects of the substitution on the magnetic properties of the samples. It is observed, with increasing substitution rate, that the saturation magnetization Ms as well as the magnetocrystalline anisotropy constant KU1 increased up to a maximum for about x=0.3, then decreased rapidly. The value of dHc\\/dT

Jianmin Bai; Xiaoxi Liu; Tian Xie; Fulin Wei; Zheng Yang

2000-01-01

120

Coral Calcifying Fluid pH (Indicated by ?11B) and Skeletal Sr/Ca in Coral Skeletons  

NASA Astrophysics Data System (ADS)

We have produced a high spatial resolution SIMS record of Sr/Ca and ?11B across ~ 1 year of a modern Porites lobata coral from Hawaii. We used skeletal ?11B to estimate the calcifying fluid pH at the time of calcification and have correlated ?11B with Sr/Ca. Our data indicate that Sr/Ca and calcification site pH are inversely correlated at high pH. This is consistent with the model for the role of the enzyme Ca-ATPase in calcification. During periods of rapid calcification e.g. under optimal light conditions, Ca-ATPase activity is high, Ca2+ is rapidly pumped to the calcification site and H+ is extruded resulting in a high pH in the calcifying fluid. Sr is either not transported by the enzyme or is transported less efficiently than Ca and the Sr/Ca of the calcifying fluid is effectively reduced. However the relationship between Sr/Ca and ?11B is not observed over the lower pH range. It is reasonable to assume that calcification is slower at these low pHs and it is possible that the contribution of Ca-ATPase to Ca transport is negligible under these conditions. We observe significant Sr/Ca heterogeneity in regions of the skeletons deposited at both high and low pH and observe a large range in Sr/Ca (>0.5mmol mol-1) deposited at any single pH value. This indicates that skeletal Sr/Ca heterogeneity is generated by other processes besides the activity of Ca-ATPase. The role of other Ca (and Sr) transport processes in generating this heterogeneity remains to be resolved.

Finch, A. A.; Allison, N.

2008-12-01

121

Evidence of downstream migration of Sakhalin taimen, Hucho perryi , as revealed by Sr?:?Ca ratios of otolith  

Microsoft Academic Search

The migratory history of Sakhalin taimen, Hucho perryi, was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith by using wavelength dispersive X-ray spectrometry on an electron microprobe. Otolioth Sr?:?Ca ratios of freshwater-reared samples remained consistently at low levels throughout the otolith. The Sr?:?Ca ratios of samples from Lake Aynskoye of Sakhalin Island showed a low

Takaomi Arai; Aya Kotake; Kentaro Morita

2004-01-01

122

(Ca/Sr)Au{sub x}Cd{sub 1-x}: Stacking variants of the CrB-FeB series  

SciTech Connect

The structural chemistry of binary 1:1 alkaline earth metallides A{sup II}M (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){sub 2}(h{sub 2}c){sub 2}), depending on the proportion of the Cd substitution a successive change to structures with increased hexagonality is observed: In SrAu{sub 0.93}Cd{sub 0.07} (monoclinic, space group P2{sub 1}/m, a=621.3(4), b=472.4(2), c=1216.1(9)pm, beta=96.97(5){sup 0}, Z=6, R1=0.0467) the stacking sequence is h{sub 2c}, i.e. the hexagonality is 66.67%. A slightly more increased Cd content in SrAu{sub 0.78}Cd{sub 0.22} (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 (h{sub 3}c){sub 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/beta-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. - SrAu{sub 0.93}Cd{sub 0.97}, one of the stacking sequences of the CrB/FeB structure type series found in the quasibinary section SrAu-SrCd.

Harms, Wiebke; Duerr, Ines; Daub, Michael [Institut fuer Anorganische und Analytische Chemie, University of Freiburg, Albertstr. 21, D-79104 Freiburg (Germany); Roehr, Caroline, E-mail: caroline@ruby.chemie.uni-freiburg.d [Institut fuer Anorganische und Analytische Chemie, University of Freiburg, Albertstr. 21, D-79104 Freiburg (Germany)

2010-01-15

123

Enhancement of the Critical Current Density in Single-Crystal Bi_2Sr_2CaCu_2O_8 Superconductors by Chemically Induced Disorder  

NASA Astrophysics Data System (ADS)

The effect of metal substitution on the critical current densities of single-crystal Pb_xBi2 - xSr_2CaCu_2O_8 (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/cm^2 to 2 x 10^6 A/cm^2 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 Bi_2Sr_2CaCu_2O_8. 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.

Wang, Yue Li; Wu, Xian Liang; Chen, Chia-Chun; Lieber, Charles M.

1990-09-01

124

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

PubMed

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. PMID:11607103

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

1990-09-01

125

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

PubMed Central

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 ?mol/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 (?44/40Cacalcite-aq = ?44/40Cacalcite ? ?44/40Caaq) correlates inversely to log R values for all experiments. In addition, an inverse relationship between ?44/40Cacalcite-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 ?44/40Cacalcite-aq relationship, Sr/Ca and ?44/40Cacalcite 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.

Tang, Jianwu; Niedermayr, Andrea; Kohler, Stephan J.; Bohm, Florian; K?sakurek, Basak; Eisenhauer, Anton; Dietzel, Martin

2012-01-01

126

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

USGS Publications Warehouse

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.

Patchett, P. J.

1980-01-01

127

Sr/Ca in Coral Aragonite: Is Night Carbonate a Good Indicator of Sea Surface Temperatures?  

NASA Astrophysics Data System (ADS)

Sr/Ca in coral skeletons has potential as an indicator of past seawater conditions but exhibits geochemical heterogeneity on a small spatial scale (<100 ?m) that does not reflect variations in sea surface temperature (SST) or chemistry. Skeletal Sr/Ca is affected by variations in skeletal calcification rate which may be dependent on the photosynthetic activity of the zooxanthellae in coral tissue. The skeleton deposited at night may be unaffected by these variations and may be a more reliable indicator of SST (Cohen et al. 2001). We used secondary ion mass spectrometry with a 10 ?m diameter analysis spot to construct records of Sr/Ca in a Porites lobata specimen from Lanakai, Oahu, Hawaii. Analyses were performed on sections cut perpendicular to the growth surface of the coral skeleton, spanning annual bands. Parallel tracks were analysed following fasciculi (composed of acicular crystals deposited during the day) and centres of calcification (composed of fusiform crystals deposited at night). The Sr/Ca of the day and night material follow similar seasonal trends but are offset with night carbonate typically enriched by 0.3-0.4 mmol mol-1. Both profiles are characterised by large Sr fluctuations of 0.4-0.5 mmol mol-1, which are deposited approximately days apart and are superimposed on the general Sr seasonal trend. These fluctuations do not reflect variations in SST but may relate to daily variations in coral calcification or linear extension rate both of which can vary markedly during the day and night. We conclude that night carbonate is affected by kinetic processes and that there are similar challenges in reconstructing SST records from night carbonate as from day carbonate. Cohen AL et al., Kinetic control of skeletal Sr/Ca in a symbiotic coral: implications for the palaeotemperature proxy, Paleoceanography, 16, 20-26, 2001.

Allison, N.; Finch, A. A.

2002-12-01

128

Dependence of Crystal Orientation of BiSrCaCuO Thin Films on Off-Angles of Vicinal SrTiO3 (110) Surfaces  

Microsoft Academic Search

Crystal orientation of BiSrCaCuO(11n) films depends on off-angles of vicinal SrTiO3(110) surfaces. Surfaces of SrTiO3(110) were cut 2°, 5° and 10° toward the [100] direction, and BiSrCaCuO thin films, which had a 2212 phase, were formed on these vicinal surfaces by RF magnetron sputtering. C-axes almost parallel to the [100] and [010] directions of the substrate were observed when the

Osamu Wada; Ken'ichi Kuroda; Junji Tanimura; Masayuki Kataoka; Kazuyoshi Kojima; Tetsuya Takami; Koichi Hamanaka; Tetsuo Ogama

1991-01-01

129

Preparation of superconducting printed thick films of Bi-Sr-Ca-Cu-O and Bi-Pb-Sr-Ca-Cu-O systems  

NASA Astrophysics Data System (ADS)

The thick films of Bi-Sr-Ca-Cu-O and Bi-Pb-Sr-Ca-Cu-O systems were prepared on various substrates by a screen printing method. Superconducting properties in these thick films were examined as a function of powder preparations for pastes and postprinting annealing conditions. By appropriate heat treatments after printing for Bi systems, highly c-axis oriented thick films on (100) MgO substrate were obtained, which showed zero resistance at 107 K. For Bi-Pb systems, the powders contained the high-Tc phase of Bi systems in a large volume fraction were prepared for a printing paste. The films were screen-printed using this paste, and then annealed. These films deposited on (100) MgO and Ag metal substrates showed zero resistance at 100 and 100 K, rekspectively.

Hoshino, K.; Takahara, H.; Fukutomi, M.

130

Neutron diffraction study of a (C,Cu) (Sr,Ca)2(Y,Ca,Sr) Cu2O7 superconductor  

NASA Astrophysics Data System (ADS)

The crystal structure of a cuprate containing CO3 groups, (C0.58Cu0.42)(Sr0.88Ca0.12)2(Y0.50Ca0.26Sr0.24) Cu2O7, and its high-pressure oxygen-annealed samples were refined by means of the Rietveld method for neutron-powder-diffraction data. The as-prepared sample (non-superconducting) has neither oxygen defect nor carbonate defect in the structure. Noticeable absence of oxygen atoms and carbonate groups are detected for the annealed (superconducting) sample. It is suggested that hole doping is achieved during high-pressure oxygen annealing by the release of some CO3 groups and by the introduction of oxygen atoms into the vacant `apical' oxygen site, when the CO3 group is not present.

Miyazaki, Y.; Yamane, H.; Kajitani, T.; Morii, Y.; Funahashi, S.; Hirai, T.

1995-02-01

131

T-tubule depolarization-induced SR Ca2+ release is controlled by dihydropyridine receptor- and Ca(2+)-dependent mechanisms in cell homogenates from rabbit skeletal muscle  

Microsoft Academic Search

In vertebrate skeletal muscle, the voltage-dependent mechanism of rapid sarcoplasmic redculum (SR) Ca 2+ release, commonly referred to as excitation- contraction (EC) coupling, is believed to be mediated by physical interaction between the transverse (T)-tubule voltage-sensing dihydropyridine receptor (DHPR) and the SR ryanodine receptor (RyR)\\/Ca 2+ release channel. In this study, differen- tial T-tubule and SR membrane monovalent ion permeabilities

KRISTIN ANDERSON; GERHARD MEISSNER

1995-01-01

132

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

DOEpatents

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.

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

1994-10-11

133

Crystal structures of the double perovskites Ba 2Sr 1? x Ca x WO 6  

Microsoft Academic Search

Structures of the double perovskites Ba2Sr1?xCaxWO6 have been studied by the profile analysis of X-ray diffraction data. The end members, Ba2SrWO6 and Ba2CaWO6, have the space group I2\\/m (tilt system a0b?b?) and Fm3¯m (tilt system a0a0a0), respectively. By increasing the Ca concentration, the monoclinic structure transforms to the cubic one via the rhombohedral R3¯ phase (tilt system a?a?a?) instead of

W. T. Fu; S. Akerboom; D. J. W. IJdo

2007-01-01

134

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

DOEpatents

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.

Dorris, Stephen E. (La Grange Park, IL); Poeppel, Roger B. (Glen Ellyn, IL); Prorok, Barton C. (Harrisville, PA); Lanagan, Michael T. (Woodridge, IL); Maroni, Victor A. (Naperville, IL)

1994-01-01

135

Interband Optical Conductivity of Bi2CaSr2Cu2O8  

NASA Astrophysics Data System (ADS)

The band structure and interband optical conductivity of Bi2CaSr2Cu2O8 superconductor in the body-centered tetragonal sub-unit is calculated self-consistently using orthogonalized linear combination of atomic orbitals method. The result shows Bi2CaSr2Cu2O8 has both semi-metal-like and semiconductor-like features with small band gap and band overlap. The interband optical conductivity shows strong anisotropy between the in-plane and z-direction components. A plasmon frequency at 6 eV is predicted.

Ching, W. Y.; Zhao, G. L.; Xu, Y. N.; Wong, K. W.

136

Enhancement of T sub c of a BiSrCaCuO sub y superconductor  

SciTech Connect

Liquid nitrogen quenching of the BiSrCaCuO{sub y} superconductor is studied. The BiSrCaCuO{sub y} superconductors were obtained by initially heating them up to 860{degrees}C for 48, 60 and 72 hours, respectively. These below 80 K superconductors were reheated to 860{degrees}C for 16 hours and then quenched in liquid nitrogen. The zero resistivity temperatures were 82 K, 85 K and 83 K for the three heating periods. X-ray diffraction patterns indicated that these superconductors had the 2212 structure. Their response to liquid nitrogen quenching point to them being the 4424 superconductor.

Eaiprasertsak, K.; Tang, I.M.; Winotai, P. (Faculty of Science, Mahidol Univ., Rama 6 Road, Bangkok 4 (TH)); Tontiwattana, W.; Methasiri, T. (Faculty of Science, Chulalongkorn Univ., Bangkok 5 (TH))

1990-01-01

137

An approach to achieve layered spintronics material using brownmillerite compound Ca2.5Sr0.5GaMn2O8  

NASA Astrophysics Data System (ADS)

Magnetic and magnetotransport properties of the naturally occurring layered compounds Ca2.5- x La x Sr0.5GaMn2O8 ( x = 0, 0.05, 0.075, and 0.1) have been reported. We have succeeded to introduce ferromagnetic ordering in the pure antiferromagnetic system Ca2.5Sr0.5GaMn2O8 by varying the ratio between Mn3+ and Mn4+ ions. The experimental results of magnetization, magnetoresistance, and neutron diffraction were interpreted on the basis of an electronic phase separation model, where a formation of ferromagnetic clusters (due to DE interactions) inside the layered antiferromagnetic matrix (due to superexchange interactions) in the La-substituted compounds is proposed. Significantly, the present study shows that the magnetic and electronic properties of the layered system Ca2.5Sr0.5GaMn2O8 can be tuned/optimized by appropriate chemical substitution to achieve a new spintronic material based on naturally occurring layered system for practical applications.

Yusuf, S. M.; Bera, A. K.

2013-05-01

138

Single crystals of HgBa{sub 2}Ca{sub n{minus}1}Cu{sub n}O{sub x} and chain compounds A{sub 1{minus}x}CuO{sub 2} (A = Sr,Ca,Ba), high pressure synthesis and properties  

SciTech Connect

High gas pressure up to 11 kbar has been applied for the synthesis and single crystal growth of Hg-based superconductors and one-dimensional A{sub 1{minus}x}CuO{sub 2} cuprates. The authors have investigated the influence of Re, Sr and Pb substitutions and oxygen content on the magnetic flux-pinning properties of single crystals of Hg-based superconductors. The best results have been obtained for Sr and Pb substituted Hg1223 single crystals. Susceptibility, neutron scattering, and torque investigations have been performed on Ca{sub 0.83}CuO{sub 2}, Sr{sub 0.73}CuO{sub 2} and Ba{sub 0.67}CuO{sub 2} compounds containing CuO{sub 2} infinite chains separated by Ca, Sr or Ba layers.

Karpinski, J.; Angst, M.; Meijer, G.I.; Kazakov, S.; Schwer, H.; Wisniewski, A.; Puzniak, R.

1999-11-01

139

[Structure and photoluminescence of ASnO3 (A = Ca, Sr and Ba) : Eu nanocrystalline].  

PubMed

The present paper reports the photoluminescence properties of nanocrytalline ASnO3 (A = Ca, Sr and Ba) : 1% Eu phosphor synthesized by the Pechini-type sol-gel method. The powder was characterized by X-ray diffraction (XRD), UV-Vis absorption spectra, transmission electron microscopy (TEM) and photoluminescence measurements. The experimental results show that BaSnO3 has the ideal cubic peroskite structure, while SrSnO3 and CaSnO3 are both distorted from cubic symmetry by an octahedral tilting distortion. The difference of structure in induced the different spectral properties of ASnO3 : 1% Eu. On the other hand, when A2+ changes from Ca2+ to Ba2+, the luminescence intensity becomes weak. So CaSnO3 : 1% Eu seems to be a good candidate for new phosphors. PMID:18051556

Fu, Xiao-Yan; Niu, Shu-Yun; Zhang, Hong-Wu; Xin, Qin

2007-09-01

140

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

Microsoft Academic Search

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

JOHN F. MARSHALL; MALCOLM T. MCCULLOCH

2002-01-01

141

Melting and Vaporization of the 1223 Phase in the System (Tl-Pb-Ba-Sr-Ca-Cu-O).  

National Technical Information Service (NTIS)

The melting and vaporization of the 1223 ((Tl,Pb):(Ba,Sr):Ca:Cu) oxide phase in the system (Tl-Pb-Ba-Sr-Ca-Cu-O) have been investigated using a combination of dynamic methods (differential thermal analysis, thermogravimetry, effusion) and post-quenching c...

L. P. Cook W. Wong-Ng P. Paranthaman

1996-01-01

142

Enthalpies of Formation of La1-xAxMnO3+/- ? (A=Ca and Sr) Measured by High-Temperature Solution Calorimetry  

NASA Astrophysics Data System (ADS)

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. .

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

2002-01-01

143

Layer-by-layer deposition of superconducting Sr-Ca-Cu-O films by the spray pyrolysis technique  

Microsoft Academic Search

Layer-by-layer deposition of Sr-Ca-Cu-O films has been carried out using the spray pyrolysis technique. Reagent-grade nitrates of strontium, calcium and copper were used to prepare starting solutions for spray pyrolysis. A two-step procedure was used for every layer of the constituents in the sequence Sr-Cu-Ca-Cu-Sr: first, deposition onto silver substrate at 350 °C, then firing at T ? 450 °C,

S. H. Pawar; P. N. Pawaskar; M. J. Ubale; S. B. Kulkarni

1995-01-01

144

The Coral and the Moon: A Biological Effect Possibly Affecting the Precision of the Sr/Ca Paleotemperature Proxy  

NASA Astrophysics Data System (ADS)

In thermodynamic equilibrium with sea water the Sr/Ca ratio of aragonite varies predictably with temperature and the Sr/Ca ratio in coral have thus become a frequently used proxy for past Sea Surface Temperature (SST). However, biological effects can offset the Sr/Ca ratio from its equilibrium value. We present high spatial resolution ion microprobe analyses of Sr/Ca variation in well defined skeletal elements in the reef-building coral Porites lutea from Watamu, Kenya. Our data reveal distinct monthly oscillations in the Sr/Ca ratio, with an amplitude in excess of ten percent of the average Sr/Ca ratio. Such large variations, which we speculate can be the result of metabolic changes synchronous with the lunar cycle, will introduce variability in Sr/Ca measurements based on conventional sampling techniques (e.g. dentist drill) well beyond the analytical precision. Monte Carlo simulations show that under such conditions the precision of the Sr/Ca paleo-thermometer can be limited to about two degrees. Aragonite precipitated during periods of reduced growth rate have smaller biological effects than aragonite precipitated during periods of accelerated growth. Thus, Sr/Ca-based temperature reconstructions from massive scleractinian corals, such as Porites, would potentially become more precise if the corals are preferentially sampled in low growth-rate regions of the skeleton. We therefore recommend a re-analysis of existing Sr/Ca records based on knowledge of temperature impacts on growth rates. If the biological effects observed in the Porites coral studied by us are also observed in other Porites specimens from which long SST records have been derived on the basis of the Sr/Ca paleothermometer using conventional sampling techniques, it may invalidate conclusions based on inferred SST variations of less than about two degrees. Our results also may help explain the notorious difficulties involved in obtaining an accurate and consistent calibration of the Sr/Ca vs. SST relationship. In general, our results point to a strong biological control on the Sr/Ca ratio in coralline aragonite and emphasize the importance of investigating and understanding the Sr/Ca micro-distribution.

Meibom, A.; Stage, M.; Wooden, J. L.; Constantz, B. R.; Dunbar, R. B.; Owen, A.; Grumet, N.; Bacon, C. R.; Chamberlain, C. P.

2003-12-01

145

Migration and Rearing Histories of Chinook Salmon (Oncorhynchus tshawytscha) Determined by Ion Microprobe Sr Isotope and Sr\\/Ca Transects of Otoliths  

Microsoft Academic Search

With the goal of monitoring fish habitat during the first year of life, we used the Stanford-USGS SHRIMP RG ion microprobe to determine 87Sr\\/86Sr and Sr\\/Ca ratios in 25 × 35 mu m areas along radial transects of otoliths from juvenile Chinook salmon (Oncorhynchus tshawytscha) native to four watersheds of markedly different geology. Otoliths from ocean-type Chinook salmon from the

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

2004-01-01

146

?SR studies of the electron-doped Ca1-xSmMnO3  

NASA Astrophysics Data System (ADS)

We have performed muon spin relaxation (?SR) experiments on undoped CaMnO3 and electron-doped Ca1-xSmMnO3 for x=0.1,0.15 and 0.3. Undoped CaMnO3 is a G-type antiferromagnet with a Néel temperature of T?122K. The ?SR signal shows three well-defined frequencies, which decrease continuously with temperature and becomes zero at T?122K. The electron-doped Ca0.85Sm0.15MnO3 which shows colossal magnetoresistive (CMR) behaviour, undergoes a structural and magnetic transition at T?125K. The ?SR signal shows heavily damped oscillating signal. The frequency decreases continuously with increasing temperature. Ca0.9Sm0.1MnO3 and Ca0.7 Sm0.3MnO3 show only relaxation and do not show any frequency. We have determined temperature variation of the muon relaxation rates below and above the magnetic and charge order transitions under zero and longitudinal magnetic fields, which give important information about the nature of these transitions.

Chatterji, Tapan; Andeica, D.; Suryanarayanan, R.; Revcolevschi, A.

2006-03-01

147

Structure and Superconductivity of GaSr2(Tm,Ca)Cu2Oz Cuprate Doped with Cobalt  

NASA Astrophysics Data System (ADS)

To address the structural mechanisms associated with Tc variations induced by Co doping, two samples of the nominal composition (Ga1-xCox)Sr2(Tm0.6Ca0.4)Cu2Oz with x = 0.5 and 0.7 have been prepared and studied by using neutron powder diffraction and transport measurements. In contrast to the x = 0.5 sample, which shows superconductivity around 35 K, the x = 0.7 sample does not exhibit superconductivity. The neutron powder diffraction studies indicate that both samples exhibit the 1212 structure with space group Ima2 and the Co atoms exclusively substitute for the Cu atoms located on the chain sites of the 123 parent structure. The depression in Tc of the x = 0.7 sample, compared to that of the x = 0.5 sample, is discussed in connection with oxygen content, disorder, and change in hole concentration on the superconducting planes.

Lee, H. K.; Kim, Y. I.

148

Modulation of SR Ca Release by Luminal Ca and Calsequestrin in Cardiac Myocytes: Effects of CASQ2 Mutations Linked to Sudden Cardiac Death  

PubMed Central

Cardiac calsequestrin (CASQ2) is an intrasarcoplasmic reticulum (SR) low-affinity Ca-binding protein, with mutations that are associated with catecholamine-induced polymorphic ventricular tachycardia (CPVT). To better understand how CASQ2 mutants cause CPVT, we expressed two CPVT-linked CASQ2 mutants, a truncated protein (at G112+5X, CASQ2DEL) or CASQ2 containing a point mutation (CASQ2R33Q), in canine ventricular myocytes and assessed their effects on Ca handling. We also measured CASQ2-CASQ2 variant interactions using fluorescence resonance transfer in a heterologous expression system, and evaluated CASQ2 interaction with triadin. We found that expression of CASQ2DEL or CASQ2R33Q altered myocyte Ca signaling through two different mechanisms. Overexpressing CASQ2DEL disrupted the CASQ2 polymerization required for high capacity Ca binding, whereas CASQ2R33Q compromised the ability of CASQ2 to control ryanodine receptor (RyR2) channel activity. Despite profound differences in SR Ca buffering strengths, local Ca release terminated at the same free luminal [Ca] in control cells, cells overexpressing wild-type CASQ2 and CASQ2DEL-expressing myocytes, suggesting that a decline in [Ca]SR is a signal for RyR2 closure. Importantly, disrupting interactions between the RyR2 channel and CASQ2 by expressing CASQ2R33Q markedly lowered the [Ca]SR threshold for Ca release termination. We conclude that CASQ2 in the SR determines the magnitude and duration of Ca release from each SR terminal by providing both a local source of releasable Ca and by effects on luminal Ca-dependent RyR2 gating. Furthermore, two CPVT-inducing CASQ2 mutations, which cause mechanistically different defects in CASQ2 and RyR2 function, lead to increased diastolic SR Ca release events and exhibit a similar CPVT disease phenotype.

Terentyev, Dmitry; Kubalova, Zuzana; Valle, Giorgia; Nori, Alessandra; Vedamoorthyrao, Srikanth; Terentyeva, Radmila; Viatchenko-Karpinski, Serge; Bers, Donald M.; Williams, Simon C.; Volpe, Pompeo; Gyorke, Sandor

2008-01-01

149

K-Ca and Rb-Sr dating of two lunar granites: Relative chronometer resetting  

NASA Astrophysics Data System (ADS)

K-Ca and Rb-Sr age determinations were made for lunar granite 12033,576. This small fragment is a subsample of soil particle 12033,507, which was collected subsurface at the north rim of Head Crater. The K-Ca mineral isochron is well-defined and yields an age of 3.62 ± 0.11 (2 ) Ga for ( 40 K ) = 0.5543 Ga -1 and an initial 40 Ca / 44 Ca of 47.160 0.006 (2 ) (normalized to 42 Ca / 44 Ca = 0.31221). The Rb-Sr mineral isochron is quite disturbed and yields an imprecise young age of 2.20 ± 0.65 Ga for ( 87 Rb ) = 0.0139 Ga -1 and a high initial 87 Sr / 86 Sr of 0.775 0.022. Assuming that the granite crystallized ~ 4.0 Ga ago (a modeled formation age), and was shock-heated 0.8 Ga ago ( 39 Ar- 40 Ar age), the intermediate Rb-Sr and K-Ca ages are interpreted as due to partial resetting by thermal diffusion of strontium and calcium. Diffusion data determined for argon in 12033,507 give a value of D / a 2 ~1 × 10 -6 s -1 for a heating temperature of 700°C; at this temperature it would require a time on the order of days to totally degas argon. The required diffusion coefficients, D , for calcium (7 ~ 9 × 10 -13 cm 2 s -1 ) and Sr (~8 × 10 -12 cm 2 s -1 ) that are predicted from the observed age resetting are in good agreement with those determined experimentally in granitic melts. The K-Ca system was about a factor of ten more resistant to resetting than the Rb-Sr system, which in turn was ~ 10 times more resistant to resetting than the K-Ar system. Diffusion data indicate that isotopic exchange of calcium and strontium was responsible for the partial resetting of the K-Ca and Rb-Sr chronometers, rather than elemental exchange of potassium and rubidium among mineral phases. Rb-Sr isotopic data also were obtained for granite 14303,206, a subsample of breccia clast 14303,204, which was collected at the Fra Mauro region about 180 km from the Apollo 12 site. The mineral isochron is quite disturbed and yields an imprecise age of 3.95 ± 0.38 Ga for ( 87 Rb ) = 0.0139 Ga -1 and initial 87 Sr / 86 Sr = 0.7046 0.0051. The Rb-Sr age is comparable to the previously determined K-Ca age of 4.04 ± 0.64 Ga. The Rb-Sr and K-Ca ages of this clast are imprecise and are statistically indistinguishable from the well-defined 39 Ar- 40 Ar degassing age of 3.83 ± 0.03 Ga or the Rb-Sr and K-Ca model ages of 4.30 ± 0.06 Ga and 4.25 ± 0.12 Ga, respectively. Because these model ages are within error of a reported zircon U-Pb age of 4.31 Ga, we assume this granitic clast crystallized ~ 4.3 Ga ago and was shock-heated ~ 3.83 Ga ago. Using the apparent resetting of the K-Ar, Rb-Sr, and K-Ca isotopic systems, and literature data for relative strontium and calcium diffusivity, we estimate a shock-reheating temperature of ~ 860°C would be necessary to partially reset the Rb-Sr and K-Ca ages to their nominal values. This reheating temperature is uncertain because of the large errors on the ages, but would be consistent with complete resetting of the K-Ar age and partial resetting of the Rb-Sr and K-Ca ages, if the hot clast was buried under ~1 m of the ejecta blanket for ~1 day.

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

1994-07-01

150

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

NASA Astrophysics Data System (ADS)

The volcano-hydrothermal system of El Chichón volcano, Chiapas, Mexico, is characterized by numerous thermal manifestations including an acid lake, steam vents and boiling springs in the crater and acid and neutral hot springs and steaming ground on the flanks. Previous research on major element chemistry reveals that thermal waters of El Chichón can be divided in two groups: (1) neutral waters discharging in the crater and southern slopes of the volcano with chloride content ranging from 1500 to 2200 mg/l and (2) acid-to-neutral waters with Cl up to 12,000 mg/l discharging at the western slopes. Our work supports the concept that each group of waters is derived from a separate aquifer (Aq. 1 and Aq. 2). In this study we apply Sr isotopes, Ca/Sr ratios and REE abundances along with the major and trace element water chemistry in order to discriminate and characterize these two aquifers. Waters derived from Aq. 1 are characterized by 87Sr/86Sr ratios ranging from 0.70407 to 0.70419, while Sr concentrations range from 0.1 to 4 mg/l and Ca/Sr weight ratios from 90 to 180, close to average values for the erupted rocks. Waters derived from Aq. 2 have 87Sr/86Sr between 0.70531 and 0.70542, high Sr concentrations up to 80 mg/l, and Ca/Sr ratio of 17-28. Aquifer 1 is most probably shallow, composed of volcanic rocks and situated beneath the crater, within the volcano edifice. Aquifer 2 may be situated at greater depth in sedimentary rocks and by some way connected to the regional oil-gas field brines. The relative water output (l/s) from both aquifers can be estimated as Aq. 1/Aq. 2-30. Both aquifers are not distinguishable by their REE patterns. The total concentration of REE, however, strongly depends on the acidity. All neutral waters including high-salinity waters from Aq. 2 have very low total REE concentrations (< 0.6 ?g/l) and are characterized by a depletion in LREE relative to El Chichón volcanic rock, while acid waters from the crater lake (Aq. 1) and acid AS springs (Aq. 2) have parallel profile with total REE concentration from 9 to 98 ?g/l. The highest REE concentration (207 ?g/l) is observed in slightly acid shallow cold Ca-SO4 ground waters draining fresh and old pyroclastic deposits rich in magmatic anhydrite. It is suggested that the main mechanism controlling the concentration of REE in waters of El Chichón is the acidity. As low pH results from the shallow oxidation of H2S contained in hydrothermal vapors, REE distribution in thermal waters reflects the dissolution of volcanic rocks close to the surface or lake sediments as is the case for the crater lake.

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

2011-08-01

151

Nonequilibrium THz Conductivity of Bi2Sr2CaCu2O8+d  

SciTech Connect

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.

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

2003-05-27

152

Cooper pair formation dynamics in Bi2Sr2CaCu2O8+delta  

SciTech Connect

We utilize ultrafast terahertz pulses to monitor the carrierdynamics in the high-TC superconductor Bi2Sr2CaCu2O8+delta. Thetemperature, density and timedependence distinctly exposes a bimolecularrecombination process of quasiparticles which underlies formation ofCooper pairs.

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

2003-11-25

153

Alkali earth metal (Ca, Sr, Ba) based thermostable metal-organic frameworks (MOFs) for proton conduction.  

PubMed

Three new alkaline earth metal based MOFs have been synthesized by using 4,4'-sulfobisbenzoic acid (SBBA) and alkaline earth metal salts M(NO(3))(2), M = Ca, Sr, Ba. These MOFs exhibit interesting structural diversity, variable chemical stability as well as proton conductivity. PMID:22509491

Kundu, Tanay; Sahoo, Subash Chandra; Banerjee, Rahul

2012-04-16

154

Ca 2+ and Sr 2+ activation: Comparison of cardiac and skeletal muscle contraction models  

Microsoft Academic Search

The mechanism of contraction in rabbit fast-twitch, and bovine and rabbit cardiac muscle was examined using functionally skinned fibers, ATPase activity of myofibrils, and cardiac or skeletal troponintropomyosin regulated actin heavy meromyosin. The Ca2+ and Sr2+ activation properties for the different measures of contraction were evaluated. (1) Tension in rabbit and bovine cardiac skinned fibers and rabbit cardiac myofibrillar ATPase

W. G. L. Kerrick; D. A. Malencik; P. E. Hoar; J. D. Potter; R. L. Coby; S. Pocinwong; E. H. Fischer

1980-01-01

155

The effect of oxidant on resputtering of Bi from Bi-Sr-Ca-Cu-O films  

SciTech Connect

The type and partial pressure of oxidant mixed with argon can affect the selective resputtering of Bi in composite-target, magnetron-sputtered Bi-Sr-Ca-Cu-O films. Comparative studies using oxygen and ozone show that ozone is a more potent oxidant, as well as a more potent source of resputterers, than is oxygen. Severe resputtering from ozone is significantly reduced by a {minus}40 V potential on the sample block. We suggest that oxygen causes resputtering by forming O{sub 2}{sup +}, which interacts with the target to produce energetic O{sup {minus}}. In contrast, ozone may form lower-energy O{sup {minus}} by electron impact in the dark space. Negative oxygen ions from the target itself may be responsible for a background resputtering effect. Our results and those found for Y-Ba-Cu-O by others are comparable. Bi in Bi-Sr-Ca-Cu-O behaves as Ba in Y-Ba-Cu-O, with regard to selective resputtering; furthermore, the response of Sr, Ca, and Cu to oxygen in sputtered Bi-Sr-Ca-Cu-O is similar to what is observed for Cu in Y-Ba-Cu-O.

Grace, J.M.; McDonald, D.B.; Reiten, M.T.; Olson, J.; Kampwirth, R.T.; Gray, K.E.

1991-09-01

156

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

PubMed

The Sr/Ca ratio of coccoliths was recently proposed as a potential indicator of past growth rates of coccolithophorids, marine algae, which play key roles in both the global carbonate and carbon cycles. We synthesize calibrations of this proxy through laboratory culture studies and analysis of monospecific coccolith assemblages from surface sediments. Cultures of coccolithophorids Helicosphaera carteri, Syracosphaera pulchra and Algirospira robusta confirm a 1-2% increase in Sr/Ca per degrees C previously identified in Emiliania huxleyi and Gephyrocapsa oceanica. This effect is not due merely to increases in growth rate with temperature and must be considered in palaeoceanographic studies. In light-limited cultures of E. huxleyi, Calcidiscus leptoporus and G. oceanica at constant temperature, coccolith Sr/Ca ratios vary by 10% across the range of possible growth and calcification rates for a given species. Among different species under similar culture conditions, Sr/Ca ratios vary by 30%. Although the highest ratios are in the cells with highest calcification and organic carbon fixation rates, at lower rates there is much scatter, indicating that different mechanisms control interspecific and intraspecific coccolith Sr/Ca variations. In field studies in the Equatorial Pacific and Somalia coastal region, coccolith Sr/Ca correlates with upwelling intensity and productivity. A more dynamic response is observed in larger coccoliths like C. leptoporus (23-55% variation in Sr/Ca) than in smaller coccoliths of G. oceanica or Florisphaera profunda (6-15% variation in Sr/Ca). This response suggests that, despite temperature effects, coccolith Sr/Ca has potential as an indicator of coccolithophorid productivity. If the variable Sr/Ca response of different species accurately reflects their variable productivity response to upwelling (and not different slopes of Sr/Ca with productivity), coccolith Sr/Ca could provide useful data on past changes in coccolith ecology. The mechanism of coccolith Sr/Ca variations remains poorly understood but is probably more closely tied to biochemical cycles during carbon acquisition than to chemical kinetic effects on Sr incorporation in the calcite coccolith crystals. PMID:12804301

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

2002-04-15

157

Environmental and biological controls on elemental (Mg/Ca, Sr/Ca and Mn/Ca) ratios in shells of the king scallop Pecten maximus  

NASA Astrophysics Data System (ADS)

The relationship between potential elemental proxies (Mg/Ca, Sr/Ca and Mn/Ca ratios) and environmental factors was investigated for the bivalve Pecten maximus in a detailed field study undertaken in the Menai Strait, Wales, U.K. An age model constructed for each shell by comparison of measured and predicted oxygen-isotope ratios allowed comparison on a calendar time scale of shell elemental data with environmental variables, as well as estimation of shell growth rates. The seasonal variation of shell Mn/Ca ratios followed a similar pattern to one previously described for dissolved Mn2+ in the Menai Strait, although further calibration work is needed to validate such a relationship. Shell Sr/Ca ratios unexpectedly were found to co-vary most significantly with calcification temperature, whilst shell Mg/Ca ratios were the next most significant control. The temporal variation in the factors that control shell Sr/Ca ratios strongly suggest the former observation most likely to be the result of a secondary influence on shell Sr/Ca ratios by kinetic effects, the latter driven by seasonal variation in shell growth rate that is in turn influenced in part by seawater temperature. P. maximus shell Mg/Ca ratio to calcification temperature relationships exhibit an inverse correlation during autumn to early spring (October to March April) and a positive correlation from late spring through summer (May June to September). No clear explanation is evident for the former trend, but the similarity of the records from the three shells analysed indicate that it is a real signal and not a spurious observation. These observations confirm that application of the Mg/Ca proxy in P. maximus shells remains problematic, even for seasonal or absolute temperature reconstructions. For the range of calcification temperatures of 5 19 °C, our shell Mg/Ca ratios in P. maximus are approximately one-fourth those in inorganic calcite, half those in the bivalve Pinna nobilis, twice those in the bivalve Mytilus trossulus, and four to five times higher than Mg/Ca ratios in planktonic and benthonic foraminifera. Our findings further support observations that Mg/Ca ratios in bivalve shell calcite are an unreliable temperature proxy, as well as substantial taxon- and species-specific variation in Mg incorporation into bivalves and other calcifying organisms, with profound implications for the application of this geochemical proxy to the bivalve fossil record.

Freitas, Pedro S.; Clarke, Leon J.; Kennedy, Hilary; Richardson, Christopher A.; Abrantes, Fátima

2006-10-01

158

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

NASA Astrophysics Data System (ADS)

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.

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

2005-12-01

159

Investigation of thermoluminescence characteristics of CaSrS: Ce nanophosphors  

NASA Astrophysics Data System (ADS)

Thermoluminescence characteristics of Ca0.75Sr0.25S: Ce nanophosphors exposed to UV radiations have been investigated. Solid state diffusion method was employed to synthesize the nanophosphors. The confirmation for the formation of the mixed lattice was done by XRD. The particles formed were found to have 45 nm size as calculated by the Debye Scherrer formula. TEM results were in close agreement with the XRD as the nanoparticles formed possess capsule like structure with an average diameter of 50 nm. TL glow curves for the low doses (110-1680 mJ/cm2) of UV show a main peak around 381 K and another peak of very low intensity around 570 K. The TL intensity increases up to 450 mJ/cm2 of UV exposure. At higher doses (3.5-80 J/cm2) the peak position varies slightly but the high temperature peak becomes more intense. Thermoluminescence characteristics of UV irradiated Ca1-xSrxS: Ce as a function of x (0.25, 0.50, and 0.75) have also been investigated. TL glow curves of Ca1-xSrxS: Ce (0.25, 0.50, and 0.75) recorded after 450 mJ/cm2 of exposure of UV radiations show almost similar structure except slight variation in the peak position. Ca0.25Sr0.75S: Ce and Ca0.50Sr0.50S: Ce have single peak at 373 and 367 K, respectively, while Ca0.75Sr0.25S: Ce has a main peak at 381 K and a less intense peak at 570 K. Ca0.75Sr0.25S: Ce shows the most intense TL peak. The trap parameters namely, activation energy (E), order of kinetics (b), and frequency factor (s) of Ca0.75Sr0.25S: Ce have been determined using Chen’s peak shape method and GCD function suggested by Kitis for second order kinetics.

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

2010-11-01

160

Magnetic properties of triangular lattice Ca4IrO6 and Ca2.5Sr1.5IrO6  

NASA Astrophysics Data System (ADS)

We report a structural, thermodynamic, and transport study of single-crystal Ca4IrO6 and Ca2.5Sr1.5IrO6. The isostructural Ca4IrO6 and Ca2.5Sr1.5IrO6 feature a triangular lattice of spin chains running along the c axis. The underlying properties of the two systems are characterized by a partial antiferromagnetic order occuring at 12 K and 9 K for Ca4IrO6 and Ca2.5Sr1.5IrO6, respectively, a small entropy removal associated with the phase transition, and a sizable low-temperature specific heat linearly proportional to temperature. The detailed results will be discussed along with comparisons drawn with other related systems such as Ca5Ir3O12.

Butrouna, K. H.; Li, L.; Qi, T. F.; Korneta, O. B.; Terzic, J.; Akbari, E.; Parkin, S.; Yuan, S. J.; Cao, G.

2013-03-01

161

Phase diagrams of advanced magnesium alloys containing Al, Ca, Sn, Sr, and Mn  

NASA Astrophysics Data System (ADS)

In this paper an overview of the most relevant phase diagrams is given comprising the unconventional alloying elements Sn, Ca, and Sr, in reasonable combinations with Al and Mn in Mg alloys as a basis for advanced applications. The focus is on magnesium-rich partial projections of the liquidus surface of five ternary systems, relevant to technological applications for lightweight materials. All phase diagrams are calculated from a coherent thermodynamic multicomponent database for magnesium alloys. These calculations are validated by key samples in the pertinent subsystems, including extensive ternary assessments and also quaternary work. Isothermal sections of magnesium-rich phase diagrams of alloys with constant aluminum and manganese content at 500°C and 550°C are given for the two five-component systems: Mg-Al-Mn-Ca-Sr and Mg-Al-Mn-Ca-Sn.

Gröbner, Joachim; Janz, Andres; Kozlov, Artem; Mirkovi?, Djordje; Schmid-Fetzer, Rainer

2008-12-01

162

Effect of Bi substitution at the Sr site on the ferroelectric properties of dense strontium bismuth tantalate ceramics  

NASA Astrophysics Data System (ADS)

Ferroelectric properties for dense bulk ceramics of Sr-deficient and Bi-excess strontium bismuth tantalate, Sr1-xBi2+xTa2O9, were investigated, and their crystal structures were analyzed by the powder x-ray diffraction Rietveld method. A successful pattern fitting was obtained under the assumption that Bi was substituted at the Sr site for samples with x<=0.16, and the lattice in the a-b plane was reduced linearly with an increase in x. Furthermore, dielectric measurements showed that the Curie temperature, TC, rose with x and the sample with x=0.27 had a TC of 430 °C, which is much higher than that of the stoichiometric sample (x=0: TC=300 °C). These results strongly support the Bi substitution at the Sr site. The polarization hysteresis measurements revealed that a small amount of Bi substitution of 5% results in a marked increase in remanent polarization, however that further Bi substitution is not effective for improving the ferroelectric properties.

Noguchi, Yuji; Miyayama, Masaru; Kudo, Tetsuichi

2000-08-01

163

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

SciTech Connect

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.

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

2004-10-19

164

Redox-Mediated Reciprocal Regulation of SERCA and Na+/Ca2+-Exchanger Contributes to SR Ca2+-Depletion in Cardiac Myocytes  

PubMed Central

Myocardial failure is associated with increased oxidative stress and abnormal excitation-contraction coupling characterized by depletion of sarcoplasmic reticulum (SR) Ca2+-stores and a reduction in Ca2+-transient amplitude. Little is known about the mechanisms whereby oxidative stress affects Ca2+-handling and contractile function; however, reactive thiols may be involved. We used an in vitro cardiomyocyte system to test the hypothesis that short-term oxidative stress induces SR Ca2+-depletion via redox-mediated regulation of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) and the sodium-Ca2+-exchanger (NCX) and that this is associated with thiol oxidation. Adult rat ventricular myocytes paced at 5 Hz were superfused with H2O2 (100 ?M, 15 min). H2O2 caused a progressive decrease in cell shortening followed by diastolic arrest, which was associated with decreases in SR Ca2+-content, systolic [Ca2+]i and Ca2+-transient amplitude, but no change in diastolic [Ca2+]i. H2O2 caused reciprocal effects on the activities of SERCA (decreased) and NCX (increased). Pretreatment with the NCX inhibitor KB-R7943 prior to H2O2 increased diastolic [Ca2+]i, and mimicked the effect of SERCA inhibition with thapsigargin. These functional effects were associated with oxidative modification of thiols on both SERCA and NCX. In conclusion, redox-mediated SR Ca2+-depletion involves reciprocal regulation of SERCA and NCX, possibly via direct oxidative modification of both proteins.

Kuster, Gabriela M.; Lancel, Steve; Zhang, Jingmei; Communal, Catherine; Trucillo, Mario P.; Lim, Chee C.; Pfister, Otmar; Weinberg, Ellen O.; Cohen, Richard A.; Liao, Ronglih; Siwik, Deborah A.; Colucci, Wilson S.

2010-01-01

165

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

PubMed

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

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

2013-01-29

166

Sintering behavior of Ca or Sr-doped LaCrO 3 perovskites including second phase of AECrO 4 (AE=Sr, Ca) in air  

Microsoft Academic Search

The sintering characteristics and mechanisms of stoichiometric alkaline earth metal (AE)-doped lanthanum chromites, including the second phase of AECrO4 with low-melting point in air, (La1?xAExCrO3, AE=Ca and Sr, 0?x?0.3), have been discussed. When x?0.2, the sintering properties of La1?xCaxCrO3 are lower than those of La1?xSrxCrO3. However, the reverse results were observed at x=0.3. The mixtures of LaCrO3 and AECrO4 showed

Masashi Mori; Yoshiko Hiei; Nigel M Sammes

2000-01-01

167

Confounding effects of coral growth and high SST variability on skeletal Sr/Ca: Implications for coral paleothermometry  

NASA Astrophysics Data System (ADS)

Massive corals offer continuous records of climate locked within their skeleton, with the most commonly applied paleo-thermometer being Sr/Ca. Recently, however, problems with Sr/Ca thermometry indicate that the intrinsic variance of single-core Sr/Ca time series differs between cores. Here, we compare the Sr/Ca records and growth parameters of two Porites lutea colonies sampled from the same reef zone, 0.72 km apart, with two gridded SST datasets, ERSST and HadISST, off NE Madagascar. Specifically, we address seasonal and interannual variability as well as trend differences between records over the same 43 year period. The two gridded SST datasets showed strong seasonality and weak positive ENSO anomalies on a slow 43 year warming trend at significantly different rates. Both the coral Sr/Ca records showed the same clear seasonality and similar amplitudes in SST. However, on interannual timescales, they displayed diverging 43 year Sr/Ca trends and opposite responses to weak ENSO anomalies. Moreover, their growth response also differed as one coral showed increasing extension/calcification rates and Sr/Ca ratios (cooling) over the 43 years, while the other coral showed decreasing extension/calcification rates and Sr/Ca ratios (warming). Further, during positive ENSO events, the calcification rates of the two corals were negatively correlated, while skeletal density anomalies were opposite. Possible explanations to why these corals are so different may be related to the corals growth response to SST changes. The growth response of individual corals to increasing SST seems to be opposite, which in turn are likely related to biological factors. Consequently, coral growth responses explain much of the inter-colony Sr/Ca variability.

Grove, Craig A.; Kasper, Sebastian; Zinke, Jens; Pfeiffer, Miriam; Garbe-SchöNberg, Dieter; Brummer, Geert-Jan A.

2013-04-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

169

Behavior and Calibration of the Sr/Ca Temperature Proxy in Vesicomyid Clams  

NASA Astrophysics Data System (ADS)

Clams of the Vesicomyidae family populate both hydrothermal vent areas and hydrocarbon cold seep areas. These habitats furnish reduced sulfides that support chemoautotrophic endosymbionts that nourish the clams. Clams of this family all grow aragonitic shells, and can have lifetimes that span many decades. The incorporation of Sr into aragonite in corals has a well-known temperature dependence and the same is true in clams, though the partitioning is reversed from that in corals. Thus the potential exists to use these clams to provide proxy temperatures for both hydrothermal and cold seep environments. Hart and Blusztajn (1998) used ion probe techniques for Sr/Ca analysis of several Calyptogena magnifica specimens from 10°N on the East Pacific Rise. Sub-monthly resolution was obtained, and large Sr/Ca variations were observed that could be correlated with known eruptive and venting episodes. The preliminary temperature calibration we reported in 1998 was obtained from an Arctica icelandica (ocean quahog), recovered from a coastal site with a 6 year instrumental temperature record (1.3° - 17.7°C). Because this species stops growing in the winter, the low temperature end of the calibration was uncertain. To refine this calibration, we report here Sr/Ca records from 3 cold seep localities (typically with 200+ analysis spots per clam): a Calyptogena ponderosa (Green Canyon, Gulf of Mexico, 720 m, ~ 6°C); a C. phaseoliformis? (Aleutian trench, 4922 m, 1.5°C); and paired C. pacifica and C. kilmeri (Monterey Canyon, 904 m, 4.2°C). All of these samples exhibited significant Sr/Ca variations, suggesting that either the sites were not isothermal (as hoped), or that the clams were processing water with anomalous, pore-water-derived, Sr/Ca. Significant stretches of each record did have low and fairly constant Sr/Ca and, when coupled with the known ambient water temperatures for each locality, substantiated a calibration only ~ 1° higher than the 1998 calibration (new calibration: T°C = 18160*(Sr/Ca) - 12.2). The C. kilmeri spent most of its early life at 9-12°C, only dropping to ambient a year or so before collection in 1996. In contrast, the nearby C. pacifica spent most of its early life near ambient, with a rapidly increasing temperature over its last few years, reaching almost 20°C just before collection in 1994. We also have determined detailed Sr/Ca records for 7 specimens of C. magnifica from a hydrothermal venting region at ~ 10°N on the East Pacific Rise. These clams were collected in 1990, 1991, 1992, 1996, 1997, and 1999, and thus provide a time series with at least one known time for each clam. This was a period of active eruption and venting at this site, and the thermal episodes can be matched fairly well across the various clams. Sporadic low temperatures for these clams are in the 3-4°C range, but large periods of their lives are spent in the 10°-20°C range, with short spikes to ~ 40°C being common. We thank Colleen Cavanaugh, Lauren Mullineaux, Dan Fornari, Tim Shank, Rich Lutz, Jim Barry and Chuck Fisher for sharing their magnificent Vesicomyids.

Hart, S. R.

2009-12-01

170

Magnetoresistive and magnetic properties of RF-magnetron sputter deposited La-Ca,Sr-Mn-O films  

Microsoft Academic Search

Epitaxial and polycrystalline La-Ca,Sr-Mn-O thin films about 1000 Å thick were grown on LaAlO3(100), MgO(100) and SiO2\\/Si(100) substrates by RF magnetron sputtering. Changes in the resistivity and magnetoresistance of the films on LaAlO3 (100) substrate were investigated as the Ca and Sr ratio was varied. The crystal structure of the La-Ca,Sr-Mn-O films was determined to be orthorhombic perovskite. Lattice constants

Seung-Iel Park; Ji-Hee Son; Soung Suk Cho; Chul Sung Kim

2000-01-01

171

A comparison of lead-doped Bi-Sr-Ca-Cu-O superconductors at the '2223' and '2234' compositions  

Microsoft Academic Search

Superconducting Bi-Pb-Sr-Ca-Cu-O ceramics have been prepared at the Bi1.2Pb0.8Sr2Ca2Cu3Ox (2223) and Bi1.6Pb0.4Sr2Ca3Cu4Oy (2234) compositions. The properties and microstructures after sintering in air at 850 degrees C for times from 2 to 156 hours are described and compared. For the 2223 composition all heat treatment times result in multiphase samples. Bulk superconductivity giving zero resistance at 106 K and a maximum

T. W. Button; N. McN Alford; J. D. Birchall; F. Wellhofer; C. E. Gough; D. A. O'Connor

1989-01-01

172

Relation between the paste characteristics and the properties of screen printed (Bi, Pb)-Sr-Ca-Cu-O thick films  

NASA Astrophysics Data System (ADS)

The paper investigates the significance of past characteristics in order to improve screen printing and the microstructural and electrical properties of superconducting (Bi,Pb)-Sr-Ca-Cu-O thick films. XRD and SEM/EDS revealed that the melted films mainly consisted of the (Bi,Pb)2Sr2Ca1Cu2Oy and (Ca,Sr)2CuO3 phases. The films made from fine powders and, based on pastes with a high content of organic vehicle, were thin, smooth, strongly textured, and able to carry currents of between 0.6 and 4 x 10 exp 7 A/sq m.

Uusimaki, A.; Rautioaho, R.; Hagberg, J.; Leppavuori, S.

173

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

NASA Astrophysics Data System (ADS)

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 ([?CO3]aragonite) below 15 ?mol 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 [?CO3]aragonite > 15 ?mol 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.

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

2006-03-01

174

Formation of infinite-layered (Ca{sub 1{minus}x}Sr{sub x})CuO{sub 2} and NaCuO{sub 2}-type (Ca{sub 1{minus}y}Na{sub y}){sub 0.85}CuO{sub 2} in tartrate route  

SciTech Connect

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

Kikkawa, Shinichi; Kato, Namie; Taya, Noriko; Tada, Masakazu; Kanamuru, Fumikazu [Osaka Univ. (Japan). Inst. of Scientific and Industrial Research

1995-05-01

175

Superconductivity in Ruthenium Doped Bi-Sr-Ca-Cu- O System  

NASA Astrophysics Data System (ADS)

Polycrystalline samples of Bi2Sr2CaCu2-xRuxO8 with (x=0.0,0.05,0.10 and 0.20) were prepared using ammonium nitrate melt method. Specifically, appropriate amounts of Bi2O3, SrCO3, CaCo3, CuO, and RuO2 powder were mixed and ground thoroughly using an agate mortar and a pestle. The mixture was placed in the melt solution of ammonium nitrate and stirred at temperature between 160-170 C. Subsequent heating at 400-500 C resulted in the formation of a black powder that was pressed into a pellet. The pellet then annealed at 1060 C in following oxygen for about 24 hours. Preliminary results of our measurments show different superconducting properties for different doping levels (i.e different values of X)

Prozorov, Ruslan; Snezhko, Alexey; Prozorov, Tanya; Strukova, Galina K.; Shovkun, D. V.; Arammash, F.

2003-11-01

176

Effective activation energy in the Bi-Sr-Ca-Cu-O systems  

SciTech Connect

Magnetic relaxation in the Bi-Sr-Ca-Cu-O systems has been investigated in a wide temperature regime. Previously reported studies of the effective activation energy, U, have been controversial in terms of temperature and field dependence of the critical current density, j[sub c]. We have considered the temperature dependence of j[sub c] and constructed the U-j (or M) curves for the Bi-Sr-Ca-Cu-O system. We found that at a constant driving force and temperature, U is considerably higher for 2245 samples than for 2223 samples. This enhancement can be attributed to the flux pinning from finely dispersed calcium- and copper- rich precipitates.

Sengupta, S.; Shi, D.; Wang, Z.; Smith, M. (Argonne National Lab., IL (United States)); McGinn, P.J. (Notre Dame Univ., IN (United States). Dept. of Electrical Engineering)

1992-08-01

177

Effective activation energy in the Bi-Sr-Ca-Cu-O systems  

SciTech Connect

Magnetic relaxation in the Bi-Sr-Ca-Cu-O systems has been investigated in a wide temperature regime. Previously reported studies of the effective activation energy, U, have been controversial in terms of temperature and field dependence of the critical current density, j{sub c}. We have considered the temperature dependence of j{sub c} and constructed the U-j (or M) curves for the Bi-Sr-Ca-Cu-O system. We found that at a constant driving force and temperature, U is considerably higher for 2245 samples than for 2223 samples. This enhancement can be attributed to the flux pinning from finely dispersed calcium- and copper- rich precipitates.

Sengupta, S.; Shi, D.; Wang, Z.; Smith, M. [Argonne National Lab., IL (United States); McGinn, P.J. [Notre Dame Univ., IN (United States). Dept. of Electrical Engineering

1992-08-01

178

Fine structure of Ca-, Sr-, Ba-, and Ra- from the many-body theory calculation  

NASA Astrophysics Data System (ADS)

Atomic many-body theory methods are used to calculate the fine structure of negative ions formed by binding a p electron into an open shell, Ca-, Sr-, Ba-, and Ra-. This binding is due to a strong correlation potential acting between the electron and the neutral atom. Comparison with experimental data shows that the second order many-body perturbation theory calculation overestimates the correlation potential by 10% to 15%. Scaling factors are introduced in the correlation potential to reproduce experimental binding energies of the lower p1/2 components. This procedure yields fine-structure intervals in excellent agreement with experiment for Ca-, Sr-, and Ba-, and allows us to predict that in Ra- the p1/2 state is bound by 100 meV, and p3/2 is a resonance at 16 meV in the continuum.

Dzuba, V. A.; Gribakin, G. F.

1997-03-01

179

The spin-ladder and spin-chain system (La,Y,Sr,Ca)14Cu24O41: Electronic phases, charge and spin dynamics  

NASA Astrophysics Data System (ADS)

The quasi-one-dimensional cuprates (La,Y,Sr,Ca)14Cu24O41, consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, although in competition with a charge-density wave (CDW). Indeed, both the gapped spin-liquid and CDW states have been established in the doped spin-ladders of Sr14-xCaCu24O41, however the relevance of these objects to electronic properties and superconductivity is still subject of intensive discussion. In this treatise, an appreciable set of experimental data is reviewed, which has been acquired in recent years, indicating a variety of magnetic and charge arrangements found in the chains and ladders of underdoped (La,Y)y(S,Ca)14-yCu24O41 and fully doped Sr14-xCaCu24O41. Based on these data, phase diagrams are constructed for the chains of underdoped systems (as a function of La, Y-substitution), as well as for the chains and ladders of the fully doped ones (as a function of Ca-substitution). We try to reconcile contradictory results concerning the charge dynamics in the ladders, like the hole redistribution between ladders and chains, collective modes and pseudogap, field-dependent transport and the temperature scales and doping levels at which the two-dimensional CDW develops in the ladder planes. The remaining open issues are clearly extracted. In the discussion the experimental results are contrasted with theoretical predictions, which allows us to conclude with two important remarks concerning the nature of the competing CDW and superconducting ground states. A density wave in ladders, characterized by a sinusoidal charge modulation, belongs to the class of broken symmetry patterns, which is theoretically predicted for strongly correlated low-dimensional electron systems; however its precise texture and nature is still an open issue. As for superconductivity, the presence of the spin gap in the normal state points towards d-wave symmetry and magnetic origin of the attractive interaction. However, there is a finite density of mobile quasi-particles that appears for high Ca contents and increases with pressure, concomitantly with increased two-dimensionality and metallicity. For this reason the superconductivity in the doped ladders of Sr14-xCaCu24O41 which occurs under high pressure cannot simply be a stabilization of the d-wave superconductivity expected for a pure single ladder system.

Vuleti?, T.; Korin-Hamzi?, B.; Ivek, T.; Tomi?, S.; Gorshunov, B.; Dressel, M.; Akimitsu, J.

2006-05-01

180

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

Microsoft Academic Search

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

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

1991-01-01

181

Explosive Consolidation of (Bi, Pb)-Sr-Ca-Cu-0 Superconductor Powders  

Microsoft Academic Search

Superconducting (2212 phase) Bi-Sr-Ca-Cu-0 (BSCCO) and BSCCO-Ag composites were explosively consolidated in silver tubing\\u000a and then drawn and rolled into tapes. These silver-sheathed tapes were then subjected to repeated cycles of pressing and heat\\u000a treatment, which resulted in enhanced texturing and grain growth and a subsequent increase in critical current density (Jc). The effect of Ag powder additions to the

H. Thomas; O. T. Inal; U. Balachandran

1995-01-01

182

Anisotropic thermal conductivity of spin ladder cuprate Sr 12Ca 2Cu 24O 41  

Microsoft Academic Search

The thermal conductivity of a single crystal of the spin ladder cuprate Sr12Ca2Cu24O41 has been measured in the temperature region between 5 and 300 K. An anomalous double-peak structure of the temperature dependence of the thermal conductivity parallel to the c-axis, i.e. along the ladder direction, is observed. The high-temperature peak is absent in the thermal conductivity parallel to the

A. V. Sologubenko; K. Giannó; H. R Ott; U. Ammerahl; A. Revcolevschi; D. F Brewer; A. L Thomson

2000-01-01

183

Surface dynamics of Bi 2CaSr 2Cu 2O 8  

Microsoft Academic Search

The high-Tc superconductor Bi2CaSr2Cu2O8 (Bi 2:1:2:2) exhibits a superstructure in the bulk which is manifested at the surface. Helium atom scattering (HAS) from the (001) Bi–O surface has revealed unusual features of the surface phonons, such as the occurrence of apparently rather dispersionless surface modes and an only weak dependence of surface mode dispersion on direction in the surface. We

U. Paltzer; F. W. de Wette; U. Schröder; E. Rampf

1998-01-01

184

FAST TRACK COMMUNICATION: Simple method for electron affinity determination: results for Ca, Sr and Ce  

Microsoft Academic Search

Benchmarking the recently developed Regge-pole methodology for electron-atom elastic scattering on the most recently measured electron affinity (EA) of the Ca atom, we illustrate the predictive power of the methodology by calculating the binding energy of the tenuously bound negative ion Sr- and predicting the value of 0.61 eV for the binding energy of the ground state of the very

Z. Felfli; A. Z. Msezane; D. Sokolovski

2008-01-01

185

Skeletal retention of 45 Ca and 85 Sr compared: Further studies on intravenously injected 85 Sr as a tracer for skeletal calcium  

Microsoft Academic Search

Summary  The physical characteristics of47Ca and45Ca make them unsuitable for studying the long-term (>30 days) handling of skeletal calcium in patients. Therefore a study\\u000a was conducted in 3 normal subjects in which the skeletal uptakes and subsequent retentions of simultaneously administered\\u000a intravenous doses of45Ca and85Sr were compared. Specific activities of45Ca (relative to40Ca) were then observed in plasma and prolonged urine collections

J. Reeve; J. R. Green; C. J. Maletskos; R. M. Neer

1983-01-01

186

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

DOEpatents

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.

Veal, Boyd W. (Downers Grove, IL); Downey, John W. (Joliet, IL); Lam, Daniel J. (Orland Park, IL); Paulikas, Arvydas P. (Downers Grove, IL)

1992-01-01

187

Crystallization of Bi--Sr--Ca--Cu--O glasses in oxygen  

SciTech Connect

A detailed study of the crystallization process for compositions near Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub {ital y}} was undertaken using differential thermal analysis (DTA), transmission and scanning electron microscopy (TEM and SEM), and x-ray diffraction (XRD). Glasses prepared by a splat-quench technique were free of secondary phases in most cases. A two-step crystallization process in oxygen was observed in which partial crystallization of the glass occurs initially with the nucleation of 2201'' and Cu{sub 2}O, and is completed with the formation of SrO, CaO, and Bi{sub 2}Sr{sub 3{minus}}{sub {ital x}}Ca{sub {ital x}}O{sub {ital y}}. No specific thermal event could be associated with the formation of the 2212'' phase. Rather, formation occurs via conversion of 2201 into 2212. This was a kinetically limited process at temperatures below 800 {degree}C as other phases were found to evolve in addition to the 2212 phase during extended anneals. In contrast, a nearly full conversion to the 2212 phase occurred after only 1 minute of annealing at 800 {degree}C and above. However, changes in resistivity data, secondary phases, and the measured 2212 composition upon extended anneals at 865 {degree}C showed that considerably longer heat treatments were necessary for the sample to reach its equilibrium state.

Holesinger, T.G. (Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States) Department of Materials Science and Engineering, Ames Laboratory and Iowa State University, 214 Wilhelm, Ames, Iowa 50011 (United States)); Miller, D.J. (Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)); Chumbley, L.S. (Department of Materials Science and Engineering, Ames Laboratory and Iowa State University, 214 Wilhelm, Ames, Iowa 50011 (United States))

1992-07-01

188

Li doping to the 2212 phase in the Bi-Sr-Ca-Cu-O system  

NASA Astrophysics Data System (ADS)

The effects of Li doping on the formation process of the 2212 phase in the Bi-Sr-Ca-Cu-O system, and its structural and superconducting features were studied. Samples with nominal compositions of Bi:Sr:Ca:Cu:Li = 2:1.5:1.5:2:x where 0 <= x <= 0.6 were heated in air at temperatures ranging between 560°C and 850°C. Li doping greatly promoted the formation of the 2212 phase; the monophasic samples were rapidly obtained for x <= 0.4 by firing even at 730°C, which is about 100°C lower than that of the non-doped 2212 phase. A newly found oxide phase containing Li, which was formed below 710°C, is considered to play an important role as a precursor to accelerate the formation of the 2212 phase. The Li content in the monophasic samples determined by ICP analysis decreased to about a half of the nominal composition due to partial Li escape during heating. Monophasic composition range of the Li-doped 2212 phase was 0 <= y <= 0.19 as Bi2Sr1.5Ca1.5Cu2LiyOz. Increase in both lattice parameter c and oxygen content z with increasing Li content y in the 2212 phase was accompanied with a rise of Tc up to 90 K.

Fujiwara, M.; Nagae, M.; Fujii, T.; Takada, J.; Kusano, Y.

1997-02-01

189

The geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro Basin, Texas  

Microsoft Academic Search

The geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro Basin of north Texas, was studied to define geochemical controls on radionuclides such as 90 Sr and 226 Ra. Published solubility data for gypsum, anhydrite, celestite, barite and RaSO 4 were first reevaluated, in most cases using the ion interaction approach of Pitzer,

Donald Langmuir; Daniel Melchior

1985-01-01

190

cAMP/PKA-Dependent Increases in Ca Sparks, Oscillations and SR Ca Stores in Retinal Arteriolar Myocytes after Exposure to Vasopressin  

PubMed Central

Purpose. To investigate the effects of arginine vasopressin (AVP) on Ca2+ sparks and oscillations and on sarcoplasmic reticulum (SR) Ca2+ content in retinal arteriolar myocytes. Methods. Fluo-4-loaded smooth muscle in intact segments of freshly isolated porcine retinal arteriole was imaged by confocal laser microscopy. SR Ca2+ store content was assessed by recording caffeine-induced Ca2+ transients with microfluorimetry and fura-2. Results. The frequencies of Ca2+ sparks and oscillations were increased both during exposure to, and 10 minutes after washout of AVP (10 nM). Caffeine transients were increased in amplitude 10 and 90 minutes after a 3-minute application of AVP. Both AVP-induced Ca2+ transients and the enhancement of caffeine responses after AVP washout were inhibited by SR 49059, a V1a receptor blocker. Forskolin, an activator of adenylyl cyclase, also persistently enhanced caffeine transients. Rp-8-HA-cAMPS, a membrane-permeant PKA inhibitor, prevented enhancement of caffeine transients by both AVP and forskolin. Forskolin, but not AVP, produced a reversible, Rp-8-HA-cAMPS insensitive reduction in basal [Ca2+]i. Conclusions. AVP activates a cAMP/PKA-dependent pathway via V1a receptors in retinal arteriolar smooth muscle. This effect persistently increases SR Ca2+ loading, upregulating Ca2+ sparks and oscillations, and may favor prolonged agonist activity despite receptor desensitization.

Jeffries, Owen; McGahon, Mary K.; Bankhead, Peter; Lozano, Maria Manfredi; Scholfield, C. Norman; Curtis, Tim M.

2010-01-01

191

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

USGS Publications Warehouse

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 is likely: (1) speleothem trace-element records may provide seasonal signals, and (2) such records may be biased toward recording climate conditions during the season when calcite is depositing. Additionally, we use our results to construct a forward model that illustrates the types of speleothem Mg/Ca and Sr/Ca variations that would result from varying controls on dripwater compositions. The model provides a basis for interpreting paleo-dripwater controls from high frequency Mg/Ca and Sr/Ca variations for speleothems from caves at which long term monitoring studies are not feasible. ?? 2011 Elsevier Ltd.

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

2011-01-01

192

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

NASA Astrophysics Data System (ADS)

A 4-year study in a central Texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites. We monitored cave-air compositions, in situ calcite growth, dripwater composition and drip rate every 4-6 weeks. Three groups of drip sites are delineated (Groups 1-3) based on geochemical variations in dripwater composition. Quantitative modeling of mineral-solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions. The covariation of Mg/Ca (and Sr/Ca) and Sr isotopes is key in delineating whether Mg/Ca and Sr/Ca variations are dictated by water-rock interaction (i.e., calcite or dolomite recrystallization) or prior calcite precipitation (PCP). Group 1 dripwater compositions reflects a narrow range of the extent of water-rock interaction followed by varying amounts of prior calcite precipitation (PCP). Group 2 dripwater compositions are controlled by varying amounts of water-rock interaction with little to no PCP influence. Group 3 dripwater compositions are dictated by variable extents of both water-rock interaction and PCP. Group 1 drip sites show seasonal variations in dripwater Mg/Ca and Sr/Ca, whereas the other drip sites do not. In contrast to the findings of most previous dripwater Mg/Ca-Sr/Ca studies, these seasonal variations (at Group 1 drip sites) are independent of changes in water flux (i.e., rainfall and/or drip rate), and instead significantly correlate with changes in cave-air CO 2 concentrations. These results are consistent with lower cave-air CO 2, related to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading to dripwater geochemical evolution via PCP. Group 1 dripwater Mg/Ca and Sr/Ca seasonality and evidence for PCP as a mechanism that can account for that seasonality, have two implications for many other regions where seasonal ventilation of caves is likely: (1) speleothem trace-element records may provide seasonal signals, and (2) such records may be biased toward recording climate conditions during the season when calcite is depositing. Additionally, we use our results to construct a forward model that illustrates the types of speleothem Mg/Ca and Sr/Ca variations that would result from varying controls on dripwater compositions. The model provides a basis for interpreting paleo-dripwater controls from high frequency Mg/Ca and Sr/Ca variations for speleothems from caves at which long term monitoring studies are not feasible.

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

2011-06-01

193

An apparent “vital effect” of calcification rate on the Sr/Ca temperature proxy in the reef coral Montipora capitata  

NASA Astrophysics Data System (ADS)

Measuring the strontium to calcium ratio in coral skeletons reveals information on seawater temperatures during skeletal deposition, but studies have shown additional variables may affect the ratio. Here we measured Sr/Ca in the reef coral Montipora capitata grown in six mesocosms continuously supplied with seawater from the adjacent reef flat. Three mesocosms were ambient controls, and three had seawater chemistry simulating "ocean acidification" (OA). We found that Sr/Ca was not affected by the OA treatment and neither was coral calcification for these small colonies (larger colonies did show an OA effect). The lack of OA effects allowed us to test the hypothesis that coral growth rate can affect Sr/Ca using the natural range in calcification rates of the corals grown at the same temperature. We found that Sr/Ca was inversely related to calcification rate (Sr/Ca = 9.385 - 0.0040 (calcification rate)). Using a previously published calibration curve for this species, a 22 mg d-1 colony-1increase in calcification rate introduced a 1°C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9°C, with mean 26.6 ± 0.9°C standard deviation. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

Kuffner, Ilsa B.; Jokiel, Paul L.; Rodgers, Ku'ulei S.; Andersson, Andreas J.; MacKenzie, Fred T.

2012-08-01

194

muSR studies of the electron-doped Ca1-xSmMnO3  

Microsoft Academic Search

We have performed muon spin relaxation (muSR) experiments on undoped CaMnO3 and electron-doped Ca1-xSmMnO3 for x=0.1,0.15 and 0.3. Undoped CaMnO3 is a G-type antiferromagnet with a Néel temperature of T≈122K. The muSR signal shows three well-defined frequencies, which decrease continuously with temperature and becomes zero at T≈122K. The electron-doped Ca0.85Sm0.15MnO3 which shows colossal magnetoresistive (CMR) behaviour, undergoes a structural and

Tapan Chatterji; D. Andeica; R. Suryanarayanan; A. Revcolevschi

2006-01-01

195

Substitutional and positional disorder in Sr(2.88)Cu(3.12)(PO4)4.  

PubMed

The title compound, a hydrothermally synthesized strontium copper(II) phosphate(V) (2.88/3.12/4), is isotypic with Sr(3)Cu(3)(PO(4))(4), obtained previously by solid-state reaction, but not with Sr(3)Cu(3)(PO(4))(4), obtained previously by the hydrothermal method. A surplus of copper was observed by both structural and chemical analysis, and the formula obtained by the structural analysis is in full agreement with results of the EDX (energy-dispersive X-ray diffraction) analysis. The structure consists of layers of Cu(3)O(12) groups which are linked via the PO(4) tetrahedra. The Cu(3)O(12) groups are formed by one Cu1O(4) and two Cu2O(5) coordination polyhedra sharing corners. The central Cu1 atom of the Cu(3)O(12) group is located at an inversion centre (special position 2a). The unique structural feature of the title compound is the presence of 12% Cu in the Sr1 site (special position 2b, site symmetry 1). Moreover, disordered Sr2 atoms were observed: a main site (Sr2a, 90%) and a less occupied site (Sr2b, 10%) are displaced by 0.48 (3) A along the b axis. Such substitutional and positional disorder was not observed previously in similar compounds. PMID:20354287

Karanovi?, Ljiljana; Sutovi?, Sabina; Poleti, Dejan; Dordevi?, Tamara; Pacevski, Aleksandar

2010-03-06

196

(11n)Oriented BiSrCaCuO Thin Film Formed on SrTiO3(110) Substrate by RF Magnetron Sputtering  

Microsoft Academic Search

A superconducting BiSrCaCuO thin film was grown on a SrTiO3(110) substrate at 660°C by sputtering a single target. The RHEED observation showed that the c-axis of the film meets at an angle of about 42° with the substrate surface. The XRD measurement showed that the film has a main peak at 2theta{=}31.2°. From these results, the film is considered to

Ken'ichi Kuroda; Kazuyoshi Kojima; Osamu Wada; Masami Tanioku; Kazuo Yokoyama; Koichi Hamanaka

1990-01-01

197

Growth mechanism study of Bi-Sr-Ca-Cu-O films with c-axis inclined to SrTiO3(110) substrate surface  

Microsoft Academic Search

Bi-Sr-Ca-Cu-O thin films, with their c-axes inclined to the substrate surface, were prepared on SrTiO3(110) substrates by coevaporation, using an MBE machine with rf oxygen plasma. Orientations were influenced by flux conditions for metal elements, particularly, initial deposition of the specific element before the coevaporation. The origin of inclined orientation was discussed with relation to the initially formed compound.

T. Miura; Y. Ishizuka; Y. Terashima; S. Ikegawa

1991-01-01

198

Excited state absorption measurements of Sm sup 2+ in CaF sub 2 , SrF sub 2 , and SrCl sub 2  

SciTech Connect

We measured the pump-probe spectrum of the Sm{sup 2+} ion in three materials: CaF{sub 2}, SrF{sub 2}, and SrCl{sub 2}. The onset of the observed prominent excited-state absorption band is consistent with an electrostatic model for impurity levels in a solid-state material. 15 refs., 4 figs., 1 tab.

Lawson, J.K.; Lee, H.W.H.; Payne, S.A. (Lawrence Livermore National Lab., CA (United States)); Boatner, L.A. (Oak Ridge National Lab., TN (United States))

1991-04-01

199

Relationship between coccolith Sr/Ca ratios and coccolithophore production and export in the Arabian Sea and Sargasso Sea  

NASA Astrophysics Data System (ADS)

Coccolithophore CaCO3 production can account for 20 80% of biogenic carbonate exported from the photic zone, and coccoliths are a dominant biogenic carbonate in many deep-sea sediments. A new method for picking individual coccoliths from sediment traps and sediments for analysis using Secondary Ion Mass Spectrometry (ion probe) allows us to make precise Sr/Ca and Mg/Ca determinations on coccoliths from single species even in samples where material is limited. There are large biological effects in Sr/Ca partitioning in coccoliths that have been related to variations in coccolithophore productivity. In sediment traps from the Sargasso Sea at Bermuda and Arabian Sea in the Somali Basin, we can identify Sr/Ca variations in several species that are consistent with inferred seasonal variations in coccolithophore productivity in surface waters. In the Arabian Sea, coccolith Sr/Ca ratios in Calcidiscus leptoporus and Helicosphaera carteri are lowest during the nonproductive intermonsoon. They are highest during the upwelling of southwest monsoon and during the nutrient entrainment from strong winds of the northeast monsoon. These Sr/Ca variations match seasonal trends in coccolith export flux. Furthermore, Sr/Ca variations in C. leptoporus are larger, and this species also has the greater variation in export flux between southwest monsoon and intermonsoon seasons. At Bermuda, a 1996 fall bloom, driven by passage of a warm mode water eddy, induced a large increase in Sr/Ca of C. leptoporus coincident with an increase of C. leptoporus export. Over an annual series for 2004, highest Sr/Ca ratios of C. leptoporus in the summer months match the typical summer peak in surface standing stock of this species and the stimulation of its productivity by mesoscale cyclonic eddies and eddy eddy interactions. High Sr/Ca did not coincide with the highest export of C. leptoporus coccoliths, likely because cyclonic eddies, unlike mode-water eddies, are dominated by small phytoplankton with low export efficiency. These data confirm a relationship between coccolith Sr/Ca ratios and productivity. Sr/Ca ratios of the smaller and more slowly sinking Emiliania huxleyi at Bermuda show very small (<4%) seasonal Sr/Ca variations. In contrast, nutrient-limited culture experiments for this species reveal significant (>35%) increases in Sr/Ca with nitrate-stimulated growth rates. The high dominance of E. huxleyi production during bloom events, coupled with suspension of small E. huxleyi coccoliths below the photic zone with very long transport times, appears to attenuate significantly the amplitude of Sr/Ca variations in trap material. Coccoliths from these traps possess low Mg/Ca ratios characteristic of low-Mg calcite, so that higher Mg ratios obtained in some extant coccoliths in cultures are not representative of typical open-ocean coccoliths recovered in sediment trap samples. A significant correlation of Mg/Ca with sea-surface temperature is observed only for H. carteri coccoliths in the Arabian Sea, and not in C. leptoporus in either site.

Stoll, Heather M.; Ziveri, Patrizia; Shimizu, Nobumichi; Conte, Maureen; Theroux, Susanna

2007-03-01

200

Temperature dependences of piezoelectric properties of vanadium substituted SrBi 2Nb 2O 9 ceramics with grain orientation  

Microsoft Academic Search

The temperature dependence of the piezoelectric properties of vanadium substituted strontium bismuth niobate, SrBi2Nb1.95V0.05O9 (SBNV) ceramics, were investigated in various vibration modes. The effects of grain orientation in SBNV ceramics on the piezoelectric properties were also studied by the hot-forging (HF) method. The anisotropy of the piezoelectric properties of each vibration mode was confirmed by observing the grain orientation. In

Shinya Inai; Yuji Hiruma; Muneyasu Suzuki; Hajime Nagata; Tadashi Takenaka

2008-01-01

201

Effect of Ge4+ and Mg2+ doping on superconductivity, fluctuation induced conductivity and interplanar coupling of TlSr2CaCu2O7-? superconductors  

NASA Astrophysics Data System (ADS)

Substitution of Ge4+ in place of Cu in Tl0.85Cr0.15Sr2CaCu2-xGexO7-? (x = 0-0.6) showed initial increase in zero critical temperature value, Tczero from 98 K (x = 0) to 100 K (x = 0.1) and in the range of 85-86 K for x = 0.2-0.3. The slow decrease in Tczero is unexpected as tetravalent Ge4+ substitution is expected to strongly reduce hole concentration in the samples and suppress Tczero. Excess conductivity analyses of resistance versus temperature data based on Asmalazov-Larkin (AL) theory revealed that the substitution induced 2D-to-3D transition of fluctuation induced conductivity with the highest transition temperature, T2D-3D observed at x = 0.1. FTIR spectroscopy analysis indicates Ge4+ substitution cause reduction in CuO2/GeO2 interplanar distance while our calculation based on Lawrence-Doniach model revealed highest superconducting coherence length, ?c(0) and interplanar coupling, J at x = 0.3. On the other hand, substitution of divalent Mg2+ for Ca2+ in (Tl0.5Pb0.5)(Sr1.8Yb0.2)(Ca1-yMgy)Cu2O7 (y = 0-1.0), which is not expected to directly vary hole concentration, surprisingly caused Tczero to increase from 89.6 K (y = 0) to an optimum value of 95.9 K (y = 0.6) before decreasing with further increase in y. Excess conductivity analyses showed 2D-to-3D transition of fluctuation induced conductivity for all samples where the highest T2D-3D was at y = 0.4. Similar calculation revealed highest values of ?c(0) and J also at y = 0.4. FTIR analysis of the samples indicates inequivalent Cu(1)O(2)Pb/Tl lengths and possible tilting of CuO2 plane as a result of Mg2+ substitution. The increased ?c(0) and J as a result of the Ge4+ and Mg2+ substitutions are suggested to contributed to sustenance of superconductivity above 80 K in the samples.

Ali Yusuf, A.; Yahya, A. K.; Khan, Nawazish A.; Salleh, F. Md.; Marsom, E.; Huda, N.

2011-06-01

202

M IIGe(PO 4) 2 ( M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion  

Microsoft Academic Search

Three earth alkali-germanium monophosphates MIIGe(PO4)2 (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO4)2 and high-temperature ?-SrGe(PO4)2 (space group C2\\/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO4)2 and low-temperature ?-SrGe(PO4)2 (C2\\/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The

Karin Popa; Gilles Wallez; Damien Bregiroux; Pascal Loiseau

2011-01-01

203

4f and 5d energy levels of the divalent and trivalent lanthanide ions in M2Si5N8 (M=Ca, Sr, Ba)  

NASA Astrophysics Data System (ADS)

Optical data of Sm, Tb and Yb doped Ca2Si5N8 and Sr2Si5N8 phosphors that have been prepared by solid-state synthesis, are presented. Together with luminescence data from literature on Ce3+ and Eu2+ doping in the M2Si5N8 (M=Ca, Sr, Ba) hosts, energy level schemes were constructed showing the energy of the 4f and 5d levels of all divalent and trivalent lanthanide ions relative to the valence and conduction band. The schemes were of great help in interpreting the optical data of the lanthanide doped phosphors and allow commenting on the valence stability of the ions, as well as the stability against thermal quenching of the Eu2+d-f emission. Tb3+ substitutes on both a high energy and a low energy site in Ca2Si5N8, due to which excitation at 4.77 eV led to emission from both the 5D3 and 5D4 levels, while excitation at 4.34 eV gave rise to mainly 5D4 emission. Doping with Sm resulted in typical Sm3+f-f line absorption, as well as an absorption band around 4.1 eV in Ca2Si5N8 and 3.6 eV in Sr2Si5N8 that could be identified as the Sm3+ charge transfer band. Yb on the other hand was incorporated in both the divalent and the trivalent state in Ca2Si5N8.

ten Kate, O. M.; Zhang, Z.; Dorenbos, P.; Hintzen, H. T.; van der Kolk, E.

2013-01-01

204

High-resolution Sr/Ca records in modern Porites lobata corals: Effects of skeletal extension rate and architecture  

NASA Astrophysics Data System (ADS)

We used ion microprobe analysis to determine the Sr/Ca composition of fasciculi (deposited during the day) and centers of calcification (COCs, deposited at night) across transects of two Porites lobata corals, of different linear extension rates, from Oahu, Hawaii. The COCs of both corals contained significantly higher Sr/Ca than the fasciculi (at the 95% confidence level). We observed no significant differences between the Sr/Ca ratios of the fasciculi (or of the COCs) of the fast and slow growing corals, and we conclude that variations in the extension rate of each colony have not affected Sr incorporation in these corals. The fasciculi and COCs in both corals exhibit large Sr/Ca heterogeneity, which is not temperature dependent. Our data do not support the hypothesis that COC analyses provide a SST signature which is unaffected by biological or kinetic effects. The heterogeneity of both features may reflect short-term (daily to weekly) variations in calcification rate which are known to occur during the day and night and which influence the relative transport rates of Sr and Ca through the coral tissue. We plotted running means through the fasciculi and COC chronologies and compared maximum and minimum Sr/Ca values in each annual cycle with the corresponding minimum and maximum mean sea surface temperature (SST) values (calculated over equivalent time periods). We found that the constants C and M of the linear equation Sr/Ca = C + (M × SST) became smaller as the time interval used to calculate the running means increased from 1 day to ˜77 days. This decrease in C and M reflects the gradual removal of the short-term Sr heterogeneity (dependent on biological and/or kinetic processes) from the data set as progressively larger numbers of data points are used to calculate the Sr/Ca running mean. We hypothesize that variations in M and C between different published Sr/Ca-SST calibrations may reflect the relative importance of biological or kinetic processes in corals at different locations.

Allison, Nicola; Finch, Adrian A.

2004-05-01

205

Growth and properties of oxygen- and ion-doped Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8+. delta. single crystals  

SciTech Connect

A directional solidification method for growing large single crystals in the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} system is reported. Ion doping, with replacement of La for Sr and Y for Ca, as well as oxygen doping in these crystals has been explored. Doped and undoped crystals have been characterized using microprobe analysis, x-ray diffraction, thermogravimetric analysis, and magnetic and Hall measurements. Ion doping results in little change of the superconducting transition for substitution levels below 20--25%, while beyond this level the Meissner signal broadens and the low-temperature Meissner signal decreases. Microprobe analysis and x-ray diffraction performed on these more highly substituted single crystals provide evidence for inhomogeneity and phase segregation into regions of distinct composition. Annealing unsubstituted crystals in increasing partial pressures of oxygen reversibly depresses the superconducting transition temperature from 90 (as made) to 77 K (oxygen pressure annealed), while the carrier concentrations, as determined from Hall effect measurements, increase from {ital n}=3.1(3){times}10{sup 21} cm{sup {minus}3} (0.34 holes per Cu site) to 4.6(3){times}10{sup 21} cm{sup {minus}3} (0.50 holes per Cu site).

Mitzi, D.B.; Lombardo, L.W.; Kapitulnik, A. (Department of Applied Physics, Stanford University, Stanford, California 94305 (USA)); Laderman, S.S.; Jacowitz, R.D. (Circuit Technology Research and Development, Hewlett-Packard Company, 3500 Deer Creek Road, Palo Alto, California 94304 (USA))

1990-04-01

206

Charge Density Wave Instability and Soft Phonon in APt3P (A=Ca, Sr, and La)  

NASA Astrophysics Data System (ADS)

The electronic and phonon properties of the platinum pnictide superconductors APt3P (A=Ca, Sr, and La) were studied using first-principles calculations. The spin-orbit coupling effect is significant in LaPt3P but negligible in CaPt3P and SrPt3P. Moreover, SrPt3P has been demonstrated to exhibit an unexpected weak charge-density-wave (CDW) instability which is neither simply related to the Fermi-surface nesting nor to the momentum-dependent electron-phonon coupling alone. The instability is absent in CaPt3P and can be quickly suppressed by the external pressure, accompanied with decreases in the phonon softening and BCS Tc. Our results suggest SrPt3P as a rare example where superconductivity is enhanced by the CDW fluctuations.

Cao, Chao; Chen, Hui; Xu, Xiaofeng; Dai, Jianhui

2013-03-01

207

Ferroelectric properties of laser-ablated Sr1-xAxBi2Ta2O9 thin films (where A=Ba, Ca)  

NASA Astrophysics Data System (ADS)

Bismuth-layered ferroelectric thin films of Sr1-xAxBi2Ta2O9, with composition x=0 and 0.2, were fabricated by using the pulsed-laser deposition technique. Structural characterization of the films by x-ray diffraction and atomic force microscopy, revealed that the films are polycrystalline in nature with average grain size of 180 nm. The films displayed spherical grains with a surface roughness of 12 nm. The ferroelectric measurements of Sr0.8Ba0.2Bi2Ta2O9, SrBi2Ta2O9, and Sr0.8Ca0.2Bi2Ta2O9 showed saturated hysteretic behavior with remanent polarization (2Pr) of 23.5, 17.9, 14 ?C/cm2 and coercive field (Ec) of 31.06, 74.2, 86.3 kV/cm for a maximum applied electric field of 360 kV/cm. Films exhibited minimal (<=17%) degradation of polarization for up to 1010 switching cycles. It was observed that the coercive field decreased with increase in the ionic size of partially substituted cations. The leakage current density of films were found to be of the order of ~10-8 A/cm2 for up to a breakdown field of about 75 kV/cm.

Das, Rasmi R.; Bhattacharya, P.; Pérez, W.; Katiyar, Ram S.; Desu, Seshu B.

2002-01-01

208

Kinetics of the Ca 2+, H +, and Mg 2+ Interaction with the Ion-Binding Sites of the SR Ca-ATPase  

Microsoft Academic Search

Electrochromic styryl dyes were used to investigate mutually antagonistic effects of Ca2+ and H+ on binding of the other ion in the E1 and P-E2 states of the SR Ca-ATPase. On the cytoplasmic side of the protein in the absence of Mg2+ a strictly competitive binding sequence, H2E1?HE1?E1?CaE1?Ca2E1, was found with two Ca2+ ions bound cooperatively. The apparent equilibrium dissociation

Christine Peinelt; Hans-Jürgen Apell

2002-01-01

209

Enhanced dielectric and ferroelectric properties of Ca2+ substituted sodium bismuth titanate  

NASA Astrophysics Data System (ADS)

In order to find the environmental friendly materials for various possible applications in near future, We have synthesized a series of new complex perovskite oxides CaxNa1-x(Bi1/2Ti1/2)O3 (CNBT) (where x = 0.00, 0.25, 0.50 and 0.75) by solid state reaction technique and studied the effect of Ca substitution in Na(Bi1/2Ti1/2)O3 through the microstructure, dielectric and ferroelectric properties. The frequency dependence of the dielectric constant at room temperature shows that the value of dielectric constant increases with Ca2+ substitution at room temperature. The analysis of real part of the dielectric permittivity shows Debye like relaxation with frequency at room temperature. The polarization hysteresis loops plotted at room temperature reveal the ferroelectric property for all compositions of the CNBT samples.

Bharti, Chandrahas; Sen, A.; Sinha, T. P.

2013-02-01

210

Green-emitting (La,M,Tb)OCl (M = Mg, Ca, and Sr) phosphors  

NASA Astrophysics Data System (ADS)

Green-emitting (La1-x-yMxTby)OCl (0 ? x ? 0.13, 0.03 ? y ? 0.15, M = Mg, Ca, and Sr) single phase phosphors were synthesized using a liquid-phase method and their photoluminescence properties were characterized. The excitation spectrum consisted of a strong broad band from 220 to 290 nm, which corresponds to the 4f-5d transition of Tb3+. The oxychloride phosphors exhibit typical emission peaks assigned to the transition from 5D4 to 7FJ (J = 6, 5, 4, and 3) of Tb3+, and the luminescence emission intensity was successfully enhanced by doping divalent alkaline earth metal ions (M = Mg2+, Ca2+, and Sr2+) into La3+ sites of the host LaOCl lattice. The highest green emission intensity was obtained for (La0.88Ca0.05Tb0.07)OCl, of which the relative emission intensity was 75% of that for a commercial green-emitting (La0.52Ce0.31Tb0.17)PO4 phosphor.

Kim, Sun Woog; Jyoko, Kazuya; Masui, Toshiyuki; Imanaka, Nobuhito

2012-12-01

211

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

SciTech Connect

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}.

Porto, S.L. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); Longo, E. [CMDMC/LIEC, Instituto de Quimica, UNESP-Araraquara, Rua Prof. Francisco Degni s/n, Araraquara, SP, CEP 14800-900 (Brazil); Pizani, P.S.; Boschi, T.M. [Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, Rodovia Washington Luiz km 235, SP, CEP 13565-905 (Brazil); Simoes, L.G.P. [Centro Multidisciplinar de Desenvolvimento de Materiais Ceramicos (LIEC/DQ), Universidade Federal de Sao Carlos, Rodovia Washington Luiz km 235, Sao Carlos, SP, CEP 13565-905 (Brazil); Lima, S.J.G. [Laboratorio de Solidificacao Rapida, Departamento de Tecnologia Mecanica (LSR/DTM/CT), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); Ferreira, J.M. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); COAMA, Area de Meio Ambiente, Centro Federal de Educacao Tecnologica da Paraiba, Av. 1o de Maio 720, Jaguaribe, Joao Pessoa, PB, CEP 58015-430 (Brazil); Soledade, L.E.B.; Espinoza, J.W.M.; Cassia-Santos, M.R.; Maurera, M.A.M.A. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); Paskocimas, C.A. [Departamento de Engenharia Mecanica, Universidade Federal do Rio Grande do Norte, Natal, RN, CEP 59072-970 (Brazil); Santos, I.M.G. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil)], E-mail: ieda@quimica.ufpb.br; Souza, A.G. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil)

2008-08-15

212

The interplay of Ca and Sr in the bulk magnetocaloric La0.7Sr(0.3- x)Ca x MnO3 ( x = 0, 0.1 and 0.3) manganite  

NASA Astrophysics Data System (ADS)

A detailed investigation of the magnetic and the magnetocaloric properties of La0.7Sr0.3MnO3, La0.7Ca0.3MnO3 and La0.7Ca0.1Sr0.2MnO3 for possible application in magnetic refrigeration is presented. The adiabatic magnetic entropy change was determined for a magnetic field change from 0 to 2.5 T by using magnetization data. A broad table-like entropy change with a relative cooling power of 111 J/kg in an applied magnetic field of 2.5 T with an operating temperature range of 54 K was observed in the La0.7Ca0.1Sr0.2MnO3 sample. The broadening in the magnetic entropy change in La0.7Ca0.1Sr0.2MnO3 is discussed in light of the tricritical mean-field theory. The tricritical exponent ( ?) was calculated for the La0.7Ca0.1Sr0.2MnO3 sample and found to be ˜ 4.76 ± 0.03, which is very close to the proposed value ? = 5 for the tricitical exponent. The studied samples can be considered as giant magnetocaloric materials for room-temperature refrigeration.

Anwar, M. S.; Ahmed, Faheem; Kim, G. W.; Heo, Si Nae; Koo, Bon Heun

2013-06-01

213

Effects of Cr\\/Zn Substitutions on Dielectric Properties of CaCu3Ti4O12 (CCTO) Ceramics  

Microsoft Academic Search

Effects of Zn and Cr substitutions on dielectric properties of CaCu3-xZnxTi4-yCryO12 ceramics are reported. Dielectric measurements at room temperature for un-substituted CaCu3-xZnxTi4-yCryO12 (x = 0, y = 0) between 102-106 Hz showed dielectric constant of 2.7×104 at 102 Hz. Substitution of Zn for Cu in CaCu3-xZnxTi4-yCryO12 (y = 0, x = 0.10, 0.50)caused dielectric constant to drop with increasing x.

R. Rajmi; A. K. Yahya; M. S. M. Deni

2010-01-01

214

Energetics of La{sub 1-x}A{sub x}CrO{sub 3-{delta}} perovskites (A=Ca or Sr)  

SciTech Connect

A series of perovskites with the general formula La{sub 1-x}A{sub x}CrO{sub 3-{delta}} (A=Ca or Sr) have been synthesized in the solid solution range 0.0Ca-doped samples, and from -440+/-150 to -290+/-50kJ/mol O{sub 2} for Sr-doped ones. This dependence of enthalpy of oxidation on composition suggests oxygen vacancies are increasingly short-range ordered in reduced samples. The higher oxidation state of chromium is stabilized by the substitution of alkaline earth ions, but with increasing doping, the enthalpy of formation of the fully oxidized sample in both Ca and Sr-doped systems becomes more endothermic. This destabilization effect is attributed to the large endothermic enthalpy of oxygen vacancy formation (395+/-30kJ/mol of V{sub O}{sup ..}) for the reaction A{sub A}{sup x}+O{sub O}{sup x}=A{sub La}{sup '}+0.5V{sub O}{sup ..}+0.5O{sub 2}(A=Ca or Sr) that over-rides the exothermic enthalpies of oxidation. At a given composition, Sr-doped LaCrO{sub 3} is more stable than its Ca-doped counterpart, which is consistent with basicity arguments.

Cheng Jihong [Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616 (United States); Navrotsky, Alexandra [Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616 (United States)]. E-mail: anavrotsky@ucdavis.edu

2005-01-15

215

Gamma-ray shielding properties of CaO-SrO-B2O3 glasses  

NASA Astrophysics Data System (ADS)

Mass attenuation coefficients, effective atomic numbers and effective electron densities have been determined experimentally for the glass system xCaO·(0.3-x)SrO·0.7B2O3 at photon energies 511, 662, 1173, and 1332 keV. The results are compared with theoretical calculations. In addition, the molar volume of the glasses has been derived from density measurements, and the excess volume has been determined as a function of composition. The reported data should be useful for potential applications of these glasses in radiation shielding.

Singh, Kulwant; Singh, Harvinder; Sharma, Gopi; Gerward, Leif; Khanna, Atul; Kumar, Rajesh; Nathuram, Rohila; Sahota, Hari Singh

2005-02-01

216

Crystallization of glass-ceramic Bi3Sr2Ca2Cu3Oy superconducting system  

NASA Astrophysics Data System (ADS)

In this study, the nucleation and the crystallization of the material with nominal composition of Bi3Sr2Ca2Cu3O? have been investigated, depending on the heat treatment conditions. It was found that 4 and 8-fold branched nuclei on the samples occurred with increasing the heat treatment temperature. Finally, crystallization occurred with further increase of the temperature. The needle-like crystals (whiskers) perpendicular to the sample surface was formed above 800 °C, which consisted of the Bi-2212 phase. The results clearly showed that the anisotropy of surface tension is the most important parameter in determining the shape of the nucleus.

Kizilaslan, O.; Aksan, M. A.

2013-10-01

217

Characterization of luminescent properties of Sr–Ca–Al–O multi-phases oxide phosphors  

Microsoft Academic Search

Multi-phases phosphors, which could exhibit red, green, and blue emission bands simultaneously, were synthesized by the solid-state\\u000a reaction method with a flux. Starting materials of SrCO3, CaCO3, and Al2O3 were mixed and fired. H3BO3 and Eu2O3 were added as a flux and a dopant, respectively. Effects of the excitation energy and the mixing ratio of starting materials\\u000a on the luminescent

Sang Hyuk Han; Sang Hyun Jung; Young Jin Kim

2008-01-01

218

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

DOEpatents

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.

Shi, Donglu (Chicago, IL)

1992-01-01

219

280-year Long Sr/Ca and ? 18O Records From Flinders Reef, Western Coral Sea  

NASA Astrophysics Data System (ADS)

The combination of parallel Sr/Ca and ? 18O records in corals allows reconstruction of past changes in sea surface temperature (SST) and seawater ? 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 ? 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 Sr/Ca record, a proxy for SST, obtained from the same coral. Low resolution (5-year intervals) Sr/Ca and ? 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 Sr/Ca-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 ? 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 ? 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, 58, 2747-2754 (1994) Quinn, T.M. et al. Paleoceanography 13, 412-426 (1998)

Calvo, E.; Marshall, J. F.; Pelejero, C.; McCulloch, M. T.; Lough, J.; Gagan, M. K.

2003-12-01

220

Effects of lithium additions on processing of Bi-Sr-Ca-Cu-O superconducting tapes  

SciTech Connect

Lithium additions to the high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) increased superconducting transition temperatures and improved resistance to effects of magnetic fields. In addition, these additions lowered the melting point of 2212 and increased reaction kinetics. Ag-clad tapes fabricated from 2212 with and without Li exhibited profound differences. For heating to temperatures less than or equal to 840{degrees}C, grain growth and sintering were much more substantial in the tapes containing Li.

Goretta, K.C.; Li, Y.F.; Poeppel, R.B. [Argonne National Lab., IL (United States); Wu, S.; Guo, J. [Illinois Univ., Urbana, IL (United States). Dept. of Nuclear Engineering; Schwartz, J. [Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Laboratory

1994-01-01

221

Test of soil extractants for their suitability in predicting Ca\\/Sr ratios in leaves and stems of sugar maple seedlings  

Microsoft Academic Search

Differential uptake and translocation of Ca and Sr in organisms have been reported, calling into question the use of Sr to\\u000a track Ca cycling in the environment. We investigated the relationship between Ca\\/Sr ratios in soil extracts of various strengths\\u000a (H2O, NH4Cl, and NH4EDTA) and seedlings of sugar maple (Acer saccharum Marsh.) grown from natural regeneration on 37 sites. Our objectives

Frieda Beauregard; Benoît Côté

2008-01-01

222

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

PubMed Central

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, IL1? and TNF? 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 NF?B. Our observations suggest that CaSR activation elevates cytokine and chemokine production through a signaling pathway involving activation of NF?B 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.

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

2013-01-01

223

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)

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.

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

2005-12-01

224

Electrochemical lithium intercalation into Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

We have prepared Li-intercalated LixBi2Sr2CaCu2O8+? (x =0-2.0) samples by using electrochemical method, and performed synchrotron x-ray diffraction, Cu K-edge x-ray absorption fine structure (XAFS), and magnetic susceptibility measurements. With increasing x, a- and c-lattice parameters monotonically increase, which shows lithium intercalation into Bi2Sr2CaCu2O8+?. Accompanied by the lithium insertion, the valence of Cu ion changes from Cu2+/Cu3+ to Cu1+/Cu2+ to realize charge neutrality. This change of the valence was detected by Cu K-edge XAFS measurement. A clear increase of spectral weight that corresponds to 1s? 4p?(3d10L) was observed at around 8982 eV with x. The superconducting (SC) transition temperature TC significantly changes from 74 K for x = 0 to 90 K for x = 0.8, which is attributed to modified density of states by the decrease of hole concentration. A volume fraction of the superconducting phase was 1-2 % for x >= 0.6 implying phase separation where Li-rich non SC phase and Li-poor SC phase coexist. Such a phase separation is universally seen in electrode active materials.

Shimono, Takahiro; Kobayashi, Wataru; Nitani, Hiroaki; Kumai, Reiji; Moritomo, Yutaka

2013-04-01

225

Anomalous phonon properties in the silicide superconductors CaAlSi and SrAlSi  

NASA Astrophysics Data System (ADS)

Lattice-dynamical properties of CaAlSi and SrAlSi with a similar layer structure to MgB2 have been first investigated by both Raman-scattering and ab initio calculations. All Raman-active phonons with E' symmetry have been clearly observed for both compounds. Their line shapes are asymmetric but their linewidths are ˜10cm-1 , which is very narrower than that of MgB2 . In addition to the Raman-active modes, several extra peaks have been observed below 160cm-1 . These low-energy extra modes can be assigned to the out-of-plane vibrations of Al perpendicular to Al-Si basal plane. Since these peak intensities are strongly affected by the incident energy (resonance Raman process), the electronic state is important for them. Moreover, in both crystals of CaAlSi and SrAlSi, we point out the energy difference for the different propagation directions along the c axis and the c plane, in spite of the very close wave vector to the Brillouin-zone center. This energy difference cannot be explained by a usual Raman-scattering scenario at this stage.

Kuroiwa, S.; Hasegawa, T.; Kondo, T.; Ogita, N.; Udagawa, M.; Akimitsu, J.

2008-11-01

226

Structure and refinement of the composition of Bi-Sr-Ca-Cu oxide crystals  

SciTech Connect

The composite structure of the red phase, which accompanies the 2212 and 2201 superconducting phases prepared upon cooling of a melt in the Bi-Sr-Ca-Cu-O system, is revealed by scanning electron microscopy and X-ray diffraction analysis. The matrix component in two crystals I and II under investigation has a monoclinic structure with space group C2/m and the unit cell parameters a = 21.832(2) and 21.8142(9) A, b = 4.3809(4) and 4.3771(2) A, c = 12.9430(12) and 12.9378(6) A, {beta} = 102.832(2) deg. and 102.839(1) deg., and V = 1207.0(2) and 1204.45(9) A{sup 3}, respectively. The composition is described by the general formula Bi{sub 4}(Ca{sub 2-x}Sr{sub 1.5+x})O{sub 9.5} with x = 0.13(2) for crystal I and x = 0.19(2) for crystal II. The matrix contains intergrowing clusters of the composition Cu{sub 2}O. It is demonstrated that the presence of the second component is structurally justified by the commensurability of the systems of body-centered subcells of cations in the host matrix and anion sublattices in the structure of the Cu{sub 2}O oxide.

Naumov, D. Yu.; Kozeeva, L. P.; Kameneva, M. Yu.; Kuratieva, N. V.; Podberezskaya, N. V. [Russian Academy of Sciences, Nikolaev Institute of Inorganic Chemistry, Siberian Branch (Russian Federation)], E-mail: podberez@che.nsk.su

2008-03-15

227

Structure and refinement of the composition of Bi-Sr-Ca-Cu oxide crystals  

SciTech Connect

The composite structure of the red phase, which accompanies the 2212 and 2201 superconducting phases prepared upon cooling of a melt in the Bi-Sr-Ca-Cu-O system, is revealed by scanning electron microscopy and X-ray diffraction analysis. The matrix component in two crystals I and II under investigation has a monoclinic structure with space group C2/m and the unit cell parameters a = 21.832(2) and 21.8142(9) Angstrom-Sign , b = 4.3809(4) and 4.3771(2) Angstrom-Sign , c = 12.9430(12) and 12.9378(6) Angstrom-Sign , {beta} = 102.832(2) Degree-Sign and 102.839(1) Degree-Sign , and V = 1207.0(2) and 1204.45(9) Angstrom-Sign {sup 3}, respectively. The composition is described by the general formula Bi{sub 4}(Ca{sub 2-x}Sr{sub 1.5+x})O{sub 9.5} with x = 0.13(2) for crystal I and x = 0.19(2) for crystal II. The matrix contains intergrowing clusters of the composition Cu{sub 2}O. It is demonstrated that the presence of the second component is structurally justified by the commensurability of the systems of body-centered subcells of cations in the host matrix and anion sublattices in the structure of the Cu{sub 2}O oxide.

Naumov, D. Yu.; Kozeeva, L. P.; Kameneva, M. Yu.; Kuratieva, N. V.; Podberezskaya, N. V., E-mail: podberez@che.nsk.su [Russian Academy of Sciences, Nikolaev Institute of Inorganic Chemistry, Siberian Branch (Russian Federation)

2008-03-15

228

Effect of dysprosium substitution on the electrical properties of SrBi4Ti4O15 ceramics  

NASA Astrophysics Data System (ADS)

The four-layer Aurivillius compound SrBi4-xDyxTi4O15 (x = 0.02 - 0.1) was synthesized by using a solid state sintering method. X-ray diffraction (XRD) analysis revealed that the dysprosium-substituted SrBi4Ti4O15 ceramics have a pure four-layer Aurivillius-type structure. The lattice parameters and densities were calculated with XRD studies. The experimental densities obtained were about 95% that of theoretical values. The effects of dysprosium oxide on the microstructure, ferroelectric, dielectric and piezoelectric properties of the ceramics were investigated. The dielectric constant of Dy-doped samples was found to decrease with increasing Dy content. At x = 0.06, the piezoelectric charge coefficient (d33) and the electromechanical coupling factor (kp) were found to be maximum.

Mamatha, B.; Ashok, K.; James, A. R.; Sarah, P.

2012-06-01

229

Crystal Orientation of BiSrCaCuO (11n) Thin Films Determined by X-ray Asymmetric Reflection  

Microsoft Academic Search

Tilt angles of the c-axes from the substrate surface of BiSrCaCuO (11n) thin films were precisely measured using a diffractometer method with X-ray asymmetric reflection. The preferred orientation was determined from the measurement of these angles. The high Tc phase composition film formed on a SrTiO3 (110) substrate had two tilt angles of 45.24° and 45.04°, and their preferred orientation

Masayuki Kataoka; Ken'ichi Kuroda; Junji Tanimura; Osamu Wada; Kazuyoshi Kojima; Tetsuya Takami; Koichi Hamanaka; Tetsuo Ogama

1991-01-01

230

Effect of Ca-Substitution on CdTiO3 Studied by Raman Scattering and First Principles Calculations  

Microsoft Academic Search

An effect of Ca-substitution on ferroelectricity of CdTiO3, whose paraelectric structure involves rotated oxygen octahedra, is studied by Raman scattering and first-principle calculations from a viewpoint of a relation between covalency and instability of lattice vibrations. Raman scattering experiments reveal that the Ca-substitution suppresses softening of a soft mode and reduces the phase transition temperature. An origin of the soft

Hiroki Taniguchi; Hwee Ping Soon; Hiroki Moriwake; Yue Jin Shan; Mitsuru Itoh

2012-01-01

231

Thermodynamic properties of perovskite ARuO{sub 3} (A=Ca, Sr, and Ba) single crystals  

SciTech Connect

Magnetic susceptibility, transport properties (including magnetoresistivity and the Hall effect), and specific heat of perovskite ARuO{sub 3} (A=Ca, Sr, and Ba) single crystals were measured. These compounds, particularly CaRuO{sub 3} (paramagnetic conductor) and SrRuO{sub 3} (ferromagnetic conductor) are believed to have a narrow {pi}{sup {asterisk}} band and their thermodynamic properties depend in an extremely sensitive way on the degree of the band filling and band width. This study reveals that the {pi}{sup {asterisk}} bandwidth of these compounds is largely determined by the ionic radii of the alkaline-earth A cations, i.e., the interaction between A s and O 2p orbitals and the electron correlation becomes progressively stronger in the series BaRuO{sub 3}, SrRuO{sub 3}, and CaRuO{sub 3}. {copyright} {ital 1997 American Institute of Physics.}

Shepard, M.; McCall, S.; Cao, G.; Crow, J.E. [National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 (United States)

1997-04-01

232

BiSrCaCuO thin film grown on SrTiO3 substrate with off-oriented (110) surface  

Microsoft Academic Search

A Bi2(Sr,Ca)3Cu2O(x) thin film with the (117) orientation was formed on a slightly off-oriented (110) SrTiO3 substrate by single-target sputtering. The (110) substrate off-oriented by 5 deg is considered to have limited film growth in one direction. From RHEED and cross-sectional TEM observations, it was found that the c-axis of the film tilts against the substrate surface by 46-47 deg

Ken'ichi Kuroda; Osamu Wada; Junji Tanimura; Kazuyoshi Kojima; Tetsuya Takami; Masayuki Kataoka; Tetsuo Ogama; Koichi Hamanaka

1991-01-01

233

A TEM study of Bi2Sr2CaCu2Ox superconducting thin films on SrTiO3 substrates  

Microsoft Academic Search

As-deposited Bi2Sr2CaCu2Ox films on (001) SrTiO3 substrates produced by laser deposition are investigated in a high-resolution electron microscope. The films are well-oriented with the crystallographic c-axis and a-axis direction of the films parallel to the [001] and [110] direction of the substrate, respectively. The substrate\\/film interface is sharp and good crystalline order is build up from the interface. Misfit dislocations

X. F. Zhang; B. Kabius; K. Urban; P. Schmitt; L. Schultz; G. Saemann-Ischenko

1991-01-01

234

Experimentally determined Mg/Ca and Sr/Ca ratios in juvenile bivalve calcite for Mytilus edulis: implications for paleotemperature reconstructions  

NASA Astrophysics Data System (ADS)

To further evaluate the potential use of Mg/Ca and Sr/Ca ratios as a paleothermometer in the shell carbonate of the blue mussel Mytilus edulis, we grew juvenile mussels (˜15 mm shell height; <2 years old) collected from Maine, USA, in controlled environments for 4 months. The four-by-three factorial design consisted of four circulating temperature baths (7, 11, 15 and 19°C), and three salinity ranges (23, 28, and 32). During the experiment, water Mg/Ca and Sr/Ca molar ratios were monitored weekly, and showed little variation across all salinity and temperature ranges. Data from sampled shells including all salinity treatments yielded relatively poor relationships between shell elemental chemistry and water temperatures. However, if only the low salinity treatment data (23) are used, the relationships between shell elemental chemistry and water temperature improve moderately. Based on the data presented here, it may be possible to use Mg/Ca and Sr/Ca ratios from the shell carbonate of juvenile M. edulis to reconstruct paleotemperatures in estuarine settings (salinity below 24) with a corresponding RMSE (root mean squared error; 95% confidence interval) of ±2.4°C and ±2.8°C, respectively. In order for this methodology to be statistically meaningful, water temperature changes must be rather large, as the errors associated with using Mg/Ca and Sr/Ca ratios from the shell material of M. edulis are substantial. Further work is required to determine if the findings presented here can be duplicated, and if the potential salinity effect is pervasive.

Wanamaker, Alan D., Jr.; Kreutz, Karl J.; Wilson, Tiffany; Borns, Harold W., Jr.; Introne, Douglas S.; Feindel, Scott

2008-10-01

235

Variations in Mg\\/Ca and Sr\\/Ca ratios of planktonic foraminifera caused by postdepositional dissolution: Evidence of shallow Mg-dependent dissolution  

Microsoft Academic Search

A comparative study has been made of two species of planktonic foraminifera, G. tumida and G. sacculifer, in a depth transect on the Ontong Java Plateau, western equatorial Pacific. G. tumida tests from core-top sediments showed decreasing Mg\\/Ca (2.65-1.25 mmol\\/mol) and Sr\\/Ca (1.50-1.16 mmol\\/mol) ratios with increasing water depth (1600-4400 m), while no such variation was found in G. sacculifer

Sarah J. Brown; Henry Elderfield

1996-01-01

236

X-ray photoelectron diffraction studies of Bi2Sr2CaCu2O8+x  

Microsoft Academic Search

A single crystal Bi2Sr2CaCu2O8+x (T0=84 K has been studied by X-ray photoelectron diffraction (XPD). Nearly full-solid-angle intensity distributions of Bi4f, Sr3d, Ca2p, Cu2p and O 1s emission from a (001)-terminated surface (=c plane) show twofold symmetric patterns with mirror planes along the a and b crystal axes, although the directions of several dominant forward scattering peaks are positioned in a

M. Shimoda; T. Greber; J. Osterwalder; L. Schlapbach

1992-01-01

237

Characterization of Ag\\/Bi 2Sr 2Ca n?1 Cu n O 2 n+4 interfacial resistivity  

Microsoft Academic Search

Silver contacts to single-crystal Bi2Sr2CaCu2Ox (Bi-2212) and polycrystalltine (Bi,Pb)2Sr2Ca2Cu3Ox (B-2223) were prepared by sputtering or sinter-forging techniques. The interfacial resistivity of Ag\\/Bi-2212, defined as interfacial resistance times contact area, decreased from 10?4 to 10?10 ? cm2 at 77 K when the thermal annealing time increased from 1 to 14 h at 600°C; it was also a function of the annealing

Y. Fang; S. Danyluk; M. T. Lanagan; C. A. Youngdahl; X. Xu; K. Numata

1995-01-01

238

Dependence of critical current density on microstructures in superconducting Bi(Pb)-Sr-Ca-Cu-O wires  

Microsoft Academic Search

The dependence of the critical current density Jc on microstructures in superconducting Ag-sheathed Bi(Pb)-SrCa-Cu-O wires has been investigated. A mixture of the oxide powders with a composition of Bi1.84Pb0.34Sr1.9Ca2.0Cu3.1Ox was calcined and the resulting powder was placed in silver tubes. The tubes were processed by drawing and rolling to give 0.3 nm thick tapes. The tapes were annealed at 825-843

T. Kanai; T. Kamo; S. Matsuda

1991-01-01

239

d-wave superconductivity of the hole-doped (SrCa)10Cu17O29 ladder compound  

Microsoft Academic Search

We performed tunneling experiments on single crystals of hole-doped two-leg ladders (SrCa)10Cu17O29 with Tc?75 K and, for reference purposes, on textured bulk samples of Bi2Sr2CaCu2O8 (Bi2212). Point-contact and break-junction (Bi2212 only) junction configurations were used. The point-contact junctions, both superconductor-insulator-normal-metal and superconductor-normal-metal, were using Ag counterelectrodes. In all experiments the tunneling direction was along Cu2O3 planes (for the ladders) and

A. I. D'yachenko; V. Yu. Tarenkov; R. Szymczak; A. V. Abal'oshev; I. S. Abal'osheva; S. J. Lewandowski; L. Leonyuk

2000-01-01

240

I-STAL, a model for interpretation of Mg/Ca, Sr/Ca and Ba/Ca variations in speleothems and its forward and inverse application on seasonal to millennial scales  

NASA Astrophysics Data System (ADS)

Trace element ratios Mg/Ca, Sr/Ca, and Ba/Ca are readily measured in speleothems and may be closely related to hydrological balance, enhancing paleoclimate information inferred from stable isotope measurements. We develop a model which simulates the variation in dripwater chemistry resulting from variable degree of water-rock interaction and prior calcite precipitation (PCP), with the latter process depending both on drip interval and drip oversaturation with respect to CaCO3. Partition coefficients between speleothem and dripwater are dependent on temperature for Mg and on speleothem growth rate for Sr and Ba, as observed in laboratory experiments. The drip oversaturation state, regulated both by cave pCO2 and the dilution and soil karst dissolution processes, strongly affects stalagmite trace element concentrations by modulating the extent of PCP and speleothem growth rates. Application of an inverse model confirms that seasonal CO2 cycles can explain the uncorrelated seasonal cycles in Mg/Ca and Sr/Ca observed in our speleothem records from NW Spain for which high CO2 coincides with dry season. In absence of seasonal variations in drip interval, cycles in cave pCO2 can produce seasonal covariation in Sr/Ca, Mg/Ca and Ba/Ca. In long time series (104 yr) where seasonal sampling resolution is not obtained in stalagmites, a change from dominance of summer to winter rainfall can shift the season of strongest stalagmite deposition to one of lower mean CO2 and hence greater PCP and higher Mg/Ca, Sr/Ca and Ba/Ca ratios. Caves best suited to record a dominantly water balance signal, such as mean drip intervals, are those with minimal seasonal variation in cave pCO2.

Stoll, Heather M.; Müller, Wolfgang; Prieto, Manolo

2012-09-01

241

Magnetic alignment in 2212 Bi-based superconducting system: I. Magnetic orientation of BiSrCa{sub 1-{ital x}}(RE){sub {ital x}}CuO{sub 8-{ital y}} [(RE)=Gd, Dy, Ho, Er] powder dispersed in epoxy resin at room temperature  

Microsoft Academic Search

The magnetic anisotropy of rare-earth substituted 2212 materials (BiSrCa{sub 0.8}RE{sub 0.2}CuO{sub {ital x}} with RE=Gd, Dy, Ho, Er) is put into evidence. Superconducting powder dispersed in epoxy resin is oriented under an external magnetic field (4T) in a direction which depends on the nature of the rare-earth used in the substitution. Both directions of observation (parallel or perpendicular to the

S. Stassen; R. Cloots; P. Vanderbemden; P. A. Godelaine; H. Bougrine; A. Rulmont; M. Ausloos

1996-01-01

242

The effect of skeletal mass accumulation in Porites on coral Sr/Ca and ?18O paleothermometry  

NASA Astrophysics Data System (ADS)

Paleotemperature estimates based on coral Sr/Ca have not been widely accepted because the reconstructed glacial-Holocene shift in tropical sea-surface temperature (˜4-6°C) is larger than that indicated by foraminiferal Mg/Ca (˜2-4°C). We show that corals over-estimate changes in sea-surface temperature (SST) because their records are attenuated during skeletogenesis within the living tissue layer. To quantify this process, we microprofiled skeletal mass accumulation within the tissue layer of Porites from Australasian coral reefs and laboratory culturing experiments. The results show that the sensitivity of the Sr/Ca and ?18O thermometers in Porites will be suppressed, variable, and dependent on the relationship between skeletal growth rate and mass accumulation within the tissue layer. Our findings help explain why ?18O-SST sensitivities for Porites range from -0.08‰/°C to -0.22‰/°C and are always less than the value of -0.23‰/°C established for biogenic aragonite. Based on this observation, we recalibrated the coral Sr/Ca thermometer to determine a revised sensitivity of -0.084 mmol/mol/°C. After rescaling, most of the published Sr/Ca-SST estimates for the Indo-Pacific region for the last ˜14,000 years (-7°C to +2°C relative to modern) fall within the 95% confidence envelope of the foraminiferal Mg/Ca-SST records. We conclude that two types of calibration scales are required for coral paleothermometry; an attenuated Porites-specific thermometer sensitivity for studies of seasonal to interannual change in SST and, importantly, the rescaled -0.084 mmol/mol/°C Sr/Ca sensitivity for studies of 20th-century trends and millennial-scale changes in mean SST. The calibration-scaling concept will apply to the development of transfer functions for all geochemical tracers in corals.

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

2012-03-01

243

The effect of element substitution on high-temperature thermoelectric properties of Ca3Co2O6 compounds  

NASA Astrophysics Data System (ADS)

Polycrystalline Ca3Co1.8M0.2O6 (M=Mn, Fe, Co, Ni, Cu) and Ca2.7Na0.3Co2O6 were synthesized by solid-state reaction to evaluate the effect of substitution on the thermoelectric properties of Ca3Co2O6. Substitution by Mn, Cu and Na appears to increase carrier density, given that electrical resistivity (?) and the Seebeck coefficient (S) were simultaneously reduced. Conversely, Fe substitution seems to reduce carrier density, resulting in a simultaneous increase in S and ?. Cu and Na substitution resulted in a significant decrease in ? due to enhancement of grain size and grain boundary connectivity, which could have a strong impact on ?. Not only the intrinsic substitution effect on the electronic state but also this modification of the microstructure plays an important role in improvement of the thermoelectric power factor, particularly in the case of the Na-substituted sample.Graphical abstractSEM images of fracture cross-sections of Ca3Co1.8M0.2O6 (M=Mn, Fe, Co, Ni and Cu) and Ca2.7Na0.3Co2O6 pellets.

Mikami, Masashi; Funahashi, Ryoji

2005-05-01

244

Specific-heat measurements on superconducting Bi-Ca-Sr-Cu and Tl-Ca-Ba-Cu oxides: Absence of a linear term in the specific heat of Bi-Ca-Sr-Cu oxides  

SciTech Connect

Specific-heat data, extending from 0.4 to 120 K in both a zero field and at 7 T, are reported for five samples of Bi-Ca-Sr-Cu oxide and one of Tl-Ca-Ba-Cu oxide. The occurrence of bulk superconductivity in all six samples is shown by Meissner-effect measurements, and confirmed for the Tl sample and two Bi samples by the specific-heat data. In a zero field, the Tl sample shows a contribution to the specific heat that is linear in temperature and comparable to those reported for YBa/sub 2/Cu/sub 3/O/sub 7/. For all samples of the Bi compound the linear term is zero within the experimental uncertainty, and is at least an order of magnitude smaller.

Fisher, R.A.; Kim, S.; Lacy, S.E.; Phillips, N.E.; Morris, D.E.; Markelz, A.G.; Wei, J.Y.T.; Ginley, D.S.

1988-12-01

245

Improved Dielectric Properties of Low-Temperature-Sintered (Ba,Sr)TiO3-Based Ceramics by Ge Substitution  

NASA Astrophysics Data System (ADS)

Multilayer microwave dielectric materials with low sintering temperature are required for microwave phase shifters, filters, and true-time delay devices. We investigated the sintering and dielectric properties of (Ba0.6Sr0.4)(Ti1-xGex)O3 (BSTG; 0.05? x? 0.3) ceramics. As the Ge concentration was increased, the lattice constant of BSTG ceramics decreased, and Ba2Ge2TiO8, which is the liquid phase at low temperature, was formed. Ba2Ge2TiO8 liquid phase may increase the sintering density. The effect of Ge substitution is the decrease in the sintering temperature from over 1400 to 1150 °C in BST system ferroelectric ceramics. With increasing Ge concentration, the dielectric constant decreased from 2190 to 530, and the dielectric loss decreased up to 0.001 (at 1 MHz) with sintering at 1150 °C for 2 h. When Ge was substituted at 0.05 and 0.1 mol of Ti in the BST at 1150 °C, the dielectric constant, dielectric loss, tunability, Curie temperature, and figure of merit were 2184 and 1529, 0.002 and 0.001, 27 and 23%, -11 and -18 °C, and 135 and 230, respectively. These compositions show microwave dielectric properties comparable to those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are the important materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

Jong-Yoon Ha,; Seok-Jin Yoon,; Dae-Yong Jeong,; Ji-Won Choi,

2010-07-01

246

Thermal expansion behaviour in the oxygen deficient perovskites Sr 2 B SbO 5.5 ( B =Ca, Sr, Ba). Competing effects of water and oxygen ordering  

NASA Astrophysics Data System (ADS)

Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr 2 B SbO 5.5 ( B =Ca, Sr, Ba). Synchrotron X-ray studies demonstrate that these oxides have a double perovskite-type structure with the cell size increasing as the size of the B cation increases from 8.2114(2) Å for B =Ca to 8.4408(1) Å for B =Ba. It is postulated that a combination of local clustering of the anions and vacancies together with water-water and water-host hydrogen bonds plays a role in defining the volume of the encapsulated water clusters and that changes in the local structure upon heating result in anomalous thermal expansion observed in variable temperature diffraction measurements.

Zhou, Qingdi; Kennedy, Brendan J.; Avdeev, Maxim

2011-09-01

247

Chemical bond characteristics, thermal expansion property and compressibility of AR 2O 4 (A = Ca, Sr, Ba; R = rare earths)  

Microsoft Academic Search

Theoretical researches were performed on the CaFe2O4-type binary rare earth oxides AR2O4 (A=Ca, Sr, Ba; R=rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations

Huaiyong Li; Siyuan Zhang; Shihong Zhou; Xueqiang Cao

2009-01-01

248

Thermal-expansion behaviors and mechanisms for Ca or Sr-doped lanthanum manganite perovskites under oxidizing atmospheres  

Microsoft Academic Search

The thermal expansion behavior and mechanism of A-site-deficient lanthanum manganite perovskites, La{sub 1-x}MnOâ (0 < x ⤠0.1), and alkaline earth metal (AE)-doped lanthanum manganite perovskites, La{sub 1-x}AEâMnOâ (AE = Ca and Sr, 0 ⤠x ⤠0.4), under oxidizing atmospheres have been investigated. The average linear thermal expansion coefficients of the AE-doped lanthanum manganites decreased with increasing Ca content

Masashi Mori; Yoshiko Hiei; Nigel M. Sammes; Geoff A. Tompsett

2000-01-01

249

Combined effects of annealing/quenching and transition metal substitution on physical properties of CaFe2As2  

NASA Astrophysics Data System (ADS)

Our previous work on CaFe2As2 single crystals 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, in a manner similar to applied pressure. With combined effect of annealing/quenching and transition metal substitution, CaFe2As2 system offers ready access to the salient low-temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and nonmagnetic/collapsed tetragonal. In this talk we will present systematic studies of the combined effects of annealing/quenching and chemical substitution with various transition metals (Co, Ni, Rh) on the physical properties of CaFe2As2 and construct phase diagrams for different substitution levels and different annealing/quenching temperatures.

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

2013-03-01

250

Vortex phase diagram of nearly stoichiometric Bi2Sr2CaCu2O8+? single crystal  

NASA Astrophysics Data System (ADS)

There have been a large number of reports on the vortex phase diagram of Bi2212. However, the Bi2212 crystals used for these studies mostly have Bi-rich composition, with typically Bi : Sr = 2.1 : 1.9. Recently, Eisaki et al. [1] reported that Tc in Bi2212 single crystal is largely depressed by the cation disorder at the Sr-site, typically the substitution of Sr-site by Bi^3+. In the present study, we found that the Bi-Sr substitution also depress the vortex pinning. We have successfully grown Bi2212 single crystals with Bi : Sr ratio very close to 2 : 2. It showed very high critical current density, 2 ¥times 10^6 A/cm^2, at 20K, and reduced reversible region (Jc = 0 region) in the magnetic phase diagram. We also show the dependence of the irreversibility field on the cation nonstoichiometry. The author thanks K. Furusawa, H. Eisaki and Y. Nakayama for growing Bi2212 single crystals.

Chikumoto, Noriko

2006-03-01

251

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

NASA Astrophysics Data System (ADS)

The synthesis and crystallography, magnetic susceptibility ?, magnetization M, specific heat Cp, in-plane electrical resistivity ?, 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 ?(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 ?(T) and M(H) data reveal anisotropic diamagnetism in the normal state, with ?c>?ab for CaPd2As2 and BaPd2As2, and ?cSrPd2As2. 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 ?-model of the BCS theory of superconductivity, which indicates that the s-wave gap in this compound is anisotropic in momentum space.

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

2013-06-01

252

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

SciTech Connect

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.

de la Fuente, G.F.; Navarro, R.; Lera, F.; Rillo, C.; Bartolome, J.; Badia, A. (Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, 50009-Zaragoza, Spain (ES)); Beltran, D.; Ibanez, R.; Beltran, A. (UIBCM, Departament de Quimica Inorganica, Universitat de Valencia, Dr. Moliner 50, Burjassot, 46100-Valencia, (Spain)); Sinn, E. (University of Hull, School of Chemistry, Cottingham Road, Kingston upon Hull, HU6 7RX, (England))

1991-04-01

253

Bipolar resistive switchings in Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

Investigations of bipolar resistive switchings in Bi2Sr2CaCu2O8+? single crystal heterostructures are reported. The current-voltage characteristics of heterocontacts with switching effects exhibit a diode nature with Schottky-like barriers on high doped semiconductors. In this case the carrier tunneling processes are responsible for the current transfer in the structure. The voltage of switching into the metastable state is determined by barrier-controlled carrier tunneling. Spatial carrier inhomogeneity produces a field influence on the potential barrier in the interface of heterostructures with the BRS effect, redistribution of carriers and first order phase transition in the phase separation system. The numerical simulation method was used to consider the influence of inhomogeneous electrical field distribution in the heterocontact interface on the BRS effect in the oxide compounds.

Tulina, N. A.; Borisenko, I. Yu; Sirotkin, V. V.

2013-09-01

254

Vortex matter in Bi2Sr2CaCu2O8 with pointlike disorder  

NASA Astrophysics Data System (ADS)

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.

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

2009-03-01

255

Electronic Magnetic and Structural Properties of A2VM0O6 Perovskites (A = Ca, Sr)  

SciTech Connect

The perovskites Sr{sub 2}VMoO{sub 6} and Ca{sub 2}VMoO{sub 6} have been synthesized by liquid-mix technique in citrate melts, and their electronic, magnetic and structural properties have been investigated. No signs of V/Mo ordering are seen by synchrotron X-ray powder diffraction, but despite the chemical disorder both oxides are highly conductive and Pauli paramagnetic. Electrical conductivities of these solid solutions are comparable or higher than those reported for polycrystalline AMoO{sub 3} end members. It is suggested that the delocalized metallic conductivity of these compounds with two different transition-metal atoms implies valence equilibrium between the degenerate oxidation-state couples V{sup 4+}Mo{sup 4+} and V{sup 3+}Mo{sup 5+}.

Karen,P.; Moodenbaugh, A.; Goldberger, J.; Santhosh, P.; Woodward, P.

2006-01-01

256

Microfilamentary Bi2Sr2Ca1Cu2O8 fibers  

NASA Astrophysics Data System (ADS)

Techniques have been developed for the fabrication of superconducting microfilaments of Bi2 Sr2 Ca1 CU2 O8 as part of a larger project to produce microfilamentary composites. The process is based on a gas jet fiberization of a viscous liquid melt to form long slender amorphous fibers. A subsequent anneal then converts the fibers to the superconducting crystalline phase. Fiber diameters range from 1 to 6 microns and length to diameter ratios range between 10 to the 3rd power and 10 to the 4th power so the dimensions are favorable for composite formation. The details of grain growth are reviewed with special emphasis on the role of the filament diameter on the morphology of the grain growth.

Miller, T. A.; Sanders, S. C.; Finnemore, D. K.; Lebeau, S. E.; Righi, J.

257

Spin-mixed doubly excited resonances in Ca and Sr spectra  

SciTech Connect

We present a joint theoretical and experimental investigation to demonstrate explicitly how the combined spin-dependent interaction and the configuration interaction may affect the mixing of different spin states along various doubly excited autoionization series for Ca and Sr as energy increases across several ionization thresholds. In particular, our study has identified the inversion of energy levels between members of a number of multiplets, i.e., in contrast to the Hund's rules, due to the presence of perturber from other overlapping resonance series. We are also able to demonstrate the beginning of the breakdown of the LS coupling for resonance series corresponding to electron configurations with higher orbital angular momenta and those above the third ionization threshold.

Chen, J. H. [Graduate Institute of Applied Science and Engineering, Fu Jen Catholic University, Taipei, Taiwan 242 (China); Fang, T. K. [Department of Physics, Fu Jen Catholic University, Taipei, Taiwan 242 (China); Chu, C. C.; Yih, T. S. [Department of Physics, National Central University, Chungli, Taiwan 32054 (China); Chang, T. N. [Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089-0484 (United States)

2009-10-15

258

Nanosecond and femtosecond laser deposition of BiSrCaCuO on MgO  

NASA Astrophysics Data System (ADS)

Pulsed laser deposition of BiSrCaCuO on MgO (100) using Q-switched Nd:YAG nanosecond laser operating at ?= 1064 nm (ns-PLD) and mode-locked Ti:Sa femtosecond laser at ?= 785 nm (fs-PLD) were performed. Rough surface with spheriodal morphology is the general microstructure of the deposited material from both nanosecond and femtosecond laser ablation. Femtosecond PLD resulted to granular morphology containing both BSCCO phase and rod-like Cu2O grains. Unlike ns-PLD, fs-PLD produced polycrystalline films even without heat treatment. These results indicate that two distinct ablation characteristic for ns-PLD and fs-PLD of BSCCO.

Vitug, Jaziel; Lampa, Krizia Isabel; Olaya, Cherrie May; De Vero, Jeffrey; Santos, Gil Nonato; Sarmago, Roland; Garcia, Wilson

2013-06-01

259

Powerful terahertz emission from Bi2Sr2CaCu2O8+? mesa arrays  

NASA Astrophysics Data System (ADS)

Stacks of intrinsic Josephson junctions in high-temperature superconductors enable the fabrication of compact sources of coherent terahertz radiation. Here, we demonstrate that multiple stacks patterned on the same Bi2Sr2CaCu2O8+? crystal can--under optimized conditions--be synchronized to emit high-power THz-radiation. For three synchronized stacks, we achieved 610 ?W of continuous-wave coherent radiation power at 0.51 THz. We suggest that synchronization is promoted by THz-waves in the base crystal. We note that synchronization cannot be achieved in all samples. However even in these cases, powers on the 100-?W scale can be generated.

Benseman, T. M.; Gray, K. E.; Koshelev, A. E.; Kwok, W.-K.; Welp, U.; Minami, H.; Kadowaki, K.; Yamamoto, T.

2013-07-01

260

Energy gaps in Bi2Sr2CaCu2O8+? cuprate superconductors  

PubMed Central

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

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

2012-01-01

261

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

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

262

Réseaux de vortex dans Bi2Sr2Ca1Cu2Ox  

NASA Astrophysics Data System (ADS)

Results of the defect influence on the flux line lattice in Bi2Sr2Ca1Cu2Ox single crystals are presented. These crystals, non irradiated or irradiated at GANIL with heavy ions (Pb^{56+}, 6 GeV) have been decorated with Ni particles in the superconducting state using the Bitter technique. The defects involved are columnar defects. Resulting decorated flux line patterns have been characterized using scanning electron microscopy and computer image analysis. Disorder of the decorated flux line networks has been found to be strongly dependent on the defect density, which results from the irradiation. In order to characterize this disorder, a method for determining elastic energy terms in the deformation of flux line patterns has been investigated. This method can be applied if Fourier transforms of the decorated flux line patterns exhibit distinct reflections. Nous présentons une étude sur l'influence des défauts vis-à-vis du piégeage des lignes de flux magnétique dans des monocristaux de Bi2Sr2Ca1Cu2Ox. Ces monocristaux, non irradiés ou irradiés sur l'accélérateur du GANIL avec des ions (Pb^{56+}) d'énergie 6 GeV ont été décorés dans l'état supraconducteur selon la technique de Bitter. Les réseaux de lignes de flux magnétique ont eté caractérisés par microscopie électronique à balayage et avec un analyseur d'images. Les résultats montrent que les réseaux de lignes de flux magnétique sont fortement dépendant de la densité de défauts résultant de l'irradiation. Pour caractériser l'état de désordre, nous avons appliqué une méthode de calcul de termes d'énergie élastique des réseaux de lignes de flux magnétique. Cette méthode ne peut être appliquée que si la transformée de Fourier des réseaux de vortex présente des réflexions discrètes.

Weiss, F.; Miramond, C.; Thomas, O.; Rouault, A.; Sénateur, J. P.; Audier, M.; Vacher, M.; Groult, D.; Hardy, V.; Provost, J.; Ruyter, A.; Simon, C.

1994-11-01

263

Y-substituted SrTiO 3–YSZ composites as anode materials for solid oxide fuel cells: Interaction between SYT and YSZ  

Microsoft Academic Search

Donor-substituted SrTiO3 ceramic materials were investigated as the anodes of solid oxide fuel cells (SOFCs). Sr0.89Y0.07TiO3?? (SYT) samples with good electrical conductivity and redox stability were prepared. The thermal and chemical expansions of SYT are both compatible with YSZ electrolyte. Half cells consisting of a flat anode substrate and an electrolyte layer with outer dimensions of 5cm×5cm were fabricated, Ni

Qianli Ma; Frank Tietz; Doris Sebold; Detlev Stöver

2010-01-01

264

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

SciTech Connect

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.

Skinner, Lawrie [State University of New York, Stony Brook; Benmore, Chris J [Argonne National Laboratory (ANL); Weber, Richard [Argonne National Laboratory (ANL); Santodonato, Louis J [ORNL; Tumber, Sonia [Materials Development, Inc., Evanston, IL; Neuefeind, Joerg C [ORNL; Lazareva, Lena [State University of New York, Stony Brook; Du, Jincheng [University of North Texas; Parise, John B [Stony Brook University (SUNY)

2012-01-01

265

Shift and Broadening of the Resonance Lines of Ca, Sr and Ba in Hot, Dense Argon and Helium.  

National Technical Information Service (NTIS)

The shift and half-width of the resonance singlet lines of Ca, Sr and Ba in emission were measured under various relative densities between 20 and 70 for Ar (at 2500 K) and between 35 and 121 for He (at 2450 K) by means of a ballistic compressor. The shif...

P. K. Henry S. Y. Ch'en

1972-01-01

266

Stability of Bi2Sr2CaCu2O8 superconductor in molten halide salts  

NASA Astrophysics Data System (ADS)

Stability of preformed Bi2Sr2CaCu2O8 phase in molten halide salts is described here. Salt systems containing Li+ and other halides except chlorides are negative in their ability to stabilize the Bi-2212 phase. Among all the salt systems evaluated, only some of the alkali chloride salt systems proved positive in stabilizing the Bi-2212 phase.

Gopalakrishnan, Sudhakar; Schulze, Walter A.

1994-08-01

267

Composite Superconducting Wires Obtained by High-Rate Tinning in Molten Bi-Pb-Sr-Ca-Cu-O System.  

National Technical Information Service (NTIS)

The preparation of high-T(sub c) superconducting long composite wires by short-time tinning of the metal wires in a molten Bi-Pb-Sr-Ca-Cu-O compound is discussed. The application of this method to the high-T(sub c) materials is tested, possibly for the fi...

A. D. Grozav L. A. Konopko N. I. Leporda

1990-01-01

268

Absorption and Fluorescence of Sm2+ in CaF2, SrF2, and BaF2  

Microsoft Academic Search

The absorption and fluorescence of the Sm2+ ion have been studied for three host lattices, CaF2, SrF2, and BaF2. Measurements of intensity, linewidth, quantum efficiency, and Zeeman splitting are reported. Energy levels belonging to the 4f shell have been identified, and a preliminary analysis of the 4f-->5d transitions is presented.

D. L. Wood; W. Kaiser

1962-01-01

269

STM Studies of Near-Optimal Doped Bi_2Sr_2CaCu_2O_8 delta  

SciTech Connect

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

Kapitulnik, Aharon

2010-04-05

270

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

PubMed

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. PMID:18444634

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

2008-04-30

271

Vortex line pinning in Bi2Sr2CaCu2O8 single crystals with columnar defects.  

National Technical Information Service (NTIS)

The ac transmittivity of heavy-ion irradiated Bi2Sr2CaCu 2O8 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...

C. J. van der Beek V. M. Vinokur G. W. Crabtree B. Schmidt M. Konczykowski

1994-01-01

272

Structural and Electronic Role of Lead in (PbBi)_2Sr_2CaCu_2O_8 Superconductors by STM  

NASA Astrophysics Data System (ADS)

The structural and electronic effects of lead substitution in the high-temperature superconducting materials Pb_xBi2-xSr_2CaCu_2O_8 have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)-O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)-O layers. STS data show that the electronic structure of the Bi(Pb)-O layers is insensitive to lead substitution within ±0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at ?1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of x(Pb) (x <= 0.7), these microscopic STM and STS data suggest that the lead-induced electronic and structural changes in the Bi(Pb)-O layer do not perturb the electronic states critical to forming the superconducting state in this system.

Wu, Xian Liang; Zhang, Zhe; Wang, Yue Li; Lieber, Charles M.

1990-06-01

273

Ca2+ and its substitutes have two different binding sites and roles in soluble, quinoprotein (pyrroloquinoline-quinone-containing) glucose dehydrogenase.  

PubMed

To investigate the mode of binding and the role of Ca2+ in soluble, pyrroloquinoline-quinone (PQQ)-containing glucose dehydrogenase of the bacterium Acinetobacter calcoaceticus (sGDH), the following enzyme species were prepared and their interconversions studied: monomeric apoenzyme (M); monomer with one firmly bound Ca2+ ion (M*); dimer consisting of 2 M* (D); dimer consisting of 2 M and 2 PQQ (Holo-Y); dimer consisting of D with 2 PQQ (Holo-X); fully reconstituted enzyme consisting of Holo-X with two extra Ca2+ ions (Holo) or substitutes for Ca2+ (hybrid Holo-enzymes). D and Holo are very stable enzyme species regarding monomerization and inactivation by chelator, respectively, the bound Ca2+ being locked up in such a way that it is not accessible to chelator. D can be converted into M* by heat treatment and the tightly bound Ca2+ can be removed from M* with chelator, transforming it into M. Reassociation of M* to D occurs spontaneously at 20 degrees C; reassociation of M to D occurs by adding a stoichiometric amount of Ca2+. Synergistic effects were exerted by bound Ca2+ and PQQ, each increasing the affinity of the protein for the other component. Dimerization of M to D occurred with Ca2+, Cd2+, Mn2+, and Sr2+ (in decreasing order of effectiveness), but not with Mg2+, Ba2+, Co2+, Ni2+, Zn2+, or monovalent cations. Conversion of inactive Holo-X into active Holo, was achieved with Ca2+ or metal ions effective in dimerization. Although it is likely that activation of Holo-X involves binding of metal ion to PQQ, the spectral and enzymatic activity differences between normal Holo- and hybrid Holo-enzymes are relatively small. Titration experiments revealed that the two Ca2+ ions required for activation of Holo-X are even more firmly bound than the two required for dimerization of M and anchoring of PQQ. Although the two binding sites related with the dual function of Ca2+ show similar metal ion specificity, they are not identical. The presence of two different sites in sGDH appears to be unique because in other PQQ-containing dehydrogenases, the PQQ-containing subunit has only one site. Given the broad spectrum of bivalent metal ions effective in reconstituting quinoprotein dehydrogenase apoenzymes to active holoenzymes, but the limited spectrum for an individual enzyme, the specificity is not so much determined by PQQ but by the variable metal-ion-binding sites. PMID:9266710

Olsthoorn, A J; Otsuki, T; Duine, J A

1997-07-15

274

Fabrication and texture characterization of bulk (Bi,Pb)(sub 2)Sr(sub 2)Ca(sub 2)Cu(sub 3)O(sub x) and Bi(sub 2)Sr(sub 2)CaCu(sub 2)O(sub x) superconductors.  

National Technical Information Service (NTIS)

Bulk (Bi,Pb)(sub 2)Sr(sub 2)Ca(sub 2)Cu(sub 3)O(sub x) (Bi-2223) and Bi(sub 2)Sr(sub 2)CaCU(sub 2)0(sub x) (Bi-2212) superconductors were fabricated by sinter forging. Bi-2223 ((approx)90% Bi-2223, 10% (Bi,Pb)(sub 2)Sr(sub 2)CaCU(sub 2)0. + other phases) ...

K. C. Goretta N. Chen A. C. Biondo B. L. Fisher M. T. Lanagan

1995-01-01

275

Polar-to-centrosymmetric phase transition in Ca 1.5Sr 1.5(VO 4) 2 and the polar phase structure  

Microsoft Academic Search

Ca1.5Sr1.5(VO4)2 was synthesized by the solid-state method at 1150°C followed by quenching in air. Crystal structure of Ca1.5Sr1.5(VO4)2 was refined by Rietveld method: space group R3c, a = 11.0152(1) Å, c = 38.8937(2) Å, Z = 21. The structure of Ca1.5Sr1.5(VO4)2 is isotypic with Ca3(VO4)2. Here the M5 site is fully occupied by calcium cations and the M4 site is

A. A. Belik; S. Y. Stefanovich; B. I. Lazoryak

2001-01-01

276

Microscopic study of an artificial grain boundary Josephson junction in a BiSrCaCuO thin film formed on a SrTiO3(110) substrate using a MgO buffer layer  

Microsoft Academic Search

An artificial grain boundary Josephson junction in a BiSrCaCuO thin film was fabricated on an off-oriented SrTiO3(110) substrate using a MgO buffer layer, and was investigated using a transmission electron microscope (TEM). The MgO buffer layer was oriented with a (110) plane parallel to the (110) plane of the 5-deg off-oriented SrTiO3 substrate. The BiSrCaCuO film was grown with the

Junji Tanimura; Tetsuya Takami; Ken'ichi Kuroda; Osamu Wada; Masayuki Kataoka; Kazuyoshi Kojima; Tetsuo Ogama

1993-01-01

277

Inducing structural collapse and superconductivity in CaFe2As2 by systematic substitutions of rare earths  

NASA Astrophysics Data System (ADS)

Recently, we have reported structural collapse and 47 K superconductivity in CaFe2As2 by aliovalent rare earth substitutions for Ca atoms [1]. We will present the evolution of structural and superconducting properties in single crystals of CaFe2As2 by systematic substitutions of R (=La, Ce, Pr, and Nd) for Ca, causing electron doping that is indirect to FeAs layer. Effect of annealing, growth method, etching, and pressure on Ca1-xRxFe2As2, indicating the intrinsic nature of this high Tc superconductivity, the highest in 122 Fe-based materials, will be discussed. Ref. [1] S. R. Saha et al. arXiv:1105.4798.

Saha, Shanta; Drye, Tyler; Butch, Nicholas; Hu, Rongwei; Kirshenbaum, Kevin; Ziemak, Steven; Paglione, Johnpierre; Zavalij, Peter; Lynn, Jeffrey

2012-02-01

278

Crystallographic identification of Ca2+ and Sr2+ coordination sites in synaptotagmin I C2B domain.  

PubMed

Synaptotagmin I has two tandem Ca(2+)-binding C(2) domains, which are essential for fast synchronous synaptic transmission in the central nervous system. We have solved four crystal structures of the C(2)B domain, one of them in the cation-free form at 1.50 A resolution, two in the Ca(2+)-bound form at 1.04 A (two bound Ca(2+) ions) and 1.65 A (three bound Ca(2+) ions) resolution and one in the Sr(2+)-bound form at 1.18 A (one bound Sr(2+) ion) resolution. The side chains of four highly conserved aspartic acids (D303, D309, D363, and D365) and two main chain oxygens (M302:O and Y364:O), together with water molecules, are in direct contact with two bound Ca(2+) ions (sites 1 and 2). At higher Ca(2+) concentrations, the side chain of N333 rotates and cooperates with D309 to generate a third Ca(2+) coordination site (site 3). Divalent cation binding sites 1 and 2 in the C(2)B domain were previously identified from NMR NOE patterns and titration studies, supplemented by site-directed mutation analysis. One difference between the crystal and NMR studies involves D371, which is not involved in coordination with any of the identified Ca(2+) sites in the crystal structures, while it is coordinated to Ca(2+) in site 2 in the NMR structure. In the presence of Sr(2+), which is also capable of triggering exocytosis, but with lower efficiency, only one cation binding site (site 1) was occupied in the crystallographic structure. PMID:15340165

Cheng, Yuan; Sequeira, Sonia M; Malinina, Lucy; Tereshko, Valentina; Söllner, Thomas H; Patel, Dinshaw J

2004-08-31

279

Oxides as thermionic sources of Mg{sup +}, Ca{sup +}, Sr{sup +}, and Ba{sup +} ions  

SciTech Connect

Group II metal oxides (MgO, CaO, SrO, and BaO) were coated on tungsten or tantalum filaments to form thermionic emitters of positive metal ions. The choice between tungsten and tantalum for optimum performance was empirically found to depend on the oxide material. Total ion emission current and ion purity were generally found to increase with temperature. A stable source of high purity (up to 97%) Ba{sup +} ions could be obtained from the BaO-coated filament at 1800 {degree}C after 150 min of heating. At 1600 {degree}C, the SrO-coated filament could produce a relatively stable ion current and purity of 97% of Sr{sup +} ions. Very pure (99.8%) Ca{sup +} ions were emitted at 1950 {degree}C. However more stable ion current though less pure ions (87% of Ca{sup +} at 1800 {degree}C) were obtained at lower temperatures. MgO-coated filaments using tungsten or tantalum wires were found to be unsuitable as a source of Mg{sup +} ions. All the filaments of MgO, CaO, SrO, and BaO were found to produce larger ion current and higher ion purity at higher temperatures. In general, the relative isotopic abundances of ions produced by a thermionic source are reproduced by the natural isotopic abundances of the corresponding metal. It implies that the slight differences in the nuclear masses of the isotopes do not introduce any significant effect on their ion production efficiency. Between tantalum and tungsten as a choice for the filament material, tantalum was found to be a better choice for Ba{sup +} and Sr{sup +} ions, while tungsten was better for Ca{sup +}. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Tan, T.L.; Zhou, Z.L.; Ong, P.P. [National University of Singapore, Department of Physics, Faculty of Science, Lower Kent Ridge Road, Singapore 0511 (Singapore)

1995-04-01

280

Multiferroicity in geometrically frustrated ?-MCr2O4 systems (M = Ca, Sr, Ba)  

NASA Astrophysics Data System (ADS)

We have successfully synthesized three quasi-two-dimensional geometrically frustrated magnetic compounds (?-MCr2O4, M= Ca, Sr, Ba) using the spark-plasma-sintering technique. All these members of the ?-MCr2O4 family consist of the stacking planar triangular lattices of Cr3+ spins (S=3/2), separated by nonmagnetic alkaline-earth ions. Their corresponding magnetic susceptibility, specific heat, dielectric permittivity, and ferroelectric polarization are systematically investigated. A long-range magnetic ordering arises below the Néel temperature (around 40 K) in each member of the ?-MCr2O4 family, which changes to the quasi-120? proper-screw-type helical spin structure at low temperature. A very small but confirmed spontaneous electric polarization emerges concomitantly with this magnetic ordering. The direction of electric polarization is found within the basal triangular plane. The multiferroicity in ?-MCr2O4 can not be explained within the frameworks of the magnetic exchange striction or the inverse Dzyaloshinskii-Moriya interaction. The observed results are more compatible with the newly proposed Arima mechanism that is associated with the d-p hybridization between the ligand and transition-metal ions, modified by the spin-orbit coupling. The evolution of multiferroic properties with the increasing interplanar spacing (as M changes from Ca to Ba) reveals the importance of interlayer interaction in this new family of frustrated magnetic systems.

Zhao, Li.; Lan, Tian-Wey; Wang, Kuen-Jen; Chien, Chia-Hua; Hung, Tsu-Lien; Luo, Jiu-Yong; Chao, Wei-Hsiang; Chang, Chung-Chieh; Chen, Yang-Yuan; Wu, Maw-Kuen; Martin, Christine

2012-08-01

281

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

SciTech Connect

Oxygen deficient perovskites Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a={radical}(2) Multiplication-Sign a{sub per}, b=2 Multiplication-Sign a{sub per}, c={radical}(2) Multiplication-Sign a{sub per} (a{sup 0}b{sup -}b{sup -} tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}x{<=}0.6 and compound Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} were prepared in air at 1573 K for 48 h. The crystal structure of Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) A, R{sub p}=0.057, R{sub wp}=0.056, {chi}{sup 2}=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92(1)} are 15.5, 15.1, and 13.8 ppm K{sup -1}, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr{sub 0.15}Ca{sub 0.6}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92}. Conductivity of Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the {sigma} value from {approx}1 to {approx}50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E{sub p}) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6. - Graphical abstract: The substitution of cobalt in the 314-phase Sr{sub 0.75}Y{sub 0.25}CoO{sub 2.62} by manganese leads to the formation of oxygen deficient compounds Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, with the cubic and orthorhombic perovskite structures. The conductivity of the x=0.5 sample (110 S/cm) at 1173 K is substantially higher in comparison with x=0.75 (44 S/cm). Together with comparable TEC values for x=0.5 (15.5 ppm K{sup -1}) and 0.75 (15.1 ppm K{sup -1}) samples this makes the former one a promising cathode material for IT-SOFC. Partial replacement of Sr by Ca in Sr{sub 0.75}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} leads to the formation of the solid solution with the orthorhombic perovskite structure, Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6. Along with Sr{sub 0.75}Y{sub 0.25}Co{sub 0.5}Mn{sub 0.5}O{sub 3-y}, novel perovskite Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} represent promising cathode material for IT-SOFC due to low TEC value (13.8 ppm K{sup -1}) and high conductivity of 135 S/cm at 1173 K. Highlights: Black-Right-Pointing-Pointer Mn-doped 314-phases Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 were synthesized. Black-Right-Pointing-Pointer Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, x=0.1--0.6, Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} were made. Black-Right-Pointing-Pointer High-temperature conductivity properties and crystal structure were studied. Black-Right-Pointing-Point

Napolsky, Ph.S.; Drozhzhin, O.A. [Department of Chemistry, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Istomin, S.Ya., E-mail: istomin@icr.chem.msu.ru [Department of Chemistry, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Kazakov, S.M.; Antipov, E.V. [Department of Chemistry, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Galeeva, A.V.; Gippius, A.A. [Department of Physics, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Svensson, G. [Department of Materials and Environmental Chemistry, Stockholm University, Stockholm S-10691 (Sweden); Abakumov, A.M.; Van Tendeloo, G. [EMAT, University of Antwerp, Groenenborgerlaan, Antwerp 171, B-2020 (Belgium)

2012-08-15

282

Thermodynamic properties of Sr-doped LaMnO{sub 3} perovskite in the La-Sr-Mn-O system  

SciTech Connect

Thermodynamic properties of Sr-doped perovskite-type lanthanum manganites (LSM) were generated by measuring the electromotive force (EMF) of test materials, using the solid galvanic cell technique. The cell consisted of an anode (SrO/SrF{sub 2}), an electrolyte (CaF{sub 2} or SrF{sub 2}) and a cathode (LSM/SrF{sub 2}). Two types of cells were tested in which type 1 used a CaF{sub 2} electrolyte and type 2 used a SrF{sub 2} electrolyte. The activity of SrO substituting into various LSM compositions was calculated using the measured EMF. The Sr content was varied from 0.16 to 0.6 mol, and the temperature of interest varied from 700 to 1000 C. It was found that the SrO activity decreased with increasing temperature (at fixed composition) and increased with increasing Sr content (at fixed temperature).

Zheng, F.; Pederson, L.R.

1999-08-01

283

Ion microprobe assessment of the heterogeneity of Mg/Ca, Sr/Ca and Mn/Ca ratios in Pecten maximus and Mytilus edulis (bivalvia) shell calcite precipitated at constant temperature  

NASA Astrophysics Data System (ADS)

Small-scale heterogeneity of biogenic carbonate elemental composition can be a significant source of error in the accurate use of element/Ca ratios as geochemical proxies. In this study ion microprobe (SIMS) profiles showed significant small-scale variability of Mg/Ca, Sr/Ca and Mn/Ca ratios in new shell calcite of the marine bivalves P. maximus and Mytilus edulis that was precipitated during a constant-temperature culturing experiment. Elevated Mg/Ca, Sr/Ca and Mn/Ca ratios were found to be associated with the deposition of elaborate shell features, i.e. a shell surface stria in P. maximus and surface shell disturbance marks in both species, the latter a common occurrence in bivalve shells. In both species the observed small-scale elemental heterogeneity most likely was not controlled by variable transport of ions to the extra-pallial fluid, but by factors such as shell Mg content influencing Sr and Mn heterogeneity, the influence of shell organic content and/or conditions at the shell crystal-solution interface. Invariant Mg/Ca ratios observed in the mid and innermost regions of the P. maximus shell suggests a potential application as a palaeotemperature proxy.

Freitas, P. S.; Clarke, L. J.; Kennedy, H.; Richardson, C. A.

2009-01-01

284

Evolution of bulk superconductivity in SrFe2As2 with Ni substitution  

NASA Astrophysics Data System (ADS)

Single crystals of the Ni-doped FeAs-based superconductor SrFe2-xNixAs2 were grown using a self-flux solution method and characterized via x-ray measurements and low-temperature transport, magnetization, and specific heat studies. A doping phase diagram has been established where the antiferromagnetic order associated with the magnetostructural transition of the parent compound SrFe2As2 is gradually suppressed with increasing Ni concentration, giving way to bulk-phase superconductivity with a maximum transition temperature of 9.8 K. The superconducting phase exists through a finite range of Ni concentrations centered at x=0.15 with full diamagnetic screening observed over a narrow range of x coinciding with a sharpening of the superconducting transition and an absence of magnetic order. An enhancement of bulk superconducting transition temperatures of up to 20% was found to occur upon high-temperature annealing of samples.

Saha, S. R.; Butch, N. P.; Kirshenbaum, K.; Paglione, Johnpierre

2009-06-01

285

Effect of Nd Substitution on PrOs4Sb12 Investigated by ?SR Experiments  

NASA Astrophysics Data System (ADS)

The pseudo ternary system Pr1-xNdxOs4Sb12 has been used as a model system to investigate the effect of ferromagnetism (FM) on the unconventional superconductivity (SC) and quantum critical behavior of PrOs4Sb12 [1]. SC in this system disappears near a critical concentration xcr,1˜0.58 and FM appears above xcr,2˜0.33 [1,2]. The new ?SR measurements have been performed on samples with x = 0.25, 0.75, and 1. For x = 1 and 0.75, the estimated frozen moments agree with the Nd^3+ CEF ground state moment. For x = 0.25, neither time reversal symmetry breaking nor evidence of freezing of Nd^3+ spins was observed in zero-field ?SR measurements, the behavior of which is very different than what is observed for x = 0.45-0.55 [2]. In the SC state, an unexpected linear T dependence of the Gaussian relaxation rate was also found in the transverse field ?SR data for x = 0.25, which is different than the plateau in PrOs4Sb12 below 1.3K [3]. [1] Ho, et al., PRB 83, 024511 (2011).[2] Ho, et al., 2010 APS March Meeting, A38.00005 (2010). [3] MacLaughlin et al., PRL 105, 019701 (2010).

Ho, P.-C.; Somsanuk, B.; Maclaughlin, D. E.; Maple, M. B.; Shu, L.; Bernal, O. O.; Yanagisawa, T.

2013-03-01

286

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

287

Effects of Cr/Zn Substitutions on Dielectric Properties of CaCu3Ti4O12 (CCTO) Ceramics  

NASA Astrophysics Data System (ADS)

Effects of Zn and Cr substitutions on dielectric properties of CaCu3-xZnxTi4-yCryO12 ceramics are reported. Dielectric measurements at room temperature for un-substituted CaCu3-xZnxTi4-yCryO12 (x = 0, y = 0) between 102-106 Hz showed dielectric constant of 2.7×104 at 102 Hz. Substitution of Zn for Cu in CaCu3-xZnxTi4-yCryO12 (y = 0, x = 0.10, 0.50)caused dielectric constant to drop with increasing x. Cr substitution at Ti-site in CaCu3-xZnxTi4-yCryO12 (x = 0, x = 0,) also caused decrease in dielectric constant. However, at x = 0.50, the dielectric constant at low frequency was enhanced compared to the un-substituted sample. Our results indicate that Cu and Ti sites play an important role in the formation of Internal Barrier Layer Capacitance (IBLC) in CCTO.

Rajmi, R.; Yahya, A. K.; Deni, M. S. M.

2010-07-01

288

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

Microsoft Academic Search

A zero-field spin-echo NMR study of ^99,101Ru has been carried out on 60 mg samples of Sr_1-xCa_xRuO3 (x=0, 0.25, and 0.50) single crystals[1]. The NMR spectrum of SrRuO3 consists of two peaks at 64.4 and 72.2 MHz, corresponding to the ^99Ru and ^101Ru isotopes, respectively, and a hyperfine field of 328 kOe. A clear modulation of the spin-echo amplitude, with

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

2000-01-01

289

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

DOEpatents

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.

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

1996-05-14

290

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

DOEpatents

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.

Marshall, Christopher D. (Livermore, CA); Payne, Stephen A. (Castro Valley, CA); Krupke, William F. (Pleasanton, CA)

1996-01-01

291

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

NASA Astrophysics Data System (ADS)

We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr3(Ru1-xMnx)2O7, performed at both Ru and Mn L-edges. Resonant magnetic superstructure reflections together with ab-initio density functional theory calculations identify the ground state as a spin checkerboard with blocks of 4 spins up and 4 spins down. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x˜0.05 Mn substitution. Perhaps more important, our results suggest that the same checkerboard instability might be present already in the parent compound Sr3Ru2O7. 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).

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

2011-03-01

292

Study on the superconducting composite material formation in the system Bi2Sr2CaCu2O8+x/Al-containing phases  

NASA Astrophysics Data System (ADS)

Phase evolution in the Bi-Sr-Ca-Cu-Al-O system was studied. Two Al-containing phases BiSr1.5Ca0.5Al2Oz and (Sr1-xCax)3Al2O6 (x = 0.4 - 0.45) were determined to be chemically compatible with Bi2.18Sr2CaCu2O8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr1.5Ca0.5Al2Oz was found to be in equilibrium only with the melt and the (Sr1-xCax)3Al2O6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr1.5Ca0.5Al2Oz <-> (Sr1-xCax)3Al2O6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr1.5Ca0.5Al2Oz and Bi-2212 + m(Sr1-xCax)3Al2O6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr1.5Ca0.5Al2Oz phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 ?m) grains of (Sr1-xCax)3Al2O6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr1-xCax)3Al2O6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content.

Kazin, P. E.; Poltavets, V. V.; Tretyakov, Y. D.; Jansen, M.; Freitag, B.; Mader, W.

1997-02-01

293

Singleparticle tunneling and Josephson effect in Bi-Sr-Ca-Cu-O:Pb and Tl-Ba-Ca-Cu-O compounds  

Microsoft Academic Search

The experimental I (V)-characteristics of break junctions for monocrystalline BiSrCaCuO: Pb (2212- phase), polycrystalline (2223- phase) samples and for samples with the ``intergrowth'' of 2212- and 2223- phases have been investigated. On the I (V)- characteristics of break junctions for samples with the ``intergrowth'' of phases a vertical current raise at V=+\\/-2delta\\/e and a ``knee''- structure typical for S1S2IS2S1- systems

B. A. Aminov; M. V. Pedyash; D. K. Petrov; H. T. Rakhimov; K. Sethupathi; M. V. Sudakova; Ya. G. Ponomarev

1991-01-01

294

Crystal structure and ferroelectric properties of ABi2Ta2O9 (A=Ca, Sr, and Ba)  

NASA Astrophysics Data System (ADS)

Crystal structures and ferroelectric properties of a series of Bi-layered compounds, CaBi2Ta2O9, SrBi2Ta2O9, and BaBi2Ta2O9, were investigated. The structures of CaBi2Ta2O9 and SrBi2Ta2O9 are orthorhombic, while that of BaBi2Ta2O9 is pseudotetragonal on the macroscopic scale but consists of microdomains with orthorhombic distortion. The ferroelectric Curie temperature of CaBi2Ta2O9 was over 600 °C, and that of SrBi2Ta2O9 was over 300 °C. BaBi2Ta2O9, in contrast, showed relaxor-type ferroelectric behavior; that is, in the plot of temperature dependence of dielectric constant, a broad peak appeared around 60 °C. As the size of the A-site cation decreases from Ba2+ to Ca2+, the lattice mismatch between TaO2 and AO planes in the perovskite-type unit of ATa2O7 increases and the structural distortion becomes more pronounced. This distortion leads to the higher Curie temperature and the larger spontaneous ferroelectric polarization.

Shimakawa, Y.; Kubo, Y.; Nakagawa, Y.; Goto, S.; Kamiyama, T.; Asano, H.; Izumi, F.

2000-03-01

295

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

PubMed

In order to enhance the corrosion resistance of the Ca65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass because of the unique properties of high-entropy alloys. Our results showed that the mechanical properties and corrosion behavior were enhanced. The in vitro tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass did not show any obvious degradation after 4weeks of implantation, and they can promote osteogenesis and new bone formation after 2weeks 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. PMID:23380208

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

2013-02-04

296

Extracellular Calcium-Sensing Receptor Inhibition of Intestinal EpithelialTNF Signaling Requires CaSR-Mediated Wnt5a/Ror2 Interaction  

PubMed Central

Tumor necrosis factor alpha (TNF?) and its receptor TNFR1 play a central role in the development of colitis-associated colon cancer. To understand a role for the extracellular calcium-sensing receptor (CaSR) and its non-canonical Wnt mediators, Wnt5a/Ror2, we used reductionistic systems. We added lipopolysaccharide (LPS) to mouse peritoneal macrophages, RAW264.7 cells, a murine macrophage cell line, and 18Co colonic myofibroblasts, to stimulate TNF? secretion and then activated endogenous CaSR. CaSR activation inhibited TNF? secretion, which in RAW264.7 cells knockdown of CaSR by short-interfering RNA (siRNA) duplex reversed. LPS-stimulated NF?B promoter activity in RAW264.7 cells was inhibited by CaSR activation with Ca2+ or other polyvalent CaSR agonists. Reducing CaSR expression with siRNA duplex prevented this inhibition. Following LPS addition to CaSR–HEK cells or RAW264.7 macrophages, CaSR stimulation deneddylated Cullin1. Wnt5a added to HT-29 cells which overexpressed Ror2 or T84 monolayers treated with 3?mM Ca2+ reduced TNFR1 protein expression ?70%. TNF?/INF? addition to high resistance T84 monolayers reduced transepithelial resistance 50% within 4?h. CaSR activation (3?mM Ca2+) together with rhWnt5a (200?ng/ml) prevented this reduction while Wnt3a addition had no effect. LPS-stimulated TNF? secretion from RAW264.7 cells was not effected by rhWnt5a but increased 10-fold by Wnt3a. Together our results suggest that following LPS challenge, CaSR activation will inhibit NF?B activity and reduce TNF? secretion from macrophages and stroma while Wnt5a/Ror2 engagement on intestinal epithelia reduces TNFR1 expression, allowing TNF? signaling to be titrated. Our results also suggest that canonical Wnt signaling may enhance TLR4 stimulation of TNF? secretion from murine macrophages.

Kelly, Jacqueline C.; Lungchukiet, P.; MacLeod, R. John

2010-01-01

297

On the phase formation of laser deposited Bi-Sr-Ca-Cu-O films on MgO, ZrO2 and silicon with YSZ buffer layers  

Microsoft Academic Search

High-Tc superconducting Bi-Sr-Ca-Cu-O films have been prepared by in-situ excimer laser induced deposition on MgO (100), ZrO2 (100) and textured yttrium stabilized zirconia (YSZ) buffer layers on silicon from Bi2Sr2Ca2Cu3Ochi (2223) targets. Epitaxial YSZ films have been grown on Si (100) and Si (111) by in-situ deposition using a Nd-YAG laser. Under optimized deposition parameters we obtained nearly single Bi2Sr2Ca1Cu2Ox

M. Lorenz; S. Becker; H.-J. Dietze; W. Schmitz; B. Brunner; K. F. Renk

1991-01-01

298

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

SciTech Connect

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

Polonka, J.

1993-09-01

299

Triadin/Junctin double null mouse reveals a differential role for Triadin and Junctin in anchoring CASQ to the jSR and regulating Ca(2+) homeostasis.  

PubMed

Triadin (Tdn) and Junctin (Jct) are structurally related transmembrane proteins thought to be key mediators of structural and functional interactions between calsequestrin (CASQ) and ryanodine receptor (RyRs) at the junctional sarcoplasmic reticulum (jSR). However, the specific contribution of each protein to the jSR architecture and to excitation-contraction (e-c) coupling has not been fully established. Here, using mouse models lacking either Tdn (Tdn-null), Jct (Jct-null) or both (Tdn/Jct-null), we identify Tdn as the main component of periodically located anchors connecting CASQ to the RyR-bearing jSR membrane. Both proteins proved to be important for the structural organization of jSR cisternae and retention of CASQ within them, but with different degrees of impact. Our results also suggest that the presence of CASQ is responsible for the wide lumen of the jSR cisternae. Using Ca(2+) imaging and Ca(2+) selective microelectrodes we found that changes in e-c coupling, SR Ca(2+)content and resting [Ca(2+)] in Jct, Tdn and Tdn/Jct-null muscles are directly correlated to the effect of each deletion on CASQ content and its organization within the jSR. These data suggest that in skeletal muscle the disruption of Tdn/CASQ link has a more profound effect on jSR architecture and myoplasmic Ca(2+) regulation than Jct/CASQ association. PMID:22768324

Boncompagni, Simona; Thomas, Monique; Lopez, Jose R; Allen, Paul D; Yuan, Qunying; Kranias, Evangelia G; Franzini-Armstrong, Clara; Perez, Claudio F

2012-07-02

300

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

301

Combinatorial pulsed laser deposition of Fe, Cr, Mn, and Ni-substituted SrTiO3 films on Si substrates.  

PubMed

Combinatorial pulsed laser deposition (CPLD) using two targets was used to produce a range of transition metal-substituted perovskite-structured Sr(Ti(1-x)M(x))O(3-?) films on buffered silicon substrates, where M = Fe, Cr, Ni and Mn and x = 0.05-0.5. CPLD produced samples whose composition vs distance fitted a linear combination of the compositions of the two targets. Sr(Ti(1-x)Fe(x))O(3-?) films produced from a pair of perovskite targets (SrTiO(3) and SrFeO(3) or SrTiO(3) and SrTi0(0.575)Fe(0.425)O(3)) had properties similar to those of films produced from single targets, showing a single phase microstructure, a saturation magnetization of 0.5 ?(B)/Fe, and a strong out-of-plane magnetoelastic anisotropy at room temperature. Films produced from an SrTiO(3) and a metal oxide target consisted of majority perovskite phases with additional metal oxide (or metal in the case of Ni) phases. Films made from SrTiO(3) and Fe(2)O(3) targets retained the high magnetic anisotropy of Sr(Ti(1-x)Fe(x))O(3-?), but had a much higher saturation magnetization than single-target films, reaching for example an out-of-plane coercivity of >2 kOe and a saturation magnetization of 125 emu/cm(3) at 24%Fe. This was attributed to the presence of maghemite or magnetite exchange-coupled to the Sr(Ti(1-x)Fe(x))O(3-?). Films of Sr(Ti(1-x)Cr(x))O(3-?) and Sr(Ti(1-x)Mn(x))O(3-?) showed no room temperature ferromagnetism, but Sr(Ti(1-x)Ni(x))O(3-?) did show a high anisotropy and magnetization attributed mainly to the perovskite phase. Combinatorial synthesis is shown to be an efficient process for enabling evaluation of the properties of epitaxial substituted perovskite films as well as multiphase films which have potential for a wide range of electronic, magnetic, optical, and catalytic applications. PMID:22353232

Kim, Dong Hun; Bi, Lei; Aimon, Nicolas M; Jiang, Peng; Dionne, Gerald F; Ross, C A

2012-02-27

302

Surface properties and catalytic performance in methane combustion of Sr-substituted lanthanum manganites  

Microsoft Academic Search

Perovskite type La1?xSrxMnO3 (x=0–0.5) oxides were prepared by the amorphous citrate process, characterised by X-ray diffraction, oxygen desorption, temperature-programmed reduction, infrared and X-ray photoelectron spectroscopic techniques, and tested for methane combustion within the 473–1073K temperature range. Since catalyst activity was found to depend strongly on BET areas and to a lesser extent, on the degree of substitution (x), intrinsic activities

S Ponce; M. A Peña; J. L. G Fierro

2000-01-01

303

Structural and dielectric behavior of pulsed laser ablated Sr0.6Ca0.4TiO3 thin film and asymmetric multilayer of SrTiO3 and CaTiO3  

NASA Astrophysics Data System (ADS)

Homogeneous thin films of Sr0.6Ca0.4TiO3 (SCT40) and asymmetric multilayer of SrTiO3 (STO) and CaTiO3 (CTO) were fabricated on Pt/Ti/SiO2/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 ??(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 Sr0.6Ca0.4TiO3 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.

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

2011-12-01

304

Collisional broadening of Mg, Sr, Ca and Na resonance lines by atomic hydrogen  

NASA Astrophysics Data System (ADS)

This paper compares different approaches used in the calculation of the broadening of spectral lines by H-atom collisions. Firstly, the validity of the semi-classical approach for the collision versus the quantum one is discussed. It is shown that, at the temperatures typical of stellar atmospheres (from 3000 to 10 000 K), a classical approach (with the advantage of reduced computation times) is sufficient. The dependence of the broadening constants on interatomic potentials is also studied. Two different approaches were used to derive these potentials: in the first approach, the interaction energy is determined by the usual methods of quantum chemistry. The second approach, developed by Anstee, Barklem and O'Mara (ABO potentials), is based on second-order perturbation theory. In the case of Mg H, a hybrid potential obtained from ab initio values for the short distances and from the perturbation method in the asymptotic region was also tested. The results for the Na resonance line show that even significant differences in the potentials lead to relatively small changes in the calculated widths. From the comparison of the results for the Mg, Sr and Ca resonance lines, it appears that ABO potentials give results of the order of 8 20% smaller than results from ab initio and hybrid potentials. This difference is attributed to the presence of an avoided ionic crossing in the upper singlet Sgr states that coincides roughly with the Weisskopf radius.

Kerkeni, B.; Barklem, P. S.; Spielfiedel, A.; Feautrier, N.

2004-02-01

305

Metastable states of the 2223 phase in the Bi(Pb)SrCaCuO system  

SciTech Connect

By the magnetically modulated microwave absorption method (MAMMA) the authors observed the modifications induced by different calcination temperatures (between 830{degree}C and 870{degree}C) on the 2223 phase formed in a system sintered at (855 {plus_minus} 5){degree}C with the starting composition Bi{sub 1.7}Pb{sub 0.3}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y}. The presence of the 2223 in almost distinct states (consequently, multiple 2223 phases) in the same sample was observed. As the calcination temperature was increased up to 850{degrees}C, the highest temperature state of the 2223 phase intensified. Higher calcination temperatures resulted in the enhancement of other low-temperature states. The homogeneity of the 2223 phase was greatly improved by annealing the samples at 800{degree}C for 5 min in a flowing nitrogen atmosphere. The authors labeled as {open_quotes}metastable{close_quotes} the lower-temperature states having excess oxygen, which, by easily losing the supplementary oxygen under the above annealing procedure, were shifted to higher temperatures.

Velter-Stefanescu, M.; Aldica, G.; Totovana, A. [Institute of Atomic Physics, Bucharest (Romania)

1996-06-01

306

Dense Bi-Sr-Ca-Cu-O superconducting films prepared by spray pyrolysis  

SciTech Connect

Dense oriented superconducting Bi-Sr-Ca-Cu-O films having zero resistance as high as 100 K have been made using a technique in which spray deposited and pyrolyzed films are densified by either melt quenching or flux sintering. The highest T/sub c/ films were those prepared with PbO as a dopant/flux on MgO substrates. Films without lead doping prepared on both BeO and MgO substrates yielded resistive transitions of 81--83 K. For these latter films, it was demonstrated that a subsequent anneal in argon enhanced the T/sub c/ to 87 K. The films were characterized by x-ray diffraction, scanning electron microscopy, and four-point probe resistance measurements. The critical current density of a film having a T/sub c/ of 81 K was 4000 A/cm/sup 2/ at 78 K and 14 000 A/cm/sup 2/ at 55K.

Hsu, H.M.; Yee, I.; DeLuca, J.; Hilbert, C.; Miracky, R.F.; Smith, L.N.

1989-03-06

307

Ion microprobe assessment of the heterogeneity of Mg/Ca, Sr/Ca and Mn/Ca ratios in Pecten maximus and Mytilus edulis (bivalvia) shell calcite precipitated at constant temperature  

NASA Astrophysics Data System (ADS)

Small-scale heterogeneity of biogenic carbonate elemental composition can be a significant source of error in the accurate use of element/Ca ratios as geochemical proxies. In this study ion microprobe (SIMS) profiles showed significant small-scale variability of Mg/Ca, Sr/Ca and Mn/Ca ratios in new shell calcite of the marine bivalves Pecten maximus and Mytilus edulis that was precipitated during a constant-temperature culturing experiment. Elevated Mg/Ca, Sr/Ca and Mn/Ca ratios were found to be associated with the deposition of elaborate shell features, i.e. a shell surface stria in P. maximus and surface shell disturbance marks in both species, the latter a common occurrence in bivalve shells. In both species the observed small-scale elemental heterogeneity most likely was not controlled by variable transport of ions to the extra-pallial fluid, but by factors such as the influence of shell organic content and/or crystal size and orientation, the latter reflecting conditions at the shell crystal-solution interface. In the mid and innermost regions of the P. maximus shell the lack of significant small-scale variation of Mg/Ca ratios, which is consistent with growth at constant temperature, suggest a potential application as a palaeotemperature proxy. Cross-growth band element/Ca ratio profiles in the interior of bivalve shells may provide more promising palaeo-environmental tools than sampling from the outer region of bivalve shells.

Freitas, P. S.; Clarke, L. J.; Kennedy, H.; Richardson, C. A.

2009-07-01

308

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

NASA Astrophysics Data System (ADS)

The decay of 40K to 40Ar forms the basis of the potassium-argon dating method, although only one out of every 10 parent atoms decays to daughter 40Ar. The other 90% decay to 40Ca giving, in principle, the 40K-40Ca decay system great potential for dating samples with high K/Ca. This method, however, has not been utilized as an ion-microprobe-based geochronometer, largely because these isotopes require a very high mass resolving power (MRP) of ~25k for full separation. We found that limiting secondary ion transmission in our ims1270 ion microprobe to ~20% permits sufficient separation of 40K from 40Ca (MRP? 20k) to permit isotope ratio analysis, albeit with 40Ca+ on the shoulder of the more intense 40K+ peak. A pegmatitic muscovite from Jack Hills (K-Ca age = 2.54 Ga; Fletcher et al., Chem. Geol. 138, 289) yields ~104 cps of both 40K+ and 40Ca+ with a 15 ?m primary spot size and O- beam current of 10 nA. The 40Ca+ signal is >90% radiogenic and reflects a “common” Ca content of ? 100 ppm. However, application of the relative sensitivity factor (RSF) calculated from the Jack Hills muscovite to unknowns yields relatively high age dispersion, perhaps related to the incompletely separated mass interferences. Theorizing that the noble gas electronic structure of K+ would likely resist further electron loss, we investigated an alternative approach involving analysis of Ca++/K++. The double-plus method provides an important advantage in that K++ species are suppressed by a factor of ~103 relative to K+, thereby effectively removing 40K++ from the spectrum at m/e? 20 and leaving 40Ca++ free from any significant interferences at an MRP? 4k. Measurement of the much more abundant 39K++ then permits 40Ca++/40K++ to be calculated from the known 39K/40K ratio. We applied this approach to Precambrian muscovite samples obtaining ages similar to, but generally younger than, their associated 40Ar/39Ar ages. This could reflect a minor matrix effect or a lower intrinsic retentivity of 40Ca* relative to 40Ar* in white micas. This approach offers the potential to develop a branched-decay thermochronometer (K-Ca-Ar) permitting simultaneous solution of temperature-time history from ?m-scale isotopic variations. A further advantage is that even low resolution SIMS instruments (e.g., ims7f) can utilize the double-plus method. Initial investigations using the same double-plus approach for Rb-Sr dating show promise. While resolving 87Rb+ from 87Sr+ requires an MRP of ~290k, unattainable using any current SIMS instrument, 87Rb++ is so strongly suppressed that determination of 87Sr++ is possible with minor peak stripping. 87Rb/86Sr can be determined either from 85Rb+/88Sr+ at MRP? 8k or by the use of energy filtering. In addition to micas, these approaches may be applicable to any mineral systems enriched in alkali metals relative to alkaline earths, such as alkali feldspars, feldspathoids, and alkaline halides.

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

2009-12-01

309

Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae = Ca, Sr, Ba, as thermoelectric materials  

NASA Astrophysics Data System (ADS)

We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb 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 Ca2Sn, Sr2Sn 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.

Parker, David; Singh, David J.

2013-10-01

310

Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae=Ca,Sr,Ba, as thermoelectric materials  

SciTech Connect

We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb 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 Ca2 Sn, Sr2 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.

Parker, David S [ORNL; Singh, David J [ORNL

2013-01-01

311

Half metallic ferromagnetism in alkaline-earth metal nitrides XN (X=Ca, Sr and Ba): A first principles study  

NASA Astrophysics Data System (ADS)

The structural, electronic, mechanical and magnetic properties of 3 alkaline-earth metal nitrides (XN: X=Ca, Sr, 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 CaN, SrN 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.

Palanichamy, R. Rajeswara; Priyanga, G. Sudha; Cinthia, A. Jemmy; Murugan, A.; Meenaatci, A. T. Asvini; Iyakutti, K.

2013-11-01

312

Universal behavior of susceptibility in the 110 K phase of the Bi-Pb-Sr-Ca-Cu-O system  

NASA Astrophysics Data System (ADS)

We demonstrate here the universal behavior of the fundamental intergranular matrix susceptibility (?m) in terms of a single parameter (?) in the 110 K phase of the Bi-Sr-Ca-Cu-O system, in the regime where flux profile is linear in the sample. Following the observation of universality of the third harmonic susceptibility ?3(T,Hdc)Hac by Shatz et al. in Y-Ba-Cu-O, we have examined the field and temperature dependences of ?(Hdc,Hac)T and ?(T,Hdc)Hac, respectively, measured in Bi1.2Pb0.3Sr1.5Ca2Cu3Oy superconductor. Our analysis shows that the field dependence of Jc is better described, for the present sample, by the power-law model and also demonstrates the universality of ?m in terms of ?.

Hari Babu, N.; Rajasekharan, T.; Ravi, S.; Seshu Bai, V.

1995-11-01

313

Thin-film Bi-Sr-Ca-Cu-O high-temperature superconductors using pulsed laser evaporation from sintered disks  

SciTech Connect

Films of the high-temperature superconductor in the Bi-Sr-Ca-Cu-O system were deposited by pulsed laser evaporation from a ceramic disk. Films deposited onto (100) MgO show x-ray diffraction patterns characteristic of c-axis textured Bi/sub 2/(Sr,Ca,Bi)/sub 3/Cu/sub 2/O/sub x/ phase following annealing for 10 min at 850 /sup 0/C in 20% O/sub 2/-80% N/sub 2/. These textured films have zero resistance at 78 K and show resistance drops near 110 K. The effects of the annealing environment on the electrical and structural properties are presented.

Guarnieri, C.R.; Roy, R.A.; Saenger, K.L.; Shivashankar, S.A.; Yee, D.S.; Cuomo, J.J.

1988-08-08

314

Evolution of the thermoelectric performance in low Ca-doped layered cobaltite Bi2Sr2Co2Oy  

NASA Astrophysics Data System (ADS)

We have synthesized a series of layered cobaltite Bi2Sr2-xCaxCo2Oy (0?x?0.3). Reduced resistivity was observed with x?0.2 due to the possible chemical pressure induced charge transfer between the Bi2Sr2O4 layer and CoO2 layer. Enhanced thermoelectric power S was also observed in the Ca-doped samples with the largest S as for x=0.2. The variation of S(T) could reflect the change of electronic correlation or the modification of local density of states and band structure near the Fermi energy. In addition, magnetic measurements show that the samples with x=0.0 exhibit abnormal and abrupt changes, revealing a possible thermally excited spin-state transition. It is found that the thermoelectric performance is obviously enhanced by the low Ca-doping.

Yin, L. H.; Ang, R.; Zhao, B. C.; Huang, Y. N.; Liu, Y.; Tan, S. G.; Song, W. H.; Sun, Y. P.

2013-03-01

315

NMR study of A2FeMO6 (A=Ca, Sr, Ba, M=Mo, Re) double perovskites  

NASA Astrophysics Data System (ADS)

A nuclear magnetic resonance study of the A2FeMO6 (A=Ba, Sr, Ca; M=Mo, Re) double perovskites is reported. Spin echo spectra have been measured at 4.2K and zero external magnetic field. Resonant signals at Mo nuclei are observed at 30-80MHz and at 750-1000MHz for Re nuclei. Frequencies of the main lines correspond to Mo hyperfine fields of 19, 24 and 23T and to Re hyperfine fields of 84, 94 and 95T for Ba, Sr and Ca compounds, respectively. From these data the values of Mo and Re magnetic moments are derived and the relation to the results of theoretical calculations is discussed.

Kapusta, Cz.; Zaja?c, D.; Riedi, P. C.; Sikora, M.; Oates, C. J.; Blasco, J.; Ibarra, M. R.

2004-05-01

316

Electronic structure of A2CrSbO6 [A=Sr, Ca]: Ab-initio study  

NASA Astrophysics Data System (ADS)

First principles calculations have been performed to study the electronic structure and magnetic properties of Cr-based double perovskite oxides Sr2CrSbO6 and Ca2CrSbO6 using full potential linearized augmented plane wave method under generalized gradient approximation (GGA) scheme. In our calculation, we have applied onsite Coulomb potential U at Cr site. The density of states (DOS) of Sr2CrSbO6 has been studied in three different crystal structures. Due to the different crystal symmetry of Sr2CrSbO6 at different temperatures, the DOS spectra differ from one another near the Fermi level. The insulating ground states have been obtained from GGA+U calculation for both the materials. It has been observed from DOS spectra that oxygen 2p-derived states hybridize strongly with Cr-d states and this hybridization plays an important role in the magnetic properties. The calculated magnetic moments for Cr are found to be 2.65, 2.60 and 2.72 ?B for monoclinic, tetragonal, cubic phases of Sr2CrSbO6, respectively and 2.68 ?B for Ca2CrSbO6. The obtained magnetic moments suggest the 3+ states of Cr (3d3) in these oxides.

Dutta, Alo; Sinha, T. P.

2013-02-01

317

Phase Determination for Intra-unit-cell Fourier Transform STM -- Picometer Registration of Zn Impurity States in Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

By studying the real and imaginary components of the Bragg peaks in Fourier transforms of electronic structure images, distinct types of intra-unit cell (IUC) symmetry breaking can be studied using SI-STM [Lawler et al., Nature 466 347 (2010)]. However, establishing the precise r-space symmetry point of each unit cell is crucial in defining the phase for such analysis. Exemplary of this challenge is the high-Tc superconductor Bi2Sr2CaCu2O8+? for which the Bi atoms in the surface BiO layer are observable, while it is the invisible Cu atoms that define the relevant CuO2 unit-cell symmetry point. We demonstrate, by imaging with pm precision the electronic impurity states at individual Zn atoms substituted at Cu sites, that the phase established using the Bi lattice produces a ˜2%(2?) error relative to the Cu lattice. In this case, IUC C4v symmetry breaking in the CuO2 plane can be determined reliably using the phase assignment from the BiO layer. Moreover, impurity atom substitution at the relevant symmetry site can be of general utility in phase determination for Bragg-peak Fourier analysis of IUC symmetry.

Firmo, Ines; Hamidian, Mohammad; Fujita, Kazuhiro; Mukhopadhyay, Sourin; Orenstein, Joseph; Eisaki, Hiroshi; Uchida, Shin-Ichi; Lawler, Michael; Kim, Eun-Ah; Davis, J. C.

2012-02-01

318

Magnetocaloric properties in La0.5Ca0.3Na0.2MnO3, Pr0.5Sr0.3Na0.2MnO3 and Nd0.5Sr0.3Na0.2MnO3 manganites  

NASA Astrophysics Data System (ADS)

The influence of 20% of Na doping upon the magnetic and magnetocaloric properties of La0.5Ca0.5MnO3, Pr0.5Sr0.5MnO3, and Nd0.5Sr0.5MnO3 perovskite manganites has been investigated. Our samples have been elaborated using the conventional solid state reaction method at high temperature. X-Ray diffraction analysis showed that our synthesized samples are single phase and crystallize in the orthorhombic system with Pbnm space group. Magnetic measurements versus magnetic applied field indicated that the substituted compounds are ferromagnetic at low temperatures. The Curie temperatures are found to be 279, 299 and 292 K for La0.5Ca0.3Na0.2MnO3 (LCNM), Pr0.5Sr0.3Na0.2MnO3 (PSNM), and Nd0.5Sr0.3Na0.2MnO3 (NSNM) respectively. Our samples exhibit an important magnetic entropy change with a maximum |?{/M Max }| found to be 1.83, 6.6 and 3.1 J/kgK for LCNM, PSNM and NSNM respectively under a magnetic applied field of 4T.

Mehri, A.; Koubaa, W. Cheikhrouhou; Koubaa, M.; Cheikhrouhou, A.

2013-08-01

319

Sr/Ca and Mg/Ca Heterogeneity Across Individual Foram Tests as Revealed by Ion Microprobe Analysis  

NASA Astrophysics Data System (ADS)

Many benthic foraminifera live for >= 1 year and the chemistry of individual tests may preserve information on seawater temperature changes over this time. Microanalysis of individual tests is complicated by the combination of thin test walls and the presence of surface contaminants, not held within the carbonate structure. We optimised conditions for the analysis of Mg and Sr in the benthic foraminifera Ammonia batavus, by ion microprobe. The use of field and contrast apertures restricted the size of the analysed area to ~10 ?m and reduced the effects of sample contamination. Sr concentrations were unaffected by any contamination encountered and Mg could be determined provided checks were made for silicate contamination using Al, Si and K intensities. Measured Mg and Sr concentrations were in reasonable agreement with previously reported values. Mn was present at a level too low to permit clean analysis, even at very low levels of contamination. Significant variations in Sr concentrations occurred within individual test chambers and may reflect the juxtapositioning of calcite of different ages as the test is deposited. Significant variations in Mg and Sr concentrations occurred between test chambers. Sr increased in concentration in the outermost (most recently deposited) parts of the test. This may reflect an increase in test calcification rate coincident with increases in bottom water temperature or food availability. The development of this method provides a valuable tool for investigating geochemical variations across individual foraminifera tests.

Austin, W. E.; Allison, N.

2002-12-01

320

Associated changes in Ca 2+ and Sr 2+ activation properties and fiber proteins in cross-reinnervated rabbit soleus  

Microsoft Academic Search

Changes in the Ca2+ and Sr2+ activation properties of functionally skinned slow-twitch soleus fibers were measured and compared with those of normal fast-twitch extensor digitorum longus (EDL) following cross-reinnervation of soleus with the nerve to EDL. Most of the fibers showed either complete transformation of activation properties (66%) or remained unchanged (34%). The change in sensitivity to divalent cations was

D. J. Secrist; W. G. L. Kerrick

1980-01-01

321

Measurements of temperature dependence of partial discharge in air gaps between insulated Bi-Sr-Ca-Cu-O tapes  

Microsoft Academic Search

Partial discharge (PD) in trapped air-filled gaps between two adjacent insulated high temperature superconducting (HTS) tapes made of Bi2Sr2Ca2Cu3Ox (BSCCO) was investigated experimentally. PD measurements were performed at several temperatures ranging from 295 K to 41 K. At each temperature a series of AC voltages of equal duration and increasing magnitude was applied to the inter-turn insulation until PD was

R. Grabovickic; D. R. James; I. Sauers; A. R. Ellis; P. C. Irwin; K. Weeber; L. Li; A. D. Gadre

2005-01-01

322

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

SciTech Connect

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

Mook, H.A.; Chakoumakos, B.C. [Oak Ridge National Lab., TN (United States). Solid State Div.

1996-12-31

323

Improvement of critical current density in the Bi-Pb-Sr-Ca-Cu-O system through hot isostatic pressing  

Microsoft Academic Search

The effects of hot isostatic pressing (HIPing) on densification and the superconducting properties of the Bi-Pb-Sr-Ca-O system were investigated. A relative density up to 95% and a critical current density greater than 1100 A\\/cm2 at 77 K were achieved through HIPing at 650°C for 2 h under 200 MPa argon. Under these conditions, the product gave a value of Jc

S. X. Dou; H. K. Liu; M. H. Apperley; K. H. Song; C. C. Sorrell; K. E. Easterling; J. Niska; S. J. Guo

1990-01-01

324

Explosive consolidation of (Bi,Pb)-Sr-Ca-Cu-O superconductor powders during powder-in-tube processing  

Microsoft Academic Search

Superconducting (2212) Bi-Sr-Ca-Cu-O (BSCCO) and BSCCO-Ag composites were explosively consolidated in silver tubing and then drawn and rolled into tapes. The silver-sheathed tapes were then subjected to repeated cycles of pressing and heat treatment, which resulted in enhanced texturing and grain growth and a subsequent increase in critical current density (J{sub c}). The effect of silver flake additions to the

H. Thomas; O. T. Inal; U. Balachandran

1995-01-01

325

Evidence for an Energy Scale for Quasiparticle Dispersion in Bi2Sr2CaCu2O8  

Microsoft Academic Search

Quasiparticle dispersion in Bi2Sr2CaCu2O8 is investigated with improved angular resolution as a function of temperature and doping. Unlike the linear dispersion predicted by the band calculation, the data show a sharp break in dispersion at 50+\\/-15 meV binding energy where the velocity changes by a factor of 2 or more. This change provides an energy scale in the quasiparticle self-energy.

P. V. Bogdanov; A. Lanzara; S. A. Kellar; X. J. Zhou; E. D. Lu; W. J. Zheng; G. Gu; J.-I. Shimoyama; K. Kishio; H. Ikeda; R. Yoshizaki; Z. Hussain; Z. X. Shen

2000-01-01

326

Evidence for abrupt change in dispersion of quasiparticles in Bi2Sr2CaCu2O8  

Microsoft Academic Search

We performed high angle and energy resolved photoemission measurements of underdoped and optimally doped Bi2Sr2CaCu2O8 as a function of temperature, doping and angle. Unlike the linear dispersion predicted by the band calculation, the data show a sharp kink in dispersion at 50±10 meV binding energy. The kink in the dispersion is evident at and away from the d-wave node line.

Pavel Bogdanov; Alessandra Lanzara; Wenjun Zheng; Scot Kellar; Xingjiang Zhou; Erdong Lu; Genda Gu; Jun-Ichi Shimoyama; K. Kishio; Zahid Hussain; Zhi-Xun Shen

2000-01-01

327

Correlations between magnetic and resistive transitions in a Bi 2Sr 2CaCu 2O 8 ceramic  

Microsoft Academic Search

Resistive and inductive transitions are measured on the same Bi2Sr2CaCu2O8 ceramic. The transition curves present accidents which appear to be correlated and amenable to physical interpretation in quantitative agreement with a granular description. We consider two characteristic temperatures: Ts which marks the appearance of superconductivity and Tc < Ts below which long-range coherence occur. In the paracoherent region Tc <

J. P. Burin; J. Dehmej; Y. Fouad; A. Raboutou; P. Peyral; C. Lebeau; J. Rosenblatt; C. Carel; A. Ouammou

1996-01-01

328

Size and topology of Bi_2Sr_2CaCu_2O_8+x Fermi surface versus doping  

Microsoft Academic Search

We have studied the size and topology of the Fermi surface of Bi_2Sr2 CaCu_2O_8+x single crystal samples from underdoped samples with superconducting transition temperature, T_c=20K to overdoped samples with T_c=55K.[1] Compared to optimally doped samples, underdoped samples exhibit: * a reduction in the size of the Fermi surface by at least a factor of (x10); * a much weaker extended

S. Larosa; H. Berger; G. Margaritondo; C. Kendziora; R. J. Kelley; A. Chubukov; M. Onellion

1996-01-01

329

Thermal contact conductance of metallic coated BiCaSrCuO superconductor\\/copper interfaces at cryogenic temperatures  

Microsoft Academic Search

The effects of vapor deposited coatings on the thermal contact conductance of cold pressed, normal state BiCaSrCuO superconductor\\/oxygen-free copper interfaces were experimentally investigated over a pressure range of 200 to 2,000 kPa. Using traditional vapor deposition processes, thin coatings of indium or lead were applied to the superconductor material to determine the effect on the heat transfer occurring at the

J. M. Ochterbeck; G. P. Peterson; L. S. Fletcher

1992-01-01

330

Growth and annealing effect on resistivity anisotropy of Bi 2Sr 2CaCu 2O 8 single crystals  

Microsoft Academic Search

High quality, large size Bi2Sr2CaCu2O8 (Bi-2212) single crystals have been grown by a self-flux method in a horizontal temperature gradient. We found that the presence of the horizontal temperature gradient is helpful for the crystal growing along the ab-plane direction. However, non-uniform distribution of temperature in the vertical direction in the furnace often causes imperfections along the c direction. This

Y Zhao; H Zhang; D. P Feng; Y. G Liu; X. F Hou; S. H Han

2000-01-01

331

Growth and annealing effect on resistivity anisotropy of Bi2Sr2CaCu2O8 single crystals  

Microsoft Academic Search

High quality, large size Bi2Sr2CaCu2O8 (Bi-2212) single crystals have been grown by a self-flux method in a horizontal temperature gradient. We found that the presence of the horizontal temperature gradient is helpful for the crystal growing along the ab-plane direction. However, non-uniform distribution of temperature in the vertical direction in the furnace often causes imperfections along the c direction. This

Y. Zhao; H. Zhang; D. P. Feng; Y. G. Liu; X. F. Hou; S. H. Han

2000-01-01

332

Enhanced luminescence by charge compensation in red-emitting Eu 3+-activated Ca 3Sr 3(VO 4) 4  

Microsoft Academic Search

The effects of charge compensation on the luminescence behavior of a red-emitting phosphor, Ca3Sr3(VO4)4:Eu3+, were investigated. It has been observed that charge compensated by monovalent ions, especially Na+, shows greatly enhanced red emission under ultraviolet excitation. It is found that Na2CO3 addition acts as a fluxing agent and plays a role in charge compensation, which clearly improves the emission intensity

Sungho Choi; Young-Min Moon; Ha-Kyun Jung

2010-01-01

333

Luminescent properties of a novel red-emitting phosphor: Eu 3+-activated Ca 3Sr 3(VO 4) 4  

Microsoft Academic Search

A new luminescent material, Eu3+ activated Ca3Sr3(VO4)4, was investigated. This compound shows a strong red emission centered at 618nm under near-UV light with two distinct absorption bands; charge transfer state of VO43? and f–f transitions of europium ions. As the europium concentration is increased, an additional red-emitting phosphor, EuVO4, which is known to be a prominent luminescent material in the

Sungho Choi; Young-Min Moon; Kyoungun Kim; Ha-Kyun Jung; Sahn Nahm

2009-01-01

334

Giant Magnetoresistance in Bulk Samples of La 1- x A x MnO 3 ( A = Sr or Ca)  

Microsoft Academic Search

Magnetoresistance measurements have been carried out on bulk samples of several members of the La1-xAxMnO3 family (A = Sr and Ca) with varying x or Mn4+ content. The magnitude of magnetoresistance (MR) is highest at the insulator-metal (I-M) transition when the transition temperature is relatively low (?250 K). The relative MR (%MR) is essentially the same (40-50%) at 4.2 K

R. Mahesh; R. Mahendiran; A. K. Raychaudhuri; C. N. R. Rao

1995-01-01

335

Slow relaxation of low temperature vortex phases in Bi_{2}Sr_{2}CaCu_{2}O_{8}  

Microsoft Academic Search

Nonlinear transport in the low temperature vortex glass state of single\\u000acrystal Bi_{2}Sr_{2}CaCu_{2}O_{8} has been investigated over long times (up to\\u000atwo weeks) with fast current pulses driven along the ab plane. It is found that\\u000aat low temperature and high magnetic field both zero field cooled (ZFC) and\\u000afield cooled (FC) samples relax towards the same equilibrium state, which

F. Portier; G. Kriza; B. Sas; L. F. Kiss; I. Pethes; K. Vad; B. Keszei; F. I. B. Williams

2001-01-01

336

Energy storage in Ce-doped LiCaAlF 6 and LiSrAlF 6 crystals  

Microsoft Academic Search

Absorption, emission and thermoluminescence (TL) of as-grown and X-irradiated pure and Ce-doped LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) crystals have been analyzed. It is shown that the energy storage is defined by the dissimilarity of basic matrix properties, intrinsic defect structure, preferred Ce3+ ion disposition and charge compensation defect type. This is the reason of higher colorability and TL efficiency of

N. Shiran; A. Gektin; S. Neicheva; V. Voronova; V. Kornienko; K. Shimamura; N. Ichinose

2004-01-01

337

Flux pinning and the irreversibility line in Bi2Sr2CaCu2O8 single crystals  

Microsoft Academic Search

Measurements of the ac-susceptibility have been used to investigate the irreversibility line (IL) for a Bi2Sr2CaCu2O8 single crystal. The activation energy, U0, determined from the frequency dependence of the ac-susceptibility, can be related to the IL if one employs the model of thermally activated flux creep. This correlation is clearly demonstrated by the observation of a kink in the IL

A. A. El-Abbar; J. R. Owers-Bradley; K. J. Maxwell; J. Lees; P. J. King; G. Balakrishnan; D. Mck Paul

1994-01-01

338

Measurement of flux creep in Bi 2Sr 2CaCu 2O 8 using electron spin resonance  

Microsoft Academic Search

Flux creep and susceptibility in a Bi2Sr2CaCu2O8 polycrystalline sample were measured using an electron spin resonance probing technique. The sample was decorated with two tiny free radical probes the signals of which superimposed at an applied field Br for T > Tc. For T < Tc the signals split: one shifted up-field to an applied field Ba1 > Br and

Michael T. Pencarinha; Charles P. Poole; Horacio A. Farach; Oscar A. Lopez

1995-01-01

339

A rapid separation of Sr from Ca by solvent extraction with dicarbollides in the presence of EDTA and polyethylene glycols  

Microsoft Academic Search

A typical composition of the solvent extraction system suitable for a rapid separation (3 min shaking) of Ca and Sr (separation factors 5000) in both tracer and macroconcentrations involves: organic phase–0.11M Li-dicarbollide and 1.65% Slovafol 909 in a mixture of 40% vol. CCl4 and 60% nitrobenzene; aqueous phase–0.15M EDTA, 0.1M (H, Li)Ac (acetate buffer), pH5.2. Replacing Slovafol 909 (suitable for

M. Kyrš; P. Selucký

1993-01-01

340

Superstructure of Bi2Sr2CaCu2O8 superconductors: a Raman scattering study  

Microsoft Academic Search

We present results of a Raman scattering study of Bi2Sr2CaCu2O8 single crystals with Tc equals 95 K in a wide temperature (65 - 365 K) and frequency (from 640 down to 10 cm-1) range. The features due to superstructure modulation are found in the low-frequency range. We also investigated additional lines seen in z(xx)z and z(yy)z scattering configurations in the

I. Loa; J. Hofmann; Alexander P. Litvinchuk; Christian Thomsen; Nicolay V. Zavaritsky

1996-01-01

341

Modification of myosin isozymes and SR Ca 2+ -pump ATPase of the diabetic rat heart by lipid-lowering interventions  

Microsoft Academic Search

To define metabolic influences on cardiac myosin expression and sarcoplasmic reticulum (SR) Ca2+-stimulated ATPase streptozotocin-diabetic rats were treated for 9–10 wk with etomoxir, an inhibitor of carnitine palmitoyl transferase I (CPT-1) and fatty acid synthesis, or an antilipolytic drug, acipimox. Etomoxir reduced myosin V3 of diabetic rats but did not normalize it. However, the high serum triglyceride, free-fatty acid and

Heinz Rupp; Vijayan Elimban; Naranjan S. Dhalla

1994-01-01

342

Influence of IIA metals (Mg, Ca, Sr, Ba) on the Co modification of gamma-Fe2O3 particles  

Microsoft Academic Search

In the reaction of Co modification of ?-Fe2O3, we found a very interesting phenomenon. When cations of Ca2+, Sr2+, or Ba2+ belonging to IIA metals are adsorbed on the surface of ?-Fe2O3 prior to Co2+ ion adsorption, the coercivity of Co modified ?-Fe2O3 is signifcantly increased compared to ?-Fe2O3 modified only with Co2+. In contrast, when the Mg2+ ion is

Yuji Fukumoto; Kazuyoshi Matsumoto; Yasushi Matsui

1991-01-01

343

Mössbauer Study on the Ordered Double Perovskite A2FeReO6 (A = Ca, Sr)  

Microsoft Academic Search

57Fe Mössbauer study on the ordered double perovskite A2FeReO6 (A = Ca, Sr) has been conducted. Fe ions are in 2.5+ states that correspond to the hybridized state of 3d t2g down-spin electrons with Re5+ 5d t2g down-spin electrons. The orbital effect due to this seems to be absent. On the metal-insulator transition of Ca2FeReO6 specimen, slight change of the

Shin Nakamura; Midori Tanaka; Hisato Kato; Yoshinori Tokura

2003-01-01

344

Determination of Mg/Ca and Sr/Ca ratios in microgram-quantity coral and foraminiferal samples with permil-level precision by cold plasma inductively coupled plasma sector field mass spectrometry  

NASA Astrophysics Data System (ADS)

A permil-level analytical technique for determination of coral and foraminiferal Mg/Ca and Sr/Ca ratios using inductively coupled plasma sector-field mass spectrometry (ICP-SF-MS, Thermo Electron ELEMENT2) has been established. Cold plasma technique with an 800-W RF power was employed to diminish spectral interference. A wet introduction system with Scott-type double-pass spray chamber and an ESI micro- nebulizer with a sample uptake rate of 50 microliter per minute were used, which can offer low blank and high stability. Intensities of ion beams, ^{24}Mg, ^{43}Ca and 86Sr, were detected in pulse-counting mode. Mg/Ca and Sr/Ca ratios were determined directly from intensity ratios using external, matrix-matched standard to correct for mass discrimination and low-frequency ratio drift. Other elemental ratios, such as Al/Ca, Mn/Ca, Fe/Ca, Cd/Ca, and Ba/Ca were also determined. Three different matrix effects were observed in this system. (1) Acid effect: Elemental intensities and ratios vary with increasing HNO3 from 1-6%. 5% HNO3 was determined to be ideal for routine measurement. (2) Ca effect: Mg/Ca ratio decreases 2.5% with [Ca] from 0.5-2.5 ppm and less than 0.5% with [Ca] from 3-5 ppm. (3) Sr/Ca effect on Mg/Ca: Sr/Ca slightly affects Mg/Ca determination with a slope of 0.18% per mmol/mol. This effect causes only 0.1 s or less for Mg/Ca ratio in both foraminiferal and coral samples. Replicate measurements made on standards and samples show that our method can give an internal precision of 1-2‰ (2RSD) and reproducibility of 4.5‰% for Mg/Ca and 3.5‰ for Sr/Ca. Corresponding errors are 0.05 °C for foraminiferal Mg thermometer and 0.5 °C for coral Sr thermometer. Advantages of this new method include (1) short measurement time of 3 minutes and (2) only 2-mircogram carbonate consumed for each sample, and (3) throughput of 10 samples per hour.

Shen, C.; Lu, C.; Lo, L.; Qu, D.; Wei, K.; Gagan, M. K.

2006-12-01

345

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

NASA Astrophysics Data System (ADS)

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

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

2000-03-01

346

Eu2+-Activated CaSrSiO4: a New Red-Emitting Oxide Phosphor for White-Light-Emitting Diodes  

NASA Astrophysics Data System (ADS)

Ca1-xSr1-xEu2xSiO4 (CaSrSiO4: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 ?'-CaSrSiO4 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 CaSrSiO4:Eu2+ is a red-emitting phosphor excited by near-UV and blue-light-emitting diodes.

Tezuka, Satoko; Sato, Yasushi; Komukai, Tetsufumi; Takatsuka, Yuji; Kato, Hideki; Kakihana, Masato

2013-07-01

347

Investigating the potential preservation of seasonal dripwater Mg/Ca and Sr/Ca variations in a speleothem from central Texas  

NASA Astrophysics Data System (ADS)

High resolution paleoclimate records are critical for improving understanding of past climate. Speleothems have the potential to record climate variations on a seasonal time scale. Fast growing (?0.5 mm/year) speleothems have been shown to preserve annual chemical laminae recorded as cyclical variations in trace elements. This study investigates the potential preservation of seasonal Mg/Ca and Sr/Ca variations in a slow growing (< ~0.05 mm/year) speleothem in central Texas. The speleothem was collected from a site that underlies a drip with observed seasonal variation in Mg/Ca and Sr/Ca, making it ideal for evaluating preservation of seasonal chemical laminae. The speleothem was cored, slabbed, dated (using U-series methods) and analyzed for high resolution variations in Mg and Sr concentrations using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Three sets of parallel transects were ablated (using a 6 x 50 ?m slit aperture) parallel to the stalagmite growth axis. The laser scanned at 1 ?m/second and made three measurements per second, resulting in sub-micron sampling. Parallel transects were ablated along different growth intervals to determine signal reproducibility of high frequency Mg and Sr variations. Wavelet analysis was conducted using detrended time series to determine presence and length of statistically significant cyclicity. Preliminary U-series ages (n=2) indicate the interval of interest (1.6 cm) grew from around 10 ka to 8 ka, but the chronology is not well constrained. The median growth rate estimated from U-series dating is 15 ?m /year with a range from approximately 4 ?m/year to >1.6 cm/year. Line scans of several standard materials (NIST 612, BHVO-2G, MACS-3) and scans perpendicular to the stalagmite growth axis were measured with the same analytical parameters used for scans parallel to the stalagmite growth axis in order to eliminate the possibility that cyclicity could be an instrumental artifact. Wavelet analysis of these scans demonstrates that cyclicity greater than 2 ?m/sec cannot be attributed to the instrument. There is good correspondence between Mg and Sr variations in three sets of paired, parallel transects. Detrended data show that Mg and Sr varied concordantly on smaller length scales despite differences in Mg and Sr variations over larger length scales. Wavelet analysis results indicate statistically significant cyclicity of Mg and Sr concentrations between 30 and 60 ?m in 5 of 6 transects, suggesting that this speleothem may be recording chemical laminae of annual growth. Growth rate estimates (30-60 ?m/year) derived from cyclical Mg and Sr variations are consistent with growth rate estimates from the preliminary U-series chronology. In addition, growth rates are comparable in magnitude to some regional speleothems from the same time interval. These results suggest that it may be possible to observe seasonal geochemical banding in a slow growing stalagmite from central Texas.

Cunningham, M. T.; Wong, C. I.; Banner, J. L.; Miller, N. R.

2011-12-01

348

Molecular layer-by-layer engineering of superconducting and superionic materials in the (AgI)Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} system  

SciTech Connect

We have developed a new interstratified system consisting of a superconducting layer alternating with a superionic conducting one, which is the AgI intercalated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} with well-defined 2-dimensional heterostructure. Before and after the intercalation of AgI, the superconducting properties remained unchanged with the T{sub c}`s of 76 K for the pristine and 63 K for the intercalate. From the extended X-ray absorption fine structure spectroscopic analysis, it is found that the intercalated AgI is formed as the {beta}-like intracrystalline structure in the 2-dimensional interlayer space of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y}. According to the ac impedance and dc relaxation measurements, the ionic transference number (t{sub i} = {sigma}{sub i}/{sigma}{sub r}) has been estimated to be 0.27 (at 167{degree}C), indicating that the substantial ionic conductivity ({sigma}{sub 1}) contributes to the total electrical one ({sigma}{sub T}). In comparison of the ionic conductivity for (AgI)Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} ({sigma}{sub i} = 10{sup -3}-10{sup -23} {Omega}{sup -1} cm{sup -1}) with those for the well-known superionic conductors of cation-substituted {beta}-aluminas, the ionic transport in (AgI)Bi{sub 2}Sr{sub 2}-CaCu{sub 2}O{sub y} turned out to be significant, even comparable with the superionic conductors. 15 refs., 4 figs., 1 tab.

Choy, J.H.; Park, N.G.; Kim, Y.I.; Hwang, S.H.; Lee, J.S.; Yoo, H.I. [Seoul National Univ. (Korea, Republic of)

1995-05-18

349

Interfacial magnetism in CaRuO3/CaMnO3 superlattices grown on (001) SrTiO3  

NASA Astrophysics Data System (ADS)

We have studied epitaxially grown superlattices of CaRuO3/CaMnO3 as well as an alloy film of CaMn0.5Ru0.5O3 on (001) SrTiO3 substrates. In contrast to previous experiments, we have studied CRO/CMO superlattices with a constant CRO thickness and variable CMO thickness. All superlattices exhibit Curie temperatures (TC) of 110 K. The saturated magnetization per interfacial Mn cation has been found to be 1.1 ?B/Mn ion. The TC's of the superlattices are much lower than the TC of the alloy film while the saturated magnetization values are larger than that of the alloy film. These observations suggest that interdiffusion alone cannot account for ferromagnetism in the superlattices and that double exchange induced FM must play a role at the interfaces.

He, C.; Zhai, X.; Mehta, V. V.; Wong, F. J.; Suzuki, Y.

2011-04-01

350

Tracing deep-sea calcite dissolution: Agreement between the Globorotalia menardii fragmentation index and elemental ratios (Mg\\/Ca and Mg\\/Sr) in planktonic foraminifers  

Microsoft Academic Search

Accurately quantifying deep-sea calcite dissolution is crucial for understanding the role of the marine carbonate system in regulating atmospheric pCO2 over millennia. We compare a foraminifer-fragmentation-based calcite dissolution proxy (Globorotalia menardii fragmentation index (MFI)) to Mg\\/Ca, Sr\\/Ca, and Mg\\/Sr in several species of deep dwelling planktonic foraminifers. We conducted microfossil and geochemical analyses on the same core top samples taken

Figen Mekik; Roger François

2006-01-01

351

A high-resolution Sr\\/Ca and 18 O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Niño  

Microsoft Academic Search

A high-resolution (near weekly) Sr\\/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the 18 O value of seawater. Using the Sr\\/Ca temperature calibration

Malcolm T. McCulloch; Michael K. Gagan; Graham E. Mortimer; Allan R. Chivas; Peter J. Isdale

1994-01-01

352

A high-resolution Sr/Ca and 18 O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Niño  

NASA Astrophysics Data System (ADS)

A high-resolution (near weekly) Sr/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the 18 O value of seawater. Using the Sr/Ca temperature calibration of et al. (1994), the Sr/Ca records exhibit seasonally controlled cyclical SST (sea surface temperature) variations of from ~21 to ~28 C. During the very strong El Niño of 1982-1983, the Sr/Ca systematics indicate a sharp drop in the winter SST to ~ 18.5 C. This represents a temperature anomaly of -3 C which is approximately twice that given by the 18 O variations, suggesting an ~×2 amplification of the anomaly by the Sr/Ca system, possibly due to the increasing dominance of inorganically controlled aragoniteseawater fractionation. The oxygen isotopic systematics show the combined effects of both temperature and changing seawater 18 O values, the latter reflecting the influx of 18 O-depleted runoff during periods of high rainfall. Due to the extremely low (~10 -3 ) Sr and Ca contents of river run off relative to seawater, it is possible to use the Sr/Ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the 18 O value of seawater. Using this approach it is possible to quantitatively reproduce the volume of runoff from the Burdekin River during the periods of major flooding that occurred in early 1979 and 1981. The results of this study demonstrate that the combined use of high-resolution Sr/Ca and 18 O systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate.

McCulloch, Malcolm T.; Gagan, Michael K.; Mortimer, Graham E.; Chivas, Allan R.; Isdale, Peter J.

1994-06-01

353

A high-resolution Sr\\/Ca and [delta][sup 18]O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Nino  

Microsoft Academic Search

A high-resolution (near weekly) Sr\\/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period of 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the [delta][sup 18]O value of seawater. Using the Sr\\/Ca temperature

M. T. McCulloch; M. K. Gagan; G. E. Mortimer; A. R. Chivas; P. J. Isdale

1994-01-01

354

Unusual Surface Metal-Insulator Transition of Single Crystal Ca1.9Sr0.1RuO4  

Microsoft Academic Search

Ca1.9Sr0.1RuO4 is a typical Mott system, exhibiting a canted antiferromagnetic insulator to paramagnetic metal transition at ˜ 155 K, and with a dramatic lattice distortion from an ideal single-layered perovskite structure. We have studied the temperature dependence of the structural and electronic properties on the surface of Ca1.9Sr0.1RuO4 by cleaving single crystals, then applying scanning tunneling microscope (STM), low energy

Jiandi Zhang; Ismail; A. P. Baddorf; Rongying Jin; D. G. Mandrus; E. W. Plummer

2003-01-01

355

Defect simulation and crystal field studies of Ln3+:LiCaAlF6 and LiSrAlF6  

Microsoft Academic Search

LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) crystal hosts doped with trivalent positive lanthanide ions (Ln3+) were studied via defect simulation techniques and crystal field parameter calculations. Depending on the ratio of ionic radius of the dopant to the host divalent cation, the luminescent ions can occupy the Sr2+ (or Ca2+) site or the Al3+. When the dopant enters at the divalent

Jomar B. Amaral; Mario E. G. Valerio; Marcos A. Couto Dos Santos; Robert A. Jackson

2004-01-01

356

Defect simulation and crystal field studies of Ln 3+:LiCaAlF 6 and LiSrAlF 6  

Microsoft Academic Search

LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) crystal hosts doped with trivalent positive lanthanide ions (Ln3+) were studied via defect simulation techniques and crystal field parameter calculations. Depending on the ratio of ionic radius of the dopant to the host divalent cation, the luminescent ions can occupy the Sr2+ (or Ca2+) site or the Al3+. When the dopant enters at the divalent

Jomar B. Amaral; Mario E. G. Valerio; Marcos A. Couto dos Santos; Robert A. Jackson

2004-01-01

357

Growth and characteristics of long persistent SrAl 2O 4- and CaAl 2O 4-based phosphor crystals by a floating zone technique  

Microsoft Academic Search

Long persistent phosphor crystals, SrAl2O4 doped with Eu and Dy, and CaAl2O4 doped with Eu and Nd have been grown by a floating zone technique. The intensities and the persistent times of the phosphorescences are found to depend on the growth atmosphere. SrAl2O4 crystals grown under H2?Ar atmosphere and CaAl2O4 crystals grown under Ar atmosphere exhibit strong and long persistent

T. Katsumata; T. Nabae; K. Sasajima; T. Matsuzawa

1998-01-01

358

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

NASA Astrophysics Data System (ADS)

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

Takesue, Renee K.; van Geen, Alexander

2004-10-01

359

Application of Sr Isotopic Data to Tuolumne Intrusive Series, Sierra Nevada, CA  

NSDL National Science Digital Library

In this problem set students are given Rb/Sr and 87Sr/86Sr data for whole rock and mineral samples from three granitic intrusions in the Sierra Nevada. They use these data (in EXCEL) to calculate isochron ages and initial ages for the intrusions and then interpret their results. This problem is intended to teach some spreadsheet skills (linear regressions, graphing) as well as having them think about the use of radiogenic isotopes.

Tepper, Jeff

360

Influence of substitution on dielectric and impedance spectroscopy of Sr 1 - xBi 2 + yNb 2O 9 ferroelectric ceramics synthesized by chemical route  

NASA Astrophysics Data System (ADS)

Nanocrystalline powders of Sr 1 - xBi 2 + yNb 2O 9 (SBN, x = 0.0, 0.1, 0.2, 0.3, and 0.4; y = 0, 0.066, 0.133, 0.200, and 0.266) were prepared by aqueous solution method using water-soluble Sr-EDTA, Bi-EDTA and Nb-tartarate as the starting materials. XRD showed that the samples were free from fluorite or pyrochlore phase within heat-treatment temperature from 550 to 600 °C. Average crystallite size and particle diameter were observed to be between 10 and 25 nm, which were analyzed through XRD and TEM, respectively. Bi-substitution has substantially improved the sinterability of SBN and enabled to achieve high density (96%), which was otherwise difficult in the case of pure SBN. The dielectric properties of SBN ceramics were significantly enhanced by the partial replacement of Sr 2+ ions by the trivalent bismuth ions. The complex impedance diagrams of Bi-substituted SBN, x = 0.4 ceramics exhibited only one semicircle indicating a significant contribution from the grains. In contrast, the impedance plots for pure and other substituted SBN ceramics show an additional low-frequency semicircle, which was attributed to the blocker size effects. The dielectric behavior of pure and Bi-substituted SBN ceramics was rationalized using the impedance and modulus data.

Dhak, D.; Dhak, P.; Pramanik, P.

2008-03-01

361

Otolith growth in trout Oncorhynchus mykiss: supply of Ca2+ and Sr2+ to the saccular endolymph.  

PubMed

Kinetic and pharmacological characteristics of Ca2+ fluxes across the saccular epithelium of trout were studied using a perfused isolated inner ear. 45Ca2+influx from the Ringer solution to the endolymph was 3-4 nmoles h(-1)microl(-1) endolymph, which corresponds to a global turnover rate of the endolymph calcium of 200 % h(-1). Ca2+ entry into the proximal endolymph was faster than into the distal fluid. Net Ca2+ movement across the saccular epithelium depended on the direction and intensity of the chemical gradient of calcium between the Ringer solution and the endolymph. Increasing the calcium concentration in the Ringer solution up to 4.4 mmol l(-1) provoked an accumulation of Ca2+ in both proximal and distal endolymphs, and equilibrium was reached about 30 min after the beginning of perfusion. Perfusion with calcium-free Ringer partially emptied the proximal compartment of calcium, whereas the calcium levels in the distal endolymph did not vary during 70 min of perfusion. Verapamil (10(-5) mol l(-1)) and cyanide (CN, 10(-3) mol l(-1)) did not modify the accumulation of Ca2+ within the endolymph in the presence of a favourable calcium chemical gradient. Furthermore the relationship between Ca2+ net fluxes and the chemical calcium gradient across the saccular epithelium was linear, indicating a passive diffusional mechanism via a paracellular pathway. Similar relationships were found for Sr2+ fluxes across the saccular epithelium in the presence of positive chemical gradients (1, 2 and 4 mmol l(-1) Sr2+). In vivo experiments in which trout were intraperitoneously injected with CaCl2 solution confirmed the tight relationship between the calcium levels in plasma and endolymph (both proximal and distal). Sampling proximal and distal endolymphs in trout and turbot saccules revealed a decreasing proximo-distal calcium gradient in endolymph of both fish species. The present results strongly suggest that the endolymph is supplied with Ca2+ and Sr2+ via a paracellular pathway located in the proximal area of the saccular epithelium. PMID:12151374

Payan, P; Borelli, G; Priouzeau, F; De Pontual, H; Boeuf, G; Mayer-Gostan, N

2002-09-01

362

Dilated Cardiomyopathy with Increased SR Ca2+ Loading Preceded by a Hypercontractile State and Diastolic Failure in the alpha1CTG Mouse  

Microsoft Academic Search

Mice over-expressing the ?1?subunit (pore) of the L-type Ca2+ channel (?1CTG) by 4months (mo) of age exhibit an enlarged heart, hypertrophied myocytes, increased Ca2+ current and Ca2+ transient amplitude, but a normal SR Ca2+ load. With advancing age (8–11 mo), some mice demonstrate advanced hypertrophy but are not in congestive heart failure (NFTG), while others evolve to frank dilated congestive

Su Wang; Bruce Ziman; Ilona Bodi; Marta Rubio; Ying-Ying Zhou; Karen D'Souza; Nanette H. Bishopric; Arnold Schwartz; Edward G. Lakatta; Pieter H. Reitsma

2009-01-01

363

Obesity-associated proinflammatory cytokines increase calcium sensing receptor (CaSR) protein expression in primary human adipocytes and LS14 human adipose cell line.  

PubMed

Obesity-associated health complications are thought to be in part due to the low-grade proinflammatory state that characterizes this disease. The calcium sensing receptor (CaSR), which is expressed in human adipose cells, plays an important role in diseases involving inflammation. To assess the relevance of this protein in adipose pathophysiology, we evaluated its expression in adipocytes under obesity-related proinflammatory conditions. As in primary adipose cells, we established that LS14, a recently described human adipose cell line, expresses the CaSR. Differentiated LS14 and primary adipose cells were exposed overnight to cytokines typically involved in obesity-related inflammation (interleukin (IL)1beta, IL6 and tumor necrosis factor (TNF)alpha). The cytokines increased CaSR abundance in differentiated adipocytes. We incubated LS14 cells with medium previously conditioned (CM) by adipose tissue from subjects with a wide range of body mass index (BMI). Cells exposed to CM from subjects of higher BMI underwent a greater increase in CaSR protein, likely resulting from the greater proinflammatory cytokines secreted from obese tissue. Our observations that proinflammatory factors increase CaSR levels in adipocytes, and the reported ability of CaSR to elevate cytokine levels, open new aspects in the study of obesity inflammatory state pathophysiology, providing a potential novel therapeutic prevention and treatment target. PMID:20595056

Cifuentes, Mariana; Fuentes, Cecilia; Mattar, Pamela; Tobar, Nicolas; Hugo, Eric; Ben-Jonathan, Nira; Rojas, Cecilia; Martínez, Jorge

2010-06-04

364

Structural, dielectric relaxation and piezoelectric characterization of Sr2+ substituted modified PMS-PZT ceramic  

NASA Astrophysics Data System (ADS)

Pyrochlore phase free [Pb0.94Sr0.06] [(Mn1/3Sb2/3)0.05(Zr0.53Ti0.47)0.95] O3 ceramics has been synthesized with pure Perovskite phase by semi-wet route using the columbite precursor method. The field dependences of the dielectric response and the conductivity have been measured in a frequency range from 50 Hz to 1 MHz and in a temperature range from 303 K to 773 K. An analysis of the real and imaginary parts of the dielectric permittivity with frequency has been performed, assuming a distribution of relaxation times. The scaling behavior of the dielectric loss spectra suggests that the distribution of the relaxation times is temperature independent. The SEM photographs of the sintered specimens present the homogenous structures and well-grown grains with a sharp grain boundary. The material exhibits tetragonal structure. When measured at frequency (100 Hz), the polarization shows a strong field dependence. Different piezoelectric figures of merit (kp, d33 and Qm) of the material have also been measured obtaining their values as 0.53, 271 pC/N and 1115, respectively, which are even higher than those of pure PZT with morphotropic phase boundary (MPB) composition. Thus the present ceramics have the optimal overall performance and are promising candidates for the various high power piezoelectric applications.

Brajesh, Kumar; Himanshu, A. K.; Sharma, Himanshu; Kumari, Kiran; Ranjan, Rajeev; Bandhopadhyay, S. K.; Sinha, T. P.

2012-02-01

365

An evaluation of temperature control on Mg/Ca, Sr/Ca and B/Ca in surface-dwelling species, Globigerinoides ruber: Comparison of sediment trap and core top systematics from the South China Sea transect  

NASA Astrophysics Data System (ADS)

Trace element ratios in planktonic foraminifera are robust proxies for reconstruction of physical and chemical changes in the past ocean. Reliable temperature and carbonate chemistry are essential for studying heat distribution and carbon cycle globally, particularly of seawater carbonate ion and atmospheric CO2 variability. This study examines systematically relationships between trace element ratios and seawater temperature for a surface-dwelling foraminiferal species, Globigerinoides ruber (white), collected from sediment traps and core top specimens in the South China Sea (SCS). Mg/Ca ratios on G. ruber (white) agree well with published data, following an equation of Mg/Ca= 0.32 (±0.04) exp (0.090×T), R2= 0.81. Partial dissolution artifacts, however, play a significant role to modify foraminiferal Mg/Ca. For the Sr/Ca ratio, it has been shown to covary consistently with ?18O-calcification temperature and Mg/Ca-based temperature, and can be described by a linear relationship: Sr/Ca= (0.020 (±0.001)×T) +0.915 (±0.010), R2= 0.78. Previous studies have demonstrated that foraminiferal Sr/Ca ratios in the surface dwellers have no temperature dependence. However, a rather large Sr/Ca in the core-top tests can be attributed to stronger dissolution effect compared with sediment trap specimens in the SCS. B/Ca ratio in G. ruber is strongly influenced by ambient temperature, B/Ca= 4.65 (±0.02) exp (0.120 (±0.018)×T), R2= 0.86, and show no conspicuous effect of partial dissolution. There is a significant difference in the relationship of shell B/Ca and seawater temperature at different ocean basins. This emphasizes the complexity of using B/Ca for oceanic pH proxy due to biological and/or environmental variations. Thus this study highlights the need for in situ empirical calibration for different hydrographic conditions before applications of down-core reconstruction of carbonate chemistry can be realized.

Huang, K.; You, C.; Rosenthal, Y.; Lin, H.; Shieh, Y.

2008-12-01

366

Oxygen reduction at a YSZ interface with cathode materials La{sub 1-x}(Ca or Sr){sub x}MnO{sub 3} or Y{sub 1-x}CaMnO{sub 3}  

SciTech Connect

Impedance spectroscopy combined with an unbonded interface cell (UIC) design, was used to assess oxygen reduction at an yttria-stabilized zirconia electrolyte interface with several substituted yttrium and lanthanum manganite cathode compositions. By analyzing impedance spectra taken using the UIC, effective length of reaction zone at the solid-gas triple phase boundary can be estimated and used to normalize the oxygen reduction reaction rate for each cell, thus effectively removing effect of interface morphology. Intrinsic reaction rates (specific oxygen activities) were determined from spectra as function of temperature and oxygen partial pressure for cathodes La{sub 1-x}(Ca or Sr){sub x}MnO{sub 3} and Y{sub 1-x}Ca{sub x}MnO{sub 3} (LCM, LSM and YCM, respectively) and for Pt. Specific activities in the temperature and P(O{sub 2}) ranges of an operating solid oxide fuel cell (SOFC) cathode, 1173--1273K and 10{sup 5}-10{sup 3} Pa, were highest for LCM intermediate for YCM and lowest for LSM. For LCM and YCM, compositions with x=0.5 gave highest specific activities. Specific activities for all of the tested manganite compositions exceeded the platinum specific activities by at least an order of magnitude. Shapes of impedance spectra for all the manganite systems were similar. Examination of spectra shapes revealed that the overall cathodic polarization process was rather complex and made up of at least two or more fundamental steps.

Youngblood, G.E.; Windisch, C.F. Jr.; Bates, J.L.

1993-09-01

367

Efficient red phosphor double-perovskite Ca3WO6 with A-site substitution of Eu(3+).  

PubMed

Luminescent properties of Eu(3+) activated double perovskite structure Ca3WO6 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 Ca3WO6, which facilitates the red emission of Eu(3+). The substitution site for Ca in Ca3WO6 was analyzed in detail by Raman spectra and calculation results. A-site substitution is responsible for the red emission of Eu(3+) activated Ca3WO6. The integrated emission intensity of optimal Ca3WO6: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. PMID:23897245

Zhao, Xin; Wang, Jiajia; Fan, Li; Ding, Yufeng; Li, Zhaosheng; Yu, Tao; Zou, Zhigang

2013-07-30

368

Probing the electronic properties of ternary AnM3n?1B2n (n = 1: A = Ca, Sr; M = Rh, Ir and n = 3: A = Ca, Sr; M = Rh) phases: observation of superconductivity  

NASA Astrophysics Data System (ADS)

We follow the evolution of the electronic properties of the titled homologous series when n as well as the atomic type of A and M are varied where for n = 1, A = Ca, Sr and M = Rh, Ir while for n = 3, A = Ca, Sr and M = Rh. The crystal structure of n = 1 members is known to be CaRh2B2-type (Fddd), while that of n = 3 is Ca3Rh8B6-type (Fmmm); the latter can be visualized as a stacking of structural fragments from AM3B2 (P6/mmm) and AM2B2. The metallic properties of the n = 1 and 3 members are distinctly different: on the one hand, the n = 1 members are characterized by a linear coefficient of the electronic specific heat ? ? 3 mJ mol?1 K?2, a Debye temperature ?D ? 300 K, a normal conductivity down to 2 K and a relatively strong linear magnetoresistivity for fields up to 150 kOe. The n = 3 family, on the other hand, exhibits ? ? 18 mJ mol?1 K?2, ?D ? 330 K, a weak linear magnetoresistivity and an onset of superconductivity (for Ca3Rh8B6, Tc = 4.0 K and Hc2 = 14.5 kOe, while for Sr3Rh8 B6, Tc = 3.4 K and Hc2 ? 4.0 kOe). These remarkable differences are consistent with the findings of the electronic band structures and density of state (DOS) calculations. In particular, satisfactory agreement between the measured and calculated ? was obtained. Furthermore, the Fermi level, EF, of Ca3Rh8B6 lies at almost the top of a pronounced local DOS peak, while that of CaRh2B2 lies at a local valley: this is the main reason behind the differences between the, e.g., superconducting properties. Finally, although all atoms contribute to the DOS at EF, the contribution of the Rh atoms is the strongest.

Takeya, Hiroyuki; ElMassalami, Mohammed; Terrazos, Luis A.; Rapp, Raul E.; Capaz, Rodrigo B.; Fujii, Hiroki; Takano, Yoshihiko; Doerr, Mathias; Granovsky, Sergey A.

2013-06-01

369

Microstructure and magnetic properties of electrospun one-dimensional Al{sup 3+}-substituted SrFe{sub 12}O{sub 19} nanofibers  

SciTech Connect

SrAl{sub x}Fe{sub 12-x}O{sub 19} (x=0-3.0) nanofibers with diameters about 100 nm have been prepared by electrospinning and subsequent heat treatment. With Al{sup 3+} ion content ranging from 0 to 3.0, the lattice parameters decrease due to Fe{sup 3+} ions substituted by smaller Al{sup 3+} ions and the average grain size calculated by the Scherrer's equation reduces from 65 to 37 nm. The magnetization shows a continuous reduction with the Al content and its value measured at 77 K is higher than at room temperature, which can be explained by Bloch's law. For the coercivity, its value initially increases, reaching a maximum value of 617 (298 K) and 547 kA m{sup -1} (77 K) at x=2.0, and then reduces with the Al content further increase largely arising from the substituted Al{sup 3+} ion arrangement in different interstitial sites of the strontium ferrite unit cell. -- Graphical abstract: Al{sup 3+} ions substituted strontium ferrite nanofibers have been prepared by the electrospinning with a diameter of about 100 nm and the Al{sup 3+} ion substitution has a great effect on the microstructure and magnetic property of SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers. Display Omitted Research highlights: {yields} SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers have been fabricated by the electrospinning. {yields} There is a relation between the Al{sup 3+} ions substitution and microstructure. {yields} The magnetic property can be tuned effectively by Al{sup 3+} ion substitution. {yields} The magnetic property is influenced by measurement temperature.

Liu, Mingquan [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Shen, Xiangqian, E-mail: shenxq@ujs.edu.c [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Song, Fuzhan; Xiang, Jun; Meng, Xianfeng [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China)

2011-04-15

370

The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+ partitioning  

SciTech Connect

Engineering the precipitation of calcium carbonate, which can co-precipitate trace metal contaminants, is a proposed strategy for remediating toxic or radioactive metals in subsurface environments. Engineering precipitation of multi-component minerals will involve injection of chemical amendments that must be mixed at a molecular level to supersaturated conditions that are sufficient to promote rapid mineral precipitation relative to natural systems. In subsurface systems this often means reactant mixing zones will be formed that are characterized by gradients in solute concentrations, saturation state, and solute activity ratios. To better understand the effect of ion activity ratios on CaCO{sub 3} precipitation kinetics and Sr{sup 2+} co-precipitation we experiments were conducted under constant composition conditions where the supersaturation state ({Omega}) with respect to calcite was held constant at 9.4, but the ion activity ratio (r = a{sub co{sub 3}{sup 2-}}/a{sub Ca{sup 2+}}) ranged from 0.003 to 4.15. Results: Under the chosen experimental conditions the CaCO{sub 3} phase formed was calcite and initial precipitation rates varied from a maximum rate of 84.7 {mu}mol/ m{sup 2}/min for a carbonate to calcium activity ratio of (0.21). However, precipitation rates were found to vary with time which could be indicative of variations in precipitation mechanisms that are related to the ion activity ratio. The observed trends in the distribution coefficients for co-precipitated Sr2+ (D{sup P}{sub Sr}{sup 2+}) relative to the calcite precipitation rate (i.e. a positive correlation) indicate that increasing calcite precipitation rates increase the incorporation of Sr{sup 2+}. Conclusion: The observed variation between the rate maxima and minima based on the ion activity ratio could have great deal of implication for sequestering radionuclides (e.g. {sup 90}Sr) and other toxic metals in engineered systems at contaminated sites. Extending our data plot range allowed us to have clues about the differences in mechanism calcite precipitation, which would have significance in our understanding of mineral precipitation modes in subsurface remediation strategies. The positive correlation between D{sup P}{sub Sr}{sup 2+} and calcite precipitation rate could be indicative of the impact calcite precipitation would have on sequestering toxic metals in subsurface environment.

Tsigabu Gebrehiwet; Mikala S. Beig; George Redden; Yoshiko Fujita; Robert W. Smith

2012-01-01

371

Necking effect on the growth of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystal by TSFZ method  

SciTech Connect

High-quality Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals have been grown by a traveling solvent floating zone method with a necking technique using a single crystal seed. The full-width at half maximum of the X-ray rocking curves was improved from 120 arcsec to 70 arcsec by the necking technique. The topographic results show that the crystals grown using the necking technique have better crystallinity. Especially, this technique is very effective on the growth of the atomically substituted single crystals. It results not only in the improvement of crystallinity but also in the enhancement of the single crystal size, especially for the crystals substituted by other elements.

Mochiku, Takashi; Hirata, Kazuto

1999-11-01

372

M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion  

SciTech Connect

Three earth alkali-germanium monophosphates M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, 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}-SrGe(PO{sub 4}){sub 2} (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO{sub 4}){sub 2} and low-temperature {alpha}-SrGe(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 SrGe(PO{sub 4}){sub 2} at room temperature ({alpha}) results from the off-centering of cation Sr{sup II}. Highlights: > Crystal structures of yavapaiite-type M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) have been solved. > Distortion and superstructure result from Ca and Sr off-centering. > A global scheme for the polymorphism of yavapaiites is proposed.

Popa, Karin ['Al.I. Cuza' University, Department of Chemistry, 11-Carol I Blvd., 700506 Iasi (Romania); Wallez, Gilles, E-mail: gilles.wallez@upmc.fr [Chimie ParisTech, UPMC Univ. Paris 06, CNRS-UMR 7574, Laboratoire de Chimie de la Matiere Condensee de Paris (LCMCP), 75005 Paris (France); Bregiroux, Damien; Loiseau, Pascal [Chimie ParisTech, UPMC Univ. Paris 06, CNRS-UMR 7574, Laboratoire de Chimie de la Matiere Condensee de Paris (LCMCP), 75005 Paris (France)

2011-10-15

373

Thermal expansion behaviour in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Competing effects of water and oxygen ordering  

SciTech Connect

Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Synchrotron X-ray studies demonstrate that these oxides have a double perovskite-type structure with the cell size increasing as the size of the B cation increases from 8.2114(2) A for B=Ca to 8.4408(1) A for B=Ba. It is postulated that a combination of local clustering of the anions and vacancies together with water-water and water-host hydrogen bonds plays a role in defining the volume of the encapsulated water clusters and that changes in the local structure upon heating result in anomalous thermal expansion observed in variable temperature diffraction measurements. - Graphical abstract: The oxides Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba) have unusual anion disorder. There is a lag in the contraction in the cell size of Sr{sub 2}CaSbO{sub 5.5}nH{sub 2}O established from X-ray diffraction measurements following the loss of water suggesting changes on the local structure are important. Highlights: > The average structures of the defect perovskites Sr{sub 2}MSbO{sub 5.5} established. > Anion and cation disorder quantified by neutron and synchrotron X-ray diffraction. > Anomalous thermal expansion due to local clustering of anions and vacancies observed.

Zhou Qingdi [School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia); Kennedy, Brendan J., E-mail: b.kennedy@chem.usyd.edu.au [School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia); Avdeev, Maxim [Bragg Institute, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234 (Australia)

2011-09-15

374

Texture analysis of monofilamentary, Ag-sheathed (Pb,Bi)2Sr2Ca2Cu3Ox tapes by electron backscatter diffraction (EBSD)  

NASA Astrophysics Data System (ADS)

Using automated orientation imaging, the grain orientations and texture of monofilamentary, Ag-sheathed (Pb,Bi)2Sr2Ca2Cu3Ox (Bi-2223) tape is analysed in detail by means of electron backscatter diffraction (EBSD). The achieved high image quality of the Kikuchi patterns enables multi-phase scans including Bi-2223, Bi2Sr2CaCu2Ox, Bi2Sr2CuOx, (Sr,Ca)14Cu24O41 and Ag to be performed. Two areas are selected for the EBSD analysis, one close to the silver sheath, the other located in the center of the sample. The grain orientation maps are presented for each phase separately allowing a new insight into the microtexture of Ag-sheathed Bi-2223 tapes. Furthermore, the EBSD analysis provides the possibility for a misorientation angle analysis within each individual phase.

Koblischka-Veneva, A.; Koblischka, M. R.; Qu, T.; Han, Z.; Mücklich, F.

2008-02-01

375

Planar Faults and Grain Boundary Precipitation in Non-Stoichiometric (Sr, Ca)TiO3 Ceramics  

NASA Astrophysics Data System (ADS)

Microstructures of non-stoichiometric-composition (Sr0.85Ca0.15O)xTiO2 ceramics (with x{=}0.98 and 1.02) were observed using high-resolution transmission electron microscopy and scanning transmission electron microscopy. Precipitation of Magnéli-phase was found at the grain boundary in the specimen for x{=}0.98, and Ruddlesden-Popper-type insertion layers in that for x{=}1.02. The crystallographic site occupancy of impurity atoms determined by ALCHEMI (Atom Location using CHanneling-Enhanced MIcroanalysis), showed that the excess TiO2 was precipitated as Magnéli phase in the specimen for x{=}0.98, and similarly that excess SrO formed insertion planar faults of NaCl type in that for x{=}1.02. No anti-site point defects were formed in either of the specimens.

Fujimoto, Masayuki; Tanaka, Junzo; Shirasaki, Shinichi

1988-07-01

376

Top Down and Bottom up: A Comparison of Coccolith Sr/Ca Ratios and Benthic Foraminiferal Accumulation Rates as Indicators of Paleoproductivity  

NASA Astrophysics Data System (ADS)

Recent studies have linked coccolith Sr/Ca ratios to the growth rate of the coccolithophorid algae (Stoll and Schrag, 2000). While this link implies a correlation between coccolith Sr/Ca ratios and primary productivity, application of this proxy has not yet been fully tested against other paleoproductivity indicators. Here we compare down-core measurements of coccolith Sr/Ca ratios to down-core changes in benthic foraminiferal accumulation rates (BFAR), a proxy for export production, from two Ocean Drilling Program sites in the Atlantic (western tropical Atlantic Site 925 and subpolar North Atlantic Site 982). The sediments used for this analysis span the late Miocene through early Pliocene (9-3 Ma), which was chosen for its significance as a period marked by a massive "biogenic bloom". Although not synchronous, increases in paleoproductivity are apparent in both BFAR records (Diester-Haass et al., submitted). Our preliminary Sr/Ca record from Site 982, which is based on a single coccolith size fraction, shows that the overall long-term trend is matched and that there are a number of synchronous maxima and minima. Statistical analysis confirms a significant correlation between coccolith Sr/Ca ratios and BFAR at this site. Our preliminary interpretations demonstrate that a relationship exists between coccolith Sr/Ca and BFAR, supporting our understanding of the proxies as paleoproductivity indicators. Further work includes a separation of discrete coccolith size fractions and down-core monitoring of species assemblages to better constrain the potential effects of nannofossil species assemblage changes on coccolith Sr/Ca ratios.

Waite, A.; Billups, K.; Diester-Haass, L.; Gibbs, S.; Rickaby, R.; Stoll, H.

2004-12-01

377

Juxtaglomerular cell CaSR stimulation decreases renin release via activation of the PLC/IP(3) pathway and the ryanodine receptor.  

PubMed

The calcium-sensing receptor (CaSR) is a G-coupled protein expressed in renal juxtaglomerular (JG) cells. Its activation stimulates calcium-mediated decreases in cAMP content and inhibits renin release. The postreceptor pathway for the CaSR in JG cells is unknown. In parathyroids, CaSR acts through G(q) and/or G(i). Activation of G(q) stimulates phospholipase C (PLC), and inositol 1,4,5-trisphosphate (IP(3)), releasing calcium from intracellular stores. G(i) stimulation inhibits cAMP formation. In afferent arterioles, the ryanodine receptor (RyR) enhances release of stored calcium. We hypothesized JG cell CaSR activation inhibits renin via the PLC/IP(3) and also RyR activation, increasing intracellular calcium, suppressing cAMP formation, and inhibiting renin release. Renin release from primary cultures of isolated mouse JG cells (n = 10) was measured. The CaSR agonist cinacalcet decreased renin release 56 ± 7% of control (P < 0.001), while the PLC inhibitor U73122 reversed cinacalcet inhibition of renin (104 ± 11% of control). The IP(3) inhibitor 2-APB also reversed inhibition of renin from 56 ± 6 to 104 ± 11% of control (P < 0.001). JG cells were positively labeled for RyR, and blocking RyR reversed CaSR-mediated inhibition of renin from 61 ± 8 to 118 ± 22% of control (P < 0.01). Combining inhibition of IP(3) and RyR was not additive. G(i) inhibition with pertussis toxin plus cinacalcet did not reverse renin inhibition (65 ± 12 to 41 ± 8% of control, P < 0.001). We conclude stimulating JG cell CaSR activates G(q), initiating the PLC/IP(3) pathway, activating RyR, increasing intracellular calcium, and resulting in calcium-mediated renin inhibition. PMID:23220722

Ortiz-Capisano, M Cecilia; Reddy, Mahendranath; Mendez, Mariela; Garvin, Jeffrey L; Beierwaltes, William H

2012-12-05

378

Effects of oxygen partial pressure and mechanical deformation on (Tl,Pb)(Ba,Sr)2Ca2Cu3Oy Ag-sheathed tapes  

Microsoft Academic Search

The powder in tube method was used to produce silver sheathed tapes of Tl0.78Pb0.5Ba0.4Sr1.6Ca2Cu3Oy. A precursor powder of Pb0.5Ba0.4Sr1.6Ca2Ca3Oy (prepared via the hydroxycarbonate coprecipitation of the metal ions from a stoichiometric nitrate solution) was thallinated and packed into a silver tube and processed into tape. The tape was then heated (in 100% oxygen or air) from 840°C by 870°C for

K. V. Salazar; E. J. Peterson; T. G. Holesinger; B. Bingham; J. Y. Coulter; R. J. Sebring; J. A. Voigt; E. P. Roth; P. Haldar

1995-01-01

379

Morphology and optical properties of Mg and Sr doped CaF2 nanocrystals  

NASA Astrophysics Data System (ADS)

Magnesium (Mg) and Strontium (Sr) doped Calcium fluoride nanocrystals were synthesized by co-precipitation method. The cubic structure of the samples was confirmed by Powder X-ray diffraction. The average crystallite size of Mg doped samples was found to be ~ 25 nm whereas in Sr doped one it was ~ 35 nm. The morphological features revealed that the nanocrystals were agglomerated, crispy and porous. The as-prepared samples showed the presence of hydroxyl groups. The optical absorption spectrum of as-prepared Mg doped samples showed a strong absorption band peaked at ~ 233 nm whereas the Sr doped one showed a prominent absorption peak at 248 nm. A strong PL emission was observed at ~ 300 nm in Mg doped samples. However, the Sr doped samples showed two prominent emissions at ~ 345 and 615 nm.

Pandurangappa, C.; Lakshminarasappa, B. N.

2012-05-01

380

Melt processing of the Bi2Sr2CaCu2O(y) superconductor in oxygen and argon atmospheres  

NASA Astrophysics Data System (ADS)

Solidification and subsequent annealing of Bi2Sr2CaCu2O(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 O2 and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutectic structure of Bi2Sr(3-x)Ca(x)O(y) and Cu2O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed, generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi(2.15)Sr2Ca(0.85)Cu2O(y).

Holesinger, T. G.; Miller, D. J.; Chumbley, L. S.

1992-08-01

381

Electronic structure, chemical bonding, and solid-state NMR spectroscopy of the digallides of Ca, Sr, and Ba.  

PubMed

Combined application of (69,71)Ga NMR spectroscopy and quantum mechanical calculations reveals the chemical bonding in the digallides of Ca, Sr, and Ba. An analysis of the electron localization function (ELF) shows honeycomb-like 6(3) nets of the Ga atoms as the most prominent structural features in SrGa(2) and BaGa(2). For CaGa(2) a description of a 3+1-coordinated Ga atom is revealed by the ELF and by an analysis of interatomic distances. The NMR spectroscopic signal shift is mainly due to the Knight shift and is almost equal for the investigated digallides, whereas the anisotropy of the signal shift decreases with the radius of the alkaline-earth metals. Calculated and observed values of the electric field gradient (EFG) are in good agreement for CaGa(2) and BaGa(2) but differ by about 21 % for SrGa(2) indicating structural instability. Better agreement is achieved by considering a puckering of the Ga layers. For BaGa(2) an instability of the structure is indicated by a peak in the density of states at the Fermi level, which is shifted to lower energies when taking puckering of the Ga layers into account. Both structural modifications are confirmed by crystallographic information. The Fermi velocity of the electrons is strongly anisotropic and is largest in the (001) plane of the crystal structure. This results in an alignment of the crystallites with the [001] axis perpendicular to the magnetic field as observed in (69,71)Ga NMR spectroscopy and magnetic susceptibility experiments. The electron transport is predominantly mediated by the Ga-Ga p(x)- and p(y)-like electrons in the (001) plane. The specific heat capacity of BaGa(2) was determined and indicated the absence of phase transitions between 1.8 and 320 K. PMID:19123208

Haarmann, Frank; Koch, Katrin; Grüner, Daniel; Schnelle, Walter; Pecher, Oliver; Cardoso-Gil, Raul; Borrmann, Horst; Rosner, Helge; Grin, Yuri

2009-01-01

382

Coccolith Sr/Ca records of productivity during the Paleocene-Eocene thermal maximum from the Weddell Sea  

NASA Astrophysics Data System (ADS)

A major perturbation of the global carbon cycle ˜55 million years ago, believed to result from release of 1000-2000 Gt of C from methane hydrates, correlates with an intense but transient greenhouse warming event known as the Paleocene Eocene Thermal Maximum (PETM). The rapid (105 years) recovery of global temperatures reflects important negative feedbacks in the climate system and carbon cycle. Enhanced marine productivity may be one important feedback, but indicators for productivity changes have yielded conflicting results. Here we use a new independent indicator, Sr/Ca in coccolith carbonate, which covaries with the productivity of coccolithophorid algae, to investigate the biotic response in the most complete PETM deep sea record which was recovered at ODP Site 690 in the Weddell Sea. In the dominant coccolithophorid genus Toweius a large (40%) Sr/Ca increase immediately after the gas hydrate release signals a dramatic productivity increase. Productivity levels remained high for 60,000 years but decreased to pre-event levels by 120,000 years after the gas hydrate release. Productivity levels during the PETM are higher than observed at any other time in our ˜400,000 year record. Other coccolithophorid genera Chiasmolithus and Discoaster show a brief modest (25% Sr/Ca increase) increase in productivity that lags behind the methane event by 50,000 years and is within the range of productivity variation elsewhere in the record. The timing of the Toweius productivity increase agrees well with Os isotope records of globally increased weathering intensity, which may have provided higher nutrient fluxes to stimulate algal productivity. If this type of productivity response occurred globally, it would also be consistent with the timing of C drawdown that may have returned temperatures to near pre-event levels.

Stoll, Heather M.; Bains, Santo

2003-06-01

383

Sr/Ca and ?18O seasonality in a Porites coral from the MIS 9 (339 303 ka) interglacial  

NASA Astrophysics Data System (ADS)

Past changes in the seasonal distribution of insolation across the Earth's surface are thought to play a critical role in Quaternary climate cycles. In this study we use Sr/Ca and ?18O as geochemical proxies in the skeleton of a fossil Porites coral to reconstruct the seasonal cycle of sea surface temperature (SST) at Henderson Island, southeast Pacific (24°S, 128°W) during the Marine Isotope Stage (MIS) 9 interglacial (˜ 339-303 ka). Previously-published closed-system U-series ages provide broad age constraints for the timing of reef growth for this unit on Henderson Island, ranging between 334 and 306 ka. We apply published ?18O-SST slope relationships to the stacked ?18O annual cycle in the fossil Porites, and find the amplitude of the seasonal cycle of SST recorded by the MIS 9 coral to be ˜ 4.1 ± 0.57°C, which agrees within error with the modern seasonal cycle of SST (˜ 4.1°C). Sr/Ca-SST slope relationships applied to the fossil Porites stacked Sr/Ca annual cycle suggest the amplitude of the seasonal cycle of SST was ˜ 4.7 ± 0.75°C, exceeding the modern cycle by ˜ 15%, but within error of the modern value. Taken together, these results suggest the seasonal cycle of SST at Henderson Island during MIS 9 equaled or exceeded the modern amplitude. Using modern latitudinal relationships between insolation seasonality and SST seasonality, we present a new application for SST amplitudes reconstructed from fossil corals that can be used in conjunction with U-series ages to provide additional geochronological constraints on the development of open-ocean, interglacial reefs.

Ayling, Bridget F.; McCulloch, Malcolm T.; Gagan, Michael K.; Stirling, Claudine H.; Andersen, Morten B.; Blake, Steve G.

2006-08-01

384

Nonlinear c -axis transport in Bi2Sr2CaCu2O8+? from two-barrier tunneling  

NASA Astrophysics Data System (ADS)

Motivated by the peculiar features observed through intrinsic tunneling spectroscopy of Bi2Sr2CaCu2O8+? mesas in the normal state, we have extended the normal-state two-barrier model for the c -axis transport [M. Giura , Phys. Rev. B 68, 134505 (2003)] to the analysis of dI/dV curves. We have found that the purely normal-state model reproduces all the following experimental features: (a) the parabolic V dependence of dI/dV in the high- T region (above the conventional pseudogap temperature), (b) the emergence and the nearly voltage-independent position of the “humps” from this parabolic behavior by lowering the temperature, and (c) the crossing of the absolute dI/dV curves at a characteristic voltage V× . Our findings indicate that conventional tunneling can be at the origin of most of the uncommon features of the c -axis transport in Bi2Sr2CaCu2O8+? . We have compared our calculations to experimental data taken in severely underdoped and slightly underdoped Bi2Sr2CaCu2O8+? small mesas. We have found good agreement between the data and the calculations, without any shift of the calculated dI/dV on the vertical scale. In particular, in the normal state (above T? ) simple tunneling reproduces the experimental dI/dV quantitatively. Below T? quantitative discrepancies are limited to a simple rescaling of the voltage in the theoretical curves by a factor ˜2 . The need for such modifications remains an open question, that might be connected to a change of the charge of a fraction of the carriers across the pseudogap opening.

Giura, M.; Pompeo, N.; Silva, E.

2009-04-01

385

Viscoelasticity of the titanate perovskites CaTiO 3 and SrTiO 3 at high temperature  

NASA Astrophysics Data System (ADS)

The frequency-dependence of the shear modulus and dissipation in polycrystalline CaTiO 3 and SrTiO 3 perovskites has been determined at high temperature using micro-creep ( ?=10 -4), seismic frequency forced oscillation ( ?=10 -5), and ultrasonic interferometric measurements. Both of these perovskites display viscoelastic behaviour in the seismic frequency regime; with the temperature of onset of this frequency-dependent behaviour being grainsize-dependent. The frequency-dependent and time-dependent data have been described in terms of the elastic, anelastic and viscous components of deformation using the Andrade model. The relatively smooth variation with temperature of G and Q-1 for CaTiO 3 (sampled at relatively widely spaced (50°C) temperature steps) suggests that the high temperature phase transitions occurring in CaTiO 3 have little effect on the viscoelastic behaviour. In the absence of grain-boundary impurities, twinning and dislocations, the long-timescale viscoelastic deformation of SrTiO 3 is attributed to grain-boundary sliding accommodated by lattice or grain-boundary diffusion, controlled by the slowest diffusing species, which is expected to be either Sr or Ti. The low viscosities determined for the CaTiO 3 samples, together with the low values (with respect to the extrapolated ultrasonic data) of shear modulus associated with Andrade model fits to the data suggest that the long-timescale viscoelastic deformation of CaTiO 3 may reflect relatively faster grain-boundary diffusion of the slowest moving species through the thin (<2 nm) impurity films and larger impurity segregations present in these samples. The ultrasonic measurements, combined with those of Kung [Kung, J., 1997. Systematics among the elastic properties of perovskite-structured compounds and geophysical implications. PhD, Australian National University, Canberra, 112 pp.] for ScAlO 3 perovskite, indicate relatively tightly clustered high-frequency (anharmonic) values of |(? KS/? T) P| and |(? G/? T) P| within the ranges 0.023-0.033 and 0.015-0.021 GPa K -1, respectively, neither of which includes the most recent determinations for MgSiO 3 perovskite. The diffusion controlled viscoelastic rheology observed here results in the magnitude of the highest temperature shear moduli determined for fine-grained CaTiO 3 and SrTiO 3 perovskite at seismic frequencies being less than one-quarter that of the ultrasonic moduli, and the temperature dependence of the seismic-frequency moduli being larger by a factor of 10. An extrapolation of the rheology of fine-grained SrTiO 3 and CaTiO 3 perovskites to 5 mm grainsize shows that a ˜20% dispersion in wavespeed is expected for the period range 1-1000 s, with dissipation ( Q-1) ˜10 -2 for 1 s period waves at 1300°C. Viscoelastic behaviour related to diffusional creep in the silicate perovskites in the lower mantle may result in a similar reduction in seismic shear-wave speed accompanied by an increase in shear-wave dissipation, and an apparent increase in the temperature dependence of seismic shear-wave speed.

Webb, Sharon; Jackson, Ian; Fitz Gerald, John

1999-10-01

386

Magnetic instability in Ca2- x Sr x RuO4 with x = 0.5  

NASA Astrophysics Data System (ADS)

We analyze the static susceptibilities for charge and spin degrees of freedom in Ca2- x Sr x RuO4 with x = 0.5 within the random phase approximation on the basis of the three-orbital Hubbard model for the Ru t 2 g orbitals. We find that the rotation of RuO6 octahedra, which is induced in the range of x < 1.5, leads to the enhancement of several modes of spin fluctuation around both q = (0, 0) and ( ?, 0).

Arakawa, Naoya; Ogata, Masao

2013-08-01

387

Zero-magnetic-field dynamic scaling in Bi2 Sr2 CaCu2 O8 thin films  

NASA Astrophysics Data System (ADS)

We investigate the zero-magnetic-field dynamic scaling in Bi2Sr2CaCu2O8 thin films from nonlinear current-voltage (I-V) characteristics and by using the concavity criterion recently proposed by Strachan [Phys. Rev. Lett. 87, 067007 (2001)]. We find that fresh samples show a BKT-like transition with z=0.8 , smaller than expected for a conventional Berezinskii-Kosterlitz-Thouless transition. The effect of sample size and finite Josephson coupling are discussed. We examine the effect of thermally-induced disorder in the oxygen sublattice finding that the BKT-like transition is suppressed by point disorder.

Sefrioui, Z.; Arias, D.; Leon, C.; Santamaria, J.; Gonzalez, E. M.; Vicent, J. L.; Prieto, P.

2004-08-01

388

Kinetics of the thermal decompositions of MC 2 O 4 to MCO 3 (M=Ca, Sr AND Ba)  

Microsoft Academic Search

The kinetics of the thermal decompositions of CaC2O4, SrC2O4 and BaC2O4 to their carbonates were studied by thermogravimetry at constant and at linearly increasing temperatures. Isothermally, the three oxalates decompose according to A1.43, R1.54 and R1 laws, respectively. Dynamically, the decompositions of the first two oxalates proceed in a similar way as under the isothermal conditions, whereas BaC2O4 decomposes according

Haruhiko Tanaka; Nobuyoshi Koga

1987-01-01

389

Fabrication and physical properties of DC SQUIDs using Bi(Pb)SrCaCuO thin films  

NASA Astrophysics Data System (ADS)

The fabrication and physical properties of DC SQUIDs using Bi(Pb)SrCaCuO thin films are reported. The total Josephson critical current of DC SQUIDs with different microbridge widths (0.5-12?m) ranges from 8 ?A to 5 mA. The observed quantum interference pattern under an applied magnetic filed is largely deformed and a discussion based on the multiple interference effect is given. The measured voltage modulation depth is found to be smaller than the calculated value. The Josephson critical current exhibits a (1-T/Trmc)n dependence on temperature where n=1-2.5.

Wen, Zhongmin; Iguchi, Ienari

1990-06-01

390

Photoluminescence property of A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] phosphors.  

PubMed

A new efficient phosphor, A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] has been synthesized by the solid-state method at high temperature. X-ray diffraction analysis confirmed the formation of the compound. Photoluminescence excitation measurements show that the phosphor can be efficiently excited by near-ultraviolet light from 300 nm to 400 nm to realize emission covering the 397-647 nm region of visible spectrum. Therefore, newly synthesized novel phosphor may be useful as green-emitting phosphor in solid-state lighting. PMID:22961920

Singh, Roshani; Dhoble, S J

2012-09-07

391

Lattice dynamics of the superconducting Bi 2 Sr 2 Ca(Cu, Sn) 2 O 8? y  

Microsoft Academic Search

Phonon anomaly was observed below 140 K for the absorption area (lnA) and the isomer shift (?) plotted against the temperature (T) in the119Sn Mössbauer study of the Bi2Sr2Ca(Cu0.995Sn0.005)2O8?y superconductor (glass-ceramic,Tc(on)=86 K), which was prepared by heat treatment of the glassy sample. The anomaly suggests that the softening (quenching) of the lattice vibration causes the superconducting transition, as was observed

T. Nishida; M. Katada; J. Kubota; Y. Takashima; F. Ichikawa; T. Fukami; T. Aomine

1994-01-01

392

Preparation of Bi-Pb-Sr-Ca-Cu-O superconductors by the spray pyrolysis method using ultrasonic atomization techniques  

NASA Astrophysics Data System (ADS)

The high Tc oxide superconductor of the Bi-Pb-Sr-Ca-Cu-O system was prepared by spray pyrolysis. X-ray diffraction patterns of the sample show a perfectly isolated 110 K phase. Superconducting transition with zero-resistance temperature at Tc = 101 K was achieved for a sample calcined at 850°C for 18 hr and sintered at the same temperature for 12 hr. The heat treatment time required to form the pure 110 K phase could be minimized by spray pyrolysis. The critical current density at 77 K in zero magnetic field was 528 A/cm2.

Tomizawa, T.; Matsunaga, H.; Fujishiro, M.; Kakegawa, K.

1990-11-01

393

Vortex dynamics in (Tl,Pb)(Sr,Ba) 2Ca 2Cu 3O y single crystal  

Microsoft Academic Search

Magnetic moment measurements performed on a single crystal sample of (Tl,Pb)(Sr,Ba)2Ca2Cu3Oy reveal an increase in magnetic moment at intermediate fields. Magnetic hysteresis (m–H) loops were taken at different constant temperatures using either a MPMS-5T SQUID magnetometer or a PPMS-9T magnetometer and within the temperature range 0.1

Shokat Keshavarzi; Joseph Horvat; Meng Jun Qin; Xiaolin Wang; Shi Xue Dou

2007-01-01

394

Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba)  

SciTech Connect

Neutron powder diffraction has been performed on the MTbF{sub 6} fluorides (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba). Four of these fluorides (Cd, Ca, Sr, {beta}-Ba) are built of a (pseudo-) tetragonal packing of [TbF{sub 6}]{sup 2-} chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb{sup 4+}-Tb{sup 4+} magnetic interactions. All the compounds displayed antiferromagnetic order (T{sub N}=2.70 K (Cd), 2.15 K (Ca), 2.60 K (Sr), 2.10 K ({beta}-Ba)), except for the {alpha} form of BaTbF{sub 6}. The crystal structure of this latter fluoroterbate has also been investigated by means of high-resolution neutron powder diffraction. From Neutron Powder Diffraction data, CdTbF{sub 6} and {beta}-BaTbF{sub 6} magnetic structures were determined, together with the metamagnetic behaviour of {beta}-BaTbF{sub 6} as a function of an external magnetic field. A tentative phase diagram is then given for {beta}-BaTbF{sub 6}. Advantage was taken of the polymorphism of the BaTbF{sub 6} fluoroterbate to analyse, on the basis of topological parameters such as bond distances and angles, the magnetic behaviour of its {alpha} and {beta} forms. It was shown that superexchange interactions are present in {beta}-BaTbF{sub 6}, and that these interactions may also rule the magnetic behaviour of the other MTbF{sub 6} (M=Ca, Sr, Cd) tetravalent terbium fluorides. - Graphical abstract: Powder neutron diffraction revealed magnetic order in four of the five investigated fluoroterbates, while crystal chemical analyses of {alpha} and {beta} forms of BaTbF{sub 6} evidenced the existence of superexchange interactions. Highlights: Black-Right-Pointing-Pointer Five fluoroterbates are investigated by Powder Neutron Diffraction (PND). Black-Right-Pointing-Pointer Four of them are antiferromagnetically ordered at 1.4 K. Black-Right-Pointing-Pointer Magnetic structures of {beta}-BaTbF{sub 6} and CdTbF{sub 6} are determined. Black-Right-Pointing-Pointer PND under magnetic field emphasises the metamagnetic behaviour of {beta}-BaTbF{sub 6}. Black-Right-Pointing-Pointer Comparison of {alpha} and {beta}-BaTbF{sub 6} evidences superexchange interactions in fluoroterbates.

Josse, M. [Laboratoire des Materiaux Inorganiques, UMR 6002 CNRS, Universite Blaise Pascal, 63171 Aubiere (France); CNRS, Universite de Bordeaux, ICMCB, Pessac (France); El-Ghozzi, M., E-mail: Malika.EL-GHOZZI@univ-bpclermont.fr [Laboratoire des Materiaux Inorganiques, UMR 6002 CNRS, Universite Blaise Pascal, 63171 Aubiere (France); Avignant, D. [Laboratoire des Materiaux Inorganiques, UMR 6002 CNRS, Universite Blaise Pascal, 63171 Aubiere (France); Andre, G.; Bouree, F. [Laboratoire Leon Brillouin, CEA-CNRS, CEA-Saclay, 91191 Gif-sur-Yvette (France); Isnard, O. [Institut Neel, CNRS/Universite Joseph Fourier, UPR2940, 38042 Grenoble (France)

2012-01-15

395

LPE growth of Bi2Sr2CaCu2O(y) from KCl solution  

NASA Astrophysics Data System (ADS)

Superconducting films of Bi2Sr2CaCu2O(y) were epitaxially grown on MgO (001) single crystals using a KCl solvent. Grown layers were characterized by microscope, XRD, and vibrating sample magnetometry. The film was grown on most of the substrate surface, and the surface morphology was fairly smooth. Typical layer thickness was 4 microns. Critical temperature was 85 K from the resistance and the ac susceptibility. Critical current density estimated from magnetization curves was 590 A/sq cm for the ab planet at zero magnetic field and 77 K.

Yasui, Koji; Ido, Toshiyuki; Terada, Hiroshi; Muto, Saburo

1992-12-01

396

Superstructure of Bi2Sr2CaCu2O8 superconductors: a Raman scattering study  

NASA Astrophysics Data System (ADS)

We present results of a Raman scattering study of Bi2Sr2CaCu2O8 single crystals with Tc equals 95 K in a wide temperature (65 - 365 K) and frequency (from 640 down to 10 cm-1) range. The features due to superstructure modulation are found in the low-frequency range. We also investigated additional lines seen in z(xx)z and z(yy)z scattering configurations in the regions of 160 - 240 cm-1 and 300 - 450 cm-1 and analyzed the temperature dependence of the latter.

Loa, I.; Hofmann, J.; Litvinchuk, Alexander P.; Thomsen, Christian; Zavaritsky, Nicolay V.

1996-06-01

397

Structure, magnetic and dielectric properties in Mn-substituted Sm1.5Sr0.5NiO4 ceramics  

NASA Astrophysics Data System (ADS)

The crystal structures, magnetic and dielectric properties were evaluated for Sm1.5Sr0.5Ni1-xMnxO4 (x = 0.03, 0.05, 0.1) ceramics. The Rietveld results of X-ray diffraction patterns confirmed single orthorhombic phase with the space group of Bmab (64) were obtained in Sm1.5Sr0.5Ni1-xMnxO4 (x = 0.03, 0.05) ceramics, while in Sm1.5Sr0.5Ni0.9Mn0.1O4 ceramics, apart from the main orthorhombic phase, a tiny secondary phase was detected. A magnetism characteristic of a spin glass was found in Sm1.5Sr0.5NiO4, while a complicated magnetic phenomenon was observed in Sm1.5Sr0.5Ni0.9Mn0.1O4 ceramics. The giant dielectric response was observed in these ceramics, and dielectric loss decreased with increasing the content of manganese ions. After comparing the activation energies of dielectric relaxation and electrical conduction, the low-temperature giant dielectric response should be attributed to the adiabatic small polaronic hopping process, while at high-temperature, the low frequency relaxation was mainly attributed to the grain boundary effect. The suppression of dielectric loss should be benefited from the various polar region caused by Mn-substitution.

Wen Jia, Bo; Qiang Liu, Xiao; Ming Chen, Xiang

2011-09-01

398

The use of external micro-PIXE to investigate the factors determining the Sr:Ca ratio in the shells of fossil aragonitic molluscs  

NASA Astrophysics Data System (ADS)

The ratio of strontium to calcium in the shells of fossil marine molluscs has been proposed as an indicator of seawater temperature in past epochs, since this is less affected by other environmental conditions (such as variation of salinity) than the more conventional seawater palaeotemperature proxy /?18O. However, in this paper, we demonstrate that the Sr:Ca ratio is influenced by several factors including temperature and growth rate. Two fossil molluscs, a large spiral gastropod, Clavilithes macrospira, and a large bivalve, Venericarda planicosta, from the Eocene-aged deposits of Southern England were selected for study. The variation of the Sr:Ca ratio as a function of distance along the growth direction was measured using PIXE in the Oxford external microbeam facility and the /?18O was measured using small samples removed by drilling at points along the same direction. The Sr:Ca profiles show a significant increase of Sr with age, as well as seasonal, possibly temperature-related variations. Comparison of the Sr:Ca profiles with those for /?18O and the spacing of the dark annual growth bands suggests that Sr incorporation is controlled primarily by metabolic activity, which in turn is influenced by factors such as temperature, salinity, age and growth rate [1].

Purton-Hildebrand, L. M. A.; Grime, G. W.; Shields, G. A.; Brasier, M. D.

2001-07-01

399

Metallic and nonmetallic double perovskites: A case study of A2FeReO6 (A=Ca, Sr, Ba)  

Microsoft Academic Search

We have investigated the structure and electronic properties of ferrimagnetic double perovskites, A2FeReO6 (A=Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m) and metallic, while the A=Ca phase is monoclinic (P21\\/n) and nonmetallic. 57Fe Mössbauer spectroscopy shows that iron is present mainly in the high spin (S=52) Fe3+ state in the Ca compound, while it occurs in an intermediate state

J. Gopalakrishnan; A. Chattopadhyay; S. B. Ogale; T. Venkatesan; R. L. Greene; A. J. Millis; K. Ramesha; B. Hannoyer; G. Marest

2000-01-01

400

Three monthly coral Sr\\/Ca records from the Chagos Archipelago covering the period of 1950–1995 A.D.: reproducibility and implications for quantitative reconstructions of sea surface temperature variations  

Microsoft Academic Search

In order to assess the fidelity of coral Sr\\/Ca for quantitative reconstructions of sea surface temperature variations, we\\u000a have generated three monthly Sr\\/Ca time series from Porites corals from the lagoon of Peros Banhos (71°E, 5°S, Chagos Archipelago). We find that all three coral Sr\\/Ca time series are\\u000a well correlated with instrumental records of sea surface temperature (SST) and air

Miriam Pfeiffer; Wolf-Ch