These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Influence of Ca substitution on the microstructure and magnetic properties of SrLaCo ferrite  

NASA Astrophysics Data System (ADS)

M-type ferrites Sr(0.55-x)CaxLa0.45Fe11.65Co0.35O19 (x=0, 0.05, 0.15, 0.25 and 0.35) were prepared by the ceramic process. Phase composition, morphology and sublattice occupation of the material were characterized by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy, respectively. Magnetic properties of the materials were tested by a vibrating sample magnetometer. The results show that the samples are all composed of single M-type hexagonal ferrite after the Ca substitution, while the lattice constant c decreases and the lattice constant a does not change basically with increase of the substitution amount. In addition, the intrinsic coercive force increases obviously when the Ca substitution amount x<0.25, while the saturation magnetization does not change after Ca addition, which is attributed to the change of the Fe3+ sublattice occupations suggested by Mössbauer spectroscopy.

Li, Xiao; Yang, Wuguo; Bao, Daxin; Meng, Xiangdong; Lou, Baiyang

2013-03-01

2

Electrical conductivity of cobalt-titanium substituted SrCaM hexaferrites  

NASA Astrophysics Data System (ADS)

A series of polycrystalline M-type hexagonal ferrites with the composition Sr 0.5Ca 0.5Co xTi xFe 12-2 xO 19 (where x=0.0-0.8) were prepared by the conventional ceramic technique. The electrical conductivity has been measured from 300 to 590 K. The dc conductivity, ?dc, exhibited a semiconductor behavior. The negative sign of thermoelectric power coefficient S reveals that all samples are n-type semiconductors. Both ?dc and mobility, ?d, increases with the substitution of Co 2+ and Ti 4+ ions, reach maximum at x=0.4 and start decreasing at x>0.4. Many conduction mechanisms were discussed to explain the electric conduction in the system. It was found that the hopping conduction is the predominant conduction mechanism. For samples with compositional parameter x=0.0 and 0.8, the band conduction mechanism shares in electric conduction beside the hopping process.

Eraky, M. R.

2012-03-01

3

Enhancement of the superconducting transition temperature of TlSr2CaCu2O7 by yttrium and vanadium substitutions  

Microsoft Academic Search

Superconductivity at 105 K has recently been observed in a family of compounds (Tl1-xMx)Sr2(Ca1-yYy)Cu2O7-delta (M = Ti, Zr, Hf, V, Nb, and Ta). An interesting feature is the enhancement of Tc in the parent TlSr2CaCu2O7 compound via substitution of high-valent 3d transition metals; this is in contrast to other high-Tc cuprates investigated so far. The effects on crystal structure and

R. S. Liu; P. P. Edwards

1991-01-01

4

Substitution of manganese by trivalent and tetravalent elements in the CMR perovskites Pr 1 - x (Ca, Sr) x MnO 3  

Microsoft Academic Search

The substitution of trivalent (M=In, Ga) and tetravalent elements (M=Sn, Ti) for Mn(III) and Mn(IV) respectively has been studied in the colossal magnetoresistant (CMR) perovskites Pr0.7Ca0.2Sr0.1MnO3 (type I) and Pr0.5Sr0.5MnO3 (type II). For the former compound, whatever the element, the temperature transition (Tmax or TC) separating the ferromagnetic metallic (FM) state and the paramagnetic semiconductinc (PSC) state decreases dramatically when

A. Maignan; C. Martin; B. Raveau

1996-01-01

5

Study of the yttrium and zinc substitutions effects in Bi 2Sr 2CaCu 2O 8+? 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 Bi 2Sr 2CaCu 2O 8+? 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

6

Structural and superconducting properties of Sr for Ba substituted La1.5Nd0.5Ca1(Ba2-xSrx)Cu5Oz system  

NASA Astrophysics Data System (ADS)

An attempt is made to investigate the effect of isovalent substitution (i. e. Sr+2 for Ba+2) and chemical pressure effect (i.e. smaller cation substitution) on the structure and superconductivity of La1.5Nd0.5Ca1(Ba2-xSrx)Cu5Oz,x = 0.0-1.0, (LNCBSCO) system. A series of LNCBSCO system has been synthesized by a solid-state reaction route. All the compounds crystallize with the tetragonal LaBa2Cu3Oz type structure with the space group P4/mmm. The structural parameters of the prepared samples are obtained using X-ray diffraction (XRD) with Rietveld analysis. The electrical properties are also carefully investigated using the four-probe temperature dependent resistivity (R-T) technique. The oxygen content is estimated through Iodometric titration. All the samples show the well superconducting behavior with decreasing Tc values ranging from 79 K to 60 K for x = 0.0 to x = 0.8. Tc exhibits a strong correlation with doping concentration. We discuss possible reasons and inherent of the Tc(x) suppression.

Bhalodia, J. A.; Mankadia, S. R.; Dalsaniya, S. M.; Okram, G. S.

2013-06-01

7

Raman spectroscopic evidence of site-selective isotopic substitution of oxygen in Bi2Sr2Ca0.8Y0.2Cu2O8+delta and mode assignments of oxygen vibrations  

Microsoft Academic Search

The site-selective substitution of 18O for 16O in Bi2Sr2Ca0.8Y0.2Cu2O8+delta has been investigated by Raman spectroscopy. Three prominent Raman bands are observed at 297, 464, and 623 cm-1. They all shift to lower wave numbers as the 18O content increases. The bands at 297 and 464 cm-1 shift at similar rates but the band at 623 cm-1 shifts at a slower

Byung-Kook Kim; Masato Kakihana; Masatomo Yashima; Masahiro Yoshimura; Soon-Ja Park; Hiro-O. Hamaguchi

1994-01-01

8

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

9

Magnetic Behaviour of Fe Substituted Bilayered Manganite La{sub 1.2}Sr{sub 1.5}Ca{sub 0.3}Mn{sub 2}O{sub 7}  

SciTech Connect

For studying the effect of low level substitution of Fe (at Mn site) on magnetic behaviour in the bilayered system La{sub 1.2}Sr{sub 1.5}Ca{sub 0.3}Mn{sub 2}O{sub 7}, dc magnetization measurements have been made on La{sub 1.2}Sr{sub 1.5}Ca{sub 0.3}Mn{sub 1.99}Fe{sub 0.01}O{sub 7}. Cooling from 300 K downwards, the system shows transition to ferromagnetic (FM) ordering in ab plane (at {approx}250 K), to antiferromagnetic state (at {approx}195 K) and to 3D FM order (at {approx}70 K). Magnetization--temperature measurements in zero field cooling and field cooling modes, made under different external magnetic fields, and the observed long time evolution of magnetization with time, are suggestive of FM disorder and high magnetic anisotropy. Substitution of Fe weakens ferromagnetism.

Saxena, Arpita; Krishnamurthy, Anjali; Srivastava, Bipin K. [Department of Physics, University of Rajasthan, Jaipur 302 055 (India)

2010-12-01

10

Synthesis and characterization of Bi 2(Sr,Ca) 3Cu 2O 8+? with different Sr\\/Ca ratio  

Microsoft Academic Search

Single-phase Bi2.2(Sr0.9?yCay)2Ca1.0Cu2.0O8.1+z (y = 0 to 0.4) was synthesized and changes in the environment around apical oxygen (Oap) induced by substitution of the Sr sites by Ca were examined. By decreasing the z value, the Tc value increases from 71.5 K to 91.5 K for the sample with y = 0, but remains unchanged for the sample with y =

Rika Sekine; Maki Kawai; Yasuhiro Murakoshi; Shousuke Teratani

1995-01-01

11

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

12

Cause of Tc depression in Sr substituted YBaSrCu 3O 7- y examined by isotope studies  

NASA Astrophysics Data System (ADS)

We have measured oxygen isotope shifts in YBa 2- xSr xCu 3O 7- y. With increasing Sr substitution, Tc decreases monotonically, while the oxygen isotope exponent ?0 remains very small. This indicates that the hole concentration in the CuO 2 planes is still optimal, since it is known that high temperature superconductors with non-optimum hole concentration have reduced Tc, but large isotope shifts. To confirm this, we carried out hole doping experiments on YBaSrCu 3O 7- y using high pressure O 2 annealing, and also by Ca substitution for Y. In both cases, with the increased holes (overdoping), Tc further decreased as expected. Thus, the significant decrease in Tc with Sr substitution is not caused by reduced charge transfer into the CuO 2 sheets, but rather is due to decreased ion size, polarizability and/or changes in the phonon spectrum.

Zhao, Guo-meng; Sinha, A. P. B.; Morris, Donald E.

13

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

E-print Network

naturally in igneous rocks (Ober 1989) and is often associated with calcium (Ca) deposits. Sr is chemically and reproductive failure, we analyzed Sr, and calcium (Ca) concentrations and Sr/Ca ratios in eggshells from 20 reproduction in regions with high Sr deposits in rock and soil, Sr concentrations in the eggshell also should

Mora, Miguel A.

14

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

15

Cause of Tc depression in Sr substituted YBaSrCu3O7-y examined by isotope studies  

NASA Astrophysics Data System (ADS)

We have measured oxygen isotope shifts in YBa2-xSrxCu3O7-y. With increasing Sr substitution, Tc decreases monotonically, while the oxygen isotope exponent ?0 remains very small. This indicates that the hole concentration in the CuO2 planes is still optimal, since it is known that high temperature superconductors with non-optimum hole concentration have reduced Tc, but large isotope shifts. To confirm this, we carried out hole doping experiments on YBaSrCu3O7-y using high pressure O2 annealing, and also by Ca substitution for Y. In both cases, with the increased holes (overdoping), Tc further decreased as expected. Thus, the significant decrease in Tc with Sr substitution is not caused by reduced charge transfer into the CuO2 sheets, but rather is due to decreased ion size, polarizability and/or changes in the phonon spectrum.

Morris, D. E.; Sinha, A. P. B.; Zhao, G.-m.

1998-03-01

16

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

2013-11-15

17

87Sr\\/86Sr and Sr\\/Ca Investigation of Jurassic mollusks from Scotland: Implications for paleosalinities and the Sr\\/Ca ratio of seawater  

Microsoft Academic Search

Measurements of 87 Sr\\/ 86 Sr, Sr\\/Ca, 18 O, and 13 C were performed on molluscan fos- sils from the Great Estuarine Group, Scot- land, to deduce paleosalinity patterns and hydrodynamic environments in this classic Jurassic marginal marine succession. Fos- sils are found as winnowed accumulations in shell beds that bear low-diversity assem- blages, consistent with deposition in a la-

Chris Holmden; John D. Hudson

2003-01-01

18

Synthesis and characterization of Bi2(Sr,Ca)3Cu2O8+delta with different Sr\\/Ca ratio  

Microsoft Academic Search

Single-phase Bi2.2(Sr0.9-yCay)2Ca1.0Cu2.0O8.1+z (y = 0 to 0.4) was synthesized and changes in the environment around apical oxygen (Oap) induced by substitution of the Sr sites by Ca were examined. By decreasing the z value, the Tc value increases from 71.5 K to 91.5 K for the sample with y = 0, but remains unchanged for the sample with y =

R. Sekine; Y. Murakoshi; S. Teratani; M. Kawai

1995-01-01

19

Sol-gel preparation and characterization of non-substituted and Sr-substituted lanthanum cobaltates  

Microsoft Academic Search

This paper reports on the results concerning the sol-gel preparation and characterization of Sr-substituted perovskite lanthanum\\u000a cobaltates La1?xSrxCoO3?? (x = 0.0, 0.25, 0.5 and 0.75). The metal ions, generated by dissolving starting materials in diluted acetic acid were complexed\\u000a by 1,2-ethanediol to obtain the precursors for the non-substituted and Sr-substituted LaCoO3. The influence of the synthesis temperature, heating time and

Sigute Cizauskaite; Aivaras Kareiva

2008-01-01

20

Sol–gel preparation and characterization of non-substituted and Sr-substituted gadolinium cobaltates  

Microsoft Academic Search

An aqueous sol–gel chemistry approach for the preparation of Sr-substituted perovskite gadolinium cobaltates Gd1?xSrxCoO3?? (x=0.0, 0.25, 0.5 and 0.75) has been applied. The metal ions, generated by dissolving starting materials in diluted acetic acid were complexed by EDTA to obtain the precursors for non-substituted and Sr-substituted GdCoO3. However, only two single-phase cobaltate samples with x=0.0 and 0.25 have been obtained

S. Cizauskaite; S. Johnsen; J.-E. Jørgensen; A. Kareiva

2011-01-01

21

Substitution effect of Ba at the Sr sites in Sr(Fe,Re)O3  

NASA Astrophysics Data System (ADS)

Substitution effect in double perovskites, Sr(FeRe)O3 (SFRO), was studied by Mössbauer spectroscopy and magnetization measurements. The samples were prepared by a sol-gel method. The fraction of alternately ordered Fe1 for SFRO is 72%, and the magnetization measured is consistent with 3× 0.72=2.16{?_B } {f.u.}, but the saturation magnetization drops to about one third of its initial value by substituting 5% Ba for Sr. It was considered to be due to the volume expansion of the lattice and the fine grains formed, as a result of the substitution of Ba ions.

Yamakoshi, T.; Nomura, K.; Kitamori, T.; Shimoyama, J.; Nemeth, Z.; Homonnay, Z.

2009-06-01

22

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

23

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

Microsoft Academic Search

To examine regional variation in strontium (Sr), which at high concentrations may reduce eggshell quality, increase egg breakage\\u000a and reproductive failure, we analyzed Sr, and calcium (Ca) concentrations and Sr\\/Ca ratios in eggshells from 20 avian species\\u000a from California, Texas, Idaho, Kansas, and Michigan. In addition, we included data previously reported from Arizona to expand\\u000a the regional comparisons and to

Miguel A. MoraBryan; Bryan Brattin; Catherine Baxter; James W. Rivers

24

Thermoelectric phase diagram in a CaTiO3-SrTiO3-BaTiO3 system  

NASA Astrophysics Data System (ADS)

Herein the authors propose a compositional thermoelectric phase diagram, which includes the density of states effective mass (md*) carrier relaxation time (?), and thermoelectric power factor (S2?, where S and ? are Seebeck coefficient and electrical conductivity) for high-quality epitaxial films composed of 20%-Nb-doped CaTiO3-SrTiO3-BaTiO3 solid solutions [(Ca ,Sr,Ba)(Ti0.8Nb0.2)O3]. The md* values almost proportionally increase with the in-plane lattice parameter of (Ca,Sr,Ba)(Ti0.8Nb0.2)O3 epitaxial film, while the ? values drastically decrease when Ca and/or Ba are substituted for Sr in Sr(Ti0.8Nb0.2)O3, indicating that the Sr-site substitution negatively affects the thermoelectric performance of Nb-doped SrTiO3.

Yamamoto, Masahiro; Ohta, Hiromichi; Koumoto, Kunihito

2007-02-01

25

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

PubMed

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 between two biological reservoirs ( Rn and R(n -1)) is measured with an observed ratio (OR) expressed by the (Sr/Ca) Rn /(Sr/Ca)( Rn-1) and (Ba/Ca) Rn /(Ba/Ca)( Rn-1) ratios. For a mammalian organism, during the whole biopurification of Ca starting with the diet to the ultimate reservoir of Ca which is the bone, the mean values for ORSr and ORBa are 0.25 and 0.2, respectively. In this study, published Sr/Ca and Ba/Ca ratios are used for three sets of soils, plants, and bones of herbivorous and carnivorous mammals, each comprising a trophic chain, to illustrate the biopurification of Ca at the level of trophic chains. Calculated ORSr and ORBa of herbivore bones in relation to plants and of bones of carnivores in relation to bones of herbivores give ORSr=0.30+/-0.08 and ORBa=0.16+/-0.08, thus suggesting that trophic chains reflect the Sr/Ca and Ba/Ca fluxes that are prevalent at the level of a mammalian organism. The slopes of the three regression equations of log(Sr/Ca) vs. log(Ba/Ca) are similar, indicating that the process of biopurification of Ca with respect to Sr and Ba is due to biological processes and is independent of the geological settings. Modifications of the logarithmic expression of the Sr/Ca and Ba/Ca relationship allow a new formula of the biopurification process to be deduced, leading to the general equation ORBa=ORSr(1.79+/-0.33), where the allometric coefficient is the mean of the slopes of the three regression equations. Some recent examples are used to illustrate this new analysis of predator-prey relations between mammals. This opens up new possibilities for the utilization of Ba/Ca and Sr/Ca in addition to stable isotope ratios (delta13C and delta15N) for the determination of the relative contribution of different food sources to an animal's diet. PMID:14745648

Balter, Vincent

2004-03-01

26

Structural and optical properties of Bi1-xAxFeO3 (A = Sr, Ca; 0.40 ? x ? 0.55)  

NASA Astrophysics Data System (ADS)

The effect of Sr2+ and Ca2+ cation substitution on BiFeO3-type (Bi1-xAxFeO3; A = Sr, Ca; 0.40 ? x ? 0.55) ceramics are investigated for structural and optical properties. X-ray diffraction patterns confirmed that Ca2+/Sr2+ substitution facilitates the formation of tetragonal phase instead of rhombohedral phase as observed in undoped BiFeO3 (BFO). The iodometric titration results show that substitution of Sr2+ has higher tendency to form oxygen vacancies than Ca2+ substituted samples. On the other hand, Ca2+ substitution shows opposite trend. The FT-IR and Raman spectra show shift in the peak positions towards higher wavenumber and diffused bands with the increasing concentration of substituent. The parameters like band gap energy, Urbach energy has been calculated from the UV-visible spectra. Sr2+ substituted samples show higher structural distortion and low optical band gap values which can be correlated to the higher oxygen vacancies and low Fe4+ content as compared to Ca2+ substituted samples.

Thakur, Samita; Pandey, O. P.; Singh, K.

2014-09-01

27

'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

2013-04-15

28

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

PubMed Central

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 Ca2+ 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 Ca2+-induced Ca2+ 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 Ca2+ release event frequency (4.14 ± 0.72 vs. 6.20 ± 0.76 events (100 ?m)?1 s?1). These individual photolytically triggered Ca2+ release events were identified as Ca2+ sparks, which originated from RyR openings. This was verified by Ca2+ spark analysis and pharmacological separation between RyR and InsP3R-dependent sarcoplasmic reticulum (SR)-Ca2+ release (2-aminoethoxydiphenyl borate, xestospongin C, tetracaine). Significant SR-Ca2+ flux but eventless SR-Ca2+ release through InsP3R were characterized using SR-Ca2+ leak/SR-Ca2+ load measurements. These results strongly support the idea that IP3ICR can effectively modulate RyR openings and Ca2+ spark probability. We conclude that eventless and highly efficient InsP3-dependent SR-Ca2+ 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

2013-01-01

29

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

30

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

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

2011-11-01

31

Efeito da adicao de chumbo na formacao de fases supercondutoras em ceramicas de Bi-Sr-Ca-Cu-O. (Effect of lead addition on the formation of superconducting phases in Bi-Sr-Ca-Cu-O ceramics).  

National Technical Information Service (NTIS)

Superconducting ceramics with starting composition Bi(sub 2) (sub -)(sub x) Pb(sub x) Sr(sub 2) Ca(sub 2) Cu(sub 3) O(sub y) (0,0 (<=) X (<=) 0,6) were prepared in order to investigate the effects of partial substitution of Pb for Bi and sintering time an...

A. E. Martinelli

1991-01-01

32

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

33

Control of the superconducting properties of Sr2-xCaxVO3FeAs through isovalent substitution  

NASA Astrophysics Data System (ADS)

The effect of the isovalent substitution of Sr2+ by Ca2+ on the structure and superconducting properties of Sr2-xCaxVO3FeAs is described in the compositional range 0?x?0.5. SQUID magnetometry measurements reveal that after an initial increase in Tc, which is maximised at 29.5 K in Sr1.95Ca0.05VO3FeAs, a rapid suppression of superconductivity is observed with increasing x. XANES spectra of Sr2-xCaxVO3FeAs collected on the Fe and V absorption K-edges show that the position of both edges are invariant with composition within the experimental uncertainty. A combination of synchrotron X-ray powder diffraction and neutron powder diffraction techniques is used to rationalise the observed changes in Tc with x, in terms of changes to the structure of the FeAs layer upon partial Ca substitution. These findings demonstrate that superconductivity in the Fe-based superconductors is extremely sensitive to the crystal structure with Tc maximised in samples with regular FeAs4-tetrahedra.

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

2014-08-01

34

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-x Sr.sub.x PbO.sub.4 wherein x is about 0.5, is disclosed.

Hults, William L. (Los Alamos, NM); Kubat-Martin, Kimberly A. (Espanola, NM); Salazar, Kenneth V. (Espanola, NM); Phillips, David S. (Los Alamos, NM); Peterson, Dean E. (Los Alamos, NM)

1994-01-01

35

Computational study of Ca, Sr and Ba under pressure  

Microsoft Academic Search

A first-principles procedure for the calculation of equilibrium properties of crystals under hydrostatic pressure is applied to Ca, Sr and Ba. The procedure is based on minimizing the Gibbs free energy G (at zero temperature) with respect to the structure at a given pressure p, and hence does not require the equation of state to fix the pressure. The calculated

F. Jona; P. M. Marcus

2006-01-01

36

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

37

Calibration of Mg\\/Ca, Sr\\/Ca and Ba\\/Ca in Sedeiment Trap Planktonic Foraminiferal Shells and Seawater  

Microsoft Academic Search

Mg\\/Ca, Sr\\/Ca and Ba\\/Ca in foraminiferal calcite are important proxies for reconstructing the past hydrological properties in the ocean. Paired Mg\\/Ca and delta 18O measurements on single foraminiferal species are especially of great merit in estimating both temperature and delta 18O in seawater. However, only a paucity of data is available for the purpose of direct calibration between seawater and

K. Huang; C. You; H. Lin; Y. Shieh; M. Li

2003-01-01

38

Sr\\/CaSea surface temperature calibration in the branching Caribbean coral Acropora palmata  

Microsoft Academic Search

We measured Sr\\/Ca ratios by thermal ionization mass spectrometry in radial and axial growth of modern Caribbean Acropora palmata corals. Comparison of our results with sea surface temperature (SST) allows radial and axial Sr\\/Ca-SST calibrations of Sr\\/Ca (mmol\\/mol) = 11.30 ? 0.07072 × SST (°C) and Sr\\/Ca (mmol\\/mol) = 11.32 – 0.06281 x SST (°C), respectively. Application of the calibrations

Christina D. Gallup; Donna M. Olson; R. Lawrence Edwards; Leah M. Gruhn; Amos Winter; Frederick W. Taylor

2006-01-01

39

?-adrenergic stimulation increases the intra-SR Ca termination threshold for spontaneous Ca waves in cardiac myocytes  

PubMed Central

?-adrenergic stimulation of cardiac myocytes enhances intracellular calcium cycling, which frequently associates with pro-arrhythmic Ca waves. The threshold level of free calcium in the sarcoplasmic reticulum ([Ca]SR) where waves initiate is increased during ?-adrenergic stimulation.1 Here, we measured [Ca]SR directly to monitor the [Ca]SR level at which spontaneous Ca waves terminated (termination threshold) during ?-adrenergic stimulation. Compared with control conditions, application of the ?-adrenergic receptor agonist isoproterenol (ISO; 1 ?M) resulted in an increase in basal [Ca]SR and an increase in the [Ca]SR at which spontaneous Ca waves terminated. When [Ca]SR was experimentally matched, ISO stimulation resulted in a decrease in the depletion amplitude of the waves. Sensitization of ryanodine receptor SR Ca release channels to Ca with a low dose of caffeine in the presence of ISO was able to decrease the termination threshold compared with control conditions. Therefore, the Ca wave termination level may represent an important mode of altering Ca depletion from the SR and reducing the arrhythmogenic potential during ?-adrenergic stimulation. PMID:23510939

Maxwell, Joshua T.; Domeier, Timothy L.; Blatter, Lothar A.

2013-01-01

40

A precise, high-throughput method for determining Sr\\/Ca, Sr\\/Ba, and Ca\\/Ba ratios in marine barite  

Microsoft Academic Search

Recent evidence suggests that marine barite, an inorganic phase preserved in oxic, deep-sea sediments, may record seawater Sr and Ca concentrations. Here we describe a novel method for determining Sr\\/Ca, Sr\\/Ba, and Ca\\/Ba ratios of discrete marine barite separates. Marine barite, separated from deep-sea sediments, is dissolved in a basic, ethylene diamine tetra acetic acid (EDTA) solution and subsequently analyzed

Kristen B. Averyt; Adina Paytan; Guangchao Li

2003-01-01

41

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

42

Effect of doping in Bi-Pb-Sr-Ca-Cu-O superconductor composites  

E-print Network

-Pb-Sr-Ca-Cu-0 and Bi-Sr- Ca-Cu-0 polycrystalline precursor powders . . . . . . . . . . , . . . . . . . . . . . . 28 12. SEM micrographs of Bi-Pb-Sr-Ca-Cu-0 superconductor bulk produced by thermal co-decomposition method and sintered at 830 C in air for 20 h... . . 29 13. SEM micrographs of Bi-Sr-Ca-Cu-0 superconductor bulk produced by thermal co-decomposition method and sintered at 830 C in air for 20 h. 29 14. SEM micrographs of Bi-Pb-Sr-Ca-Mn-0 non superconductor bulk produced by thermal co...

Ertekin, Abdullah

2012-06-07

43

Computational study of Ca, Sr and Ba under pressure  

NASA Astrophysics Data System (ADS)

A first-principles procedure for the calculation of equilibrium properties of crystals under hydrostatic pressure is applied to Ca, Sr and Ba. The procedure is based on minimizing the Gibbs free energy G (at zero temperature) with respect to the structure at a given pressure p, and hence does not require the equation of state to fix the pressure. The calculated lattice constants of Ca, Sr and Ba are shown to be generally closer to measured values than previous calculations using other procedures. In particular for Ba, where careful and extensive pressure data are available, the calculated lattice parameters fit measurements to about 1% in three different phases, both cubic and hexagonal. Rigid-lattice transition pressures between phases which come directly from the crossing of G(p) curves are not close to measured transition pressures. One reason is the need to include zero-point energy (ZPE) of vibration in G. The ZPE of cubic phases is calculated with a generalized Debye approximation and applied to Ca and Sr, where it produces significant shifts in transition pressures. An extensive tabulation is given of structural parameters and elastic constants from the literature, including both theoretical and experimental results.

Jona, F.; Marcus, P. M.

2006-05-01

44

Ankyrin-B reduction enhances Ca spark-mediated SR Ca release promoting cardiac myocyte arrhythmic activity  

PubMed Central

Ankyrin-B (AnkB) loss-of-function may cause ventricular arrhythmias and sudden cardiac death in humans. Cardiac myocytes from AnkB heterozygous mice (AnkB+/?) show reduced expression and altered localization of Na/Ca exchanger (NCX) and Na/K-ATPase (NKA), key players in regulating [Na]i and [Ca]i. Here we investigate how AnkB reduction affects cardiac [Na]i, [Ca]i and SR Ca release. We found reduced NCX and NKA transport function but unaltered [Na]i and diastolic [Ca]i in myocytes from AnkB+/? vs. wild-type (WT) mice. Ca transients, SR Ca content and fractional SR Ca release were larger in AnkB+/? myocytes. The frequency of spontaneous, diastolic Ca sparks (CaSpF) was significantly higher in intact myocytes from AnkB+/? vs. WT myocytes (with and without isoproterenol), even when normalized for SR Ca load. However, total ryanodine receptor (RyR)-mediated SR Ca leak (tetracaine-sensitive) was not different between groups. Thus, in AnkB+/? mice SR Ca leak is biased towards more Ca sparks (vs. smaller release events), suggesting more coordinated openings of RyRs in a cluster. This is due to local cytosolic RyR regulation, rather than intrinsic RyR differences, since CaSpF was similar in saponin-permeabilized myocytes from WT and AnkB+/? mice. The more coordinated RyRs openings resulted in an increased propensity of pro-arrhythmic Ca waves in AnkB+/? myocytes. In conclusion, AnkB reduction alters cardiac Na and Ca transport and enhances the coupled RyR openings, resulting in more frequent Ca sparks and waves although the total SR Ca leak is unaffected. This could enhance the propensity for triggered arrhythmias in AnkB+/? mice. PMID:22406428

Camors, Emmanuel; Mohler, Peter J.; Bers, Donald M.; Despa, Sanda

2012-01-01

45

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

46

Variability of Mg\\/Ca and Sr\\/Ca between and within the planktonic foraminifers Globigerina bulloides and Globorotalia truncatulinoides  

Microsoft Academic Search

The variability in Mg\\/Ca and Sr\\/Ca within individual tests and chambers of tests, and samples consisting of differing numbers of individuals, was determined for Globigerina bulloides and Globorotalia truncatulinoides in a North Atlantic core top sample (52.918°N 16.917°W'). The variability in Mg\\/Ca and Sr\\/Ca within individual tests and chambers was determined by electron microprobe, and samples consisting of variable sample

Pallavi Anand; Henry Elderfield

2005-01-01

47

High Precision Determination of Sr\\/Ca and Mg\\/Ca Elemental Ratios in Massive Coral Skeletons  

Microsoft Academic Search

Summary The Thermo Scientific ELEMENT 2, a single collector double focusing sector field ICP-MS, was used for the determination of Sr\\/Ca and Mg\\/Ca elemental ratios in microgram samples taken from seasonal growth bands in a coral skeleton (Diploria strigosa). Variations in ?18O values were found to be in good agreement with the results for Sr\\/Ca and Mg\\/Ca elemental ratio deter-

Henning Kuhnert; Julian D. Wills; Meike Hamester; Thermo Fisher; Charles B. Douthitt; S. Raven Ridge

48

Variability of Mg\\/Ca and Sr\\/Ca between and within the planktonic foraminifers Globigerina bulloides and Globorotalia truncatulinoides  

Microsoft Academic Search

The variability in Mg\\/Ca and Sr\\/Ca within individual tests and chambers of tests, and samples consisting of differing numbers of individuals, was determined for Globigerina bulloides and Globorotalia truncatulinoides in a North Atlantic core top sample (52.918°N 16.917°W?). The variability in Mg\\/Ca and Sr\\/Ca within individual tests and chambers was determined by electron microprobe, and samples consisting of variable sample

Pallavi Anand; Henry Elderfield

2005-01-01

49

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

PubMed

The synthesis, structure, and properties of the ordered double perovskites Sr2FeOsO6, Ca2FeOsO6, and SrCaFeOsO6 are reported. The latter two compounds have monoclinic P2?/n symmetry and a(-)a(-)b(+) tilting of the octahedra, while Sr2FeOsO6 is tetragonal with I4/m symmetry and a(0)a(0)c(-) tilting. Magnetic measurements indicate and neutron powder diffraction studies confirm that Ca2FeOsO6 is a ferrimagnet with a Curie temperature of 350 K. The ferrimagnetism is retained if half of the Ca(2+) ions are replaced with larger Sr(2+) ions to form SrCaFeOsO6 (T(C) = 210 K). This substitution reduces the degree of octahedral tilting, but unlike most perovskites, the magnetic ordering temperature decreases as the Fe-O-Os bond angles approach a linear geometry. In contrast, Sr2FeOsO6 orders antiferromagnetically, as previously reported. X-ray absorption spectroscopy confirms the assignment of Fe(III) and Os(V) oxidation states for all three compounds. In these insulating double perovskites, the magnetic ground state is governed by a competition between the four-bond Fe-O-Os-O-Fe antiferromagnetic superexchange coupling of Fe(III) ions and the two-bond Fe-O-Os antiferromagnetic superexchange coupling between neighboring Fe(III) and Os(V) ions. When the Fe-O-Os bonds are linear, as they are in the c direction in Sr2FeOsO6, the four-bond coupling between Fe(III) ions prevails. The competition shifts in favor of antiferromagnetic coupling of Fe(III) and Os(V) as the Fe-O-Os bond angles bend in response to chemical pressure. PMID:25025612

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

2014-08-01

50

Ca Sparks Do Not Explain all Ryanodine Receptor-Mediated SR Ca Leak in Mouse Ventricular Myocytes  

PubMed Central

Abstract Diastolic Ca leak from the sarcoplasmic reticulum (SR) of ventricular myocytes reduces the SR Ca content, stabilizing the activity of the SR Ca release channel ryanodine receptor for the next beat. SR Ca leak has been visualized globally using whole-cell fluorescence, or locally using confocal microscopy, but never both ways. When using confocal microscopy, leak is imaged as “Ca sparks,” which are fluorescent objects generated by the local reaction-diffusion of released Ca and cytosolic indicator. Here, we used confocal microscopy and simultaneously measured the global ryanodine-receptor-mediated leak rate (Jleak) and Ca sparks in intact mouse ventricular myocytes. We found that spark frequency and Jleak are correlated, as expected if both are manifestations of a common phenomenon. However, we also found that sparks explain approximately half of Jleak. Our strategy unmasks the presence of a subresolution (i.e., nonspark) release of potential physiological relevance. PMID:20483318

Santiago, Demetrio J.; Curran, Jerald W.; Bers, Donald M.; Lederer, W.J.; Stern, Michael D.; Ríos, Eduardo; Shannon, Thomas R.

2010-01-01

51

Two-photon transitions in Ca+, Sr+ and Ba+ ions  

NASA Astrophysics Data System (ADS)

Two-photon (2E1) decay rates are calculated for metastable 3dj states in Ca+, 4dj states in Sr+ and 5dj states in Ba+ to evaluate contributions of these transitions to the corresponding lifetimes. The calculations are carried out using the relativistic single-double method, where single and double excitations of Dirac-Fock wavefunctions are included to all orders of perturbation theory. We find that lowest-order calculations of the two-photon rates are strongly modified when correlation corrections are included.

Safronova, M. S.; Johnson, W. R.; Safronova, U. I.

2010-04-01

52

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

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

53

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

54

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

55

High precision measurements of Mg\\/Ca and Sr\\/Ca ratios in carbonates by cold plasma inductively coupled plasma quadrupole mass spectrometry  

Microsoft Academic Search

We present a new high precision analytical method for the determination of Mg\\/Ca and Sr\\/Ca ratios in carbonates using an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS) with a 650-W cold plasma technique and a desolvation introduction system. Signal intensities are detected in pulse-counting mode and Mg\\/Ca and Sr\\/Ca ratios are calculated directly from intensity ratios of 24Mg\\/43Ca and 86Sr\\/43Ca

Chuan-Chou Shen; Han-Yi Chiu; Hung-Wei Chiang; Mei-Fei Chu; Kuo-Yen Wei; Stephan Steinke; Min-Te Chen; Yu-Shih Lin; Li Lo

2007-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

57

BiCaSrCuO superconductors: Powder synthesis, wire fabrication and hot extrusion experiments  

Microsoft Academic Search

BiCaSrCuO and BiPbCaSrCuO powders were synthetized. Different research methods (SEM, EDS, XRF, XRD, DTA) were used to characterize the bulk specimen and wires. Resistance and current density were measured as a function of temperature. The ceramic products contained several phases. Lead containing specimen gave the best results and the synthesis was easily reproducible.

V. M. Polvi; K. J. Niemi

1989-01-01

58

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

59

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

PubMed

Proxies for past seawater chemistry, such as Mg/Ca and Sr/Ca ratios, provide a record of the dynamic exchanges of elements between the solid Earth, the atmosphere, and the hydrosphere and the evolving influence of life. We estimated past oceanic Mg/Ca and Sr/Ca ratios from suites of 1.6- to 170-million-year-old calcium carbonate veins that had precipitated from seawater-derived fluids in ocean ridge flank basalts. Our data indicate that before the Neogene, oceanic Mg/Ca and Sr/Ca ratios were lower than in the modern ocean. Decreased ocean spreading since the Cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early Tertiary may explain the recent rise in these ratios. PMID:20133522

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

2010-02-26

60

RBPO5 (R=Ca, Sr)-based storage phosphors for neutron detection  

Microsoft Academic Search

Storage characteristics of RBPO5 (R=Ca, Sr)-based phosphors have been investigated for neutron detection. To increase the photostimulated luminescence (PSL) yields of CaBPO5:Ce3+ and SrBPO5:Ce3+ phosphors, fluorine atoms were introduced and the molar ratio of the fluorine atoms was optimized for the PSL yields. In addition, the authors found that the PSL yields of SrBPO5:Eu2+ phosphors were significantly increased by adding

K. Sakasai; M. Katagiri; M. Matsubayashi; T. Nakamura; Y. Kondo

2005-01-01

61

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

SciTech Connect

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

Matsuda, M.; Katsumata, K. [Inst. of Physical and Chemical Research, Wako, Saitama (Japan); Shapiro, S.M.; Shirane, G. [Brookhaven National Lab., Upton, NY (United States). Physics Dept.

1998-08-20

62

Author's personal copy Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells (Arctica  

E-print Network

Keywords: Metal-to-calcium ratio Bivalve shell Vital effect Sea surface temperature Longevity The Sr. With increasing ontogenetic age and decreasing growth rate, a distinct trend toward increasing Sr/Ca (max. 5 explanations for these trends include a reduced capacity for element selection due to cell ageing, changing

Schöne, Bernd R.

63

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

NASA Astrophysics Data System (ADS)

The ratio of strontium to calcium (Sr/Ca) in coral skeletons is widely used to construct continuous, highly-resolved records of past sea-surface temperature (SST) variability. Typically, paleo-SST estimates are derived using Sr/Ca-SST functions created by regressing Sr/Ca from a single modern coral against instrumental SST. However, several studies have found that while coral Sr/Ca may strongly covary with SST, the absolute Sr/Ca values in corals growing on the same reef often differ significantly. As such, the uncertainties associated with coral-derived paleo-SST estimates based on the calibration approach outlined above are poorly constrained. To assess reproducibility of coral Sr/Ca and extent of intercolony variability at Palmyra Island (6°N, 162°W; Cobb et al., 2003; Nurhati et al., 2011), we measure mm- and ?m-scale Sr/Ca in four overlapping modern Porites cores. Conventional mm-scale Sr/Ca records from these modern cores are well correlated with each other (R = 0.65 to 0.68) and with SST (R = -0.73 to -0.85), but the absolute Sr/Ca values of these records exhibit baseline offsets of ×0.11mmol/mol (1?). Secondary ion mass spectrometry (SIMS) is used to generate 2-3 year long, weekly-resolved, Sr/Ca records from 3 overlapping modern coral segments. While the SIMS Sr/Ca analyses from each core exhibit relatively large point-to-point variations of ~0.17mmol/mol (1?), compared to ~0.06mmol/mol (1?) in mm-scale Sr/Ca, their monthly-scale variability resolves the annual SST cycles observed at Palmyra reasonably well (R = -0.46 to -0.64). Furthermore, the intercolony offsets observed in mm-scale Sr/Ca records are reproduced in the SIMS Sr/Ca records. These large offsets imply that paleo-SST estimates derived from a single fossil coral Sr/Ca dataset would be associated with uncertainties of ×1.4°C (1?). We build a coral Sr/Ca 'stack' for Palmyra Island using Sr/Ca records from the 4 modern cores. This composite Sr/Ca record is more strongly correlated with SST (R=-0.86), as intercolony variability is averaged out. In ongoing work, we apply this composite calibration to fossil coral Sr/Ca stacks, generated from multiple overlapping cores, from Palmyra Island to provide robust SST estimates for select intervals of the last millennium. References: Cobb, K. M., et al., Nature 424, 271-276 (2003). Nurhati, I. S., et al., Journal of Climate 24, 3294-3308 (2011).

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

2013-12-01

64

Otolith Sr:Ca and Ba:Ca may give inconsistent indications of estuarine habitat use for American eels ( Anguilla rostrata )  

Microsoft Academic Search

Temporal patterns in otolith Sr:Ca and Ba:Ca ratio values of American eels Anguilla rostrata from two sites in western Newfoundland gave insight into the use of freshwater and saline habitats. Mean Sr:Ca and Ba:Ca\\u000a values at the core zone did not differ between sites, indicative of a common oceanic origin. At the otolith edge, representing\\u000a continental life, both Sr:Ca and

Brian M. Jessop; Chia-Hui Wang; Wann-Nian Tzeng; Chen-Feng You; Jen-Chieh Shiao; Shih-Huan Lin

65

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

USGS Publications Warehouse

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

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

2004-01-01

66

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

67

Low lattice thermal conductivity suppressed by Sr-deficiency in Sr0.9Ca0.1Si2  

NASA Astrophysics Data System (ADS)

We present a study of the temperature-dependent electrical resistivity, Seebeck coefficient, and thermal conductivity in Sr0.9-?Ca0.1Si2 alloys to shed light on Sr-deficient effect on the thermoelectric performance, as characterized by the dimensionless thermoelectric figure-of-merit, ZT. It is found that the thermal conductivity is considerably reduced upon introducing Sr deficiency in Sr0.9Ca0.1Si2. In particular, a marked low lattice thermal conductivity of about 1.1 W/m-K at room temperature is achieved for Sr0.77Ca0.1Si2. Such a promising result leads to a relatively high ZT of 0.27 at room temperature for this material. Furthermore, with the extrapolation of thermoelectric parameters to high temperatures, a possible maximum ZT of about 0.52 at 850 K can be realistically estimated for Sr0.77Ca0.1Si2.

Lue, C. S.; Tseng, Y. S.; Huang, J. Y.; Hsieh, H. L.; Liao, H. Y.; Kuo, Y. K.

2013-07-01

68

Structures and self-activating photoluminescent properties of Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca) materials  

SciTech Connect

The synthesis, structures and photoluminescent properties of mixed oxyfluorides of the type Sr{sub 3-x}A{sub x}GaO{sub 4}F are compared to Sr{sub 3-x}A{sub x}AlO{sub 4}F (A=Ca, Ba) materials. In these compounds the F{sup -} and O{sup 2-} ions are ordered and located on two distinct crystallographic sites. When substituting Sr{sup 2+} by Ba{sup 2+} and Ca{sup 2+}, we find in Sr{sub 3-x}A{sub x}GaO{sub 4}F materials an ordering of the alkaline earth cations over the two crystallographic sites. The amount of Ba{sup 2+} ions that can be substituted into Sr{sub 3-x}A{sub x}GaO{sub 4}F is x{<=}1.2, which is slightly more than can be incorporated into the previously reported Al-analog Sr{sub 3-x}A{sub x}AlO{sub 4}F (x=1.0). Conversely, the amount of Ca{sup 2+} ions that can be substituted into Sr{sub 3-x}Ca{sub x}GaO{sub 4}F (x=0.3) is significantly less than in Sr{sub 3-x}Ca{sub x}AlO{sub 4}F (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. - Graphical abstract: TOC Statement The structures of the self-activating phosphors Sr{sub 3-x}A{sub x}MO{sub 4}F (A=Ba, Ca and M=Al, Ga) can be rationalized as alternating layers of bond compression and elongation, which impact the photoluminescence. Highlights: Black-Right-Pointing-Pointer Comparison of the structural changes in Sr{sub 3-x}A{sub x}AlO{sub 4}F and Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca) and its influence on the photoluminescence of these self-activating phosphors. Black-Right-Pointing-Pointer Analysis of the Global Instability Index of the Sr{sub 3-x}A{sub x}AlO{sub 4}F and Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca). Black-Right-Pointing-Pointer Comparison of the photoluminescence between the self-activating phosphors Sr{sub 3-x}A{sub x}AlO{sub 4}F and Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca).

Green, Robert [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States)] [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Vogt, Thomas, E-mail: tvogt@mailbox.sc.edu [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States)] [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States)

2012-10-15

69

Direct observation of substitutional Au atoms in SrTi O3  

NASA Astrophysics Data System (ADS)

Ion implantation and subsequent high-temperature annealing is an effective way to prepare metal nanoclusters dispersed in a dielectric for useful optical and electrical properties. However, there is very little understanding of the nucleation and growth process of these nanoclusters, their correlations with the sites of the implanted ions, and the behavior of defects (such as vacancies) generated during the ion-implantation process. Using high-angle annular dark-field imaging in aberration-corrected scanning transmission electron microscopy, we have directly observed that, at a dilute concentration, Au atoms implanted in SrTiO3 are in a substitutional lattice position for both Sr and Ti. The congregation of Au atoms by diffusion to a critical concentration leads to the nucleation of an Au lattice within the SrTiO3 . The Au nanocluster and SrTiO3 were found to maintain an orientation relationship of Au[001]//SrTiO3[001] and Au(100)//SrTiO3(100) , which corroborated the results of a first-principles total-energy calculation. The interface between the Au cluster and SrTiO3 was bridged by an O/Ti plane. The Au-O bond length was found to be 2.2Å , which is the same as the Au-O bond length in AuO. Furthermore, the atomic planes adjacent to the interface in both Au and SrTiO3 were found to be slightly stretched. The high concentration of vacancies generated during the Au implantation aggregated to form cavities in the SrTiO3 lattice, and were faceted mostly along the SrTiO3 {100} and (110) planes. The Au and vacancy clusters were spatially associated, indicating a strong interaction. Thus, the formation of cavities in Au-implanted materials indicates that the vacancy-clustering process prevails over the Frenkel-pair recombination.

Wang, C. M.; Shutthanandan, V.; Zhang, Y.; Thevuthasan, S.; Duscher, G.

2004-11-01

70

Stability of superconducting phases in Bi-Sr-Ca-Cu-O and the role of Pb doping  

SciTech Connect

The effects of heat treatment, partial oxygen pressure ({ital P}{sub O{sub 2}}), and Pb substitution on the oxygen nonstoichiometry and on the stability of superconducting phases in the Bi-Sr-Ca-Cu-O systems were examined. The Pb substitution promoted and stabilized the 110-K phase, with a reproducible zero resistance at 107 K achieved in Pb-substituted samples. {ital P}{sub O{sub 2}} hardly affects the superconducting transition temperature ({ital T}{sub {ital c}}) in Pb stabilized samples while a large variation of {ital T}{sub {ital c}} in Bi-Sr-Ca-Cu-O systems was observed by changing {ital P}{sub O{sub 2}} from 0.01 to 1.0 atm. The Cu{sup 3+} concentrations determined by a volumetric measurement technique vary little with {ital P}{sub O{sub 2}} over the range studied, so this ion is not critical for superconductivity in Bi-Sr-Ca-Cu-O, as it is in Y-Ba-Cu-O. The higher extra oxygen content obtained from iodometric titration is attributed to the oxygen associated with Bi{sup 5+} ions in Bi-O{sub 2} layers which are not measured by the volumetric method. Such ions result from cationic vacancies. In doped 2:2:2:3 compounds Pb{sup 4+} ions, most likely located in the Bi layers, lower the charge states of both Bi and Cu which are otherwise raised by cationic vacancies.

Dou, S.X.; Liu, H.K.; Bourdillon, A.J.; Kviz, M.; Tan, N.X.; Sorrell, C.C. (School of Materials Science and Engineering, The University of New South Wales, P.O. Box 1, Kensington, New South Wales, Australia 2033 (AU))

1989-09-01

71

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

72

Dynamic Regulation of SR Ca2+ Stores by STIM1 and Sarcolipin During Muscle Differentiation  

PubMed Central

During muscle development, the sarco/endoplasmic reticulum (SR/ER) undergoes remodeling to establish a specialized internal Ca2+ store for muscle contraction. We hypothesized that store operated Ca2+ entry (SOCE) is required to fill Ca2+ stores and is therefore critical to creating a mature SR/ER. Stromal interaction molecule 1 (STIM1) functions as a sensor of internal Ca2+ store content and an activator of SOCE channels. Myocytes lacking STIM1 display reduced SR Ca2+ content and altered expression of key SR proteins. Sarcolipin (SLN), an inhibitor of the SR calcium pump, was markedly increased in the muscle of mutant STIM1 mice. SLN opposes the actions of STIM1 by limiting SOCE, reducing SR Ca2+ content and delaying muscle differentiation. During mouse muscle development SLN is highly expressed in embryonic muscle, while the expression of STIM1 is upregulated postnatally. These results suggest that SOCE regulates SR/ER specialization and that SLN and STIM1 act in opposing fashions to govern SOCE during myogenesis. PMID:22411552

Seth, Malini; Li, Tianyu; Graham, Victoria; Burch, Jarrett; Finch, Elizabeth; Stiber, Jonathan A.; Rosenberg, Paul B.

2012-01-01

73

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

74

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

75

Characteristics (Delta44\\/40Ca, Mg\\/Ca and Sr\\/Ca) of Mytilus edulis and Arctica islandica Shells formed in a Temperature-Salinity Matrix  

Microsoft Academic Search

We investigated the influence of temperature (5°C to 15°C (A. islandica) resp. 25°C (M. edulis)) and salinity (15 to 35 psu) regimes on the calcium (Ca) isotope fractionation (Delta44\\/40Ca) and on Mg\\/Ca and Sr\\/Ca in cultured bivalves (Mytilus edulis and Arctica islandica). In an orthogonal 2-factorial (temperature vs. salinity) experiment, the bivalves were allowed to grow for 15 weeks under

C. Hiebenthal; A. Eisenhauer; M. Wahl

2008-01-01

76

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

77

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

78

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

NASA Astrophysics Data System (ADS)

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 and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of ±0.2°C and ±0.5°C, respectively. The analysis of foraminifera suggests an interlaboratory variance of about ±8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about ±2-3°C. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about ±1-2°C) and a bias (about 1°C) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.

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

2004-04-01

79

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

NASA Astrophysics Data System (ADS)

The major ions, strontium concentrations, ?[44/40]Ca, [87]Sr/^[86]Sr and ?[88/86]Sr ratios were measured in rainwater samples collected at an urban site in Guiyang, southwest China, over a period of one year. The pH values ranged between 4.2 and 8.6, with a volume-weighted mean (VWM) of 6.2. About 30% of the rainwater studied were acidic rain with pH values less than 5.6. Ca[2+] was the most dominant cation in rainwater samples and the VWM value was175?mol/L (21-1631 ?mol/L). SO[4][2-] was the predominant anion with VWM value of 137 ?mol/L (5-2019 ?mol/L), next was NO3- with VWM value of 26 ?mol/L(1.4-444 ?mol/L).Using Na as an indicator of marine origin, and Al for the terrestrial inputs, the proportions of sea salt and terrestrial elements were estimated from elemental ratios. More than 99% of Ca[2+] and 98% of SO[4][2-] in rainwater samples are non-sea-salt origin. The ?[44/40]Ca values of rainwater samples from Guiyang city, ranged from 0.51×0.18‰to 1.09×0.14‰, are very similar to the range of ?[44/40]Ca values in natural rivers. The [87]Sr/^[86]Sr ratios spanned a range of 0.70800 to 0.72742, with a mean value of 0.71080. The ?[88/86]Sr of rainwater samples ranged from 0.215×0.004‰ to 0.333×0.004‰, with a mean ?88/86Sr of rainwater is 0.296×0.01‰. The radiogenic strontium isotope data ([87]Sr/^[86]Sr) can infer the sources of Sr of the rainwater samples. The [87]Sr/^[86]Sr vs. Cl/Na suggests that the sources of rainwater samples come from dissolved carbonate minerals and anthropogenic inputs. The ?[44/40]Ca values and the stable Sr isotope (?[88/86]Sr) may be affected by biological processes.

Han, G.; Tang, Y.

2013-12-01

80

An intensity ratio calibration method for the accurate determination of Mg\\/Ca and Sr\\/Ca of marine carbonates by ICP-AES  

Microsoft Academic Search

An inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method for the accurate and precise simultaneous measurement of the Mg\\/Ca and Sr\\/Ca content of carbonates was established. While a precision of <0.3% (1? standard deviation (SD)) is easily obtainable for both Mg\\/Ca and Sr\\/Ca analysis, a Ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures. An alternative ratio

Stephanie de Villiers; Mervyn Greaves; Henry Elderfield

2002-01-01

81

An intensity ratio calibration method for the accurate determination of Mg\\/Ca and Sr\\/Ca of marine carbonates by ICP-AES  

Microsoft Academic Search

An inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method for the accurate and precise simultaneous measurement of the Mg\\/Ca and Sr\\/Ca content of carbonates was established. While a precision of <0.3% (1sigma standard deviation (SD)) is easily obtainable for both Mg\\/Ca and Sr\\/Ca analysis, a Ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures. An alternative ratio

Stephanie de Villiers; Mervyn Greaves; Henry Elderfield

2002-01-01

82

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

PubMed

Despite the important role of electromechanical alternans in cardiac arrhythmogenesis, its molecular origin is not well understood. The appearance of calcium alternans has often been associated to fluctuations in the sarcoplasmic reticulum (SR) Ca loading. However, cytosolic calcium alternans observed without concurrent oscillations in the SR Ca content suggests an alternative mechanism related to a dysfunction in the dynamics of the ryanodine receptor (RyR2). We have investigated the effect of SR release refractoriness in the appearance of alternans, using a mathematical model of a single human atrial cell, based on the model by Nygren et al. (30), where we modified the dynamics of the RyR2 and of SR Ca release. The genesis of calcium alternans was studied stimulating the cell for different periods and values of the RyR2 recovery time from inactivation. At fast rates cytosolic calcium alternans were obtained without concurrent SR Ca content fluctuations. A transition from regular response to alternans was also observed, changing the recovery time from inactivation of the RyR2. This transition was found to be hysteretic, so for a given set of parameters different responses were observed. We then studied the relevance of RyR2 refractoriness for the generation of alternans, reproducing the same protocols as in recent experiments. In particular, restitution of Ca release during alternans was studied with a S1S2 protocol, obtaining a different response if the S2 stimulation was given after a long or a short release. We show that the experimental results can be explained by RyR2 refractoriness, arising from a slow RyR2 recovery from inactivation, stressing the role of the RyR2 in the genesis of alternans. PMID:24610921

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

2014-06-01

83

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

USGS Publications Warehouse

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

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

1997-01-01

84

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

85

Asynchronous skeletal Mg\\/Ca, Sr\\/Ca, Ba\\/Ca and U\\/Ca seasonal cycles in a multi-decades of modern coral Porites from Nanwan, southern Taiwan  

Microsoft Academic Search

Variations of coral skeletal Mg, Sr, Ba, and U levels have widely been used for reconstructing local and regional thermal and hydrological conditions. We present decades of sub-monthly Mg\\/Ca, Sr\\/Ca, Ba\\/Ca and U\\/Ca records from a modern coral Porites core, drilled in Nanwan, southern Taiwan, analyzed on an ICP-MS, Finnigan Element II, with permil-level external precisions (2 sigma). Asynchroneity between

H. Chiang; Y. Chen; C. Shen

2008-01-01

86

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

Microsoft Academic Search

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

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

2006-01-01

87

Ca2+ and Sr2+ activation properties of skinned muscle fibres with different regulatory systems from crustacea and rat.  

PubMed

1. The contractile activation properties of long- (sarcomere length (SL) > 6 microns) and short- (SL < 4 microns) sarcomere fibres from the claw muscle of the yabby (freshwater crustacean, Cherax destructor) and the fast- and slow-twitch fibres from the rat have been investigated using single skinned muscle fibres activated in solutions containing Ca2+ or Sr2+ or both Ca2+ and Sr2+. 2. Sr2+ could not fully activate the contractile apparatus of either the long- or the short-sarcomere yabby preparations and the force-pSr curves for both fibre types were biphasic in shape. 3. The long- and short-sarcomere fibres from the yabby differed in their Ca(2+)- and Sr(2+)-activation properties. Thus the long-sarcomere fibres required a significantly lower [Ca2+] to produce 10% maximum force, had Ca(2+)-activation curves which were significantly shallower, and had a significantly higher ratio between maximum Sr(2+)- and maximum Ca(2+)-activated force than the short-sarcomere fibres. 4. Simultaneous activation with Ca2+ and Sr2+ showed a synergistic effect in the rat muscle fibres where Sr2+ could fully replace Ca2+ in activation. In contrast the results with the long- and short-sarcomere fibres from the yabby showed that in some functional states Sr2+ binds but cannot (or can only partially) activate the regulatory system while in others Sr2+ can fully replace Ca2+ in activating contraction. 5. The synergistic effect between Sr2+ and Ca2+ in mammalian muscle could be quantitatively explained if all regulatory sites involved in contractile activation have a similar value for the ratio between their affinity for Ca2+ and Sr2+. 6. Three distinguishable functional states (based on the fibre's ability to be activated by Sr2+ and Ca2+) were identified in the long-sarcomere fibres from the yabby: one where both Ca2+ and Sr2+ were able to activate contraction and had a relatively high sensitivity to Sr2+; one where both Ca2+ and Sr2+ were able to activate contraction but where the sensitivity to Sr2+ was lower and was more sensitive to a decrease in ionic strength; and one where Sr2+ binding to the regulatory system could not activate contraction. Equivalent states of the three described for the long-sarcomere fibres were also found in the short-sarcomere preparations. However, the short-sarcomere fibres had, in addition, a fourth state which was characterized by the ability of Sr2+ to activate contraction at reduced ionic strength but not at standard ionic strength.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:8331593

West, J M; Stephenson, D G

1993-03-01

88

Ca2+ and Sr2+ activation properties of skinned muscle fibres with different regulatory systems from crustacea and rat.  

PubMed Central

1. The contractile activation properties of long- (sarcomere length (SL) > 6 microns) and short- (SL < 4 microns) sarcomere fibres from the claw muscle of the yabby (freshwater crustacean, Cherax destructor) and the fast- and slow-twitch fibres from the rat have been investigated using single skinned muscle fibres activated in solutions containing Ca2+ or Sr2+ or both Ca2+ and Sr2+. 2. Sr2+ could not fully activate the contractile apparatus of either the long- or the short-sarcomere yabby preparations and the force-pSr curves for both fibre types were biphasic in shape. 3. The long- and short-sarcomere fibres from the yabby differed in their Ca(2+)- and Sr(2+)-activation properties. Thus the long-sarcomere fibres required a significantly lower [Ca2+] to produce 10% maximum force, had Ca(2+)-activation curves which were significantly shallower, and had a significantly higher ratio between maximum Sr(2+)- and maximum Ca(2+)-activated force than the short-sarcomere fibres. 4. Simultaneous activation with Ca2+ and Sr2+ showed a synergistic effect in the rat muscle fibres where Sr2+ could fully replace Ca2+ in activation. In contrast the results with the long- and short-sarcomere fibres from the yabby showed that in some functional states Sr2+ binds but cannot (or can only partially) activate the regulatory system while in others Sr2+ can fully replace Ca2+ in activating contraction. 5. The synergistic effect between Sr2+ and Ca2+ in mammalian muscle could be quantitatively explained if all regulatory sites involved in contractile activation have a similar value for the ratio between their affinity for Ca2+ and Sr2+. 6. Three distinguishable functional states (based on the fibre's ability to be activated by Sr2+ and Ca2+) were identified in the long-sarcomere fibres from the yabby: one where both Ca2+ and Sr2+ were able to activate contraction and had a relatively high sensitivity to Sr2+; one where both Ca2+ and Sr2+ were able to activate contraction but where the sensitivity to Sr2+ was lower and was more sensitive to a decrease in ionic strength; and one where Sr2+ binding to the regulatory system could not activate contraction. Equivalent states of the three described for the long-sarcomere fibres were also found in the short-sarcomere preparations. However, the short-sarcomere fibres had, in addition, a fourth state which was characterized by the ability of Sr2+ to activate contraction at reduced ionic strength but not at standard ionic strength.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:8331593

West, J M; Stephenson, D G

1993-01-01

89

Electron correlation in Sr(Ca)RuO3 by GWA and LSDA+U  

NASA Astrophysics Data System (ADS)

We have investigated the role of electron-electron correlation in SrRuO3 and CaRuO3 bulk structures. At first, the DOS of SrRuO3 and CaRuO3 is obtained using the full potential linearized augmented plane wave method by LSDA. We have then calculated the electronic structure, dielectric function, self-energy, and spectral function for the bulk SrRuO3 and CaRuO3 by GWA. The shifting of the Ru t 2 g orbitals, broadening in Ru valance bands, and also the enhancement in exchange splitting shows better agreement between the GWA many-body correction with the bulk experimental results. But, in spite of the many-body correction, the GWA results is not completely consistent with the PES experimental results due to small shifting of the Ru t 2 g bands and small broadening of the valance states specially in the Ca-based system. Inclusion of Coulomb correlation by LSDA+ U for both Sr- and Ca-based compounds shows significant difference in the results as compared with the LSDA and GWA calculations, and is consistent with the PES results. So, the discrepancy between the bulk ab-initio calculation and experiment is attributed to the surface effects which is not considered in the both LSDA and GWA bulk calculations. Due to the more distorted structure of CaRuO3, electron correlation at surface in the Ca-based system is more important than that in the Sr-based system. Hence, the bulk character of both SrRuO3 and CaRuO3 experimental results can be well described by GWA.

Hadipour, H.; Akhavan, M.

2011-11-01

90

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

91

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

PubMed Central

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

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

1990-01-01

92

Effect of crystalline quality and substitution on magnetic anisotropy of SrRuO3 thin films  

Microsoft Academic Search

Magnetic anisotropy of pure and substituted laser-ablated SrRuO3 and SrRu0.9Cr0.1O3 thin films has been studied by rotational magnetization experiments in a superconducting quantum interference device (SQUID) magnetometer. The magnetic easy axis for epitaxial (single domain) SrRuO3 and SrRu0.92O3 thin films lies in the (001) plane and is tilted away from the normal to the surface by 23°-26°. Its direction lies

S. Kolesnik; Y. Z. Yoo; O. Chmaissem; B. Dabrowski; T. Maxwell; C. W. Kimball; A. P. Genis

2006-01-01

93

(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

94

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

95

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

NASA Astrophysics Data System (ADS)

We present calcium stable isotope and strontium radiogenic isotope data for soils and sediments developed on volcanic and igneous rocks forming small catchments in the Massif Central (France). Measurements of 44/40Ca isotope ratios (44/40Ca measured by the double spike method on TIMS and normalized to the value for seawater Ca in delta units) in rocks, sediments and soils from silicate catchments (e.g. granite and basalts) together with 87Sr/86Sr isotope ratios permit an examination of the relationships of these isotope systematics during weathering of silicate rocks. We have analysed the granite, weathered granite (arene) and saprolite, sediment and soil overlying the granite on one hand and the basanite, sediment and soil overlying the basanite on the other. The main bedrock in the volcanic zone (e.g. Allanche catchment) is 11 to 2.5 Ma basanite (nephelinitic to leucitic basalts) having SiO2 between 41-45 wt. %, Na2O + K2O <5%, modal or normative nepheline or leucite and a ground mass of clinopyroxene and plagioclase. Surrounding rocks are feldspathic basalts having SiO2 between 46-49 wt. %, Na2O + K2O <5%, normative nepheline, hyperstene and olivine, with plagioclase as the main crystalline phase. The granite massif (e.g. Margeride, 332 ± 12Ma) consists of light and dark facies as a result of the fractional crystallisation of a crustal magma in a sub-horizontal laccolith, with leucogranites dated at 298±2 Ma intruding this granite. The average mineral composition is 37% quartz, 30% oligoclase, 23% K-feldspar and 10% biotite (light facies) and 31% quartz, 30% andesine, 20% K-feldspar and 19% biotite (dark facies). Sr isotope ratios in the arene, sediment and soil diverge strongly from those in the granite bedrock and are positively correlated with Rb/Sr ratios. The 87Sr/86Sr and Rb/Sr ratios both increase from the whole rock to the arene, reflecting the weathering of low 87Sr/86Sr, low-Rb/Sr minerals such as plagioclase and apatite. Sediments collected on a river bank have 87Sr/86Sr ratios greater than that of the arene with values increasing in the sediment from the surface down to soil. The 87Sr/86Sr vs. Rb/Sr variation observed in the volcanic area likewise confirms the weathering of low 87Sr/86Sr, low Rb/Sr phases in the bedrock, and there is a linear increase in 87Sr/86Sr and Rb/Sr ratios from those in the sediment up to the values observed in the soils. In the volcanic area, the basanite bedrock has 44/40Ca = -0.94 ± 0.05‰ (n = 7), while the soils and sediments have 44/40Ca of -0.75 to -1.13‰ and -0.79 to -1.01‰, respectively. These results suggest that Ca isotopes are not strongly fractionated during weathering of the basalt. The granite whole-rock has 44/40Ca of -1.29‰, while the soil and sediments have 44/40Ca of -1.93 to -2.07‰ and -1.98 to -2.81‰, respectively, with values decreasing as the Ca content decreases. The 44/40Ca ratios of arene, soil and sediment are similar to or less than that of K- feldspar, reflecting complete loss of the relatively heavy Ca from plagioclase and apatite during weathering. Comparison of the 44/40Ca and 87Sr/86Sr ratios further revealed the role of mineralogical assemblage in sediments and soils, particularly for the lesser 44/40Ca - greater 87Sr/86Sr samples, when compared to the bedrock.

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

2013-04-01

96

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

Microsoft Academic Search

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

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

2006-01-01

97

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

SciTech Connect

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

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

1984-01-01

98

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

99

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

100

Synthesis, Structure, and Properties of A14AlSb11 (A = Ca, Sr, Ba)  

Microsoft Academic Search

A14AlSb11 (A = Ca, Sr, Ba) is synthesized by reacting the elements in stoichiometric amounts at high temperature (1250°C). Single-crystal X-ray diffraction data (130 K: a = 17.493 (4) Å, c = 23.480 (8) Å (Sr); a = 18.293 (2) Å, c = 24.222 (9) Å (Ba)) were refined (tetragonal, I41\\/acd (142), Z = 8; R = 4.02%, Rw =

Stephanie L. Brock; Laura J. Weston; Marilyn M. Olmstead; Susan M. Kauzlarich

1993-01-01

101

Adiponectin regulates SR Ca(2+) cycling following ischemia/reperfusion via sphingosine 1-phosphate-CaMKII signaling in mice.  

PubMed

The adipocyte-secreted hormone adiponectin (APN) exerts protective effects on the heart under stress conditions. Recent studies have demonstrated that APN induces a marked Ca(2+) influx in skeletal muscle. However, whether APN modulates [Ca(2+)]i activity, especially [Ca(2+)]i transients in cardiomyocytes, is still unknown. This study was designed to determine whether APN modulates [Ca(2+)]i transients in cardiomyocytes. Adult male wild-type (WT) and APN knockout (APN KO) mice were subjected to myocardial ischemia/reperfusion (I/R, 30min/30min) injury. CaMKII-PLB phosphorylation and SR Ca(2+)-ATPase (SERCA2) activity were downregulated in I/R hearts of WT mice and further decreased in those of APN KO mice. Both the globular domain of APN and full-length APN significantly reversed the decrease in CaMKII-PLB phosphorylation and SERCA2 activity in WT and APN KO mice. Interestingly, compared with WT littermates, single myocytes isolated from APN KO mice had remarkably decreased [Ca(2+)]i transients, cell shortening, and a prolonged Ca(2+) decay rate. Further examination revealed that APN enhances SERCA2 activity via CaMKII-PLB signaling. In in vivo and in vitro experiments, both APN receptor 1/2 and S1P were necessary for the APN-stimulated CaMKII-PLB-SERCA2 activation. In addition, S1P activated CaMKII-PLB signaling in neonatal cardiomyocytes in a dose dependent manner and improved [Ca(2+)]i transients in APN KO myocytes via the S1P receptor (S1PR1/3). Further in vivo experiments revealed that pharmacological inhibition of S1PR1/3 and SERCA2 siRNA suppressed APN-mediated cardioprotection during I/R. These data demonstrate that S1P is a novel regulator of SERCA2 that activates CaMKII-PLB signaling and mediates APN-induced cardioprotection. PMID:24852843

Yan, Wenjun; Zhang, Fuyang; Zhang, Ronghuai; Zhang, Xing; Wang, Yanru; Zhou, Fen; Xia, Yunlong; Liu, Peilin; Gao, Chao; Wang, Han; Zhang, Lijian; Zhou, Jingjun; Gao, Feng; Gao, Erhe; Koch, Walter J; Wang, Haichang; Cheng, Heping; Qu, Yan; Tao, Ling

2014-09-01

102

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

103

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

104

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

105

Crystal growth and twinned crystal structure of Sr2CaWO6.  

PubMed

Single crystals of Sr(2)CaWO(6) have been prepared by sintering at high temperature. Powder samples were compressed into rods and heated up to 1953 K. This seems a promising new route for further studies of the structure and physical properties of double perovskites. The structural model of Sr(2)CaWO(6) includes a quantitative description of the twinning shown by the diffraction pattern that should be present in almost any single-crystal specimen for this type of compound. PMID:20305344

Madariaga, G; Faik, A; Breczewski, T; Igartua, J M

2010-04-01

106

Monthly Sr/Ca oscillations in symbiotic coral aragonite: Biological effects limiting the precision of the 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 report high spatial resolution ion microprobe analyses of 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. These extreme Sr/Ca variations, which likely result from metabolic changes synchronous with the lunar cycle, introduce variability in Sr/Ca measurements based on conventional sampling techniques 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 2oC. Aragonite precipitated during periods of reduced growth rate have relatively small biological effects. Thus, Sr/Ca-based temperature reconstructions from massive scleractinian corals, such as Porites, would 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 corals studied by us are confirmed in other Porites specimens from which long SST records have been derived on the basis of the Sr/Ca paleothermometer, it may invalidate conclusions based on inferred SST variations of less than 2oC. Our results also may help explain the notorious difficulties involved in obtaining an accurate and consistent calibration of the Sr/Ca vs. SST relationship.

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

2003-04-01

107

High-temperature resistivity and thermoelectric properties of coupled substituted Ca3Co2O6  

NASA Astrophysics Data System (ADS)

Polycrystalline samples of Ca3-xNaxCo2-xMnxO6 (x=0.0-0.5) have been prepared by the sol-gel cum combustion method using sucrose in order to investigate the effects of the coupled substitution of Na and Mn on Ca and Co sites on the transport properties of Ca3Co2O6(Co326). The products were characterized by Fourier transform infrared spectroscopy, powder x-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis and scanning electron microscopy. XRD patterns reveal the formation of single-phase products up to x=0.5. Coupled substitution increases the solubility of both Na and Mn on Ca and Co sites, respectively, in contrast to the limited solubility of Na and Mn (x=0.2) when separately substituted. TGA confirms the formation of the Ca3Co2O6 phase at temperatures ~720 °C. The grain size of the parent and substituted products is in the range 150-250 nm. Electrical resistivity and Seebeck coefficient were measured in the temperature range 300-800 K. Resistivity shows semiconducting behavior for all the compositions, particularly in the low-temperature regime. The Seebeck coefficient increases with temperature throughout the measured temperature range for all compositions. The maximum Seebeck coefficient (200 ?V K-1) is observed for x=0.5 at 825 K, and this composition may be optimal for high-temperature thermoelectric applications.

Senthilkumar, Meenakshisundaram; Vijayaraghavan, Rajagopalan

2009-01-01

108

Biologically Controlled Variations in Stable Isotope, Sr\\/Ca, Mg\\/Ca and U\\/Ca Ratios in Deep-Sea Corals  

Microsoft Academic Search

Recently both Sr\\/Ca and Mg\\/Ca ratios in coral and foraminifera carbonate have been proposed as temperature proxies. While empirical calibrations of these new tracers have been impressive, there are still large differences between the biogenic temperature slopes and those found inorganically in the lab. Because they grow in constant seawater conditions without photosynthetic symbionts, modern deep-sea corals provide a natural

J. F. Adkins

2002-01-01

109

Sr\\/Ca as a Potential Proxy of Subsurface Temperature Variability in C. secundum  

Microsoft Academic Search

There is increasing interest in the development of proxy records of oceanographic variability from intermediate and deep-water environments using deep-sea corals. Recent work has focused on isotopic and elemental ratios as proxies for temperature with limited success. Here we explore the potential uses of Mg\\/Ca and Sr\\/Ca in the same Corallium secundum sample using LA-ICP-MS. C. secundum samples where collected

E. Roark; S. J. Fallon; T. P. Guilderson; R. B. Dunbar; M. T. McCulloch

2009-01-01

110

Processing and characterization of thin films of the one layer phase in the Bi-Sr-Ca-Cu-O system; Ca solubility  

Microsoft Academic Search

This paper reports on thin films in the Bi-Sr-Ca-Cu-O system which have been synthesized from liquid ethyl hexanoate precursors by spin pyrolysis. The extension of the ternary one-layer phase field into the quaternary system has been determined through the replacement of Sr by Ca in single-phase, c-axis oriented thin films. A significant Ca solubility in the one-layer phase was found,

Steve J. Golden; Fred F. Lange; Kaushik J. Vaidya; Tamara E. Bloomer

1991-01-01

111

Processing and characterization of thin films of the one-layer phase in the Bi-Sr-Ca-Cu-O system - Ca solubility  

Microsoft Academic Search

Thin films in the Bi-Sr-Ca-Cu-O system have been synthesized from liquid ethyl hexanoate precursors by spin pyrolysis. The extension of the ternary one-year phase field into the quaternary system has been determined through the replacement of Sr by Ca in single-phase, c-axis oriented thin films. A significant Ca solubility in the one-layer phase was found, the maximum being around 0.4

Steve J. Golden; Fred F. Lange; Kaushik J. Vaidya; Tamara E. Bloomer

1991-01-01

112

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

Microsoft Academic Search

Deep-sea corals are a new tool in paleoceanography with the potential to provide century long records of deep ocean change at sub-decadal resolution. Complicating the reconstruction of past deep-sea temperatures, Mg\\/Ca and Sr\\/Ca paleothermometers in corals are also influenced by non-environmental factors, termed vital effects. To determine the magnitude, pattern and mechanism of vital effects we measure detailed collocated Sr\\/Ca

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

2007-01-01

113

Ferroelectricity in strained Ca0.5Sr0.5TiO3 from first principles  

E-print Network

We present a density-functional theory investigation of strained Ca[subscript 0.5]Sr[subscript 0.5]TiO[subscript 3] (CSTO). We have determined the structure and polarization for a number of arrangements of Ca and Sr in a ...

Halilov, Samed

114

Method of making Tl-Sr-Ca-Cu-Oxide superconductors comprising heating at elevated pressures in sealed container  

Microsoft Academic Search

High T(c) superconducting compounds are made by forming a reaction mixture of the oxides of Sr, Cu, Ca and Tl, compressing these into a hardened body, and placing the hardened body into a container. The container is then evacuated and sealed. The hardened body is heated under pressure until the oxides of Sr, Ca, Cu, and Tl react to form

William L. Lechter; Michael S. Osofsky; Earl S. Skelton; Louis E. Toth

1992-01-01

115

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

116

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 Mn 2+ 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

117

Strain relaxation in buried SrRuO3 layer in (Ca1-xSrx)(Zr1-xRux)O3\\/SrRuO3\\/SrTiO3 system  

Microsoft Academic Search

A novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1-xSrx)(Zr1-xRux)O3\\/SrRuO3\\/SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1-xSrx)(Zr1-xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of corrugations on the surface, due to the

Soo Gil Kim; Yudi Wang; I.-Wei Chen

2006-01-01

118

Strain relaxation in buried SrRuO3 layer in (Ca1?xSrx)(Zr1?xRux)O3?SrRuO3?SrTiO3 system  

Microsoft Academic Search

A novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1?xSrx)(Zr1?xRux)O3?SrRuO3?SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1?xSrx)(Zr1?xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of ?100? corrugations on the surface, due to

Soo Gil Kim; Yudi Wang; I-Wei Chen

2006-01-01

119

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

120

Annealing effects on the properties of BFe2As2 (B = Ca, Sr, Ba) superconducting parents.  

PubMed

The effects of thermal-annealing on the antiferromagnetic (TN) and structural (Ts) transition temperatures of ThCr2Si2-type BaFe2As2 and SrFe2As2 ('122') crystals are reported and compared to that of CaFe2As2. Although the shift in transition temperature for CaFe2As2 can be as high as 75 K, we find modest changes of ?6 K for BaFe2As2 and SrFe2As2. Such findings are based on the measurements of temperature dependence of electrical resistivity, magnetization, and heat capacity. Residual resistivity ratios show an improvement of crystal quality upon annealing for both BaFe2As2 and SrFe2As2. We confirm the pressure-like influence of annealing on the 122 crystals. PMID:24901039

Saparov, Bayrammurad; Sefat, Athena S

2014-10-28

121

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

DOEpatents

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

Hinks, David G. (Lemont, IL); Capone, II, Donald W. (Northbridge, MA)

1992-01-01

122

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

123

Ca2+ and Sr2+ entry induced Ca2+ release from the intracellular Ca2+ store in smooth muscle cells of rat portal vein.  

PubMed Central

1. Changes in cytosolic free Ca2+ concentration ([Ca2+]i) induced by membrane depolarizations were investigated using indo-1 microspectrofluorimetry in single patch-clamped smooth muscle cells of rat portal vein at room temperature (20-21 degrees C) and in the presence of 2 mM Ca2+. 2. During a 1 s depolarization from -50 to -30 mV [Ca2+]i rose, but, although the Ca2+ current was terminated by repolarization to -50 mV, [Ca2+]i continued to increase in a regenerative manner. The delay between the end of the voltage step and the peak of the [Ca2+]i rise was reduced by increasing the depolarization. 3. When a second identical depolarization was rapidly applied (8-13s) after the first one, it induced an identical Ca2+ current but a smaller increase in [Ca2+]i which started to decay upon repolarization. 4. A low concentration of caffeine (0.05 mM), applied to cells showing a small depolarization-induced [Ca2+]i transient which reached a peak at the end of the voltage step, produced an increase in amplitude and in duration of the [Ca2+]i rise without changing the amplitude of the depolarization-induced Ca2+ current. 5. The depolarization-induced [Ca2+]i rise was shortened and reduced in amplitude after noradrenaline- (NA 10 microM) or caffeine- (5 mM) induced release of Ca2+ store and when the patch pipette solution contained ryanodine (100 microM). Under these conditions, the depolarization-induced [Ca2+]i transient was maximal at the end of the voltage step and declined immediately when the membrane was repolarized at -50 mV. 6. Experiments were done by replacing extracellular Ca2+ by Sr2+. Depolarization-induced Sr2+ entry through voltage-dependent Ca2+ channels could evoke an increase in indo-1 fluorescence which occurred after the termination of the voltage step. This delayed component of fluorescence increase displayed properties similar to those of the regenerative [Ca2+]i rise recorded in the Ca(2+)-containing solution. 7. The inefficiency of the second of two successive depolarizations to produce the delayed component of [Ca2+]i rise was not due to the emptiness of the intracellular Ca2+ store since, under these conditions, caffeine was still able to induce a Ca2+ release. 8. It is concluded that depolarization-evoked Ca2+ or Sr2+ entry through voltage-dependent Ca2+ channels induced the release of Ca2+ from an intracellular store, which could occur in a regenerative manner, independent of the termination of the triggering current. PMID:8145155

Gregoire, G; Loirand, G; Pacaud, P

1993-01-01

124

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-SO 4 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 H 2S 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

125

Enhancement of Seebeck coefficient for SrO(SrTiO3)2 by Sm substitution: Crystal symmetry restoration of distorted TiO6 octahedra  

NASA Astrophysics Data System (ADS)

We found that Sm3+ substitution in SrO(SrTiO3)2 is effective in improving the Seebeck coefficient (S). The ?S? value increases notably with temperature, benefiting from an enhancement of the density of states (DOS) effective mass md* from ˜3m0 (300K)to˜7.5m0 (1000K), due to an improvement of the local symmetry of TiO6 octahedra, enhancing the degeneracy in the Ti 3d orbitals, which form the conduction band (CB), and also to an accompanying lattice expansion, which gives rise to a higher DOS at the bottom of the CB and, consequently, a larger md*.

Wang, Yifeng; Lee, Kyu Hyoung; Hyuga, Hideki; Kita, Hideki; Inaba, Katsuhiko; Ohta, Hiromichi; Koumoto, Kunihito

2007-12-01

126

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

PubMed Central

We have produced mice in which expression of the rat cardiac Na+/Ca2+ exchanger (NCX1) transgene was switched on when doxycycline was removed from the feed at 5 wk. At 8 to 10 wk, NCX1 expression in induced (Ind) mouse hearts was 2.5-fold higher but protein levels of sarco(endo)plasmic reticulum Ca2+-ATPase, ?1- and ?2-subunits of Na+-K+-ATPase, phospholamban, ryanodine receptor, calsequestrin, and unphosphorylated and phosphorylated phospholemman were unchanged compared with wild-type (WT) or noninduced (non-Ind) hearts. There was no cellular hypertrophy since WT, non-Ind, and Ind myocytes had similar whole cell membrane capacitance. In Ind myocytes, NCX1 current amplitude was ?42% higher, L-type Ca2+ current amplitude was unchanged, and action potential duration was prolonged compared with WT or non-Ind myocytes. Contraction and intracellular Ca2+ concentration ([Ca2+]i) transient amplitudes in Ind myocytes were lower at 0.6, not different at 1.8, and higher at 5.0 mM extracellular Ca2+ concentration ([Ca2+]o) compared with WT or non-Ind myocytes. Despite similar Ca2+ current amplitude and sarcoplasmic reticulum (SR) Ca2+ uptake, SR Ca2+ content at 5.0 mM [Ca2+]o was significantly higher in Ind compared with non-Ind myocytes, indicating that NCX1 directly contributed to SR Ca2+ loading. Echocardiography demonstrated that heart rate, left ventricular mass, ejection fraction, stroke volume, and cardiac output were similar among the three groups of animals. In vivo close-chest catheterization demonstrated similar contractility and relaxation among the three groups of mice, both at baseline and after stimulation with isoproterenol. We conclude that induced expression of NCX1 transgene resulted in altered [Ca2+]i homeostasis, myocyte contractility, and action potential morphology. In addition, heart failure did not occur 3 to 5 wk after NCX1 transgene was induced to be expressed at levels found in diseased hearts. PMID:19525383

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

2009-01-01

127

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

NASA Astrophysics Data System (ADS)

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 tests in excess of 355 µm (average Mg/Ca, 3.6 mmol/mol, Sr/Ca, 1.4 mmol/mol). Artificial dissolution of G. tumida tests led to a decrease in both Mg/Ca and Sr/Ca, but in G. sacculifer, there was no significant change in the ratios. Analyses by electron microprobe revealed that Mg/Ca of the inner (chamber) calcite in G. tumida tests was much higher than that of the calcite crust (keel), whereas Sr/Ca was only slightly elevated. There were no consistent spatial differences in either Mg/Ca or Sr/Ca for G. sacculifer tests. Dissolution in the oceans gives rise to the removal of the chamber calcite in G. tumida (about 30% of the total calcite), leaving the keel calcite. Although G. tumida is thought of as a dissolution-resistant form, the majority of Mg/Ca and Sr/Ca depletion (and chamber loss) occurs above the lysocline. It is also possible that much of the Mg-enriched gametogenic calcite has been lost by dissolution from G. sacculifer above 1600 m. Mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera. Calculations show that the saturation horizon for Mg-rich parts of tests may be elevated by several hundred meters compared with normal calcite.

Brown, Sarah J.; Elderfield, Henry

1996-10-01

128

Local atomic configuration and Auger valence electron spectra in BiSrCaCuO single crystals  

Microsoft Academic Search

Bi2Sr2CaCu2Oy (2212) and Ca-doped Bi2Sr2CuOy (2201) single crystals were systematically investigated by Auger valence electron spectroscopy (AVES). In AVES measurements on two kinds of crystals, a drastic difference was observed in the spectral shape of Ca[2p,3p,3p] reflecting a difference in spin-orbit splitting induced by local atomic configuration in the vicinity of Ca atoms. Furthermore, a Ca[2p,3p,4s] spectrum appeared in both

Y. Fujiwara; S. Hirata; M. Nishikubo; T. Kobayashi; H. Nakayama; H. Fujita

1991-01-01

129

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

130

Paradoxical SR Ca2+ release in guinea-pig cardiac myocytes after ?-adrenergic stimulation revealed by two-photon photolysis of caged Ca2+  

PubMed Central

In heart muscle the amplification and shaping of Ca2+ signals governing contraction are orchestrated by recruiting a variable number of Ca2+ sparks. Sparks reflect Ca2+ release from the sarcoplasmic reticulum (SR) via Ca2+ release channels (ryanodine receptors, RyRs). RyRs are activated by Ca2+ influx via L-type Ca2+ channels with a specific probability that may depend on regulatory mechanisms (e.g. ?-adrenergic stimulation) or diseased states (e.g. heart failure). Changes of RyR phosphorylation may be critical for both regulation and impaired function in disease. Using UV flash photolysis of caged Ca2+ and short applications of caffeine in guinea-pig ventricular myocytes, we found that Ca2+ release signals on the cellular level were largely governed by global SR content. During ?-adrenergic stimulation resting myocytes exhibited smaller SR Ca2+ release signals when activated by photolysis (62.3% of control), resulting from reduced SR Ca2+ content under these conditions (58.6% of control). In contrast, local signals triggered with diffraction limited two-photon photolysis displayed the opposite behaviour, exhibiting a larger Ca2+ release (164% of control) despite reduced global and local SR Ca2+ content. This apparent paradox implies changes of RyR open probabilities after ?-adrenergic stimulation, enhancing local regenerativity and reliability of Ca2+ signalling. Thus, our results underscore the importance of phosphorylation of RyRs (or of a related protein), as a regulatory physiological mechanism that may also provide new therapeutic avenues to recover impaired Ca2+ signalling during cardiac disease. PMID:15774509

Lindegger, Nicolas; Niggli, Ernst

2005-01-01

131

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

132

Strain Relaxation in Buried SrRuO3 Thin Film under a Biaxial Compression: CaZrO3\\/SrRuO3\\/SrTiO3 System  

Microsoft Academic Search

We have observed a novel strain relaxation phenomenon in the buried thin film that develops during the deposition of an overcoat layer. In SrRuO3\\/SrTiO3 (100) system, the SrRuO3 film is initially in biaxial compression, but the strain relaxation develops after a CaZrO3 overcoat is deposited, manifested as misfit dislocations at the CaZrO3\\/SrRuO3 interface and a cross-hatch pattern of surface corrugation

Soo Gil Kim; Yudi Wang; I.-Wei Chen

2006-01-01

133

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

NASA Astrophysics Data System (ADS)

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

Somaily, Hamoud H.

134

Synthesis of Superconducting Bi-Sr-Ca-Cu-O Oxides via Mechanical Alloying  

NASA Astrophysics Data System (ADS)

Bi-Sr-Ca-Cu-O superconductors have been prepared from the constituent pure metals by mechanical alloying in air and succeeding sintering at high temperatures in flowing oxygen. X-ray patterns from the milled powders indicate that the dissolution of excess Cu and Bi in the Bi-Sr-Ca-Cu matrix occurs progressively with milling. However, a prolonged milling resulted in amorphous-like diffraction patterns with the first peak centered around 30°. The particle size rapidly asymptotes to a fixed value near 30 h milling. The X-ray patterns of the sintered materials are in good agreement with those of the orthorhombic structure reported in the superconducting Bi-base oxides. The low Tc phase in the Bi-base oxides was identified from the resistivity and susceptibility measurements. The superconducting temperature appears to be sensitive to the milling conditions.

Whang, S. H.; Li, Z. X.

135

Anisotropic Dirac electronic structures of AMnBi2 (A=Sr,Ca)  

NASA Astrophysics Data System (ADS)

Low-energy electronic structures in AMnBi2 (A=alkaline earths) are investigated using a first-principles calculation and a tight binding method. An anisotropic Dirac dispersion is induced by the checkerboard arrangement of A atoms above and below the Bi square net in AMnBi2. SrMnBi2 and CaMnBi2 have a different kind of Dirac dispersion due to the different stacking of nearby A layers, where each Sr (Ca) of one side appears at the coincident (staggered) xy position of the same element at the other side. Using the tight binding analysis, we reveal the chirality of the anisotropic Dirac electrons as well as the sizable spin-orbit coupling effect in the Bi square net. We suggest that the Bi square net provides a platform for the interplay between anisotropic Dirac electrons and the neighboring environment such as magnetism and structural changes.

Lee, Geunsik; Farhan, Muhammad A.; Kim, Jun Sung; Shim, Ji Hoon

2013-06-01

136

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

137

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

138

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

PubMed

In the myometrium SR Ca(2+) depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca(2+) sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca(2+)-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca(2+) transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 ?M), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca(2+)]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca(2+) spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca(2+) and depolarization continued a point was reached when electrical and Ca(2+) spikes and phasic contractions ceased, and a maintained, tonic force and Ca(2+) was produced. Lanthanum, a non-selective blocker of store-operated Ca(2+) entry, but not the L-type Ca(2+) channel blocker nifedipine (1-10 ?M), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca(2+) depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca(2+) release is coupled to marked Ca(2+) entry, via store operated Ca(2+) channels, leading to depolarization and enhanced electrical and mechanical activity. PMID:25084623

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

2014-09-01

139

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

PubMed Central

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

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

2014-01-01

140

Determination of the complete stoichiometry of Bi-Pb-Sr-Ca-Cu-O-superconductors  

Microsoft Academic Search

A convenient analytical method based on complexometric and iodometric titration for determining the complete stoichiometry of Bi-Pb-Sr-Ca-Cu-O-superconductors (PBSCCO) has been developed. It is shown that the individual contents of Cu3+, Bi5+, Pb4+ are not required for calculating the oxygen content of such materials. It turned out that the lead content and the oxygen content of sintered samples are much lower

S. Scheurell; E. Kemnitz; G. N. Maso; S. Y. Kasin; S. W. Naumov; Y. N. Badun

1991-01-01

141

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

Microsoft Academic Search

Taking advantage of the availability of a continuous sea surface temperature (SST) record at Kenting, southern Taiwan, we have carried out a calibration of D[Sr\\/Ca]-SST (D: distribution coefficient) relationships for Porites lobata and P. lutea. Between 22°C ? 28°C, the best fitting linear relationships for the two species agree within their respective errors with a maximum deviation less than 0.3°C.

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

1996-01-01

142

Patterning polymer metal precursors for high temperature superconducting Bi-Sr-Ca-Cu-O-films  

SciTech Connect

Bi-Sr-Ca-Cu-O HTSC thin films were prepared from polymer metal precursors in a special annealing procedure. The precursor films can be patterned before the annealing process in which the superconducting phase is generated. The authors have investigated the patterning of precursor films by UV radiation, and the thermal degradation process by thermogravimetry and mass spectroscopy. The HTSC films were characterized by X-ray diffraction and electrical resistivity measurements.

von Lampe, I.; Goetze, S.; Zygalsky, F. [Institut fuer Anorganische und Analytische Chemie, Berlin (Germany)

1996-12-01

143

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

144

Inhibition of transport of 47Ca and 85Sr by lanthanum in canine cortical bone  

PubMed Central

Deposition of 85Sr and 47Ca and blood flow (measured by iodoantipyrine washout) were determined in the tibial cortex of adult dogs after injection of graded doses of lanthanum chloride (LaCl3) and potassium cyanide (KCN) into the right tibial nutrient artery. Deposition of 85Sr and 47Ca, expressed in milliliters per gram of cortical bone in 10 min, was decreased after injections of lanthanum, 0.045 ± 0.008 (mean ± SE) compared to 0.097 ± 0.01 in control experiments (P < 0.005). Blood flow was unchanged. Injection of KCN did not affect the mean value of uptake of mineral (0.108 ± 0.01 vs. 0.097 ± 0.01) over the whole range of KCN dosage. Blood flow tended to be slightly higher with lower doses of KCN. These data support the concept of a transport system in bone for bone-seeking isotopes such as 85Sr and 47Ca. PMID:4811382

Paradis, Gaston R.; Bassingthwaighte, James B.; Kelly, Patrick J.

2010-01-01

145

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

DOEpatents

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

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

1992-12-22

146

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

147

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

148

(Sr,Na)(Zn,Mn)2As2: A diluted ferromagnetic semiconductor with the hexagonal CaAl2Si2 type structure  

NASA Astrophysics Data System (ADS)

A new diluted ferromagnetic semiconductor (Sr,Na)(Zn,Mn)2As2 is reported, in which charge and spin doping are decoupled via Sr/Na and Zn/Mn substitutions, respectively, being distinguished from classic (Ga,Mn)As, where charge and spin doping are simultaneously integrated. Different from the recently reported ferromagnetic (Ba,K)(Zn,Mn)2As2, this material crystallizes into the hexagonal CaAl2Si2 type structure. Ferromagnetism with a Curie temperature up to 20 K has been observed from magnetization. The muon spin relaxation measurements suggest that the exchange interaction between Mn moments of this new system could be different from the earlier diluted magnetic semiconductors (DMS) systems. This system provides an important means for studying ferromagnetism in DMS.

Chen, B. J.; Zhao, K.; Deng, Z.; Han, W.; Zhu, J. L.; Wang, X. C.; Liu, Q. Q.; Frandsen, B.; Liu, L.; Cheung, S.; Ning, F. L.; Munsie, T. J. S.; Medina, T.; Luke, G. M.; Carl, J. P.; Munevar, J.; Uemura, Y. J.; Jin, C. Q.

2014-10-01

149

Study of the optical conductivity of Bi 2Sr 2CaCu 2O 8+ ? material  

NASA Astrophysics Data System (ADS)

We studied the optical conductivity of the Bi 2Sr 2CaCu 2O 8+ ? materials in the normal state as well as in the superconducting state as a function of temperature and doping within the rotating antiferromagnetism theory (RAFT) using the Marginal Fermi Liquid (MFL) ansatz for self-energy. The optical conductivity is calculated using Nambu formalism and Kubo’s formula. Experimental data for Bi 2Sr 2CaCu 2O 8+ ? are discussed.

Bhuiyan, E. H.; Presenza-Pitman, G.; Azzouz, M.

2012-02-01

150

Properties of Bi-Pb-Sr-Ca-Cu-O Glass-Ceramic Fibers Formed by Glass-Drawing Method  

Microsoft Academic Search

Flexible Bi-Pb-Sr-Ca-Cu-O glass fibers were prepared by the glass-drawing method. They showed superconducting properties after crystallization by heat treatment. The Tc and Jc values of the fibers were very sensitive to starting compositions and heat treatment conditions. The fiber with the starting composition of Bi2.1Pb0.9Sr2Ca2Cu3Oy showed superconductivity with a Jc=1480 A\\/cm2 (77 K, zero magnetic field).

Masashi Onishi; Minoru Watanabe

1991-01-01

151

Identifying weathering sources and processes in an outlet glacier of the Greenland Ice Sheet using Ca and Sr isotope ratios  

NASA Astrophysics Data System (ADS)

Chemical and isotope data (?40Ca, ?44/42Ca, 87Sr/86Sr, ?18O) of river water samples were collected twice daily for 28 days in 2009 from the outlet river of Leverett Glacier, West Greenland. The water chemistry data was combined with detailed geochemical analysis and petrography of bulk rock, mineral separates and sediment samples in order to constrain the mineral weathering sources to the river. The average isotopic compositions measured in the river, with 2SD of all the values measured, were ?40Ca = +4.0 ± 1.4, ?44/42Ca = +0.60 ± 0.10‰ and 87Sr/86Sr = 0.74243 ± 0.00327. Based on changes in bulk meltwater discharge, the hydrochemical data was divided into three hydrological periods. The first period was marked by the tail-end of an outburst event and was characterised by water with decreasing suspended sediment concentrations (SSC), ion concentrations and pH. During the second hydrological period, discharge increased whilst 87Sr/86Sr decreased from 0.74550 to 0.74164. Based on binary mixing diagrams using 87Sr/86Sr with Na/Sr, Ca/Sr and ?40Ca, this is interpreted to reflect an increase in reactive mineral weathering, in particular epidote, as the water residence time decreases. The decrease in water residence time is a result of the evolution from a distributed (long water residence time) to a channelised (short water residence time) subglacial drainage network. The third hydrological period was defined as the period when overall discharge was decreasing. This hydrological period was marked by prominent diurnal cycles in discharge. During this period, significant correlations between ?44/42Ca and SSC and ?18O were observed which are suggestive of fractionation during adsorption. This study demonstrates the potential of radiogenic Ca to both identify temporally changing mineral sources in conjunction with 87Sr/86Sr values and to separate source and fractionation effects in ?44/42Ca values.

Hindshaw, Ruth S.; Rickli, Jörg; Leuthold, Julien; Wadham, Jemma; Bourdon, Bernard

2014-11-01

152

Role of oxygen vacancies in room-temperature ferromagnetism in cobalt-substituted SrTiO3  

NASA Astrophysics Data System (ADS)

Ferromagnetic insulating behavior has recently been demonstrated in cobalt-substituted SrTiO3 at room temperature [Posadas et al., Phys. Rev. B 87, 144422 (2013), 10.1103/PhysRevB.87.144422]. Experimentally it was found that a well-defined hysteresis loop only occurs at high Co concentrations of 30%-40%. X-ray photoelectron spectroscopy also indicated that Co substitutes for Ti with Co being in high-spin +2 oxidation state. In this work we employ density-functional theory to explain the experimentally observed properties of cobalt-substituted SrTiO3. We examine in detail the role of oxygen vacancy (OV) defects and their formation of defect complexes with the Co ions as the origin of the ferromagnetic insulating behavior. Our first-principles thermodynamic calculations indicate that OV defects are much more likely to occur next to Co atoms where their formation energies could be reduced by as much as 1.28 eV compared to that in bulk SrTiO3. We also find that Co in these Co-OV complexes occurs in the high-spin state in agreement with core level spectroscopy, and identify a linear arrangement of the Co-OV defect complexes to be the most energetically favorable structure. These defect complexes are also shown to interact ferromagnetically and that their magnetic interaction is found to be short ranged, consistent with the relatively high Co concentrations needed experimentally for ferromagnetism to be observed in cobalt-substituted SrTiO3.

Mitra, Chandrima; Lin, Chungwei; Posadas, Agham B.; Demkov, Alexander A.

2014-09-01

153

Improvement of Surface Morphology of Bi2Sr2CaCu2Ox Thin Films by using Nano-structured SrTiO3 Thin Films  

Microsoft Academic Search

Surface morphology of Bi2Sr2CaCu2Ox (BSCCO) thin films prepared by metalorganic decomposition (MOD) method is successfully improved by using nano-structured SrTiO3 (STO) buffer layer prepared by MOD method. The nano-structured STO thin films were obtained by 2-step thermal treatment at 870C for 2 hours followed by high temperature of 1000C in O2 atmosphere for 1 hour. In the case of BSCCO

Takayuki Ishibashi; Tetsuya Kawata; Shuta Yufune; Katsuaki Sato

2006-01-01

154

Mg\\/Ca, Sr\\/Ca and U\\/Ca ratios of a porites coral from Sanya Bay, Hainan Island, South China Sea and their relationships to sea surface temperature  

Microsoft Academic Search

High-resolution Mg\\/Ca, Sr\\/Ca and U\\/Ca ratios are reported in the skeleton of Porites sp. collected from Sanya Bay, on the south coast of the Hainan Island, China using inductively coupled plasma mass spectrometry combined with isotope dilution technique (ICP–MS–ID). The coralline Mg\\/Ca ratios covary with sea-surface temperatures (SST) for the 10year interval, giving the relationship between Mg\\/Ca and SST as

Gangjian Wei; Min Sun; Xianhua Li; Baofu Nie

2000-01-01

155

Microdistribution of Mg\\/Ca, Sr\\/Ca, and Ba\\/Ca ratios in Pulleniatina obliquiloculata test by using a NanoSIMS: Implication for the vital effect mechanism  

Microsoft Academic Search

The Mg\\/Ca ratio within foraminiferal calcareous tests (shells) is widely used to reconstruct past seawater temperature. However, recent studies reported that the organic components within a test affect the Mg\\/Ca distribution. In this study, we have measured the Mg\\/Ca, Sr\\/Ca, and Ba\\/Ca ratios within the planktonic foraminifera Pulleniatina obliquiloculata by using a NanoSIMS (secondary ion mass spectrometer (SIMS)), which has

Daisuke Kunioka; Kotaro Shirai; Naoto Takahata; Yuji Sano; Takashi Toyofuku; Yurika Ujiie

2006-01-01

156

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

SciTech Connect

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

Poddar, Asok; Mazumdar, Chandan, E-mail: chandan.mazumdar@saha.ac.in

2011-05-15

157

Metal (Ca, Ba, Sr, Pb) heptafluorotantalates(V): Synthesis, Raman spectra and crystal structures  

NASA Astrophysics Data System (ADS)

MTaF 7 (M = Ca, Sr, Ba, Pb) were prepared by the reaction of MF 2 + Ta + F 2 (Ca, Sr, Ba) or MF 2 + TaF 5 in anhydrous HF. CaTaF 7 crystallizes in a monoclinic P2 1/ a space group, a = 9.793(3) Å, b = 11.608(3) Å, c = 13.359(4) Å, ? = 90.539(13)°, V = 1518.5(7) Å 3. All Ta atoms possess distorted pentagonal-bipyramidal environment with Ta-F distances of 1.878(14)-2.044(13) Å. Three crystallographically independent Ca atoms have coordination number 8. Ca-F distances lie in the range of 2.239(16)-2.836(17) Å. Each Ca 2+ and TaF 72- moiety is bonded to 6 counter-ions. BaTaF 7 crystallizes in a cubic system, space group Pa3¯,a = 9.9009(3)Å, V = 970.56(5) Å 3. Coordination sphere around Ta atom is mono-capped trigonal prism with a Ta-F distance of 1.916(5)-2.004(5) Å. Two crystallographically independent barium atoms have different coordination numbers: for Ba1 C.N. is 12 with Ba1-F distances of 6 × 2.761(5) Å and 6 × 2.858(5) Å, for Ba2 C.N. is 14 with Ba2-F bond lengths 6 × 2.718(5), 2 × 2.814(8) and 6 × 3.236(5) Å. Ba 2+ and TaF 72- moieties are bonded to 8 neighbors. Isostructural PbTaF 7 and SrTaF 7 appear to be monoclinic, space group P2 1/ m, a = 4.8657(11) Å, b = 7.2298(16) Å, c = 6.7370(16) Å, ? = 93.932(13)°, V = 236.44(9) Å 3 for PbTaF 7, and a = 4.875(3) Å, b = 7.196(4) Å, c = 6.7218(13) Å, ? = 94.265(10), V = 235.2(2) Å for SrTaF 7. Tantalum coordination polyhedron may be described as a distorted mono-capped trigonal prism with the capping atom located on one of the rectangular faces with Ta-F distances of 1.868(3)-1.982(3) Å (PbTaF 7) and 1.908(16)-2.019(12) Å (SrTaF 7). Lead (or strontium) atoms are 9-coordinated and may be viewed as strongly distorted tri-capped trigonal prism, Pb-F 2.438(4)-2.669(3) Å, Sr-F 2.501(19)-2.860(19) Å. Each cation is connected to 8 anions.

Buni?, Tina; Tramšek, Melita; Goreshnik, Evgeny; Žemva, Boris

2007-01-01

158

Multiple Magnetic Transitions and Magnetocaloric Effect in (La,Pr,M)MnO3 (M = Ca, Sr, Ba) Mixed Phase Manganites  

NASA Astrophysics Data System (ADS)

The manganite compound (La,Pr,Ca)MnO3 is a well-studied system that is known to exhibit a complex phase diagram featuring ``strain liquid'' and ``strain glass'' regions in combination with competing ferromagnetic (FM) and charge-ordered antiferromagnetic (CO/AFM) phases. The balance of these phases is sensitive to various perturbations including magnetic and electric field, strain, bandwidth, and A-site cation disorder. The A-site disorder and bandwidth of this compound can be tuned through the replacement of Ca with larger Sr and Ba ions. We report here a systematic study of the influence of cation substitution on the magnetic and magnetocaloric properties of La0.35Pr0.275M0.375MnO3 (M = Ca, Sr, Ba). Structural properties, including lattice parameters and Mn--O--Mn bond angles, were determined from X-ray diffraction patterns. DC magnetometry studies reveal multiple magnetic transitions in each sample which are probed by magnetocaloric effect (MCE) and transverse susceptibility (TS) experiments. Increasing the average A-site cationic radius is found to strongly impact the magnetic properties and phase behavior of the system.

Lampen, P. J.; Bingham, N. S.; Phan, M. H.; Srikanth, H. S.; Phan, T. L.; Yu, S. C.; Cheong, S. W.

2012-02-01

159

Flexible and superconducting properties of sintered Bi-Pb-Sr-Ca-Cu-O tapes  

Microsoft Academic Search

Flexible Bi(1.81)Pb(0.43)Sr(1.71)Ca(2.14)Cu3O(x) superconducting tapes have been fabricated by the powder-in-silver tubing technique followed by appropriate sintering. The sintered tape, Jc greater than 10,000 A\\/sq cm at 77 K, can be bent into an arc with a 0.9-cm radius of curvature without deteriorating the transport properties at liquid nitrogen temperature. This indicates that the superconducting a-b plane of the Bi-based tape

K. Chen; L. Horng; H. S. Koo; C. Y. Shei; L. P. Wang; C. Chiang; T. J. Yang; W. H. Lee; P. T. Wu

1991-01-01

160

Phase evolution and superconductivity emergence in repetitively annealed Bi-Sr-Ca-Cu-O thin films  

NASA Astrophysics Data System (ADS)

Bi(Pb)-Sr-Ca-Cu-O superconducting thin films on MgO (100) substrates have been made by laser deposition in combination with repetitive post-annealing treatments. The films of nominal composition (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+? were deposited at 400°C and then heated in air at a rate of 75-80°C/min, held at 845-847°C for 10 min, quenched to 600°C at a rate of 80°C/ min, and slowly cooled at a rate of 3.3°C/min to room temperature. The Bi 2Sr 2CaCu 2O 8+? (2212) phase was found to crystallize first in these as-deposited amorphous films, whereas the (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+? (2223) phase was grown in large quantities by repeating the annealing cycle. With this protocol, the 2223 phase is developed more effectively than that observed in the long period of annealing, and the formation of pinholes on the surface is significantly reduced. Surface morphologies examined by scanning electron microscopy (SEM) are improved for films repetitively annealed under reduced pressure conditions. The results of magnetic susceptibility measurements on these films correspond well with the phase behavior seen by X-ray diffractometry (XRD) analyses. The transport critical current densities, Tc, of the film are 9.0×10 5 and 5.5×10 4 A/cm 2 at 5 and 40 K, respectively. The magnetization critical current densities derived from M( H) data at 6 K are two orders of magnitude higher in the orientation of H? c-axis than of H? c-axis. As a preliminary study, XRD line-broadening analysis was performed to investigate the effects of lattice strain and crystallite size in the set of films that were annealed at various temperatures for 3-6 h. The microstrain values are in the range of 10 -4-10 -3, and the crystallite sizes in films obtained for the 2212 and 2223 phases depend on annealing time, temperature, and cooling rate. Microstrain associated with the 2223 phase is more sensitive to annealing parameters. These results suggest that XRD line-broadening analysis may be a valuable method to study the growth mechanism and material properties of the repetitively annealed films.

Kung, P. J.; Peterson, E. J.; Flynn, E. R.; Mombourquette, C. B.; Foltyn, S. R.; Brainard, R. J.

1994-04-01

161

Quantum creep in a Bi 2Sr 2CaCu 2O x single crystal  

NASA Astrophysics Data System (ADS)

According to the theory of quantum collective creep (QCC) of Blatter, Geshkenbein and Vinokur, the quantum creep rate is enhanced in superconductors with short coherence length ?, high normal state resistivity ? n, weak collective pinning and strong anisotropy. We have investigated quantum tunneling in a single crystal of the highly anisotropic Bi 2Sr 2CaCu 2O x. In the configuration with the external field parallel to the c-axis we measure tunneling rates at T = 7 mK which are a factor of 4 to 5 higher than our previous measurements in Y 1Ba 2Cu 4O y.

Aupke, K.; Teruzzi, T.; Visani, P.; Amann, A.; Mota, A. C.; Zavaritsky, V. N.

1993-04-01

162

Spectroscopy of LiCa and RbSr Molecules on Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

We report on the investigation of mixed alkali metal (Ak) - alkaline earth metal (Ake) molecules on the surface of helium nanodroplets (He_{N}). These molecules have recently attracted considerable attention as candidates for the formation of ultracold molecules with a magnetic and an electronic dipole moment. In our experiments, LiCa and RbSr molecules are formed in a sequential pick-up process in their X^{2}?^{+} ground state and cool down rapidly to the droplet temperature of 0.38 K. Excitation spectra of LiCa and RbSr were recorded by using resonance enhanced multi-photon ionization time-of-flight (REMPI-TOF) spectroscopy and laser induced fluorescence (LIF) spectroscopy. On the helium droplet, vibronic transitions in Ak-Ake molecules are broadened and show a characteristic asymmetric peak form, which is caused by the interaction between the molecule and the superfluid He_{N} environment. For the lower electronic transitions in LiCa and RbSr progressions of vibrational bands excited from the X^{2}?^{+} (?'' = 0) state are observed. The LiCa spectra can be compared to molecular beam experiments, which enables the assignment of three band systems near 15260 cm^{-1}, 19300 cm^{-1} and 22120 cm^{-1} as ^{2}?^{+}, ^{2}?_{?} and ^{2}? band, respectively. In the RbSr excitation spectrum we observe a vibrationally resolved band system near 14020 cm^{-1}. Upon electronic excitation, a fraction of the molecules desorb from the droplet surface and dispersed fluorescence spectra allow to study the X^{2}?^{+} ground state and excited states of free Ak-Ake molecules. H. Hara, Y. Takasu, Y. Yamaoka, J.M. Doyle, Y. Takahashi, Phys. Rev. Lett. 106, 205304 (2011) C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) L. M. Russon, G. K. Rothschopf, M. D. Morse, A. I. Boldyrev, J. Simons, J. Chem. Phys. 109, 6655-6665 (1998)

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

2013-06-01

163

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

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

164

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

165

Superconducting and electrical properties of Ca-substituted YBa 2Cu 3O 6  

NASA Astrophysics Data System (ADS)

Superconducting properties of sintered Y1- xCaxBa2Cu3O6 (0 < x ? 0.31)have been investigated. Measurements of resistivity, Hall effect and X-ray diffraction as a function of Ca content x were carried out. It was found that Y 1- xCa xBa 2Cu 3O 6 becomes superconducting above x ? ? 0.2, as had been reported previously, and Tc shows a maximum at x ? 0.26 and declines at larger x. By increasing the Ca content, the carrier number in the CuO 2 plane increased suddenly in the range x ? 0.2, where samples were superconducting. A part of the carrier introduced by Ca substitution, however, was localized at Cu sites forming CuO chains. About 40% of the doped carrierr was conductive in x < ? 0.2 and ? 80% was conductive in x ? ? 0.2 at room temperature and these results agree fairly well with the analysis for the results of the iodometric titration measurement. Finally, we pointed out that slight oxidation for these samples brought about the release of carrier localization at low temperatures and a remarkable rise of Tc, indicating the crucial importance of the CuO chain or orthorhombicity for high Tc in YBa 2Cu 3O 6+ z.

Watanabe, T.; Fujiwara, M.; Suzuki, N.

1995-02-01

166

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. PMID:22449852

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

2013-01-01

167

Magnetic frustration in (LaA)CoNbO{sub 6} (A=Ca, Sr, and Ba) double perovskites  

SciTech Connect

The crystal and magnetic structures of the (LaA)CoNbO{sub 6} (A=Ca, Sr, and Ba) double perovskites have been investigated. The A=Ca and Sr compounds crystallize with a monoclinic P2{sub 1}/n superstructure while the larger A=Ba gives a tetragonal I4/m superstructure. These materials have a rocksalt ordered arrangement of Co and Nb with almost no inversion (<1%) for A=Ca and 4% inversion for A=Sr and Ba. Magnetic susceptibility measurements reveal antiferromagnetic ordering transitions with Neel temperatures of 17 K (A=Ca), 16 K (A=Sr), and 10 K (A=Ba). The low temperature antiferromagnetic ordering is described by the magnetic propagation vector k=((1/2) 0 (1/2)) for all materials. The saturated cobalt magnetic moment decreases from 2.97(2) {mu}{sub B} to 2.52(3) {mu}{sub B} to 1.85(5) {mu}{sub B} for A=Ca, Sr, and Ba, respectively. The decrease of ordering temperature and moment with increasing size of A evidences magnetic frustration due to competition between 90 deg. superexchange pathways. This is shown to be a general feature in antiferromagnetic double perovskites.

Bos, Jan-Willem G.; Attfield, J. Paul [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW (United Kingdom); Centre for Science at Extreme Conditions, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ (United Kingdom)

2004-11-01

168

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

NASA Astrophysics Data System (ADS)

Stable Ca and radiogenic Sr isotope compositions were measured in different compartments (stream water, soil solutions, rocks, soils and soil leachates and vegetation) of a small permafrost-dominated watershed in the Central Siberian Plateau. The Sr and Ca in the area are supplied by basalt weathering and atmospheric depositions, which significantly impact the Sr isotopic compositions. Only vegetation significantly fractionates the calcium isotopes within the watershed. These fractionations occur during Ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and Ca oxalate crystallisations during Ca circulation or storage within plant organs. Biomass degradation significantly influences the Ca isotopic compositions of soil solutions and soil leachates via the release of light Ca, and organic and organo-mineral colloids are thought to affect the Ca isotopic compositions of soil solutions by preferential scavenging of 40Ca. The imprint of organic matter degradation on the ?44/40Ca of soil solutions is much more significant for the warmer south-facing slope of the watershed than for the shallow and cold soil active layer of the north-facing slope. As a result, the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil-water system in permafrost areas. Finally, the obtained ?44/40Ca patterns contrast with those described for permafrost-free environments with a much lower ?44/40Ca fractionation factor between soils and plants, suggesting specific features of organic matter decomposition in permafrost environments. The biologically induced Ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the ?44/40Ca signature may be controlled by the heterogeneity of lithological sources.

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

2013-08-01

169

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

170

Ferromagnetism in 2212 phase Bi-Sr-Ca-Cu-O nano-superconductors  

NASA Astrophysics Data System (ADS)

Superconductors are characterized by zero resistance and Meissner effect. At below critical temperature (Tc), these materials exhibit diamagnetic properties. On the other hand, materials in nano-crystal size have specific properties that differ from bulk state. Nanomaterials are characterized by surface effect which influences physical and chemical properties of the materials. Combining these two mayor fields, it can be obtained superconductors in nano-crystal size (below 200 nm) using simple method (called as nano-superconductors). Generally, ceramic-oxides in nano-crystal size, even in cuprate-superconductors, may have ferromagnetic behavior at room temperature. In this research, Bi and Bi, Pb-based nano-superconductors synthesized by wet mixing technique have Tc ˜80 K for 2212 (Bi2Sr2CaCu2O8-? and Bi1,6Pb0,4Sr2CaCu2O8-?) phases. They also exhibit ferromagnetism effect and hysteresis curve although at well above Tc. This is unusual phenomenon because superconductor materials are generally diamagnetic at below Tc and paramagnetic at normal state. This phenomenon is possibly due to magnetic moments which may possibly come from oxygen vacancies of the nanoparticles surface.

Baqiya, Malik A.; Widodo, Henry; Rochmawati, Lidya; Darminto, Adachi, Tadashi; Koike, Yoji

2012-06-01

171

Cu valence states in superconducting Bi-Pb-Sr-Ca-Cu-O system  

SciTech Connect

The oxidation states of Bi, Pb, and Cu in the Bi-Pb-Sr-Ca-Cu-O (BPSCCO) system have been determined by a combination of volumetric measurement technique and iodometric titration. It was found that, in contrast to previous reports, the concentration of the Cu{sup 3+} ions decreased with increasing Pb content, and Cu{sup 3+} ions were absent in samples of Bi{sub 1.6}Pb{sub 0.4}Sr{sub 1.6}Ca{sub 2}Cu{sub 3}O{sub 9.8}, while a T{sub c} at 108 K and a J{sub c} of greater than 12,000 A/cm{sup 2} at 77 K were observed. The 110 K phase in BPSCCO was stabilized and showed a high tolerance to change in oxygen partial pressure during sintering. In Pb-doped materials, Bi appears to be trivalent while Pb was determined to be mixed-valence Pb{sup 4+}/Pb{sup 2+}. It is suggested that superconductivity in BPSCCO may result from a dynamic transfer of holes from Bi/Pb-O layers toward Cu-O{sub 2} planes.

Liu, H.K.; Dou, S.X.; Song, K.H.; Sorrell, C.C. (Univ. of New South Wales, Kensington (Australia)); Easterling, K.E. (Lulea Univ. of Technology (Sweden)); Jones, W.K. (State Univ. of Florida, Miami (USA))

1990-08-01

172

High precision glacial–interglacial benthic foraminiferal Sr\\/Ca records from the eastern equatorial Atlantic Ocean and Caribbean Sea  

Microsoft Academic Search

Glacial–interglacial variation in the marine Sr\\/Ca ratio has important implications for coral Sr thermometry [J.W. Beck et al., Science 257 (1992) 644–647]. A possible variation of 1–3% was proposed based on ocean models [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107–1118]. Subsequently, studies have used fossil foraminifera to test this prediction [P.A. Martin et al., Geochem. Geophys.

Chuan-Chou Shen; David W. Hastings; Typhoon Lee; Chin-Hsin Chiu; Meng-Yang Lee; Kuo-Yen Wei; R. Lawrence Edwards

2001-01-01

173

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

174

Age, growth rate and season of recruitment of Pinna nobilis (L) in the Croatian Adriatic determined from Mg:Ca and Sr:Ca shell profiles  

Microsoft Academic Search

Stable oxygen isotope analyses of U-shaped spines removed at intervals along profiles of the outer shell surface of Pinna nobilis (L) were used to reconstruct sea surface temperature (SST) and validate the periodicity of adductor muscle scar rings on the inner shell surface. Elemental ratios (Mg:Ca and Sr:Ca) of spines, determined using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), were compared

C. A. Richardson; M. Peharda; H. Kennedy; P. Kennedy; V. Onofri

2004-01-01

175

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

Microsoft Academic Search

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,

Renee K. Takesue; Alexander van Geen

2004-01-01

176

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

Microsoft Academic Search

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,

Renee K. Takesue; Alexander van Geen

2004-01-01

177

Sr\\/Ca and Mg\\/Ca ratios of ontogenetically old, long-lived bivalve shells ( Arctica islandica) and their function as paleotemperature proxies  

Microsoft Academic Search

The Sr\\/Ca and Mg\\/Ca ratios of many biogenic skeletons provide useful paleotemperature estimates. As yet however, it has remained largely impossible to obtain such information from bivalve shells. In the present study, metal-to-calcium values in the hinge plate (aragonite, outer shell layer) of four ontogenetically old (85 to 374year-old) specimens of the long-lived bivalve, Arctica islandica, were measured on a

Bernd R. Schöne; Zengjie Zhang; Pascal Radermacher; Julien Thébault; Dorrit E. Jacob; Elizabeth V. Nunn; Anne-France Maurer

2011-01-01

178

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

NASA Astrophysics Data System (ADS)

Modern analogs are an essential part of palaeoclimate studies, because they provide the basis for the understanding of geochemical signatures of fossils. Ostreoids are common in many sedimentary sequences and because of their fast growth, high temporal resolution sampling of past seasonal variability is possible. Here, two shell structures of modern Giant Pacific Oysters (Crassostrea gigas), the chalky substance and foliate layers, have been sampled for trace element distributions (Mg, Sr, Mn) and stable isotope variability (C, O, Ca). Oxygen isotopes exhibit a clear seasonal signature. Mean carbon isotope values of different oysters agree within 0.1‰, but ontogenic variability is complicated by shell growth patterns and potential small vital effects. The calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of ?44/40Ca = 0.68 ± 0.16‰ (2 sd) SRM-915a which is consistent with other bivalve species. Calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios. Element/Ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high Sr/Ca and Mn/Ca ratios are observed for the first growth season of the oysters. Mg/Ca ratios in the chalky substance show a negative correlation with ?18O values, compatible with a temperature dependence, whereas this correlation is absent in the foliate layers. Seasonal changes of Sr/Ca are controlled by metabolic processes, whereas for Mn/Ca an additional environmental control is evident.

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

2013-10-01

179

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

180

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

NASA Astrophysics Data System (ADS)

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

Petralanda, U.; Etxebarria, I.

2014-02-01

181

P-type Ca doped SrCu 2O 2 thin film: Synthesis, optical property and photovoltaic application  

Microsoft Academic Search

P-type transparent conducting oxide Sr0.9Ca0.1Cu2O2 (SCCO) films were prepared by pulsed laser deposition (PLD) technique on glass and n-Si (100) substrates. Some critical experiment factors were investigated, and it was found that well-crystallized, single phase SCCO films could be obtained with the substrate temperature higher than 350°C, and the crystallinity was improved with the increase of laser energy fluence. Sr0.9Ca0.1Cu2O2\\/n-Si

Yiping Zhao; Weiwei Dong; Xiaodong Fang; Yikai Zhou; Gang Meng; Ruhua Tao; Zanhong Deng; Shu Zhou; Songyuan Dai

182

On the composition of 110 K superconductor in a (Bi,Pb)-Sr-Ca-Cu-O system  

Microsoft Academic Search

The 110-K superconductor of the (Bi,Pb)-Sr-Ca-Cu-O sysem is prepared in single-phase form at the composition Bi(1.6)Pb(0.4)Sr(2.01)Ca(2.71)Cu(3.93)O(y). Disks of the material with favorable texture can be obtained in relatively short durations in an O2-poor atmosphere. The literature on the compositions of the 110-K superconductor is reviewed to reveal that the material can be synthesized in single-phase form in a range of

V. S. Bai; S. Ravi; T. Rajasekharan; R. Gopalan

1991-01-01

183

Introduction of artificial pinning centres in Bi2Sr2CaCu2O8 ceramics  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

184

Clusters of native point defects and high-coercive state in films of Ca, Ge-substituted magnetic garnet  

NASA Astrophysics Data System (ADS)

The method of X-ray diffuse scattering (XDS) is used to characterize the point defect structure in epitaxial films of Ca, Ge-substituted magnetic garnet showing a high level of coercivity. It has been discovered that a high-coercive state is induced by clusters of ionic vacancies. The geometrical parameters and concentration of microdefects were obtained by fitting the XDS intensity profiles calculated for model microdefects to the experimental triple-crystal rocking curves. The origin of point defect clusters in the calcium-rich Ca,Ge-substituted garnet is discussed.

Bublik, V. T.; Tkalich, A. K.; Shupegin, M. L.

1994-06-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

186

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

187

Effect of Ag-doping on the intergranular properties of the superconducting Bi(Pb)-Sr-Ca-Cu-O system  

Microsoft Academic Search

The effect of Ag-doping and of heat treatment on the superconducting properties have been investigated for sintered Bi-(Pb)-Sr-Ca-Cu-O ceramics consisting of the high-Tc (2223) phase, where the samples were cooled at different rates immediately after the sintering. For undoped samples the impurity phases of (2212), Ca2PbO4 and (3221) were produced, while for doped samples the impurity phases were only (2201)

Katsukuni Yoshida; Yasushi Sano; Yoichi Tomii

1994-01-01

188

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

189

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. PMID:22355760

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

190

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

191

Superconductivity in the Bi - Sr/K - Ca/Na - Cu - O system  

NASA Astrophysics Data System (ADS)

Samples with the stoichiometric composition 0953-2048/9/9/008/img7 with x = 0.1 and y = 0.1, 0.2, 0.3 and 0.4 were prepared by the solid state reaction method. The role of Na and K doped at the Ca and Sr sites simultaneously in the Bi-2212 composition was studied. From the x-ray diffraction data it was found that the structure is single-phase Bi-2212. From the resistivity data the 0953-2048/9/9/008/img8 varies from 63 to 67 K for different dopant levels. The diamagnetic nature of the samples was confirmed by ac susceptibility measurements. The oxygen content was determined by the two-step iodometric titration technique. The present results on the effect of double doping are compared with those of single dopants published earlier by our group. The microstructures of the samples were examined by scanning electron microscopy.

Sekhar, M. Chandra; Gopala Krishna, B.; Varadaraju, U. V.; Suryanarayana, S. V.

1996-09-01

192

Inter- and intragranular irreversibilities in ceramic Bi 2Sr 2Ca 2Cu 3O 10  

NASA Astrophysics Data System (ADS)

We examined ceramic Bi 2Sr 2Ca 2Cu 3O 10 samples by means of DC-magnetization measurements in order to separate intra- and intergranular irreversibility effects. In contrast to previous literature, the field-dependent Meissner-fraction shows a maximum at ?2.5 G. It is explained by a mixture of inter- and intragranular flux pinning. In the low-field range, the Josephson-coupling of the grains renders additional pinning in the intergranular network possible, while the pinning capability of the grains decreases down to small field. Furthermore, we confirm a particular temperature of approximately 20 K, at which a maximum in the relaxation rate d M/dln t is observed and where the sum rule for the remanent magnetization breaks down. The irreversibility line, determined from the departure of FC- from ZFC-magnetization, follows the usual H{2}/{3}-behavior and reflects only intragranular pinning down to 15 G.

Schulz, B.; Schliepe, B.; Wisny, W.; Baberschke, K.

1992-09-01

193

Cation nonstoichiometry in (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+?  

NASA Astrophysics Data System (ADS)

X-ray lattice parameter measurements of the (Bi, Pb) 2- xSr 2- yCa 2- zCu 3O 10+? system show that a continuously varying solid-solution cation nonstoichiometry exists within -0.1< x<0.1, 0< y<0.3, and 0< z<0.3. However, the system cannot incorporate any defect at its Cu site. The oxygen content determined by titration decreases linearly with increasing cation-vacancy concentration. The critical temperature, Tc, shows a maximum value at the stoichiometric cation composition and decreases to a lower constant value across the nonstoichiometric composition region with increasing alkaline-earth deficiency. Flux pinning in this system is increased by the cation-vacancy concentration only in the low-temperature range, while it decreased in the high-temperature range. The flux-pinning behavior is discussed in view of its two-dimensionality in the superconductivity for this system.

Nomura, Shunji; Yoshino, Hisashi; Ando, Ken

1994-04-01

194

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

195

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

SciTech Connect

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

Belala, K; Mosbah, M. F. [Material Sciences and Applications Research Unit, Physics Department, Constantine 1 University, B.P. 325 Route d'Ain El Bey, 25017 Constantine (Algeria)

2013-12-16

196

Tunneling measurements of as grown Bi 2Sr 2CaCu 2O 8+ ? single crystals  

NASA Astrophysics Data System (ADS)

Tunneling experiments of Bi 2Sr 2CaCu 2O 8+ ? single crystals with T c=86 K have been performed in the temperature range of 77-250 K. The gap structure observed at 77 K does not disappear at Tc. Further, another gap-like structure is observed in several junctions beyond ?180 K.

Sezaki, Yoshie; Ekino, Toshikazu; Fujii, Hironobu

1999-01-01

197

Neonatal Severe Hyperparathyroidism due to Compound Heterozygous Mutation of Calcium Sensing Receptor (CaSR) Gene Presenting as Encephalopathy.  

PubMed

The authors report a 14-d-old neonate who presented with lethargy, polyuria and dehydration and was found to have severe hypercalcemia with hyperparathyroidism. This neonate was treated with saline hydration, diuresis and injection pamidronate. Genetic analysis revealed a compound heterozygous mutation of CaSR. PMID:24763815

Kulkarni, Abhishek; Mohite, Mahesh; Vijaykumar, Ramaa; Bansode, Prasanna; Murade, Sachin; Tamhankar, Parag M

2014-11-01

198

Processing of Bi sbnd (Pb) sbnd Sr sbnd Ca sbnd Cu oxide superconductor thin films by metal alkoxide route  

NASA Astrophysics Data System (ADS)

High- Tc superconducting thin films in the Bi sbnd Pb sbnd Sr sbnd Ca sbnd Cu sbnd O system were prepared through reaction controls in organic solution by a metal-organic route. Thin films with preferred orientation were successfully prepared on MgO (100) single crystal substrates by a dip coating method. The films of the (243) phase (high- Tc phase) and the (232) phase (low- Tc phase) were synthesized from solutions with composition of Bi:Pb:Sr:Ca:Cu = 2:0.35:2:2:3 and Bi:Sr:Ca:Cu = 2:2:1:2, respectively. The Jc of films was much improved through the UV irradiation during calcination as well as the proper selection of composition for starting solutions. A film prepared from a solution composition of Bi:Pb:Sr:Ca:Cu = 2:0.35:2:2:3 with UV irradiation showed the sharp onset of Tc at 117 K, zero resistance at 79.5 K and Jc of 840 A/cm 2 (77.3 K) after heat treatment at 845°C.

Hirano, S.; Yogo, T.; Kikuta, K.; Tomonaga, H.; Ishii, M.

199

Geochemistry of alkaline earth elements (Mg, Ca, Sr, Ba) in the surface sediments of the Yellow Sea  

Microsoft Academic Search

The concentrations of alkaline earth elements were measured in the surface sediments of the Yellow Sea in an attempt to establish their sources from horizontal distributions. The maximum concentrations of Mg are found in the central Yellow Sea, and its horizontal distribution is mainly controlled by quartz dilution. The concentrations of Ca and Sr increase toward the southeastern Yellow Sea

Guebuem Kim; Han-Soeb Yang; Thomas M. Church

1999-01-01

200

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

NASA Technical Reports Server (NTRS)

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

Kaesche, Stefanie; Majewski, Peter; Aldinger, Fritz

1995-01-01

201

Effect of vibrational excitation on the molecular beam reactions of Ca and Sr with HF and OF  

E-print Network

of this technique to Ca and Sr. For the latter reagents, un- like Ba, the reaction with HF (v =0) is endothermic excitation on an endothermic process. Odiorne, Brooks, and Kaspers report for K+ HCl- KCl + H that reagent vibration is necessary to promote endothermic reactions. 4 While the present investigation only

Zare, Richard N.

202

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

SciTech Connect

A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi-Sr-Ca-Cu-O-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO{sub 2}). A liquid immiscibility region between oxide and Ag liquids in the 8--98 at% range was found above 900 C. Two eutectics were found in the Bi2212-Ag pseudobinary. On the oxide rich side, a eutectic exists at approximately 4 at% Ag. On the Ag rich side, a eutectic exists at approximately 98 at% Ag at a temperature of 15 C below the melting point of pure Ag. Six distinct solid phases were found to be in equilibrium with the partial melt within the Ag content and PO{sub 2} range studied. The stability of these solid phases were found to be highly sensitive to PO{sub 2}, and to a much lesser extent Ag content. High temperature x-ray diffraction (HTXRD) studies of this system are in conflict with these results. It is suggested that these discrepancies are due to experimental artifacts caused by the significant thermal gradients and lack of full bulk sampling which is inherent in conventional HTXRD designs. In part 2, a new furnace design compatible with synchrotron radiation sources is introduced to address these problems. This design allows for full bulk sampling in a low thermal gradient environment using Debye-Scherrer transmission geometry. Sample spinning is also introduced in the design to eliminate preferred orientation and incomplete powder averaging and allow for quantitative phase analysis and structural refinement. Studies on model systems are presented to demonstrate the capabilities for high resolution structural studies (Al{sub 2}O{sub 3}) and time resolved phase transformation studies (SrCO{sub 3}). Finally, the Bi2212 system is examined to confirm the quenching results of part 1, and to demonstrate the degree to which this new HTXRD design solves the problems associated with conventional designs.

Margulies, Lawrence

1999-11-08

203

Crystal structure and magnetic properties and Zn substitution effects on the spin-chain compound Sr{sub 3}Co{sub 2}O{sub 6}  

SciTech Connect

The effects of substituting Co on the spin-chain compound Sr{sub 3}Co{sub 2}O{sub 6} with Zn were investigated by synchrotron X-ray diffraction, magnetic susceptibility, isothermal magnetization, and specific heat measurements. To the best of our knowledge, this is the first report to describe the successful substitution of Co in Sr{sub 3}Co{sub 2}O{sub 6} with Zn. The substitution was carried out by a method involving high pressures and temperatures to obtain Sr{sub 3}CoZnO{sub 6}, which crystalized into a K{sub 4}CdCl{sub 6}-derived rhombohedral structure with a space group of R-3c, similar to the host compound. With the Zn substitution, the Ising-type magnetic anisotropy of the host compound remarkably reduced; the newly formed Sr{sub 3}CoZnO{sub 6} became magnetically isotropic with Heisenberg-type characteristics. This could probably be ascribed to the establishment of a different interaction pathway, –Co{sup 4+}(S=1/2)–O–Zn{sup 2+}(S=0)–O–Co{sup 4+}(S=1/2)–. Details of the magnetic properties of Zn substituted Sr{sub 3}Co{sub 2}O{sub 6} were reported. - Graphical abstract: Crystal structure of the spin-chain compound Sr{sub 3}CoZnO{sub 6} synthesized at 6 GPa. Zn atoms preferably occupy the trigonal prism sites rather than the octahedral sites. As a result, the compound is much magnetically isotropic. Highlights: • Effects of substituting Co with Zn on spin-chain magnetism of Sr{sub 3}Co{sub 2}O{sub 6} were studied. • High-pressure synthesis resulted in a solid solution of Sr{sub 3}CoZnO{sub 6}. • Sr{sub 3}CoZnO{sub 6} showed more isotropic magnetism than the host Sr{sub 3}Co{sub 2}O{sub 6}.

Wang, Xia [Superconducting Properties Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Guo, Yanfeng, E-mail: Yangfeng.Guo@physics.ox.ac.uk [Superconducting Properties Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Sun, Ying [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Tsujimoto, Yoshihiro [Materials Processing Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba Ibaraki 305-0047 (Japan); Matsushita, Yoshitaka [Materials Analysis Station, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba Ibaraki 305-0047 (Japan); Yamaura, Kazunari, E-mail: yamaura.kazunari@nims.go.jp [Superconducting Properties Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan)

2013-08-15

204

Nicotinic Acid Adenine Dinucleotide Phosphate Analogs Containing Substituted Nicotinic Acid: Effect of Modification on Ca2+ Release  

PubMed Central

Analogs of nicotinic acid adenine dinucleotide phosphate (NAADP) with substitution at either the 4- or the 5-position position of the nicotinic acid moiety have been synthesized from NADP enzymatically using Aplysia californica ADP-ribosyl cyclase or mammalian NAD glycohydrolase. Substitution at the 4-position of the nicotinic acid resulted in the loss of agonist potency for release of Ca2+-ions from sea urchin egg homogenates and in potency for competition ligand binding assays using [32P]NAADP. In contrast, several 5-substituted NAADP derivatives showed high potency for binding and full agonist activity for Ca2+ release. 5-Azido-NAADP was shown to release calcium from sea urchin egg homogenates at low concentration and to compete with [32P]NAADP in a competition ligand binding assay with an IC50 of 18 nM, indicating that this compound might be a potential photoprobe useful for specific labeling and identification of the NAADP receptor. PMID:20942470

Jain, Pooja; Slama, James T.; Perez-Haddock, LeRoy A.; Walseth, Timothy F.

2011-01-01

205

Reversible melting and equilibrium phase formation of (Bi, Pb)2Sr2Ca2Cu3O10+?  

NASA Astrophysics Data System (ADS)

The decomposition and the re-formation of the (Bi, Pb)2Sr2Ca2Cu3O10+? (Bi, Pb(2223)) phase have been investigated in situ by means of high-temperature neutron diffraction, both in sintered bulk samples and in Ag-sheathed monofilamentary tapes. Several decomposition experiments were performed at various temperatures and under various annealing atmospheres, under flowing gas as well as in sealed tubes, in order to study the appropriate conditions for Bi,Pb(2223) formation from the melt. The Bi,Pb(2223) phase was found to melt incongruently into (Ca, Sr)2CuO3, (Sr, Ca)14Cu24O41 and a Pb,Bi-rich liquid phase. Phase re-formation after melting was successfully obtained both in bulk samples and in Ag-sheathed tapes. The possibility of crystallizing the Bi,Pb(2223) phase from the melt was found to be extremely sensitive to the temperature and strongly dependent on the Pb losses. The study of the mass losses due to Pb evaporation was complemented by thermogravimetric analysis which proved that Pb losses are responsible for moving away from equilibrium and therefore hinder the re-formation of the Bi,Pb(2223) phase from the melt. Thanks to the full pattern profile refinement, a quantitative phase analysis was carried out as a function of time and temperature and the role of the secondary phases was investigated. Lattice distortions and/or transitions were found to occur at high temperature in Bi,Pb(2223), Bi,Pb(2212), (Ca, Sr)2CuO3 and (Sr, Ca)14Cu24O41, due to cation diffusion and stoichiometry changes. The results indicate that it is possible to form the Bi,Pb(2223) phase from a liquid close to equilibrium conditions, such as Bi(2212) and Bi(2201), and open new unexplored perspectives for high-quality Ag-sheathed Bi,Pb(2223) tape processing.

Giannini, E.; Savysyuk, I.; Garnier, V.; Passerini, R.; Toulemonde, P.; Flükiger, R.

2002-11-01

206

Synthesis and characterization of strontium–calcium phosphate ?-Ca 3? x Sr x (PO 4) 2 (0 ? x ? 2)  

Microsoft Academic Search

The solid solutions of strontium–calcium phosphate, ?-Ca3?xSrx(PO4)2 (0?x?2), have been synthesized under high-pressure and high-temperature conditions. The products were well characterized by powder X-ray diffraction measurements and Micro-Raman spectroscopy. All the products are isostructural and belong to R-3m space group. With the increasing content of Sr in ?-Ca3?xSrx(PO4)2, the unit cell parameters (a, c, c\\/a, V) linearly increase, and the

Shuangmeng Zhai; Masami Kanzaki; Tomoo Katsura; Eiji Ito

2010-01-01

207

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

208

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

209

Sr  

NASA Astrophysics Data System (ADS)

In this investigation, the effect of hot extrusion process has been studied on the microstructure and tensile properties of aluminum matrix composite containing different amounts (10, 15, and 20 wt pct) of Al4Sr intermetallic phase. Microstructural examinations assessed by scanning electron microscopy revealed that hot extrusion breaks large Al4Sr particles and reduces their length tremendously. It was also found that although the addition of Al4Sr content in the composite reduces ultimate tensile strength and elongation values, hot extrusion improves tensile results significantly. Remarkable result of this study was concerned with significant improvement in the toughness of hot-extruded Al-10 wt pct Al4Sr composite in which elongation values raised up to 22 pct. Therefore, optimum amount of Al4Sr intermetallic in the composite was found to be 10 wt pct. Fractographic examinations revealed that hot extrusion encourages ductile mode of fracture by introducing homogeneous distribution of fine dimples on the fracture surface of the composites.

Sharifian, K.; Emamy, M.; Tavighi, K.; Vaziri Yeganeh, S. E.

2014-11-01

210

Genetic changes associated with glycopeptide resistance in Staphylococcus aureus: predominance of amino acid substitutions in YvqF/VraSR  

PubMed Central

Objectives To further understand the mechanism of intermediate-level glycopeptide resistance, resulting from multiple endogenous mutations, in both laboratory-derived and clinically isolated Staphylococcus aureus. Methods Laboratory-derived S. aureus strains were generated under selection using a variety of cell-wall-active antibiotics. Complete sequences of 27 genes, including 17 two-component histidine kinase sensors, were then compared with those of their susceptible parent strain. Further genetic analysis was performed on 125 clinical S. aureus isolates and 42 geographically diverse isolates of vancomycin-intermediate S. aureus (VISA). Results Selective pressure using imipenem resulted in single point mutations leading to amino acid substitutions in two genes: vraS, encoding a two-component histidine kinase sensor; and SA1702 (also called yvqF, located immediately upstream of vraS), encoding a conserved hypothetical protein. The accumulation of the mutation in two distinct proteins—MsrR, a peptide methionine sulphoxide reductase regulator, and TcaA, a teicoplanin-resistance-associated protein—correlated with further increases in the glycopeptide MIC. The prevalence of YvqF/VraSR mutants among 125 clinical isolates along with the corresponding teicoplanin MICs was as follows: 0% (0/39), ?1 mg/L; 48.6% (17/35), 2 mg/L; 72.7% (24/33), 4 mg/L; 93.8% (15/16), 8 mg/L; and 100% (2/2), 16 mg/L. Genetic analysis of 42 VISA isolates also identified the predominant amino acid substitutions in YvqF/VraS: 9 isolates (21.4%) revealed mutations in YvqF, followed by 7 isolates with mutations in VraS (16.7%). Conclusions Our findings provide novel insights into the high prevalence and genetic diversity of YvqF/VraSR mutants among clinical S. aureus isolates with reduced susceptibility to teicoplanin. PMID:19889788

Kato, Yoshihisa; Suzuki, Takahisa; Ida, Takashi; Maebashi, Kazunori

2010-01-01

211

The Effects of Substitution of Alkaline Earths or Y for La on Structure and Electrical Properties of LaSrFeO 4  

NASA Astrophysics Data System (ADS)

The effects of the substitution of alkaline earths or Y for La on the structure and electrical properties of LaSrFeO 4 with K 2NiF 4 structure have been investigated. EDTA titration confirmed that Fe 3+ was oxidized to Fe 4+ in an amount corresponding to that of divalent alkaline earth ions substituted for La 3+. The change in the lattice constants was interpreted in terms of the ionic radius of the substituted ions and the Jahn-Teller distortion of the Fe(IV)O 6 octahedra having d4 electronic configuration. All the substituted LaSrFeO 4 samples were semiconducting over the temperature range from 100 to 300 K. The measurement of the Seebeck coefficient revealed that the conduction carriers of LaSrFeO 4 were holes and the carrier concentration increased with increasing amount of Fe 4+. La 1- xAxSrFeO 4 exhibited a monotonic decrease in resistivity and activation energy for conduction with increasing Fe 4+ abundance. The activation energy for conduction did not change by changing the lattice constant where the Fe 4+ abundance did not change with various substituents.

Fujihara, Shinobu; Nakata, Toshiyuki; Kozuka, Hiromitsu; Yoko, Toshinobu

1995-03-01

212

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

213

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

214

Reconstructing twentieth-century sea surface temperature variability in the southwest Pacific: A replication study using multiple coral Sr/Ca records from New Caledonia  

NASA Astrophysics Data System (ADS)

Coral-based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation, analytical expense, and time constraints. Coral Sr/Ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of Amédée Island, New Caledonia. Different sampling resolutions were examined in coral Sr/Ca (fortnightly and monthly) and ?18O (fortnightly, monthly, and seasonally) as well as similar scale subsampling of the daily in situ sea surface temperature (SST) record. The mean coral Sr/Ca, ?18O, and SST values do not change as a function of sampling resolution. The coral Sr/Ca signal is highly reproducible; the average absolute offset between coeval monthly Sr/Ca determinations between any two coral time series is 0.035 ± 0.026 mmol/mol (1?) (˜0.65°C), which is less than twice the analytical precision of the coral Sr/Ca measurements. The stack average of the monthly coral Sr/Ca variations and monthly anomalies are significantly correlated with monthly in situ SST (1967-1992; r = -0.96 and -0.64, respectively; p < 0.05; and n = 302) and 1° grid monthly SST data product (1900-1999; r = -0.95 and -0.56, respectively; p < 0.05; and n = 1198). The coral Sr/Ca-SST reconstruction exhibits interannual and decadal- timescale fluctuations that exceed those observed in the gridded SST record, which may reflect true differences between SST at a shallow reef site and those averaged over a 1° grid box or inadequacies in the methodology used to create the gridded SST product when few observations are available. A warming trend of ˜0.6°C is observed in the twentieth century coral Sr/Ca-SST record.

Delong, Kristine L.; Quinn, Terrence M.; Taylor, Frederick W.

2007-12-01

215

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

SciTech Connect

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

Samal, Saroj L. [Ames Laboratory; Gulo, Fakhili [Ames Laboratory; Corbett, John D. [Ames Laboratory

2013-02-18

216

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

217

Crystal structure and resistivity of substituted LaSrYCu{sub 2}O{sub 6}  

SciTech Connect

A series of Y-based 2126 compounds, La{sub 1{minus}x}Sr{sub 1+x}YCu{sub 2}O{sub 6} (x = 0 to 0.5), has been prepared. Crystal structure and cation distribution are determined by Rietveld analysis of X-ray powder diffraction data. Small Y ions occupy (2a) site preferentially. All the studied samples including HIP treated ones are semiconducting and no superconducting transition is observed down to 20K. VRH model is applicable as a transport mechanism at low temperatures.

Takano, Yoshihiko; Noro, Sumiko; Yamadaya, Tokio [Yokohama City Univ. (Japan). Dept. of Physics] [Yokohama City Univ. (Japan). Dept. of Physics; Isobe, Masaaki; Ami, Takaaki; Suzuki, Masayuki; Tanaka, Masahiro [Sony Corp. Research Center, Yokohama (Japan)] [Sony Corp. Research Center, Yokohama (Japan)

1995-02-01

218

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

219

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

220

Drastic differences between the local and the average structures of Sr2MSbO5.5 (M = Ca, Sr, Ba) oxygen-deficient double perovskites.  

PubMed

For many disordered materials, knowing their average crystal structure is insufficient for explaining and predicting their macroscopic properties. It has been found that a description of the short-range atomic arrangements is needed to understand such materials. In order to understand the conduction pathways in ionic conductors which have random distributions of vacancies it is imperative to know the local structures which are present. In this study the local structures of three oxygen-deficient double perovskites, Sr(2)MSbO(5.5) (M = Ca, Sr, Ba), have been investigated by neutron pair distribution function analysis. The ions in these compounds are all found to have local coordination environments which are radically different than those given by their average structures. While there is no long-range ordering of the oxygen vacancies in these compounds, a considerable amount of short-range order does exist. The conditions which drive the short-range ordering are discussed as are the possible mechanisms for achieving it. It is proposed that the SbO(5) polyhedra form distorted trigonal bipyramids by moving oxygen atoms into interstitial positions. In the M = Sr compound 45° rotations of SbO(6) octahedra are also present, which add additional oxygen atoms into the interstitial sites. Large displacements of the Ca(2+), Sr(2+), and Ba(2+) cations are also present, the directions of which are correlated with the occupancies of the interstitial oxygen sites. Reverse Monte Carlo modeling of the pair distribution function data has provided the actual bond length distributions for the cations. PMID:23151311

King, Graham; Thomas, Kyle J; Llobet, Anna

2012-12-01

221

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

NASA Technical Reports Server (NTRS)

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

Bansal, Narottam P.

1989-01-01

222

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

NASA Technical Reports Server (NTRS)

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

Bansal, Narottam P.

1990-01-01

223

BiPbSrCaCuO superconductors prepared by the multiple pressing and sintering process  

SciTech Connect

Pellets of bulk density 5.5 g/cm{sup 3}, {ital T}{sub {ital c}} of 107 K, and magnetic critical current of 10{sup 4} A/cm{sup 2} (77 K, 3{times}4{times}10 mm{sup 3}) were achieved under the multiple pressing and sintering process in the Bi{sub 1.84}Pb{sub 0.34}Sr{sub 1.91}Ca{sub 2.03}Cu{sub 3.06}O{sub {ital x}} bulk samples. The powder x-ray diffraction shows the existence of the single high-{ital T}{sub {ital c}} phase. Highly textured microstructures with strong (001) reflections were confirmed by x-ray diffraction on the surface of the pellets. The internal textured microstructures were obviously observed by a scanning electron microscope. No second stage was observed, and the superconducting volume fractions of the Meissner and shielding effects were more than 70% and 90%, respectively, as observed by dc magnetic susceptibility.

Wang, W.; Zhou, M.; Zuo, T.; Huang, J.; Cai, J.; Zhou, X.; Wei, Q. (Department of Materials Science and Engineering, Central South University of Technology, Changsha 410083, China (CN))

1990-12-01

224

Surface morphology and nucleation of infinite-layer (Sr,Ca)CuO 2 films on atomically flat SrTiO 3 (100) substrates studied by atomic force microscopy  

Microsoft Academic Search

The surface morphology and nucleation of molecular beam epitaxy-grown ‘infinite-layer’ structure, (Sr,Ca)CuO2 films on atomically flat SrTiO3 are studied by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The SrTiO3 (100) surfaces were prepared by an ultra-high vacuum (UHV) annealing and displayed regular arrays of 0.4 nm steps spaced by atomically flat terraces of about 400 nm. The

A. Brazdeikis; A. S. Flodström

1996-01-01

225

Triadin/Junctin Double Null Mouse Reveals a Differential Role for Triadin and Junctin in Anchoring CASQ to the jSR and Regulating Ca2+ Homeostasis  

PubMed Central

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 Ca2+ imaging and Ca2+ selective microelectrodes we found that changes in e-c coupling, SR Ca2+content and resting [Ca2+] 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 Ca2+ 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.

2012-01-01

226

Effects of cation substitution on thermal expansion and electrical properties of lanthanum chromites  

Microsoft Academic Search

The effects of cation substitution on the sintering characteristics, thermal expansion and electrical conductivity properties of La(AE)Cr(M)O3 (AEMg, Ca, Sr, MNi, Cu, Co) were investigated. The sinterability of alkaline metal earth (AE)-doped LaCrO3 increased with AE contents in a sequence of Ca>Sr>Mg. Sr-doped LaCrO3 sample had a TEC compatible with that of 8YSZ electrolyte. The transition metals of Ni, Co

Xifeng Ding; Yingjia Liu; Ling Gao; Lucun Guo

2006-01-01

227

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

SciTech Connect

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

Haas, O., E-mail: otto.haas@bluewin.ch [Energy and Material Research Consulting, CH-6648 Minusio (Switzerland); Ludwig, Chr. [General Energy Research, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Ecole Polytechnique Federale de Lausanne, ENAC-IIE, CH-1015 Lausanne (Switzerland); Bergmann, U. [Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 (United States); Singh, R.N. [Banaras Hindu University, Chemistry Department, Varanasi 221005 (India); Braun, A.; Graule, T. [Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for High Performance Ceramics, CH-8600 Duebendorf (Switzerland)

2011-12-15

228

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

229

Optical and Electromagnetic Properties of LaCoO3:Li+;M2+ (M = Ca, Sr, Ba)  

NASA Astrophysics Data System (ADS)

Lanthanum cobaltates modified by alkaline-earth-metal (0.10 mol%) and lithium (0.05 mol%) ions were synthesized. The samples had an orthorhombic distorted perovskite-like structure according to x-ray diffraction phase analysis. Addition of Li+ and M2+ (M = Ca, Sr, Ba) to the LaCoO3 matrix was shown to increase the unit-cell parameters, the optical band width (Eg), and the average Co oxidation state (Con+). Pure and doped LaCoO3 were characterized by the presence of paramagnetic centers as isolated structural and surface Co2+ ions and adsorption complexes [Co3 + ⋯ O{2/-}]· on the surface of the oxide matrix at a concentration that increased in the order Ba > Sr > Ca. The cobaltates were found to possess Mott hopping conduction in the temperature range 77-298 K.

Fesich, I. V.; Trachevsky, V. V.; Dziazko, A. G.; Nedilko, S. A.; Melnik, A. K.

2014-09-01

230

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

NASA Astrophysics Data System (ADS)

Tropical sea surface temperature (SST) has been implicated as a driver of climate changes during the Medieval Climate Anomaly (MCA, 950-1300 A.D.) but little data exists from the tropical oceans during this time period. We collected three modern and seven sub-fossil Diploria strigosa coral colonies from an overwash deposit on Anegada, British Virgin Islands (18.73 °N, 63.33 °W) in order to reconstruct climate in the northeastern Caribbean and Tropical North Atlantic during the MCA. The first step in our reconstruction was to verify the climate signal from this species at this site. We sub-sampled the modern corals along thecal walls with an average sampling resolution of 11-13 samples per year. Sr/Ca ratios measured in the sub-samples were calibrated to temperature using three different calibration techniques (ordinary least squares, reduced major axis, and weighted least squares (WLS)) on the monthly data that includes the seasonal cycles and on the monthly anomaly data. WLS regression accounts for unequal errors in the x and y terms, so we consider it the most robust technique. The WLS regression slope between gridded SST and coral Sr/Ca is similar to the previous two calibrations of this species. Mean Sr/Ca for each of the three modern corals is 8.993 × 0.004 mmol/mol, 9.127 × 0.003 mmol/mol, and 8.960 × 0.007 mmol/mol. These straddle the mean Diploria strigosa Sr/Ca found by Giry et al., (2010), 9.080 mmol/mol, at a site with nearly the same mean SST as Anegada (27.4 °C vs. 27.5 °C). The climatological seasonal cycles for SST derived from the modern corals are statistically indistinguishable from the seasonal cycles in the instrumental SST data. The coral-based seasonal cycles have ranges of 2.70 × 0.31 °C, 2.65 × 0.08 °C and 2.71 × 0.53 °C. These results indicate that this calibration can be applied to our sub-fossil coral data. We applied the WLS calibration to monthly-resolution Sr/Ca data from multiple sub-fossil corals dating to the medieval period with initial U-series dates near the top of the cores ranging from 1277 × 5 A.D. to 1327 × 5 A.D. Initial Sr/Ca results from the first sub-fossil coral have a seasonal range of 2.65 × 0.27 °C when converted to temperature units with our modern calibration, indicating no significant change from modern times. However, the mean Sr/Ca for this coral is very high (9.388 mmol/mol) compared to the modern corals. We explore the potential causes for this discrepancy in our study. Because reconstructing the mean SST during the Medieval Climate Anomaly may be difficult without temporal overlap with modern corals, our focus is on interannual variability. The coral Sr/Ca based monthly SST anomalies for both modern and sub-fossil corals have larger interannual variances than the instrumental record. One explanation for this is that the SSTs derived from sub-fossil corals are local data for which one expects larger variances than the instrumental data averaged over a 2 x 2 ° grid. This species shows great promise for future paleoclimate reconstructions.

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

2013-12-01

231

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

232

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

233

Direct measurements of SR free Ca reveal the mechanism underlying the transient effects of RyR potentiation under physiological conditions  

PubMed Central

Aims Most of the calcium that activates contraction is released from the sarcoplasmic reticulum (SR) through the ryanodine receptor (RyR). It is controversial whether activators of the RyR produce a maintained increase in the amplitude of the systolic Ca transient. We therefore aimed to examine the effects of activation of the RyR in large animals under conditions designed to be as physiological as possible while simultaneously measuring SR and cytoplasmic Ca. Methods and results Experiments were performed on ventricular myocytes from canine and ovine hearts. Cytoplasmic Ca was measured with fluo-3 and SR Ca with mag-fura-2. Application of caffeine resulted in a brief increase in the amplitude of the systolic Ca transient accompanied by an increase of action potential duration. These effects disappeared with a rate constant of ?3 s?1. Similar effects were seen in cells taken from sheep in which heart failure had been induced by rapid pacing. The decrease of Ca transient amplitude was accompanied by a decrease of SR Ca content. During this phase, the maximum (end-diastolic) SR Ca content fell while the minimum systolic increased. Conclusions This study shows that, under conditions designed to be as physiological as possible, potentiation of RyR opening has no maintained effect on the systolic Ca transient. This result makes it unlikely that potentiation of the RyR has a maintained role in positive inotropy. PMID:24947416

Greensmith, David J.; Galli, Gina L.J.; Trafford, Andrew W.; Eisner, David A.

2014-01-01

234

First principle prediction of half-metallic ferromagnetism in zinc-blende MBi (M=Ca, Sr, Ba)  

Microsoft Academic Search

The first-principle calculations have been performed to investigate the zinc-blende compounds of alkaline elements with the Bi atom to find new half-metallic ferromagnets. It is found that CaBi, SrBi and BaBi are true half-metallic ferromagnets with the magnetic moment of 1mu\\/formula unit. Their half-metallicity can be maintained within a wide range of lattice constants.

K. L. Yao; J. L. Jiang; Z. L. Liu; G. Y. Gao

2006-01-01

235

First principle prediction of half-metallic ferromagnetism in zinc-blende MBi ( M = Ca , Sr, Ba)  

Microsoft Academic Search

The first-principle calculations have been performed to investigate the zinc-blende compounds of alkaline elements with the Bi atom to find new half-metallic ferromagnets. It is found that CaBi, SrBi and BaBi are true half-metallic ferromagnets with the magnetic moment of 1?B\\/formula unit. Their half-metallicity can be maintained within a wide range of lattice constants.

K. L. Yao; J. L. Jiang; Z. L. Liu; G. Y. Gao

2006-01-01

236

Transport properties of Tl-Ba\\/Sr-Ca-Cu-O metal sheathed superconducting tapes in magnetic fields  

Microsoft Academic Search

Ag- or Au-sheathed taped with a Tl-Ba\\/Sr-Ca-Cu-O core were fabricated by a drawing-rolling and subsequent pressing method. The tape prepared at an optimized condition yielded a transport Jc of 15900 A\\/cm2 at 77 K in the absence of a magnetic field, and 1100 A\\/cm2 in a magnetic field of 1 T. The enhancement of J c in a magnetic field

K. Aihara; M. Okada; T. Matsumoto; S. Matsuda; F. Hosono; M. Seido

1991-01-01

237

Excitation spectra of CaAr, SrAr and BaAr molecules in a supersonic jet  

NASA Astrophysics Data System (ADS)

Laser-induced excitation spectra of CaAr, SrAr, and BaAr produced in a supersonic jet apparatus were determined in the vicinity of the lowest 1S 0- 1P 0 resonance lines of the free metal atoms. Spectroscopic constants of the X 1? + and A 1? states of these molecules were determined and compared to those of the analogous MgAr states.

Kowalski, Andrzej; Funk, David J.; Breckenridge, W. H.

1986-12-01

238

Doping dependence of the superconducting gap in Bi2Sr2CaCu2O8+delta  

Microsoft Academic Search

Bi2Sr2CaCu2O8+delta crystals with varying hole concentrations (0.12

K. C. Hewitt; J. C. Irwin

2002-01-01

239

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

240

Paleoprecipitation record from coral Sr\\/Ca and ?18O during the mid Holocene in the northern South China Sea  

Microsoft Academic Search

Coupled high-resolution Sr\\/Ca and ?18O records of a modern and a mid-Holocene coral from Sanya in the southern Hainan Island, northern South China Sea (SCS), were reported and the residual ?18O (??18O) were calculated to indicate precipitation change in this region. Unlike other paleoclimate studies, this study focused on changes of precipitation time rather than precipitation amount. As negative ??18O

Wen-feng Deng; Gang-jian Wei; Xian-hua Li; Ke-fu Yu; Jian-xin Zhao; Wei-dong Sun; Ying Liu

2009-01-01

241

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

242

Anharmonic effective pair potentials in CaTiO3, SrTiO3 and CaGeO3 perovskite.  

PubMed

The temperature dependence of EXAFS Debye-Waller factors in CaTiO3, SrTiO3 and CaGeO3 perovskite was investigated with the cumulant expansion method. The CaGeO3 perovskite as an analogue of the Earth's lower-mantle mineral was synthesized in a cubic anvil type apparatus under 10 GPa 1250 K The Ca, Ti and Ge K-edge EXAFS spectra were measured in transmission mode at temperature up to 1100 K The effective pair potentials, V(u)= alpha (u2/2+ beta u3/3!, were evaluated and the Grüneisen parameter were calculated. The potential coefficients alpha and beta for Ti-O bond in CaTiO3 are 6.9 eVA(-2) and -38 eVA(-3), respectively. Those for Ge-O bond in CaGeO3 are 9.8 eVA(-2) and -36 eVA(-3), respectively. PMID:11512986

Yoshiasa, A; Nakajima, K; Murai, K; Okube, M

2001-03-01

243

Texture improvements in the high-temperature superconducting Bi?Sr?Ca?Cu?Ox̳/Ag system via surface energy driven grain alignment  

E-print Network

The relation between processing, microstructure, and material property was investigated in the high-temperature superconducting Bi?Sr?Ca?Cu?Ox̳/Ag system. Experiments were based on a theoretical surface energy model ...

Vodhanel, Mark E

2005-01-01

244

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

245

Antioxidants prevented oxidative injury of SR induced by Fe2+/H2O2/ascorbate system but failed to prevent Ca2+-ATPase activity decrease.  

PubMed

Dysfunction of sarcoplasmic reticulum (SR) Ca2+-ATPase induced by oxidative stress may be a contributing factor to the development of serious age related diseases. Incubation of sarcoplasmic reticulum (SR) vesicles of rabbit skeletal muscles with Fe2+/H2O2/ascorbate decreased the SH group content of SR approximately to 35% and Ca2+-ATPase activity to 50% of control not oxidized sample. Protein carbonyls increased twofold, lipid peroxidation was also significantly elevated. The antioxidant effects of trolox, the pyridoindole derivative stobadine and of the standardized extracts from bark of Pinus Pinaster PycnogenolR (Pyc) and from leaves of Ginkgo biloba (EGb 761) were studied on oxidatively injured SR. All antioxidants exerted preventive effects against the oxidized lipids and protein SH groups of SR vesicles. Trolox and stobadine did not influence protein carbonyl formation, while flavonoid extracts prevented carbonyl generation, probably by binding to protein. The preventive effects of the antioxidants studied on lipids and protein SH groups were however not associated with protection of Ca2+-ATPase activity. Stobadine and trolox exerted no effect on enzyme activity, Pyc and EGb 761 enhanced the inhibitory effect of Ca2+-ATPase activity in oxidatively injured SR. Concluding, under the conditions of oxidative stress induced by Fe2+/H2O2/ascorbate against SR of rabbit skeletal muscle, the agents studied demonstrated antioxidant effects yet failed to protect Ca2+-ATPase activity. PMID:16403969

Horáková, Lubica; Strosová, Miriam; Skuciová, Mária

2005-01-01

246

Processing and characterization of thin films of the two-layer superconducting phase in the Bi-Sr-Ca-Cu-O system; Evidence for solid solution  

Microsoft Academic Search

Thin films in the Bi-Sr-Ca-Cu-O system have been synthesized from liquid ethylhexanoate precursors by spin pyrolysis. An extensive solid-solution range was found for the two-Cu-layer phase through the study of c-axis- oriented, single-phase thin films fabricated on single- crystal, (100)-oriented, MgO substrates. All two-layer compositions were excess in Bi and deficient in Sr + Ca relative to the ideal 2212

A. K. Cheetham; A. M. Segadaes; S. J. Golden; T. E. Bloomer; F. F. Lange; K. J. Vaidya

1991-01-01

247

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

248

Sr\\/Ca and delta18O in a fast-growing Diploria strigosa coral: Evaluation of a new climate archive for the tropical Atlantic  

Microsoft Academic Search

This study provides the first monthly resolved, 41-year record of geochemical variations (delta18O and Sr\\/Ca) in a fast-growing Diploria strigosa brain coral from Guadeloupe, Caribbean Sea. Linear regression yields a significant correlation of coral Sr\\/Ca (delta18O) with instrumental sea surface temperature (SST) on both monthly and mean annual scales (e.g., r = -0.59 for correlation between Simple Ocean Data Assimilation

Steffen Hetzinger; Miriam Pfeiffer; Wolf-Christian Dullo; Eberhard Ruprecht; Dieter Garbe-Schönberg

2006-01-01

249

Sr\\/Ca and ?18O in a fast-growing Diploria strigosa coral: Evaluation of a new climate archive for the tropical Atlantic  

Microsoft Academic Search

This study provides the first monthly resolved, 41-year record of geochemical variations (?18O and Sr\\/Ca) in a fast-growing Diploria strigosa brain coral from Guadeloupe, Caribbean Sea. Linear regression yields a significant correlation of coral Sr\\/Ca (?18O) with instrumental sea surface temperature (SST) on both monthly and mean annual scales (e.g., r = ?0.59 for correlation between Simple Ocean Data Assimilation

Steffen Hetzinger; Miriam Pfeiffer; Wolf-Christian Dullo; Eberhard Ruprecht; Dieter Garbe-Schönberg

2006-01-01

250

Upper critical field of isoelectron substituted SrFe2(As1-xPx)2  

SciTech Connect

The upper critical field H-c2 of optimally doped, iron-based superconductor SrFe2(As1-xPx)(2) (x = 0.35, T-c = 25 K) was measured as a function of temperature down to 1.6K for two principal directions of magnetic field H parallel to c and H parallel to a. Measurements were performed in pulsed magnetic fields up to 65 T using a tunnel-diode resonator technique on as-grown and heavy-ion-irradiated single crystals, with columnar defect density corresponding to a matching field B-phi = 25 T. The H-c2,(c) (T) is close to T linear, while clear saturation is observed for H-c2,(a) (T), leading to a strongly temperature-dependent anisotropy parameter gamma. The linear shape of H-c2,(c) (T) is very similar to that observed in nodal KFe2As2, but very different from full-gap LiFeAs. Irradiation does not introduce any additional features on the H-c2(T) line corresponding to the matching field. Instead, it suppresses uniformly both T-c and H-c2, keeping their ratio constant.

Yeninas, S. [Ames Laboratory; Tanatar, M. A. [Ames Laboratory; Murphy, J. [Ames Laboratory; Strehlow, C. P. [Ames Laboratory; Ayala-Valenzuela, O. E. [Los Alamos National Laboratory; McDonald, R. D. [Los Alamos National Laboratory; Welp, U. [Argonne National Laboratory; Kwok, W. K. [Argonne National Laboratory; Kobayashi, T. [Osaka University; Miyasaka, S. [Osaka University; Tajima, S. [Osaka University; Prozorov, Ruslan [Ames Laboratory

2013-03-06

251

The SR Ca[sup 2+] ATPase of the Antarctic scallop Adamussium colbecki: Cold adaptation and heavy metal effects  

SciTech Connect

Cell calcium is accumulated in intracellular stores by sarco-endoplasmic reticulum Ca[sup 2+] ATPases functionally interacting with the membrane lipid environment. Cold adaptations of membrane lipids in Antarctic Sea organisms suggest possible adaptive effects also on sarco-endoplasmic reticulum Ca[sup 2+] ATPases. The authors investigated the SR Ca[sup 2+] ATPase of an Antarctic scallop, Adamussium colbecki, by characterizing the enzyme activity and studying temperature effects. Ca[sup 2+] ATPase, assayed by following ATP hydrolysis was thapsigargin- and vanadate-sensitive showed maximum activity under 2 [micro]M Ca[sup 2+], 200 mM KCl and pH 7.2, and had a K[sub M] for ATP of 22 [+-] 7 [micro]M. Temperature effects showed an Arrhenius inversion between [minus]1.8 and 0 C, indicating cold adaptation, an Arrhenius break at 10 C, and a collapse above 20 C. A. colbecki accumulates high amounts of cadmium in the digestive gland; heavy metal effects on sarco-endoplasmic reticulum Ca[sup 2+] ATPases were therefore tested, finding an IC[sub 50] = 0.9 [micro]M for Hg[sup 2+] and 3 [micro]M for Cd[sup 2+]. Finally, SDS-PAGE analysis showed a main band at about 100 kDa, which was identified as sarco-endoplasmic reticulum Ca[sup 2+] ATPase after trypsin digestion, and accounted for 60% total protein.

Viarengo, A.; Burlando, B. (Univ. del Piemonte Orientale, Alessandria (Italy). Dipt. di Scienze e Tecnologie Avanzate); Mancinelli, G.; Marchi, B.; Panfoli, I. (Univ. de Genova, Genoa (Italy))

1999-01-01

252

Growth and characterization of laser-deposited superconducting Bi-Sr-Ca-Cu-O thin films  

NASA Astrophysics Data System (ADS)

Superconducting Bi-Sr-Ca-Cu-O thin films with thickness 400-3,500 A have been deposited on (100) MgO and (100) LaAlO3 by a pulsed excimer XeCl laser (gamma = 308 nm, tau = 20 ns, and energy density = 4-5 J/sq cm). Oxygen pressure during deposition and substrate temperature are 0.1-100 mTorr and 350-750 C, respectively. The as-deposited films were annealed either inside (in situ) or outside (ex situ) the deposition chamber to improve the crystallinity and the superconducting transition of the films. Formation of 2212 and 2223 phases was controlled by tailoring the deposition and annealing parameters. Corresponding (T(sub c))'s of these phases in the ex situ films measured by zero-field cooled diamagnetic transition at 10 Oe are 80 and 110 K; however, the in situ mirror-like shiny films with 2223 phase only exhibit (T(sub c)) = 81 K (or 98 K in an a.c. field of 0.1 Oe at 125 Hz). These films were also characterized by SEM, TEM, SQUID magnetometer, and AC susceptometer to study their morphology, microstructure, and magnetic properties. The critical magnetization current density (J(sub c)) of the ex situ films is of the order of 10(exp 7)-10(exp 8) A/sq cm and 10(exp 5)-10(exp 6) A/sq cm for H (perpendicular) c-axis and H (parallel) c-axis, respectively, at 7 K up to 5 T. The J(sub c) of the in situ films is two orders of magnitude lower than that of the ex situ films, and further enhancement of J(sub c) appears promising if better crystallinity of the in situ films can be achieved. A qualitative phase diagram with respect to the development of 2212 and 2223 phases are discussed.

Kung, P. J.; Muenchausen, R. E.

253

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

254

Effects of antimony substitution on bismuth based superconductors  

NASA Technical Reports Server (NTRS)

The effect of Sb substitution and simultaneous substitution of Pb and Sb on the superconducting transition temperatures in the BiSrCaCuO system is investigated. The 2:2:2:3 phase is of particular interest since any small increase in the transition temperature could be of great interest. More that 90 different samples were prepared based on 2:2:2:3 stoichiometry in the BiSrCaCuO system. After this preliminary attempt, four different families of samples were investigated. In the first family of samples, Bi was substituted by Sb to form Bi(1.9)Sb(0.1)Sr2Ca2Cu3O(y). The second group of samples were prepared by simultaneous addition of Pb and Sb with nominal composition Bi(1.8)Pb(0.1)Sb(0.1)Sr2Ca2Cu3O(y). The third and fourth groups were prepared to determine the effect created when the Pb concentration is increased with the nominal compositions being Bi(1.7)Pb(0.1)Sr2Ca2Cu3O(y) and Bi(1.6)Sb(0.1)Sr2Ca2Cu3O(y). The results of these investigations are presented with a discussion.

Barrientos, Alfonso

1990-01-01

255

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

256

Metal-insulator phenomena in single crystals of Pr_0.65(Ca_1-ySr_y)_0.35MnO3 with controlled charge-ordering instability  

NASA Astrophysics Data System (ADS)

The competition between the ferromagnetic state due to double exchange and the ordering of Mn^3+/Mn^4+ with 1:1(E.O. Wollan and W.C. Koehler, Phys. Rev. 100), 545 (1955). (charge ordering), have been investigated in single crystals of Pr_0.65(Ca_1-ySr_y)_0.35MnO3 prepared by the floating zone (FZ) technique. The charge ordering in Pr_1-xCa_xMnO3 appears in broader region of x (0.3<=x<0.75)(Z. Jirak et al)., J. Mag. Mag. Matter. 53, 153 (1985)., and!!Pr_0.65Ca0 .35MnO3 (x=0.35) undergoes the charge-ordering transition at T ~230 K. As the Ca is substituted with Sr in Pr_0.65(Ca_1-ySr_y)_0.35MnO_3, however, the temperature of the charge-ordering transition becomes lower. Furthermore, for a y=0.3 sample which undergoes to a charge-ordered state below 200 K, an insulator-to-metal transition with change in resistivity by 5-6 orders magnitude is observed at T ~100 K. The phenomenon indicates that as the averaged ionic radius in (R, A) sites increases the chrage-ordered state collapses perhaps due to the increased transfer interaction as in the case under a magnetic field. This research was supported by NEDO (New Energy and Industrial Technology Development Organization) of Japan.

Tomioka, Y.; Asamitsu, A.; Tokura, Y.

1996-03-01

257

Secondary ionization coefficient ? of MgO, SrO and CaO and the correlation between ? and charge accumulated on CaO in argon  

NASA Astrophysics Data System (ADS)

An experimental investigation of Townsend's secondary ionization coefficient ? is carried out for MgO, SrO and CaO film electrodes. These oxides are utilized, or are to be utilized, in next-generation plasma display panels. All of the experiments are performed in argon. In particular, in the case of CaO film, our attention is attracted to the effect of charge accumulated on CaO film. For this purpose, the breakdown voltage Vs is observed from waveforms of the gap voltage and charge accumulated on the dielectric film electrodes with the repeated breakdown. Townsend's criterion is utilized to estimate ? from the breakdown voltage. In the case of the CaO film, ? increases gradually with repeated breakdowns and reaches a stationary value. The increase of ? is considered to be due to the charge that accumulates on the dielectric electrode triggering the next breakdown. Therefore, it is concluded that the increased ? is sustained by a combined process consisting of restarted electrons that have accumulated on the CaO film and the original ? action, as observed in metallic electrodes in a low-pressure gas discharge.

Suzuki, S.; Itoh, H.

2014-12-01

258

Targeted ablation of the histidine-rich Ca2+-binding protein (HRC) gene is associated with abnormal SR Ca2+-cycling and severe pathology under pressure-overload stress  

PubMed Central

The histidine-rich Ca2+-binding protein (HRC) is located in the lumen of the sarcoplasmic reticulum (SR) and exhibits high capacity Ca2+ binding properties. Overexpression of HRC in the heart resulted in impaired SR Ca2+ uptake and depressed relaxation through its interaction with SERCA2a. However, the functional significance of HRC in overall regulation of calcium cycling and contractility is not currently well defined. To further elucidate the role of HRC in vivo under physiological and pathophysiological conditions, we generated and characterized HRC-knockout (KO) mice. The KO mice were morphologically and histologically normal compared to wild type (WT) mice. At the cellular level, ablation of HRC resulted in significantly enhanced contractility, Ca2+ transients, and maximal SR Ca2+ uptake rates in the heart. However, after-contractions were developed in 50% of HRC-KO cardiomyocytes, compared to 11% in WT mice under stress conditions of high frequency stimulation (5 Hz) and isoproterenol application. A parallel examination of the electrical activity revealed significant increases in the occurrence of Ca2+ spontaneous SR Ca2+ release and delayed after depolarizations (DADs) with ISO in HRC-KO, compared to WT cells. The frequency of Ca2+ sparks was also significantly higher in HRC-KO cells with ISO, consistent with the elevated SR Ca2+ load in the KO cells. Furthermore, HRC-KO cardiomyocytes showed significantly deteriorated cell contractility and Ca2+-cycling caused possibly by depressed SERCA2a expression after transverse-aortic constriction (TAC). Also HRC null mice exhibited severe cardiac hypertrophy, fibrosis, pulmonary edema and decreased survival after TAC. Our results indicate that ablation of HRC is associated with poorly regulated SR Ca2+-cycling, and severe pathology under pressure-overload stress, suggesting an essential role of HRC in maintaining the integrity of cardiac function. PMID:23553082

Park, Chang Sik; Chen, Shan; Lee, Hoyong; Cha, Hyeseon; Hong, Sunghee; Han, Peidong; Ginsburg, Kenneth S.; Jin, Sora; Park, Inju; Singh, Vivek P.; Wang, Hong-Sheng; Franzini-Armstrong, Clara; Park, Woo Jin; Bers, Donald M.; Kranias, Evangelia G.; Cho, Chunghee; Kim, Do Han

2014-01-01

259

Characterization of Sr-substituted W-type hexagonal ferrites synthesized by sol-gel autocombustion method  

NASA Astrophysics Data System (ADS)

The magnetic and microwave characterization of single phase hexaferrites of entirely new composition Ba1-xSrxCo2AlFe15O27 (x=0.2-1.0) for application in a microwave absorber, have been reported. The samples synthesized by sol-gel method were investigated by differential thermal analyzer, Fourier transform infrared spectroscope, X-ray diffractometer, field emission gun scanning electron microscope, vibrating sample magnetometer and vector network analyzer. Platelet grains exhibit well defined hexagonal shape which is a better shape for microwave absorption. M-H loops for a selected sample were measured for a temperature range of 4.2-400 K. Moreover M-H loops for all Sr-substituted samples were also measured at room temperature up to a maximum applied field of 9 T. Saturation magnetization values were calculated by the law of approach to saturation. The room temperature coercivity for all the samples is found to be a few hundred oersteds which is necessary for electromagnetic materials and makes these ferrites ideal for microwave devices, security, switching and sensing applications. The complex permittivity, permeability and reflection losses of a selected ferrite-epoxy composite were also investigated over a frequency range of 0.5-13 GHz.

Ahmad, Mukhtar; Grössinger, R.; Kriegisch, M.; Kubel, F.; Rana, M. U.

2013-04-01

260

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

261

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

262

High-pressure synthesis of the cubic perovskite BaRuO3 and evolution of ferromagnetism in ARuO3 (A = Ca, Sr, Ba) ruthenates  

PubMed Central

The cubic perovskite BaRuO3 has been synthesized under 18 GPa at 1,000°C. Rietveld refinement indicates that the new compound has a stretched Ru–O bond. The cubic perovskite BaRuO3 remains metallic to 4 K and exhibits a ferromagnetic transition at Tc = 60 K, which is significantly lower than the Tc ? 160 K for SrRuO3. The availability of cubic perovskite BaRuO3 not only makes it possible to map out the evolution of magnetism in the whole series of ARuO3 (A = Ca, Sr, Ba) as a function of the ionic size of the A-site rA, but also completes the polytypes of BaRuO3. Extension of the plot of Tc versus rA in perovskites ARuO3 (A = Ca, Sr, Ba) shows that Tc does not increase as the cubic structure is approached, but has a maximum for orthorhombic SrRuO3. Suppressing Tc by Ca and Ba doping in SrRuO3 is distinguished by sharply different magnetic susceptibilities ?(T) of the paramagnetic phase. This distinction has been interpreted in the context of a Griffiths' phase on the (Ca Sr)RuO3 side and bandwidth broadening on the (Sr,Ba)RuO3 side. PMID:18480262

Jin, C.-Q.; Zhou, J.-S.; Goodenough, J. B.; Liu, Q. Q.; Zhao, J. G.; Yang, L. X.; Yu, Y.; Yu, R. C.; Katsura, T.; Shatskiy, A.; Ito, E.

2008-01-01

263

Phase stability and microstructural evolution in the system Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}  

SciTech Connect

The dependence of the oxygen nonstoichiometry of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} (2212) on temperature and oxygen partial pressure has been determined in the temperature range of 300 to 1,000 C and the oxygen partial pressure range of 3 {times} 10{sup {minus}3} to 1 atm (1 atm = 10{sup 5} Pa). The solidus temperature of 2212 was identified by differential thermal analysis over the same ranges of temperature and oxygen partial pressure. The nature of the decomposition of 2212 was determined by thermogravimetric analysis in the temperature range of 800 to 1,000 C and oxygen partial pressure range of 3 {times} 10{sup {minus}3} tp 1 atm. Microstructural evolution was examined by quenching materials, equilibrated with atmospheres of fixed partial pressures of oxygen, at various stages in the decomposition and identifying the phases present by electron microscopy and wavelength dispersive spectroscopy. With increasing temperature, at fixed oxygen partial pressure, the decomposition of 2212 in the presence of 1.9 mol% Sr{sub 0.4}Ca{sub 0.6}CuO{sub 2} follows the sequence 2212 + Sr{sub 0.4}Ca{sub 0.6}CuO{sub 2} {yields} 2212 + Sr{sub 0.4}Ca{sub 0.6}CuO{sub 2} + Sr{sub 0.2}Ca{sub 1.8}CuO{sub 3} {yields} Sr{sub 0.5}Ca{sub 0.5}CuO{sub 2} + Sr{sub 0.3}Ca{sub 1.7}CuO{sub 3} + Sr{sub 0.5}Ca{sub 0.5}Cu{sub 2}O{sub 3} + L{sub 1} {yields} Sr{sub 0.5}Ca{sub 0.5}CuO{sub 2} + Sr{sub 0.3}Ca{sub 1.7}CuO{sub 3} + L{sub 2} {yields} L{sub 3}.

Medendorp, N.W. Jr.; Gaskell, D.R. [Purdue Univ., West Lafayette, IN (United States). School of Materials Engineering

1999-08-01

264

Functional Expression of the Extracellular Calcium Sensing Receptor (CaSR) in Equine Umbilical Cord Matrix Size-Sieved Stem Cells  

PubMed Central

Background The present study investigates the effects of high external calcium concentration ([Ca2+]o) and the calcimimetic NPS R-467, a known calcium-sensing receptor (CaSR) agonist, on growth/proliferation of two equine size-sieved umbilical cord matrix mesenchymal stem cell (eUCM-MSC) lines. The involvement of CaSR on observed cell response was analyzed at both the mRNA and protein level. Methodology/Principal Findings A large (>8 µm in diameter) and a small (<8 µm) cell line were cultured in medium containing: 1) low [Ca2+]o (0.37 mM); 2) high [Ca2+]o (2.87 mM); 3) NPS R-467 (3 µM) in presence of high [Ca2+]o and 4) the CaSR antagonist NPS 2390 (10 µM for 30 min.) followed by incubation in presence of NPS R-467 in medium with high [Ca2+]o. Growth/proliferation rates were compared between groups. In large cells, the addition of NPS R-467 significantly increased cell growth whereas increasing [Ca2+]o was not effective in this cell line. In small cells, both higher [Ca2+]o and NPS R-467 increased cell growth. In both cell lines, preincubation with the CaSR antagonist NPS 2390 significantly inhibited the agonistic effect of NPS R-467. In both cell lines, increased [Ca2+]o and/or NPS R-467 reduced doubling time values.Treatment with NPS R-467 down-regulated CaSR mRNA expression in both cell lines. In large cells, NPS R-467 reduced CaSR labeling in the cytosol and increased it at cortical level. Conclusions/Significance In conclusion, calcium and the calcimimetic NPS R-467 reduce CaSR mRNA expression and stimulate cell growth/proliferation in eUCM-MSC. Their use as components of media for eUCM-MSC culture could be beneficial to obtain enough cells for down-stream purposes. PMID:21437284

Martino, Nicola Antonio; Lange-Consiglio, Anna; Cremonesi, Fausto; Valentini, Luisa; Caira, Michele; Guaricci, Antonio Ciro; Ambruosi, Barbara; Sciorsci, Raffaele Luigi; Lacalandra, Giovanni Michele; Reshkin, Stephan Joel; Dell'Aquila, Maria Elena

2011-01-01

265

Disorder effects in (LaTb)0.5(CaSr)0.5MnO3 compounds  

NASA Astrophysics Data System (ADS)

Electrical, magnetotransport, and magnetization measurements have been carried out on half-doped (La0.5-xTbx)(Ca0.38-ySr0.12+y)MnO3 (0.025?x?0.125; y=0.8x) compounds. The increase in Tb3+ and Sr2+ contents keeps the average A-site ionic radius constant at ˜1.215 Å but introduces increasing size disorder. The insulator-metal transition temperature (Tp) falls from 191 to 107 K and the Curie temperature (TC) falls from 230 to 106 K as x increases from 0.025 to 0.125. Interestingly, with increasing size disorder, the disparity between TC and Tp disappears and magnetoresistance increases around Tp but decreases at low temperatures. This is discussed in the light of phase segregation.

Rana, D. S.; Mavani, K. R.; Thaker, C. M.; Kuberkar, D. G.; Kundaliya, D. C.; Malik, S. K.

2004-06-01

266

?SR study on multi-layered HgBa 2Ca 4Cu 5O y (Hg-1245) superconductor  

NASA Astrophysics Data System (ADS)

We have carried out zero-field muon spin relaxation (ZF-?SR) measurements in multi-layered HgBa2Ca4Cu5Oy (Hg-1245) superconductor with Tc of 108 K. The variation of ZF-?SR time spectra from Gaussian-type to exponential-type behavior was observed with decreasing temperature below 60 K and the muon precessions were also observed below 45 K. These results indicate the appearance of a static magnetic order of Cu moments at muon sites below Tc. Compared with the results of NMR measurements, they suggest that this magnetic order is caused in three under-doped inner planes of five CuO2 planes in Hg-1245.

Tokiwa, K.; Ito, S.; Okumoto, H.; Higemoto, W.; Nishiyama, K.; Iyo, A.; Tanaka, Y.; Watanabe, T.

2003-05-01

267

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

268

Sex differences in SR Ca(2+) release in murine ventricular myocytes are regulated by the cAMP/PKA pathway.  

PubMed

Previous studies have shown that ventricular myocytes from female rats have smaller contractions and Ca(2+) transients than males. As cardiac contraction is regulated by the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway, we hypothesized that sex differences in cAMP contribute to differences in Ca(2+) handling. Ca(2+) transients (fura-2) and ionic currents were measured simultaneously (37°C, 2Hz) in ventricular myocytes from adult male and female C57BL/6 mice. Under basal conditions, diastolic Ca(2+), sarcoplasmic reticulum (SR) Ca(2+) stores, and L-type Ca(2+) current did not differ between the sexes. However, female myocytes had smaller Ca(2+) transients (26% smaller), Ca(2+) sparks (6% smaller), and excitation-contraction coupling gain in comparison to males (23% smaller). Interestingly, basal levels of intracellular cAMP were lower in female myocytes (0.7±0.1 vs. 1.7±0.2fmol/?g protein; p<0.001). Importantly, PKA inhibition (2?M H-89) eliminated male-female differences in Ca(2+) transients and gain, as well as Ca(2+) spark amplitude. Western blots showed that PKA inhibition also reduced the ratio of phospho:total RyR2 in male hearts, but not in female hearts. Stimulation of cAMP production with 10?M forskolin abolished sex differences in cAMP levels, as well as differences in Ca(2+) transients, sparks, and gain. To determine if the breakdown of cAMP differed between the sexes, phosphodiesterase (PDE) mRNA levels were measured. PDE3 expression was similar in males and females, but PDE4B expression was higher in female ventricles. The inhibition of cAMP breakdown by PDE4 (10?M rolipram) abolished differences in Ca(2+) transients and gain. These findings suggest that female myocytes have lower levels of basal cAMP due, in part, to higher expression of PDE4B. Lower cAMP levels in females may attenuate PKA phosphorylation of Ca(2+) handling proteins in females, and may limit positive inotropic responses to stimulation of the cAMP/PKA pathway in female hearts. PMID:25066697

Parks, Randi J; Ray, Gibanananda; Bienvenu, Laura A; Rose, Robert A; Howlett, Susan E

2014-10-01

269

Fine structure of Ca , Sr , Ba , and Ra from the many-body theory calculation V. A. Dzuba* and G. F. Gribakin  

E-print Network

.e., correlations between the three valence electrons ns2 np and the Ca2 core indeed reduce the binding energy see Table I . Even smaller electron af- finities were obtained in the configuration-interaction calcu by binding a p electron into an open shell, Ca , Sr , Ba , and Ra . This binding is due to a strong

Gribakin, Gleb

270

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

271

Sr/Ca profile of long-lived Tridacna gigas bivalves from South China Sea: A new high-resolution SST proxy  

NASA Astrophysics Data System (ADS)

High-resolution ?18O and Sr/Ca ratio profiles of a modern (live-caught) and a fossil (dead-collected) giant bivalve shell (Tridacna gigas) from northern South China Sea were analyzed. The high-resolution ?18O profiles, as documented in most of previous studies, showed pronounced seasonal cycles and recorded the combined influence of seawater ?18O and sea surface temperature. The Sr/Ca ratio profiles derived from ICP-OES had well-defined annual cycles and significant and negative correlation with sea surface temperature, while the Sr/Ca profiles derived from LA-ICP-MS did not reveal clear annual cycles. This difference was likely caused by the organics contents in T. gigas shells, which had a chemical composition different than CaCO3 crystals and a heterogeneous distribution across the shell, the sampling methods, and the experimental errors. Two calibration equations between Sr/Ca ratios, determined by ICP-OES, of modern T. gigas shell and instrumental SST were calculated based on all monthly and extremum SST data, and the equation from extremum data produced better SST predictions. These results suggested that the high-resolution ICP-OES derived Sr/Ca ratios of T. gigas in the South China Sea had the potential of providing a good proxy of historical SST.

Yan, Hong; Shao, Da; Wang, Yuhong; Sun, Liguang

2013-07-01

272

Effect of anionic substitution on the structural and magneto-electrical properties of La-Ca-Mn-O perovskite manganites  

NASA Astrophysics Data System (ADS)

The role of anion substitution of oxygen by fluorine in La0.7Ca0.3MnO3-?Fx (x=0.0 and 0.6) system has been investigated by means of X-ray powder diffraction, electrical resistivity and magnetization measurements. The oxygen content of the samples, estimated by a redox back titration method, decreases with doping while the lattice parameters and unit cell volume increase slightly. The Curie temperature and the metal-insulator transition temperatures of the samples are also found to increase with doping. The deduced magnetoresistance is slightly higher for the doped sample.

Altintas, S. P.; Mahamdioua, N.; Amira, A.; Terzioglu, C.

2014-11-01

273

A RRKM study and a DFT assessment on gas-phase fragmentation of formamide-M(2+) (M = Ca, Sr).  

PubMed

A kinetic study of the unimolecular reactivity of formamide-M(2+) (M = Ca, Sr) systems was carried out by means of RRKM statistical theory using high-level DFT. The results predict M(2+), [M(NH2)](+) and [HCO](+) as the main products, together with an intermediate that could eventually evolve to produce [M(NH3)](2+) and CO, for high values of internal energy. In this framework, we also evaluated the influence of the external rotational energy on the reaction rate constants. In order to find a method to perform reliable electronic structure calculations for formamide-M(2+) (M = Ca, Sr) at a relatively low computational cost, an assessment of different methods was performed. In the first assessment twenty-one functionals, belonging to different DFT categories, and an MP2 wave function method using a small basis set were evaluated. CCSD(T)/cc-pWCVTZ single point calculations were used as reference. A second assessment has been performed on geometries and energies. We found BLYP/6-31G(d) and G96LYP/6-31+G(d,p) as the best performing methods, for formamide-Ca(2+) and formamide-Sr(2+), respectively. Furthermore, a detailed assessment was done on RRKM reactivity and G96LYP/6-31G(d) provided results in agreement with higher level calculations. The combination of geometrical, energetics and kinetics (RRKM) criteria to evaluate DFT functionals is rather unusual and provides an original assessment procedure. Overall, we suggest using G96LYP as the best performing functional with a small basis set for both systems. PMID:24921953

Martín-Sómer, Ana; Gaigeot, Marie-Pierre; Yáñez, Manuel; Spezia, Riccardo

2014-07-28

274

Fabrication of spherical CaO-SrO-ZnO-SiO? particles by sol-gel processing.  

PubMed

This study was concerned with the fabrication of ceramic CaO-SrO-ZnO-SiO(2) spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol-gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO-SrO-ZnO-SiO(2) particles by sol-gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H(2)O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3-5 mum homogenous spherical particles were obtained at a H(2)O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO(3)):Ca(NO(3))(2):Zn(NO(3))(2):Si(OC(2)H(5))(4) = x:0.12:(0.40 - x):0.48 (0

Kim, Ill Yong; Towler, Mark R; Wren, Anthony; Ohtsuki, Chikara

2009-11-01

275

Optimization of an inductively coupled plasma–optical emission spectrometry method for the rapid determination of high-precision Mg\\/Ca and Sr\\/Ca in foraminiferal calcite  

Microsoft Academic Search

The ability to measure Mg\\/Ca and Sr\\/Ca in foraminiferal calcite has increased in importance following their identification as palaeoceanographic tracers with significant potential to constrain past changes in ocean chemistry and temperature. However, in order to tackle palaeoceanographic problems, it is essential to develop methods for the determination of these ratios that have both rapid sample throughput and high analytical

D. R. H. Green; M. J. Cooper; C. R. German; P. A. Wilson

2003-01-01

276

Optimization of an inductively coupled plasma-optical emission spectrometry method for the rapid determination of high-precision Mg\\/Ca and Sr\\/Ca in foraminiferal calcite  

Microsoft Academic Search

The ability to measure Mg\\/Ca and Sr\\/Ca in foraminiferal calcite has increased in importance following their identification as palaeoceanographic tracers with significant potential to constrain past changes in ocean chemistry and temperature. However, in order to tackle palaeoceanographic problems, it is essential to develop methods for the determination of these ratios that have both rapid sample throughput and high analytical

D. R. H. Green; M. J. Cooper; C. R. German; P. A. Wilson

2003-01-01

277

Superconductivity in the C32 intermetallic compounds AAl 2- xSi x, with A=Ca and Sr; and 0.6< x<1.2  

NASA Astrophysics Data System (ADS)

The intermetallic compounds AAl 2- xSi x, where A=Ca, Sr or Ba, crystallize in the C32 structure, same as the recently discovered MgB 2 with a high superconducting transition temperature of 39 K. For x=1, superconductivity has been observed in AAlSi with A=Ca and Sr, but not with A=Ba. The transition temperatures are 7.8 and 5.1 K, respectively for CaAlSi and SrAlSi. The CaAl 2- xSi x compound system display a Tc-peak at x=1, a possible x-induced electronic transition at x?0.75 and a possible miscibility gap near x?1.1 which results in a very broad superconducting transition. The Seebeck coefficients of AAlSi indicate that their carriers are predominantly electrons in nature, in contrast to the holes in MgB 2.

Lorenz, B.; Lenzi, J.; Cmaidalka, J.; Meng, R. L.; Sun, Y. Y.; Xue, Y. Y.; Chu, C. W.

2002-12-01

278

Substitution of H- for O- and H- emissions of 12CaO•7Al2O3  

NASA Astrophysics Data System (ADS)

By using an anion-exchanging method, about 90% of the O- anions in the C12A7-O - microporous crystal ([Ca24Al28O64]4+•4O-) have been substituted primarily by the H- anions, leading to the successful formation of a new H- emission material, C12A7-H -([Ca24Al28O64]4+•4H-). A sustainable and stable emission of H-, in a current density of ?A /cm2 level, has been obtained by supplying H2 and electrons on the backside of the C12A7-H - sample. The emission features of C12A7-H -, including temperature and field effects, have been investigated. It is expected that the present material could be practically used as an H- anion generator.

Huang, F.; Li, J.; Xian, H.; Tu, J.; Sun, J. Q.; Yu, S. Q.; Li, Q. X.; Torimoto, Y.; Sadakata, M.

2005-03-01

279

Enhanced red fluorescence in Sr2Si1-xGexO4:Eu3+ phosphors by the substitution of Si by Ge for white light emitting diodes  

NASA Astrophysics Data System (ADS)

Eu3+-doped Sr2Si1-xGexO4 (x=0-1) phosphors have been prepared by the high temperature solid-state reaction method. The luminescent properties of these phosphors were investigated. Red fluorescence of Eu3+ is enhanced gradually in the samples with increasing substitution of Si by Ge upon the excitation of 393 nm light. The intensity is increased by 50% with full substitution of Si by Ge. These results are originated from the structural changes and the phonon energy reduction in the samples due to the substitution of Si by Ge. The CIE chromaticity coordinates of the phosphors vary slightly around (0.62, 0.37) and all are in the red color region. The results indicate that these phosphors could be promising red phosphors for white light emitting diodes.

Huang, Lihui; Xu, Shiqing; Guo, Meiquan; Wang, Chenyue; Hua, Youjie; Zhao, Shilong; Deng, Degang; Wang, Huanping; Jia, Guohua

2012-07-01

280

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

281

Preparation of a Ag-doped Bi-Sr-Ca-Cu-O bulk sample by the floating-zone method  

Microsoft Academic Search

Bulk samples with nominal composition of Bi2Sr2CaCu2O(y) doped with 0, 10 and 20 wt pct Ag were prepared by the floating-zone method at growth rates of 2 mm\\/h and 5 mm\\/h. Ag-doping seems to slightly enhance J(c) while annealing is very effective for J(c) enhancement. From preliminary ac susceptibility measurements, the J(c) enhancement by annealing is considered to be due

Yukio Kubo; Kazuo Michishita; Noriyuki Shimizu; Yutaka Higashida; Hisanori Yokoyama; Yumi Hayami; Eikichi Inukai; Akira Saji; Noboru Kuroda; Hiroshi Yoshida

1989-01-01

282

Third-order elastic constants of the high temperature superconductor Bi 2Sr 2CaCu 2O 8  

Microsoft Academic Search

The complete set of non-vanishing third-order elastic moduli of high temperature superconductor Bi2Sr2CaCu2O8 (Bi-2:2:1:2) is obtained theoretically. The interactions of nine nearest neighbours of each atom in the unit cell of Bi-2:2:1:2 are taken into account, while estimating the strain energy density. Here the finite strain elasticity theory is used to obtain the strain energy density of the Bi-2:2:1:2 system.

K. P. Jayachandran; C. S. Menon

1999-01-01

283

Europium doped thiosilicate phosphors of the alkaline earth metals Mg, Ca, Sr and Ba: Structure and luminescence  

NASA Astrophysics Data System (ADS)

Divalent europium is notorious for the tunability of its emission, depending on the host material in which it is used as a dopant. In europium-doped alkaline earth thiosilicates, two distinct emission bands can be observed for the alkaline earth metals Mg, Ca and Sr while only a single band is found for barium thiosilicate. In this work, we first complete the data with europium-doped magnesiumthiosilicate. Then, the solid solution of calcium and magnesium thiosilicate is presented. To conclude, the presence of multiple emission peaks in some compounds is explained on a structural basis, by analysing the possibilities for preferential orientation of the europium d-orbitals.

Parmentier, Anthony B.; Smet, Philippe F.; Poelman, Dirk

2010-12-01

284

Dimensional crossover of quantum collective creep in Bi2Sr2CaCu2O8+ y  

NASA Astrophysics Data System (ADS)

We studied magnetic field dependence of magnetization relaxation in Bi2Sr2CaCu2O8+ y single crystals down to 500 mK. In the quantum collective creep (QCC) regime at low temperatures, the normalized relaxation rate S as a function of field shows a characteristic dip at low fields. We ascribe the origin of this dip to the 2D-3D dimensional crossover in the vortex system. At higher temperatures, the field dependence of S is more complicated. We discuss the field dependence of S based on two competing mechanisms due to QCC and thermally activated motion of vortices.

Tamegai, T.; Sato, M.; Yamamoto, T.; Ooi, S.; Shibauchi, T.

1996-03-01

285

Chemical diffusion of oxygen in dense, textured (Bi,Pb) 2Sr 2Ca 2Cu 3O x  

NASA Astrophysics Data System (ADS)

Dense polycrystalline (Bi,Pb) 2Sr 2Ca 2Cu 3O y specimens were fabricated by sinter forging. The specimens exhibited excellent phase purity and strong texture of c-axes, which were preferentially aligned parallel to the forging direction. The chemical diffusion coefficient of oxygen, D˜, measured in pure O 2 could be represented as D˜ab?1.78×10 -3 exp(-0.96 eV/ kT), where the subscript ab refers to diffusion within the a- b-plane. The measurements suggested that D˜ab? D˜c, where the subscript c refers to diffusion in the c-direction.

Park, J.-H.; Goretta, K. C.; Murayama, Norimitsu

1999-02-01

286

LiCaAlF 6 and LiSrAlF 6: tunable solid state laser host materials  

NASA Astrophysics Data System (ADS)

Tunable all-solid-state lasers find more and more applications in different fields. Chromium-doped ternary colquiriites, LiCaAlF 6 (LiCAF) and LiSrAlF 6 (LiSAF), show a tunable laser activity in the region of 720-840 nm and 780-1010 nm, respectively. Other interesting properties enable them to be used as scintillators and window materials. Single crystals of LiCAF and LiSAF have been grown by various methods, including the Czochralski, Bridgeman, zone melting and top-seeded solution growth techniques. Vertical gradient freezing (VGF) is proposed for producing high optical quality crystals.

Samtleben, Till A.; Hulliger, Jürg

2005-03-01

287

The effect of light on intrashell trace metal variability (Mg/Ca and Sr/Ca) in the planktic foraminifer Orbulina universa  

NASA Astrophysics Data System (ADS)

The shell walls of many planktic foraminifers contain alternating bands of high and low Mg/Ca calcite. These bands have been attributed to chamber formation, light-modulated (circadian-like) biological effects, and light (e.g. pH change in the calcifying environment driven by the photosynthesis/respiration of photosynthetic symbionts). Previous experiments on the living planktic foraminifer Orbulina universa confirm a diurnal nature in the banding of O. universa: a wide band of low-Mg calcite forms during the day (12-hour light) and a narrower band of high Mg calcite forms at night (12-hour dark) (Spero et al., in prep). During the summer of 2011, we explored the response of Mg banding to light by culturing foraminifera at constant temperature, salinity, and ambient seawater pH, but with different light schedules: reverse light cycles (day/night cycle shifted by 12 hours), constant (24-hour) light, and constant (24-hour) dark conditions. We used an artificial Ba spike to mark 12-hour intervals of growth, regardless of the imposed light regime. In specimens grown with a reversed day/night light/dark cycle, we observe an immediate shift in the timing of Mg/Ca banding. The timing of high and low Mg/Ca bands in these specimens is indistinguishable from specimens grown under a normal day/night light/dark cycle. Mg/Ca bands are present in some of the specimens cultured in constant light and in all specimens grown in constant dark conditions. Banding in the constant light and constant dark specimens is not paced by a diurnal cycle. The amplitude of the banding in these specimens is diminished and the average Mg/Ca ratios are 30% lower in comparison to those kept on a 12-hour light/dark cycle. Additionally, we find the Sr/Ca ratios are similar in both the constant light and reverse light/dark specimens, but are statistically significantly lower in the constant dark specimens (8% lower, p-value << 0.05). These results indicate that changes in microenvironment pH due to symbiont photosynthesis are not pacing Mg/Ca banding in Orbulina universa, although photosymbiont/pH activity could modify Mg/Ca band amplitude. The presence of Mg/Ca banding in some specimens of both the constant light and constant dark experiments are consistent with a light-modulated biological mechanism that is disrupted by the absence of a day/night cycle and is no longer paced by a 24-hour cycle.

Fehrenbacher, J. S.; Spero, H. J.; Russell, A. D.; Gagnon, A. C.; Vetter, L.; Snyder, J.; Naumann, E.; Grimm, B. L.; Holland, K.

2012-12-01

288

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

289

Effects of silver and lead on the phase stability of Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8+x] and Bi[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub 10+x] above and below the solidus temperature  

SciTech Connect

A solid-state ionic technique has been used to determine the effects of Ag on the phase stability of Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8+x] (Bi-2212), and Ag and Pb on the phase stability of Bi[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub 10+x] (Bi-2223), over a temperature range of 600 to 910 C and oxygen partial pressure range of 10[sup [minus]6] to 10[sup 0] atm (10[sup [minus]1] to 10[sup 5] Pa). The addition of Ag to Bi-2212 leads to a marginal decrease in the stability of the phase above 883 [+-] 3 C and 7 [times] 10[sup [minus]2] atm (7 kPa) oxygen, resulting in a reduction in the incongruent melting point by 15 C in air. The substitution of Pb for Bi in the (Bi,Pb)-2223 phase leads to an increase in phase stability below the solidus, but to only a minor change in stability above the solidus. For both phases, several incongruent melting reactions have been identified over the range of reduced oxygen partial pressures studies. In addition, the phase equilibria both above and below the stability line have been determined for certain regions of the stability diagrams. From the thermodynamic information obtained in this study an improved melt-processing route for Bi-2212 has been found which minimizes unwanted phases. In addition, the optimum precursors for the formation of more phase-pure (Bi,Pb)-2223 during shorter time periods have been found by determining the initial decomposition products of (Bi,Pb)-2223, both above and below the solidus.

MacManus-Driscoll, J.L.; Bravman, J.C. (Stanford Univ., CA (United States). Dept. of Materials Science and Engineering); Savoy, R.J.; Gorman, G.; Beyers, R.B. (IBM Almaden Research Center, San Jose, CA (United States))

1994-09-01

290

Crystal structures and chemistry of double perovskites Ba{sub 2}M(II)M'(VI)O{sub 6} (M=Ca, Sr, M'=Te, W, U)  

SciTech Connect

Structures of the double perovskites Ba{sub 2}M(II)M '(VI)O{sub 6} (M=Ca, Sr, M'=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2/m (M' =W) and R3-bar (M'=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P2{sub 1}/n (M'=U) or cubic Fm3-bar m (M'=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba{sub 2}SrTeO{sub 6} and Ba{sub 2}CaUO{sub 6}, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba{sub 2}SrWO{sub 6} and Ba{sub 2}CaWO{sub 6} in the temperature range between 80 and 723 K. It was found that the rhombohedral R3-bar structure exists in Ba{sub 2}SrWO{sub 6} above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba{sub 2}CaWO{sub 6} undergoes a structural phase transition at low temperature to the tetragonal I4/m structure. - Graphical abstract: Evolution of structures as function of temperature in Ba{sub 2}SrWO{sub 6} (left) and Ba{sub 2}CaWO{sub 6} (right). The existence of two phase region in Ba{sub 2}SrWO{sub 6} can be clearly seen by the progressive increase of the rhombohedral R3-bar phase marked by asterisk (*)

Fu, W.T. [Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands)], E-mail: w.fu@chem.leidenuniv.nl; Au, Y.S.; Akerboom, S.; IJdo, D.J.W. [Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden (Netherlands)

2008-09-15

291

Influence of Cu-site substitution on La2Ca1Ba2Cu5Oz superconducting system  

NASA Astrophysics Data System (ADS)

We have prepared a series of La2CaBa2Cu5-xCoxOz; x = 0.0, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 (La-2125) compounds by the standard solid state reaction method and characterized for their structural, superconducting, magnetic properties and oxygen content through X-ray diffraction, scanning electron microscopy, d. c. resistivity, magnetic susceptibility and iodometric titration respectively. All the compounds crystallize with the tetragonal LaBa2Cu3Oz type structure, space group P4/mmm. Here the effect of higher Co substitution for Cu in the La2CaBa2Cu5-xCoxOz system has been studied. It is observed that only 2 at. % Co substitution for Cu destroys the superconductivity of the sample. For heavily doped samples (with x >= 0.1) are found non-superconducting presumably because of magnetic pair- breaking effect. These samples do not show superconductivity but are of interest for understanding the interplay between superconductivity and magnetism. Possible reasons for destruction of superconductivity are discussed in this communication.

Bhalodia, J. A.; Mankadia, S. R.; Dalsaniya, S. M.; Gonal, M. R.

2012-07-01

292

Thermal conductivity of insulating Bi2Sr2YCu2O8 and superconducting Bi2Sr2CaCu2O8: Failure of the phonon-gas picture  

NASA Astrophysics Data System (ADS)

The ab-plane thermal conductivity ?(T) of insulating Bi2Sr2YCu2O8 and superconducting Bi2Sr2CaCu2O8 is measured from T=10 to 300 K on single-crystal samples. Metallic Bi2Sr2CaCu2O8 has a significantly higher ? than Bi2Sr2YCu2O8; the difference ?? agrees well in magnitude with a Wiedemann-Franz estimate of the electronic contribution to ? in Bi2Sr2CaCu2O8. The shape of ?(T) in insulating Bi2Sr2YCu2O8 differs from normal insulators described by the Peierls-Boltzmann theory. Assuming that atomic vibrations are the main heat carrier, and noting that ? is more similar to that of silica glass than to a normal insulating crystal like CuO, we suggest that the ``phonon'' mean free path is sufficiently short that the Peierls-Boltzmann theory is not applicable. This is consistent with evidence from neutron scattering that phonons are poorly defined. Our data support the idea that the peak in ?(T) observed below Tc in superconducting samples originates from electronic rather than vibrational heat currents.

Allen, Philip B.; Du, Xiaoqun; Mihaly, Laszlo; Forro, Laszlo

1994-04-01

293

Influence of tungsten substitution and oxygen deficiency on the thermoelectric properties of CaMnO{sub 3??}  

SciTech Connect

Polycrystalline tungsten-substituted CaMn{sub 1?x}W{sub x}O{sub 3??} (0.00???x???0.05) powders were synthesized from a polymeric precursor, pressed and sintered to high density. The impact of tungsten substitution on the crystal structure, thermal stability, phase transition, electronic and thermal transport properties is assessed. Tungsten acts as an electron donator and strongly affects high-temperature oxygen stoichiometry. Oxygen vacancies form in the high figure-of-merit (ZT)-region starting from about T?=?1000?K and dominate the carrier concentration and electronic transport far more than the tungsten substitution. The analysis of the transport properties yields that in the investigated regime the band filling is sufficiently high to overcome barriers of polaron transport. Therefore, the Cutler-Mott approach describes the electrical transport more accurately than the Mott approach for small polaron transport. The lattice thermal conductivity near room temperature is strongly suppressed with increasing tungsten concentration due to mass-difference impurity scattering. A ZT of 0.25 was found for x?=?0.04 at 1225?K.

Thiel, Philipp; Eilertsen, James; Populoh, Sascha, E-mail: sascha.populoh@empa.ch; Saucke, Gesine; Shkabko, Andrey; Sagarna, Leyre; Karvonen, Lassi [Laboratory for Solid State Chemistry and Catalysis, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf (Switzerland); Döbeli, Max [Ion Beam Physics, Schafmattstrasse 20, ETH Hönggerberg, Swiss Federal Institute of Technology, CH-8093 Zürich (Switzerland); Weidenkaff, Anke [Laboratory for Solid State Chemistry and Catalysis, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf (Switzerland); Materials Chemistry, Institute for Materials Science, University of Stuttgart, Heisenbergstr. 3, DE-70569 Stuttgart (Germany)

2013-12-28

294

Influence of strontium for calcium substitution in bioactive glasses on degradation, ion release and apatite formation.  

PubMed

Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO(2)-P(2)O(5)-CaO-Na(2)O) with 0-100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition-structure-property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions. PMID:21993007

Fredholm, Yann C; Karpukhina, Natalia; Brauer, Delia S; Jones, Julian R; Law, Robert V; Hill, Robert G

2012-05-01

295

Influence of strontium for calcium substitution in bioactive glasses on degradation, ion release and apatite formation  

PubMed Central

Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO2–P2O5–CaO–Na2O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions. PMID:21993007

Fredholm, Yann C.; Karpukhina, Natalia; Brauer, Delia S.; Jones, Julian R.; Law, Robert V.; Hill, Robert G.

2012-01-01

296

Giant Enhancement in the Physical Properties of LaFeO3 by Substitution of Divalent Ions  

NASA Astrophysics Data System (ADS)

Perovskites with the general formula La1-xMxFeO3, x = 0.0 and x = 0.3, M = Ca2+, Sr2+ and Ba2+ were prepared by the double sintering ceramic technique. The X-ray powder diffraction, IR and TEM were carried out to characterize the samples. The molar magnetic susceptibility (?M) was enhanced by substitution the divalent metal ion (M2+ = Ca2+, Sr2+ and Ba2+) instead of La+3. The saturation magnetization for both Ca2+ and Sr2+ substituted samples is increased up to 10 times its values for the parent which allow to use these samples in many applications. The Ca substitution improves the conductivity by more than 18 times while the Sr enhances it by 25 times.

Ahmed, M. A.; Dek, S. I.; Arman, M. M.

2013-03-01

297

Improvement of critical current density in the Bi-Pb-Sr-Ca-Cu-O system through hot isostatic pressing  

NASA Astrophysics Data System (ADS)

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/cm 2 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 four times that without HIPing. To was unaffected by HIPing for samples encapsulated with a combination of glass and silver tubes. However, To was suppressed from 103 K to 86 K for samples encapsulated with stainless steel and silver tubes while Jc increased from 260 A/ cm 2 to 1086 A/cm 2 during HIPing, indicating that the weak links were significantly improved. A new minor phase, having a composition of Bi/Pb/Sr/Ca/Cu=0.58/2.8/3.0/2.1/1.1, was observed in HIPed samples but its effect on Jc is not clear.

Dou, S. X.; Liu, H. K.; Apperley, M. H.; Song, K. H.; Sorrell, C. C.; Easterling, K. E.; Niska, J.; Guo, S. J.

1990-05-01

298

New ordered perovskites containing bismuth (v) [BaLaMBiO{sub 6} (M = Mg, Ca, Sr)  

SciTech Connect

New Bi (V) containing perovskites oxides of the type, BaLaMBiO{sub 6} (M = Mg, Ca, Sr) have been synthesized under high oxygen pressure conditions using the thermal decomposition of peroxides in a tetrahedral anvil apparatus. These compounds have been characterized by X-ray powder diffraction and iodometric titration. All the BaLaMBiO{sub 6} (M + Mg, Ca, Sr) compounds show 1:1 type ordering of cations at the octahedral sites of the perovskite structure. In the case of magnesium and calcium containing perovskites, comparison of the observed and the calculated X-ray powder diffraction intensities show that the A sites are occupied by barium and lanthanum in a disordered manner, and the octahedral sites are occupied by an ordered arrangement of bismuth and magnesium or bismuth and calcium. This is in contrast to the strontium containing phase, where the A sites are found to be occupied by barium and strontium in a disordered arrangement and the octahedral sites are occupied by lanthanum and bismuth. The oxygen content, hence the oxidation state of Bi, in the samples depends on the synthetic conditions employed. The electrical properties of the synthesized materials are discussed briefly.

Subramanian, M.A. [Dupont Company, Wilmington, DE (United States). Central Research and Development] [Dupont Company, Wilmington, DE (United States). Central Research and Development

1995-03-01

299

Structural and transport properties of A2HoTaO6 [A=Ba, Sr, and Ca  

NASA Astrophysics Data System (ADS)

Double perovskite oxides A2HoTaO6 [A=Ba, Sr, and Ca] are synthesized by a solid state reaction technique. The Rietveld refinement of the X-ray diffraction pattern shows that Ba2HoTaO6 crystalizes in cubic Fm3m symmetry whereas Sr2HoTaO6 and Ca2HoTaO6 adopt the monoclinic P21/n symmetry. The field cooled and zero field cooled magnetic susceptibilities of the materials are measured in the temperature range from 5 K to 300 K. The temperature dependence of inverse magnetic susceptibility shows the antiferromagnetic behavior of these systems. The dielectric relaxation of the samples is investigated by the Cole-Cole model in the frequency range from 50 Hz to 1 MHz and in the temperature range from 303 K to 673 K. The frequency dependent conductivity spectra follow the power law. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures.

Dutta, Alo; Sinha, T. P.; Das, Dipankar

2014-06-01

300

Correlations between bond lengths, Tc, and O vibration frequencies: Raman-scattering and infrared-absorption study of the 1:2:1:2 structure (Ca1-yYy)Sr2(Tl0.5Pb0.5)Cu2O7 as a function of doping  

Microsoft Academic Search

Raman-scattering and infrared-absorption measurements on optical phonons are used to investigate the doping-induced changes in the electronic structure of (Ca1-yYy)Sr2(Tl0.5Pb0.5)Cu2O7 (Tl\\/Pb-1:2:1:2). In contrast to YBa2Cu3O7-delta (YBCO), the doping of the CuO2 planes is achieved by direct substitution of Ca2+ for Y3+ in between the CuO2 planes, enabling the effects of the dynamic out-of-plane charge transfer and doping to be separated.

T. Mertelj; D. Mihailovic; F. C. Matacotta; R. S. Liu; J. R. Cooper; I. Gameson; P. P. Edwards

1993-01-01

301

Overcoming phase instability of RBaCo2O5+ (R = Y and Ho) by Sr substitution for application as cathodes in solid oxide fuel cells  

SciTech Connect

Phase instabilities of the RBaCo2O5+ (R = Y and Ho) layered-perovskites and their decompositions into RCoO3 and BaCoO3-z at 800 oC in air were investigated. This will restrict their high temperature applications such as cathodes in solid oxide fuel cell (SOFC). However, appropriate amount of Sr substitution ( 60 % for R = Y and 70 % for R = Ho) for Ba successfully stabilized the R(Ba1-xSrx)Co2O5+ phase at elevated temperatures. This can be explained by decreasing oxygen vacancies at R-O layer, decreasing R-O bonding length, and consequent improvement of structural integrity. In addition, the Sr substitution (x = 0.6 - 1.0) for Ba provided added benefit with respect to the chemical stability against Ce0.8Gd0.2O1.9 (GDC) electrolyte, which is a critical requirement for the cathodes in SOFC. Among the various compositions investigated, the Y(Ba0.3Sr0.7)Co2O5+ + GDC composite cathode delivered the optimum electrochemical performances with a stable phase demonstrating the potential as a cathode in SOFC.

Kim, Jung-Hyun [ORNL; Young Nam, Kim [University of Texas at Austin; Bi, Zhonghe [ORNL; Manthiram, Arumugam [University of Texas at Austin; Paranthaman, Mariappan Parans [ORNL; Huq, Ashfia [ORNL

2013-01-01

302

The North Atlantic Oscillation Reconstructed at Bermuda for 220 Years Using Sr/Ca Ratios in Diploria labyrinthiformis (brain coral)  

NASA Astrophysics Data System (ADS)

The North Atlantic Oscillation (NAO) is a meridional oscillation in atmospheric mass measured by pressure anomalies between Iceland (65°N, 23°W) and the Azores (38°N, 26°W) (Hurrell, 1995). Changes between the positive and negative phase of the NAO strongly influence weather patterns across the US, Europe and the Middle East. A shift in recent decades toward a sustained positive NAO has raised questions about the influence of greenhouse gas emissions on this system. Unfortunately, instrumental records are too short to identify the natural baseline variability of the NAO, and NAO reconstructions generally encompass only land-based proxies, excluding ocean processes. Winter-time sea surface temperatures (SST) in the Sargasso Sea have previously been shown to correlate to the NAO (Visbeck et al., 2001), and thus a long winter SST record based on proxy data could be used to reconstruct NAO variability back in time. Here we present an annually resolved winter-time strontium to calcium ratio (Sr/Ca) record from a 220-year old brain coral (Diploria labyrinthiformis) collected from the south shore of Bermuda. Brain coral is prevalent in Bermuda and shows distinct annual banding in its skeleton providing precise age models. Winter-time coral Sr/Ca has previously been shown to accurately record winter SST free from growth rate influences (Goodkin et al., 2005), and that relationship is confirmed here. Cross-spectral analysis between winter-time coral Sr/Ca and four instrumental and proxy records of the NAO (Hurrell, 1995, Jones et al., 1997, Luterbacher et al., 2001, Cook et al., 2002) show two frequencies of coherence with >95% confidence. At periods greater than 20 years and between 3 and 5 years, the coral Sr/Ca effectively captures the NAO variability. Filtering the coral record to these frequencies and comparing to the instrumental and proxy records, including another marine-based NAO reconstruction from the North and Norwegian Seas (Schoene et al., 2003), show strong agreement and provide information about the differences between high and low frequency responses to the NAO. At high frequencies, SST at Bermuda shows a positive correlation to the NAO, as predicted by the tri-pole SST response (Visbeck et al., 2001), and succeeds well at capturing amplitude variability. At low frequencies, however, Bermuda SST shows a negative correlation to the NAO, different than the response predicted by the high frequency tri-pole pattern. One possible explanation for this shift is a response to changes in the meridional overturning circulation (MOC), which is believed to show variability at lower frequencies (Curry et al., 2003) and which may be driving changes in both SST and the NAO. Over 50 years during the late 20th century warming (1950-1999), the amplitude of the Sr/Ca-based NAO record at 3-5 year periods is 20% greater than that found during an equivalent interval at the end of the LIA (1800- 1849). Low-frequency (20-50 year) variability also appears larger during the second half of the 20th century, compared to the LIA. These results indicate a change in NAO variability at different mean temperatures, with larger amplitude changes during warmer climates. However, a sustained positive NAO during the late LIA does not appear to support the hypothesis of a linear relationship between mean NAO and mean hemispheric temperature, as observed during the late 20th century warming.

Goodkin, N. F.; Hughen, K. A.; Cohen, A. L.; Curry, W. B.; Doney, S. C.

2006-12-01

303

An experimental study of the effect of temperature, fluid chemistry and reaction rate on Sr-Ca partitioning in anhydrite: Implications for subseafloor hydrothermal alteration processes  

NASA Astrophysics Data System (ADS)

Anhydrite (CaSO4) is an important mineral in subseafloor hydrothermal systems. Its solubility likely plays a role in controlling mass transfer reactions in the relatively low temperature and ultramafic-hosted Lost City Hydrothermal Field (LCHF), while also precipitating from seawater during recharge of more widespread high-temperature hydrothermal systems at mid-ocean ridges. Strontium partitions into anhydrite, although the magnitude and mechanism by which this occurs, is still unclear, as is the effect of precipitation rate. In the absence of these data it is not possible to predict accurately the geochemical implications of Sr/Ca ratios of vent fluids. Accordingly, the potential usefulness of these data to constrain temperature, and as a means to understand the flux of seawater derived Sr into deeper portions of subseafloor hydrothermal systems, is limited. Here we report results of experiments designed to assess Ca-Sr exchange during anhydrite-fluid reaction as a function of temperature, fluid chemistry and distance from equilibrium. Anhydrite used for the experiments was synthesized to avoid compositional impurities and annealed to achieve grain sizes (10-100 micron) and uniform crystalline properties. NaCl fluids (0.55 m) with known Sr/Ca ratios were used for the experiments. Experiments were performed at 200° and 250°C, 500 bars, while time series changes in fluid chemistry were monitored by fluid sampling at experimental conditions. Isobaric temperature change as well as chemical perturbation by addition of fluids with anomalous Sr/Ca ratio permitted phase equilibria to be unambiguously assed. Moreover, the chemical perturbation experiments provided information on the effect of rate of reaction on Sr-Ca exchange. Isobaric temperature jumps demonstrate that initially anhydrite precipitation incorporates Sr preferentially. With further reaction progress and approach to equilibrium Sr uptake by anhydrite recrystallization becomes less effective. Long-term equilibration (~3 months) of fluid and anhydrite at 250°C produces aSr/aCa*1000 of 2.8425. Results from the isothermal spike experiments indicate that the rate of exchange (dF/dt) for aSr/aCa is on the order of 0.01/day. Applying the experimentally determined Sr/Ca data to endmember vent fluids from LCHF suggests subseafloor temperatures near 200°C, in good agreement with constraints imposed by observed Ca and sulfate concentrations assuming anhydrite-fluid equilibria. Furthermore, the effect of supersaturated partitioning and experimentally determined rate at which Sr is incorporated into anhydrite suggests that seawater Sr uptake by anhydrite may be very effective, especially if the rate of formation is rapid, as might be expected owing to the sharply increasing geothermal gradient likely for the recharge portions of most of basalt-hosted hydrothermal systems at mid-ocean ridges. This would have important implications for the flux of radiogenic Sr and calculations of fluid/rock ratios at depth in the ocean crust.

Syverson, D.; Seyfried, W. E.

2010-12-01

304

Vanishing of superconductivity at a transition from itinerant-electron to small-polaron conduction in nominal Bi/sub 4-//sub x/Pb/sub x/(Sr/sub 3/Ca)Ca/sub 2-//sub x/Y/sub x/Cu/sub 4/O/sub 16/  

SciTech Connect

Lead was found to substitute for bismuth on cosubstitution of yttrium for calcium in nominal Bi/sub 4/(Sr/sub 3/Ca)Ca/sub 2/Cu/sub 4/O/sub 16/. Variations with x in the lattice parameters, the oxidation parameter determined by iodometric titration, and the temperature dependence of resistance have revealed a correlation of the variation of T/sub c/ and c parameter versus x with a metal-to-semiconductor transition. It is argued that this correlation manifests a transition from itinerant-electron to small-polaron conduction. This conclusion is related to the observed shifts in c-axis oxygen that appear to be associated with a transition from antiferromagnetic semiconductor to a superconductor in other copper-oxide systems.

Manthiram, A.; Goodenough, J.B.

1988-12-26

305

Optimization of growth conditions of Bi?CaSr?Cu?O??x? superconducting films on NdGaO? substrates by LPE technique and their characterization  

E-print Network

-temperature research developments in ceramic superconductors. . . 4 IV Lattice parameters of Bi2Ca?Sr2Cun+tOy (n=l, 2 and 3). . . . Some physical properties of perovskite substrates. . . . . . . . . . . . Some physical properties of non-perovskite substrates...-T diagram of type II superconductor . . . . . . . . . . . . . 5 Idealized structure of perovskite ABO3 . . 10 Crystal substructure for the Bi phases of general formula Bi2Can tSr2CunOy with n=l, 2 and 3...

Solayappan, Narayanan

2012-06-07

306

Ca, Sr, Mo and U isotopes evidence ocean acidification and deoxygenation during the Late Permian mass extinction  

NASA Astrophysics Data System (ADS)

The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained. Here we use multiple isotope systems - Ca, Sr, Mo and U - measured from well dated Upper Permian- Lower Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry and the effects of ocean acidification and de-oxygenation through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing ?44/40Ca compositions, from ~-1.4‰ to -2.0‰ in the interval preceding the main extinction. These values remain low during most of the Griesbachian, to finally return to -1.4‰ in the middle Dienerian. The limestone succession from southern Turkey also displays a major decrease in the ?88/86Sr values from 0.45‰ to 0.3‰ before the extinction. These values remain low during the Griesbachian and finally increase to 0.55‰ by the middle Dienerian. The paired negative anomalies on the carbonate ?44/40Ca and ?88/86Sr suggest a decrease in the carbonate precipitation and thus an episode of ocean acidification coincident with the major biotic crisis. The Mo and U isotope records also exhibit significant rapid negative anomalies at the onset of the main extinction interval, suggesting rapid expansion of anoxic and euxinic marine bottom waters during the extinction interval. The rapidity of the isotope excursions in Mo and U suggests substantially reduced residence times of these elements in seawater relative to the modern, consistent with expectations for a time of widespread anoxia. The large C-isotope variability within Lower Triassic rocks, which is similar to that of the Lower-Middle Cambrian, may reflect biologically controlled perturbations of the oceanic carbon cycle. These findings strengthen the evidence for a global ocean acidification event coupled with rapid expansion of anoxic zones as drivers of end-Permian extinction in the oceans.

Silva-Tamayo, Juan Carlos; Payne, Jon; Wignall, Paul; Newton, Rob; Eisenhauer, Anton; Weyer, Stenfan; Neubert, Nadja; Lau, Kim; Maher, Kate; Paytan, Adina; Lehrmann, Dan; Altiner, Demir; Yu, Meiyi

2014-05-01

307

Variations in the Sr/Ca, ?44Ca and ?18O composition of calcite as a function of solution chemistry and crystal growth rate  

NASA Astrophysics Data System (ADS)

The trace element and isotopic composition of calcite can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The accuracy with which these effects can be interpreted is limited by our ability to distinguish signatures arising from equilibrium partitioning versus kinetic or mass transport effects. Our focus in this work is on mass transport effects in aqueous environments, and specifically, the growth rate-dependence of trace element and isotopic incorporation into calcite. This requires experiments in which the degree of supersaturation, or the solution chemistry, is held constant and the rate of crystal growth can be determined. In our experiments, N2+CO2 gas mixture is bubbled through a beaker containing 1300 mL of solution (30 mM CaCl2 + 5 mM NH4Cl + 0.1 mM SrCl2). The degree of supersaturation with respect to calcite is controlled by the pCO2 of the gas mixture, which is constantly replenished from a gas source. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls and the pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. During an experiment we control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate. At the same time we monitor the total alkalinity, the pCO2 of the gas outflow, the gas outflow rate, and the amount of NaOH added. The rate of calcite precipitation can be determined in three ways: (1) the change in total alkalinity due to Ca2+ removal, mass balance of C in the system, and (3) post-run measurement of [Ca2+] in aliquots of solution taken during an experiment. We present results from experiments where growth rates are estimated to range from 0.5 to 16 mmol/m2/hr. Our experiments thus far have yielded calcite crystals that are out of calcium and oxygen isotopic equilibrium with the parent solution. Crystals are enriched in the light isotope of Ca by 0.4 to 1.8‰. The light isotope enrichment increases with growth rate and is correlated with Sr/Ca in calcite. These results are in excellent agreement with the results of Tang et al. (2008) for crystals grown at 25°C and suggest that mass discrimination is controlled by mass transport kinetics at the mineral-solution interface. Oxygen isotopes are more complicated because of the addition of CO2 to the bulk solution. For crystals grown from our stock solution, the O composition is highly variable and not correlated with growth rate. We attribute this to relatively slow kinetics of O isotope exchange between gaseous or dissolved CO2 and water. For crystals grown in the presence of 0.01 grams of bovine carbonic anhydrase (CA), an enzyme which catalyzes the interconversion of CO2 and H2O to bicarbonate and protons, the O isotope composition of calcite appears to be independent of growth rate. Hence addition of CA to solution might offer a means of determining the equilibrium fractionation factor for oxygen isotopes in carbonate minerals. We will present results from additional experiments that test how CA and other organic molecules in solution affect the growth rate and mass discrimination during mineral precipitation.

Watkins, J. M.; DePaolo, D. J.; Ryerson, F. J.

2012-12-01

308

The generation of 25.05 T using a 5.11 T Bi2Sr2CaCu2Ox superconducting insert magnet  

NASA Astrophysics Data System (ADS)

A 25.05 T magnetic field was generated by a 5.11 T superconducting Bi2Sr2CaCu2Ox insert magnet within a 19.94 T resistive magnet. The Bi2Sr2CaCu2Ox magnet is constructed using fully reacted powder-in-tube conductor and insulated stainless steel reinforcement. Three concentric sections are used to minimize the total stress in the Bi2Sr2CaCu2Ox conductor: two double pancake stacks and an outer layer-wound section. The insert coil operates at 4.2 K in a 0.168 m diameter cryostat fitted to the resistive magnet. Here we provide an overview of the design and construction of the insert and the results of self-field and in-field testing. Mechanical and electrical safety issues, related to testing in a large resistive magnet, are discussed.

Weijers, H. W.; Trociewitz, U. P.; Marken, K.; Meinesz, M.; Miao, H.; Schwartz, J.

2004-04-01

309

Synthesis, Structure, and Magnetic Properties of Sr2NiOsO6 and Ca2NiOsO6: Two New Osmium-Containing Double Perovskites  

SciTech Connect

Two new double perovskite oxides, Ca{sub 2}NiOsO{sub 6}and Sr{sub 2}NiOsO{sub 6}, have been prepared as polycrystalline powders by solid state synthesis. The two oxides were structurally characterized by variable-temperature powder neutron diffraction. Ca{sub 2}NiOsO{sub 6} was found to adopt a monoclinic structure (P2{sub 1}/n), while Sr{sub 2}NiOsO{sub 6} was found to be tetragonal (I4/m). Magnetic susceptibility measurements indicate that Ca2NiOsO6 orders in a canted antiferromagnetic state at about 175 K while Sr{sub 2}NiOsO{sub 6} orders antiferromagnetically at about 50 K.

Macquart,R.; Kim, S.; Gemmill, W.; Stalick, J.; Lee, Y.; Vogt, Tzur Loye, H.

2005-01-01

310

X-ray crystal truncation rod scattering from MBE grown (CaF 2-SrF 2)/Si(111) superlattices  

NASA Astrophysics Data System (ADS)

Flouride CaF 2-SrF 2 superlattices (SLs) grown by molecular beam epitaxy have been studied by means of X-ray diffractometry for the first time. The diffraction patterns showed reasonably good crystalline quality of the SLs and a type-B epitaxial relation to the Si(111) substrate. From the analysis of the crystal truncation rod (CTR) profiles, based on the pseudomorphic model, it was obtained that despite the same high temperature (770°C) of formation of the CaF 2/Si(111) interface its structure depended on the growth temperature of the SLs. The shape of the CTR profiles confirmed the existence of the superlattice which consists of one or two monolayer thick SrF 2 layers. Some CaF 2/SrF 2-interface roughness was noticeable.

Harada, J.; Itoh, Y.; Shimura, T.; Takahashi, I.; Alvarez, J. C.; Sokolov, N. S.

1994-01-01

311

Synthesis, structure, and magnetic properties of Sr2NiOsO6 and Ca2NiOsO6: two new osmium-containing double perovskites.  

PubMed

Two new double perovskite oxides, Ca(2)NiOsO(6) and Sr(2)NiOsO(6), have been prepared as polycrystalline powders by solid state synthesis. The two oxides were structurally characterized by variable-temperature powder neutron diffraction. Ca(2)NiOsO(6) was found to adopt a monoclinic structure (P2(1)/n), while Sr(2)NiOsO(6) was found to be tetragonal (I4/m). Magnetic susceptibility measurements indicate that Ca(2)NiOsO(6) orders in a canted antiferromagnetic state at about 175 K while Sr(2)NiOsO(6) orders antiferromagnetically at about 50 K. PMID:16363836

Macquart, René; Kim, Seung-Joo; Gemmill, William R; Stalick, Judith K; Lee, Yongjae; Vogt, Tom; zur Loye, Hans-Conrad

2005-12-26

312

Effect of V substitution in Ca4Mn3O10  

NASA Astrophysics Data System (ADS)

Compounds with general formula Ca4Mn3-xVxO10 have been produced for x<=0.3. The studied compounds show a ferromagnetic component that we attribute to an uncompensated antiferromagnetic alignment of the local moments. Measurements of resistivity as a function of temperature show semiconducting behaviour over all measured temperature range.

Girão, A. V.; Carvalho, M. D.; Melo Jorge, M. E.; Costa, F. M.; Bonfait, G.; Borges, R. P.; Cruz, M. M.; Godinho, M.

2004-05-01

313

Effect of V substitution in Ca 4Mn 3O 10  

NASA Astrophysics Data System (ADS)

Compounds with general formula Ca 4Mn 3- xV xO 10 have been produced for x?0.3. The studied compounds show a ferromagnetic component that we attribute to an uncompensated antiferromagnetic alignment of the local moments. Measurements of resistivity as a function of temperature show semiconducting behaviour over all measured temperature range.

Girão, A. V.; Carvalho, M. D.; Melo Jorge, M. E.; Costa, F. M.; Bonfait, G.; Borges, R. P.; Cruz, M. M.; Godinho, M.

314

4f and 5d energy levels of the divalent and trivalent lanthanide ions in M{sub 2}Si{sub 5}N{sub 8} (M=Ca, Sr, Ba)  

SciTech Connect

Optical data of Sm, Tb and Yb doped Ca{sub 2}Si{sub 5}N{sub 8} and Sr{sub 2}Si{sub 5}N{sub 8} phosphors that have been prepared by solid-state synthesis, are presented. Together with luminescence data from literature on Ce{sup 3+} and Eu{sup 2+} doping in the M{sub 2}Si{sub 5}N{sub 8} (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 Eu{sup 2+}d-f emission. Tb{sup 3+} substitutes on both a high energy and a low energy site in Ca{sub 2}Si{sub 5}N{sub 8}, due to which excitation at 4.77 eV led to emission from both the {sup 5}D{sub 3} and {sup 5}D{sub 4} levels, while excitation at 4.34 eV gave rise to mainly {sup 5}D{sub 4} emission. Doping with Sm resulted in typical Sm{sup 3+}f-f line absorption, as well as an absorption band around 4.1 eV in Ca{sub 2}Si{sub 5}N{sub 8} and 3.6 eV in Sr{sub 2}Si{sub 5}N{sub 8} that could be identified as the Sm{sup 3+} charge transfer band. Yb on the other hand was incorporated in both the divalent and the trivalent state in Ca{sub 2}Si{sub 5}N{sub 8}. - Graphical abstract: Energy level schemes showing the 4f ground states of the trivalent ( Black-Down-Pointing-Small-Triangle ) and divalent ( Black-Up-Pointing-Small-Triangle ) lanthanide ions and lowest energy 5d states of the trivalent ({nabla}) and divalent ({Delta}) ions with respect to the valence and conduction bands of Ca{sub 2}Si{sub 5}N{sub 8} (left) and Sr{sub 2}Si{sub 5}N{sub 8} (right). Highlights: Black-Right-Pointing-Pointer Construction of energy level schemes of all lanthanides within the M{sub 2}Si{sub 5}N{sub 8} hosts. Black-Right-Pointing-Pointer Construction was done by analyzing existing as well as new spectroscopic data. Black-Right-Pointing-Pointer Tb{sup 3+}d-f emission from two different Ca sites in Ca{sub 2}Si{sub 5}N{sub 8} has been observed. Black-Right-Pointing-Pointer Observation of the Sm{sup 3+} charge transfer band in Ca{sub 2}Si{sub 5}N{sub 8} and Sr{sub 2}Si{sub 5}N{sub 8}. Black-Right-Pointing-Pointer Ytterbium has been found in the divalent and trivalent state in Ca{sub 2}Si{sub 5}N{sub 8}.

Kate, O.M. ten, E-mail: o.m.tenkate@tudelft.nl [Luminescent Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Energy Materials and Devices, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, 5600MB Eindhoven (Netherlands); Zhang, Z. [Energy Materials and Devices, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, 5600MB Eindhoven (Netherlands); Dorenbos, P. [Luminescent Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Hintzen, H.T. [Energy Materials and Devices, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, 5600MB Eindhoven (Netherlands); Kolk, E. van der [Luminescent Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands)

2013-01-15

315

Evidence of Sr/Ca and Mg/Ca Temperature Invariance in Live Aragonitic Hoeglundina elegans Tests from the Little Bahama Bank  

NASA Astrophysics Data System (ADS)

Mg/Ca and Sr/Ca were analyzed from core-top individual Hoeglundina elegans aragonitic tests collected from three continental slope depths within the South Carolina and Little Bahama Bank continental slope environs (220 m to 1084 m). Our study utilized only individuals that labeled with the vital probe CellTracker Green - unlike bulk core-top material often stained with Rose Bengal, which has known inconsistencies in distinguishing live from dead foraminifera. DSr x 10 values were consistently 1.74 $ pm 0.23 across all sampling depths. The analytical error in DSr values (0.7%) determined by ICP-MS between repeated measurements on individual H. elegans tests across all depths was less than analytical error on repeated measurements from standards. Variation in DSr values was not directly explained by a linear temperature relationship (p=0.0003, R2=0.44) over the temperature range of 4.9-11.4°C with a sensitivity of 59.8 ?mol/mol/1°C. The standard error by regressing DSr across temperature yields + 3.4°C, which is nearly 3x greater that reported in previous studies. Sr/Ca was more sensitive for calibrating temperature than Mg/Ca in H. elegans. Observed scatter in DSr was too great across individuals of the same size and of different sizes to resolve ontogenetic effects. However, higher DSr values were associated with smaller individuals and warmer/shallower sampling depths. The highest DSr values were observed at the intermediate sampling depth (~600 m). No significant ontogenetic relationship was found across DSr values in different sized individuals due to tighter overall constrained variance; however lower DSr values were observed from several smaller individuals. Several dead tests of H. elegans showed no significant differences in DSr values compared to live specimens cleaned by standard cleaning methods, unlike higher dead than live DMg values observed for the same individuals. There were no significant deviations in DSr across batches cleaned on separate days, unlike the observed sensitivity of DMg across batches. A subset of samples were reductively cleaned (hydrazine solution); and exhibited DMg values within analytical precision of those observed for non-reductively cleaned samples. Therefore, deviations in DMg values resulting from the removal of the reductive cleaning step did not explain analytical errors greater than published values for Mg/Ca or the high variance across same sized individuals. Variation in DMg values across the same cleaning methods and from dead individuals suggests the need for a careful look into how foraminiferal aragonite should be processed. These findings provide evidence that both Mg and Sr in benthic foraminiferal aragonite reflect factors in addition to temperature and pressure that may interfere with absolute temperature calibrations. Funded by NSF OCE 0351029, OCE 0437366, and OCE-0350794.

Blanks, J. K.; Hintz, C. J.; Chandler, G. T.; Shaw, T. J.; McCorkle, D. C.; Bernhard, J. M.

2007-12-01

316

Synthesis and luminescence properties of red-emitting M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors by a simple nitrate reduction  

NASA Astrophysics Data System (ADS)

M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) red-emitting phosphors are fabricated at relatively low temperature (1200°C) and atmospheric pressure using a simple solid-state reaction process. Several processing parameters are systematically investigated to optimize the phosphors structural characterization and photoluminescence performance, including the amount of europium and the properties of the precursor materials. The as-prepared M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors are orange in color and are intensively emitted in the red region of 580-670 nm under 465 nm excitation.

Chen, ChangCheng; Xie, ErQing

2014-01-01

317

Synthesis and luminescence properties of red-emitting M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors by a simple nitrate reduction  

NASA Astrophysics Data System (ADS)

M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) red-emitting phosphors are fabricated at relatively low temperature (1200°C) and atmospheric pressure using a simple solid-state reaction process. Several processing parameters are systematically investigated to optimize the phosphors structural characterization and photoluminescence performance, including the amount of europium and the properties of the precursor materials. The as-prepared M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors are orange in color and are intensively emitted in the red region of 580-670 nm under 465 nm excitation.

Chen, ChangCheng; Xie, ErQing

2014-03-01

318

Damage ingrowth and recovery in alpha-irradiated CaF2, SrF2, and BaF2  

Microsoft Academic Search

Single crystals of CaF2, SrF2, and BaF2 were irradiated at room temperature with alpha particles emitted from an effectively semi-infinite PuO2 source to a cumulative dose of 3 × 10 alpha particles\\/m. Although no change in the lattice parameter of CaF2 was observed, the crystals exhibited increasing coloration with dose. The lattice parameters of both SrF2 and BaF2 increased exponentially

W. J. Weber

1983-01-01

319

Preparation and characterization of nano-sized Sr 0.7Ca 0.3TiO 3 crystallines by low temperature aqueous synthesis method  

Microsoft Academic Search

Nano-sized calcium strontium titanate (Sr0.7Ca0.3TiO3) particles were prepared by low temperature aqueous synthesis method at temperature as low as 90 °C and under ambient pressure. To improve the morphology and crystallinity of the particles, the hydrothermal treatment was used. The lattice structure, particle size, particle morphology, and hydroxyl defects of Sr0.7Ca0.3TiO3 particles were investigated by using XRD, TEM, FE-SEM, TG and

Ping He; Hua-Rong Cheng; Yuan Le; Jian-Feng Chen

2008-01-01

320

Crystal structures and chemistry of double perovskites Ba 2 M(II) M?(VI)O 6 ( M=Ca, Sr, M?=Te, W, U)  

Microsoft Academic Search

Structures of the double perovskites Ba2M(II)M ?(VI)O6 (M=Ca, Sr, M?=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2\\/m (M? =W) and R3¯ (M?=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P21\\/n (M?=U) or

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

2008-01-01

321

Effect of Sr Substitution on Catalytic Activity of La 1-X Sr x MnO 3 (0?x?0.8) Perovskite-Type Oxides for Catalytic Decomposition of Hydrogen Peroxide  

Microsoft Academic Search

La1?x SrxMnO3 (0?x?0.8) perovskite-type oxides were synthesized by the combined EDTA-citrate complexing method and their catalytic activity\\u000a for the decomposition of hydrogen peroxide was investigated. Hydrogen peroxide decomposition was observed as a first-order\\u000a reaction on these catalysts. With the increase of Sr substitution, the catalytic activity increased accordingly. Through analysis\\u000a of the kinetic results, the compensation effect was found for

Huanghe Yang; Tao Zhang; Hanjing Tian; Junwang Tang; Dezhu Xu; Weishen Yang; Liwu Lin

2001-01-01

322

Domain state properties of weakly doped SrTiO3:Ca  

Microsoft Academic Search

Linear birefringence, Raman scattering, dielectric, and second-harmonic generation (SHG) studies on Sr1-xCax TiO3, x=0.007, reveal a smeared transition into a ferroelectric-improper ferroelastic phase at Tc=18 K. Polar disorder persists on a nanometric scale as a consequence of the percolative nature of the transition under the constraint of quenched random fields. The ferroelectric nanoregions exhibit superparaelectric response to an external ac

W. Kleemann; U. Bianchi; A. Bürgel; M. Prasse; J. Dec

1995-01-01

323

The effect of element substitution on high-temperature thermoelectric properties of Ca{sub 3}Co{sub 2}O{sub 6} compounds  

SciTech Connect

Polycrystalline Ca{sub 3}Co{sub 1.8}M{sub 0.2}O{sub 6} (M=Mn, Fe, Co, Ni, Cu) and Ca{sub 2.7}Na{sub 0.3}Co{sub 2}O{sub 6} were synthesized by solid-state reaction to evaluate the effect of substitution on the thermoelectric properties of Ca{sub 3}Co{sub 2}O{sub 6}. Substitution by Mn, Cu and Na appears to increase carrier density, given that electrical resistivity ({rho}) and the Seebeck coefficient (S) were simultaneously reduced. Conversely, Fe substitution seems to reduce carrier density, resulting in a simultaneous increase in S and {rho}. Cu and Na substitution resulted in a significant decrease in {rho} due to enhancement of grain size and grain boundary connectivity, which could have a strong impact on {rho}. 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.

Mikami, Masashi [National Institute of Advanced Industrial Science and Technology, Research Institute of Ubiquitous Energy Devices, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577 (Japan) and CREST, Japan Science and Technology Agency, 4-1-8, Honcho Kawaguchi, Saitama 332-0012 (Japan)]. E-mail: m-mikami@aist.go.jp; Funahashi, Ryoji [National Institute of Advanced Industrial Science and Technology, Research Institute of Ubiquitous Energy Devices, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577 (Japan); CREST, Japan Science and Technology Agency, 4-1-8, Honcho Kawaguchi, Saitama 332-0012 (Japan)

2005-05-15

324

Enhanced thermoelectric figure-of-merit ZT for hole-doped Bi2Sr2Co2Oy through Pb substitution  

NASA Astrophysics Data System (ADS)

Single crystals of Bi2-xPbxSr2Co2Oy (0 ? x ? 0.55) have been grown using optical floating-zone method. The chemical compositions were determined using combined electron probe microanalysis and iodometric titration. Physical properties including electrical resistivity (?), Seebeck coefficient (S), and thermal conductivity (?) were measured using single crystal specimens. Successful hole doping through Pb substitution is confirmed through combined iodometry titration, electrical transport, and Seebeck coefficient measurements. Significant reduction on both in-plane resistivity and thermal conductivity was found as a result of Pb substitution to the Bi site. The thermoelectric figure-of-merit ZT for x ˜ 0.55 is raised 20 folds from the undoped sample at room temperature.

Hsu, H. C.; Lee, W. L.; Wu, K. K.; Kuo, Y. K.; Chen, B. H.; Chou, F. C.

2012-05-01

325

Magnetic hysteresis and relaxation in Ag-sheathed TlBaCaCuO (1223) and Bi(Pb)SrCaCuO (2223) superconducting tapes  

SciTech Connect

Magnetic hysteresis (7--75 K in magnetic fields up to 5 T) and relaxation characteristics (5--50 K in magnetic fields up to 2 T) have been measured with the field perpendicular to the surface of Ag-sheathed TlBaCaCuO (1223 phase) and Bi(Pb)SrCaCuO (2223 phase) superconducting tapes. A study of the difference in the magnetic hysteresis between precursor powders and as-processed tapes was also carried out. The relaxation data were curve-fit using a rate equation for thermally activated flux motion, U{sub eff}/[kG(T)] = {minus}T[ln(dM/dt) {minus} ln (H{omega}{sub o} a/2{pi}d)] with the temperature dependence of U{sub eff} scaled by the functional form G(T) = 1 {minus} (T/Tx){sup 2}. By comparing the results obtained from magnetic characterization with those from transport current measurement, these observations suggest that (1) Tl-1223 tapes have a weaker field dependence for J{sub c} at T > 35 K than Bi-2223 tapes due to the special crystal structure of the 1223 phase, and (2) weak links limit the transport critical current densities in Tl-1223 tapes to 10{sup 3} A/cm{sup 2} at 5 T and 35 K, for instance.

Kung, P.J.; Maley, M.P.; Coulter, J.Y.; Willis, J.O.; Peterson, D.E. [Los Alamos National Lab., NM (United States); McHenry, M.E. [Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Metallurgical Engineering and Materials Science; Wahlbeck, P.G. [Wichita State Univ., KS (United States). Dept. of Chemistry

1992-05-01

326

Magnetic hysteresis and relaxation in Ag-sheathed TlBaCaCuO (1223) and Bi(Pb)SrCaCuO (2223) superconducting tapes  

SciTech Connect

Magnetic hysteresis (7--75 K in magnetic fields up to 5 T) and relaxation characteristics (5--50 K in magnetic fields up to 2 T) have been measured with the field perpendicular to the surface of Ag-sheathed TlBaCaCuO (1223 phase) and Bi(Pb)SrCaCuO (2223 phase) superconducting tapes. A study of the difference in the magnetic hysteresis between precursor powders and as-processed tapes was also carried out. The relaxation data were curve-fit using a rate equation for thermally activated flux motion, U{sub eff}/(kG(T)) = {minus}T(ln(dM/dt) {minus} ln (H{omega}{sub o} a/2{pi}d)) with the temperature dependence of U{sub eff} scaled by the functional form G(T) = 1 {minus} (T/Tx){sup 2}. By comparing the results obtained from magnetic characterization with those from transport current measurement, these observations suggest that (1) Tl-1223 tapes have a weaker field dependence for J{sub c} at T > 35 K than Bi-2223 tapes due to the special crystal structure of the 1223 phase, and (2) weak links limit the transport critical current densities in Tl-1223 tapes to 10{sup 3} A/cm{sup 2} at 5 T and 35 K, for instance.

Kung, P.J.; Maley, M.P.; Coulter, J.Y.; Willis, J.O.; Peterson, D.E. (Los Alamos National Lab., NM (United States)); McHenry, M.E. (Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Metallurgical Engineering and Materials Science); Wahlbeck, P.G. (Wichita State Univ., KS (United States). Dept. of Chemistry)

1992-01-01

327

Synthesis and reaction mechanism of the high- Tc 2223 phase in the (Bi,Pb)?Sr?Ca?Ca?Cu?O system  

NASA Astrophysics Data System (ADS)

The synthesis and reaction mechanisms of the (Bi,Pb) 2Sr 2Ca 2Cu 3O 10+? superconducting compound have been investigated. Based on density curves evolution, on simulation of different kinetic models, and on SEM observations confirming directly some proposed hypotheses, the formation mechanisms are explored and discussed in this paper. It was found that the conversion process of Bi-2212 to the Bi-2223 phase was competitive, consisting of a one-dimensional diffusion-controlled nucleation-growth reaction with edge dislocation at early sintering stages and a two-dimensional heterogeneous growth at grain interfaces with prolonged sintering. It was suggested that the origin of the liquid phase accounting for the fast transformation of 2212 to 2223 comes from the reaction between Ca 2PbO 4 and PbO. A reproducible processing protocol to develop the synthesis of the 110 K high- Tc phase in the solid-state regime in large quantitites is also presented, as is needed for applications.

Nhien, S.; Desgardin, G.

1996-02-01

328

Effects of Cl(-) substitution on electrophysiological properties, Ca(2+) influx and prolactin secretion of rat lactotropes in vitro.  

PubMed

In this study, we compared the effects of different chloride (Cl(-)) substitutes - methane sulfonate (CH(3)SO(-)(3)), bromide (Br(-)), nitrate (NO(-)(3)), thiocyanate (SCN(-)) and perchlorate (ClO(-)(4)) - on the secretory activity and calcium current activation of rat lactotropes in primary culture. We observed that CH(3)SO(-)(3) decreased basal prolactin (PRL) secretion. Br(-) had no effect, whereas the more lyotropic anions, such as NO(-3), SCN(-) and C1O(-4), increased basal PRL secretion. The latter three substitutes induced a significant shift in the voltage dependence of T-type calcium channel activation towards hyperpolarized values. However, this shift alone cannot explain the increase in secretion. Anion permeability studies also demonstrated that the organic anion CH(3)SO(-3) was less permeant than Cl(-), whereas monovalent inorganic anions were more permeant, with the following anion permeability sequence: SCN(-) > ClO(-4) > NO(-3) > Br(-). In conclusion, deprivation of Cl(-) ions has converse consequences on basal and induced secretion; permeating anions result in a transient increase in intracellular Ca(2+) ions. This process involves voltage-dependent Ca(2+) channels. We propose that an alteration in intracellular anion concentrations may influence the activation of internal effectors such as G proteins or channel proteins and, therefore, interfere with exocytosis. These effects are correlated with an external action of lyotropic anions, particularly NO(-3), ClO(-4) and SCN(-), on the gating properties of T-type calcium channels, probably through changes in cell surface charges. The results demonstrate the modulatory effect of anions on the secretory activity of rat lactotropes and underline the specific role played by chloride in stimulus-secretion coupling. PMID:10567859

Garcia, L; Couderc, B; Odessa, M F; Dufy-Barbe, L; Sartor, P

1999-11-01

329

Distinct origins of magnetic -field -induced resistivity irreversibility in two manganites with similar ground states : Pr0.5Sr0.41Ca0.09MnO3 and La0.5Ca0.5MnO3  

Microsoft Academic Search

Our investigation of the magnetotransport in two charge ordered mangan- ites with similar magnetic ground states reveals that the origin of magne- toresistance can not be concluded from the isofield resistivity, ?(T, con- stant H), measurements alone. Both Pr0.5Sr0.41Ca0.09MnO3 (PrSrCa) and La0.5Ca0.5MnO3 (LaCa) show a ferromagnetic transition (TC = 260 K for PrSrCa, 230 K for LaCa) followed by an

R. Mahendiran; A. Maignan; C. Martin; M. Hervieu; B. Raveau

330

Infrared study of Ca-substituted YBa2Cu4O8 high-Tc superconductors  

Microsoft Academic Search

A detailed far-infrared reflectivity study on ceramic samples of the high-Tc superconductor Y1-0.75xBa2-0.25xCaxCu4O8 was made as a function of temperature (T=30-300 K) and Ca concentration (x=0.0, 0.025, 0.075, and 0.1) in the frequency range 20-5000 cm-1. Kramers-Kronig analysis of the reflectivity was used to extract the phonon frequencies. Phonons at 114, 130, 192, 294, 501, and 597 cm-1 (at 30

M. E. Ziaei; B. P. Clayman; R. G. Buckley; E. M. Haines

1992-01-01

331

Reinforced fluropolymer nanocomposites with high-temperature superconducting Bi2Sr2CaCu2Oy  

NASA Astrophysics Data System (ADS)

Bismuth Strontium Calcium Copper Oxide (Bi2Sr2CaCu2Oy)/Polyvinylidene fluoride (PVDF) nanocomposite was prepared and their thermal properties were analyzed. The composite consists of the polyvinylidene fluoride (PVDF) as an insulating polymer matrix, and homogenously distributed Bismuth strontium calcium copperoxide (2212) nanoparticles. SEM data shows flaky grains of the superconductor coated and linked by polymer. Differential scanning calorimetry (DSC) results indicated that the melting point was not affected significantly by the addition of BSCCO. However, the addition of superconducting ceramic resulted in an extra melting peak at a lower temperature (145°C). Thermogravimetric analysis of the samples shows that the onset decomposition temperature of the PVDF matrix was decreased by the addition of SC filler.

Jayasree, T. K.

2014-10-01

332

Magnetic properties of the 110K superconducting phase in Pb-doped Bi-Sr-Ca-Cu-O thin films  

NASA Technical Reports Server (NTRS)

The relaxation of the remnant moment induced in a nearly single phase high T(sub c) thin film of Pd-doped Bi-Sr-Ca-Cu-O was investigated. Measurements reveal that the relaxation obeys a logarithmic time dependence for observation times up to 2000 seconds. The temperature dependence of the initial magnetization of the film and its decay rate are obtained. The initial magnetization monotonically decreases. However, the decay rate normalized by initial magnetization has a peak at approximately 14 K for an applied field of 500 gauss. The peak shifts to lower temperature for a stronger magnetic field. These data are compared with existing data on other high T(sub c) superconducting materials.

Tanaka, Atsushi; Crain, Jason; Kamehara, Nobuo; Niwa, Koichi

1990-01-01

333

Direct imaging of hot spots in Bi2Sr2CaCu2O8+? mesa terahertz sources  

NASA Astrophysics Data System (ADS)

Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi2Sr2CaCu2O8+? (Bi-2212) (BSCCO) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs, hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power. Here, we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612 nm fluorescence line of Eu3+ in a europium chelate. The images directly reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission.

Benseman, T. M.; Koshelev, A. E.; Kwok, W.-K.; Welp, U.; Vlasko-Vlasov, V. K.; Kadowaki, K.; Minami, H.; Watanabe, C.

2013-04-01

334

Coexistence of periodic modulation of quasiparticle states and superconductivity in Bi2Sr2CaCu2O8+?  

PubMed Central

In this article we show, using scanning tunneling spectroscopy, the existence of static striped density of electronic states in nearly optimally doped Bi2Sr2CaCu2O8+? in zero field. This modulation is aligned with the Cu—O bonds, with a periodicity of four lattice constants, and exhibits features characteristic of a two-dimensional system of line objects. We further show that the density of states modulation manifests itself as a shift of states from above to below the superconducting gap. The fact that a single energy scale (i.e., the gap) appears for both superconductivity and stripes suggests that these two effects have the same origin. PMID:12913127

Howald, C.; Eisaki, H.; Kaneko, N.; Kapitulnik, A.

2003-01-01

335

Numerical Investigation of the Quench Behavior of Bi2Sr2CaCu2Ox Wire  

SciTech Connect

The quench behavior of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi2212) wire is investigated through numerical simulations. This work is part of the U.S. Very High Field Superconducting Magnet Collaboration (VHFSMC). Numerical simulations are carried out using a one-dimensional computational model of thermal transport in Bi2212 composite wires. A quench is simulated by introducing heat in a section of the wire, and the voltage and temperature are monitored as function of time and position. The quench energy, normal zone propagation velocity, and spatial distribution of temperature are calculated for varying transport current and applied magnetic field. The relevance of these simulations in defining criteria for experimental measurements is discussed.

Arbelaez, D.; Prestemon, S. O.; Dietderich, D. R.; Godeke, A.; Ye, L.; Hunte, F.; Schwartz, J.

2010-08-01

336

Reconstructed Fermi Surface of Underdoped Bi2Sr2CaCu2O8 Cuprate Superconductors  

SciTech Connect

The Fermi surface topologies of underdoped samples of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} have been measured with angle resolved photoemission. By examining thermally excited states above the Fermi level, we show that the observed Fermi surfaces in the pseudogap phase are actually components of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the magnetic zone boundary, creating the illusion of Fermi 'arcs.' The area of the pockets as measured in this study is consistent with the doping level, and hence carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by phenomenological models of the pseudogap phase as a spin liquid.

H Yang; J Rameau; Z Pan; G Gu; P Johnson; H Claus; D Hinks; T Kidd

2011-12-31

337

Gap-Inhomogeneity-Induced Electronic States in Superconducting Bi2Sr2CaCu2O8+delta  

SciTech Connect

In this Letter, we analyze, using scanning tunneling spectroscopy, the density of electronic states in nearly optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} in zero magnetic field. Focusing on the superconducting gap, we find patches of what appear to be two different phases in a background of some average gap, one with a relatively small gap and sharp large coherence peaks and one characterized by a large gap with broad weak coherence peaks. We compare these spectra with calculations of the local density of states for a simple phenomenological model in which a 2{zeta}{sub 0} x 2{zeta}{sub 0} patch with an enhanced or suppressed d-wave gap amplitude is embedded in a region with a uniform average d-wave gap.

Fang, A.C.

2010-02-25

338

Rotational symmetry breaking in Bi2Sr2CaCu2O8+? probed by polarized femtosecond spectroscopy  

NASA Astrophysics Data System (ADS)

The quasiparticle (QP) dynamics with different symmetry is investigated in the superconducting (SC) and normal state of the high-temperature superconductor Bi2Sr2CaCu2O8+? (Bi2212) using optical pump-probe experiments with different light polarizations at different doping levels. The observation of distinct selection rules for SC excitations present in A1g and B1g symmetries, and for the pseudogap (PG) excitations present in A1g and B2g symmetries by the probe, and absence of any dependence on the pump beam polarization leads to the unequivocal conclusion of the existence of a spontaneous spatial symmetry breaking in the PG state not limited to the sample surface.

Toda, Y.; Kawanokami, F.; Kurosawa, T.; Oda, M.; Madan, I.; Mertelj, T.; Kabanov, V. V.; Mihailovic, D.

2014-09-01

339

Effect of substituting cerium-rich mischmetal with lanthanum on high temperature properties of die-cast Mg–Zn–Al–Ca–RE alloys  

Microsoft Academic Search

Mg–Zn–Al–Ca–RE alloys have been found to be promising materials for substituting aluminum alloys used for automatic transmission case applications in the automobile industry. Particularly, Mg–0.5%Zn–6%Al–1%Ca–3%RE (ZAXE05613) alloy exhibits comparable creep resistance as ADC12 die-casting aluminum alloy that is currently used for automatic transmission case applications. Changing the rare earth (RE) content of the alloy from mischmetal to lanthanum gives a

Ifeanyi A Anyanwu; Yasuhiro Gokan; Atsuya Suzuki; Shigeharu Kamado; Yo Kojima; Suguru Takeda; Taketoshi Ishida

2004-01-01

340

San Francisco Estuary Striped Bass Migration History Determined by Electron-microprobe Analysis of Otolith Sr/Ca Ratio  

SciTech Connect

Habitat use has been shown to be an important factor in the bioaccumulation of contaminants in striped bass. This study examines migration in striped bass as part of a larger study investigating bioaccumulation and maternal transfer of xenobiotics to progeny in the San Francisco Estuary system. Habitat use, residence time and spawning migration over the life of females (n = 23) was studied. Female striped bass were collected between Knights Landing and Colusa on the Sacramento River during the spawning runs of 1999 and 2001. Otoliths were removed, processed and aged via otolith microstructure. Subsequently, otoliths were analyzed for strontium/calcium (Sr/Ca) ratio using an electron-microprobe to measure salinity exposure and to distinguish freshwater, estuary, and marine habitat use. Salinity exposure during the last year before capture was examined more closely for comparison of habitat use by the maternal parent to contaminant burden transferred to progeny. Results were selectively confirmed by ion microprobe analyses for habitat use. The Sr/Ca data demonstrate a wide range of migratory patterns. Age of initial ocean entry differs among individuals before returning to freshwater, presumably to spawn. Some fish reside in freshwater year-round, while others return to more saline habitats and make periodic migrations to freshwater. Frequency of habitat shifts and residence times differs among fish, as well as over the lifetime of individual fish. While at least one fish spent its final year in freshwater, the majority of spawning fish spent their final year in elevated salinity. However, not all fish migrated to freshwater to spawn in the previous year. Results from this investigation concerning migration history in striped bass can be combined with contaminant and histological developmental analyses to better understand the bioaccumulation of contaminants and the subsequent effects they and habitat use have on fish populations in the San Francisco Estuary system.

Ostrach, D J; Phillis, C C; Weber, P K; Ingram, B L; Zinkl, J G

2004-09-17

341

Composite superconducting wires obtained by high-rate tinning in molten Bi-Pb-Sr-Ca-Cu-O system  

NASA Technical Reports Server (NTRS)

The preparation of high-T(sub c) superconducting long composite wires by short-time tinning of the metal wires in a molten Bi-Pb-Sr-Ca-Cu-O compound is discussed. The application of this method to the high-T(sub c) materials is tested, possibly for the first time. The initial materials used for this experiment were ceramic samples with nominal composition Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) and T(sub c) = 80 K prepared by the ordinary solid-state reaction, and industrial copper wires from 100 to 400 microns in diameter and from 0.5 to 1 m long. The continuously moving wires were let through a small molten zone (approximately 100 cubic mm). The Bi-based high-T(sub c) ceramics in a molten state is a viscous liquid and it has a strongly pronounced ability to spread on metal wire surfaces. The maximum draw rate of the Cu-wire, at which a dense covering is still possible, corresponds to the time of direct contact of wire surfaces and liquid ceramics for less than 0.1 s. A high-rate draw of the wire permits a decrease in the reaction of the oxide melt and Cu-wire. This method of manufacture led to the fabrication of wire with a copper core in a dense covering with uniform thickness of about h approximately equal to 5 to 50 microns. Composite wires with h approximately equal to 10 microns (h/d approximately equal to 0.1) sustained bending on a 15 mm radius frame without cracking during flexing.

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

1990-01-01

342

Fidelity of radially viewed ICP-OES and magnetic-sector ICP-MS measurement of Mg\\/Ca and Sr\\/Ca ratios in marine biogenic carbonates: Are they trustworthy together?  

Microsoft Academic Search

Improving interlaboratory reproducibility (in both precision and accuracy) of Mg\\/Ca and Sr\\/Ca determination in marine biogenic carbonates is critical in optimizing their utility as paleothermometers. Coupled with a need for uniform sample cleaning practices, there is a need for more exacting methods and procedures across laboratories using varied instrumentation. Here we employ an intensity ratio\\/matrix-effect correction methodology to a suite

Dyke H. Andreasen; Sindia Sosdian; Suzanne Perron-Cashman; Caroline H. Lear; Thibault deGaridel-Thoron; Paul Field; Yair Rosenthal

2006-01-01

343

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  

Microsoft Academic Search

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

C. Shen; C. Lu; L. Lo; D. Qu; K. Wei; M. K. Gagan

2006-01-01

344

Creep of polycrystalline (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}  

SciTech Connect

Plastic deformation has proved to be essential to the manufacture of bulk (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) superconductors. Compressive creep of dense, forged Bi-2223, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi-2212), and Bi{sub 2}Sr{sub 2}CuO{sub x} (Bi-2201) superconductors has been studied. These previous studies left unanswered questions about the large variation in Q among the Bi-superconductors and the rate-controlling deformation mechanism. The goals of this work were to test high-quality bulk Bi-2223 to determine whether steady state can be established, and if so, to determine the dominant creep mechanism and the values of n and Q.

Martinez-Fernandez, J.; Dominguez-Rodriguez, A.; Routbort, J.L.; Goretta, K.C.

2000-04-14

345

Amorphous Bi2Pb0.6Sr2Ca2Cu3Ox obtained by melt-spinning and its superconductivity after crystallisation  

E-print Network

de type 2223 à base de bismuth avec addition de plomb. Des échantillons de Bi2Pb0.6Sr2Ca2Cu3Ox respectivement. Abstract. - Previous quenching experiments on 2212 bismuth containing high Tc oxides have been). The glass transition was found to occur at Tg = 680 K and the onset of crystallisation at T = 730 K. After

Paris-Sud XI, Université de

346

X-ray photoelectron spectroscopy study of CaS:Eu and SrS:Eu phosphors Moonsup Han and S.-J. Oh  

E-print Network

to be ex- cited, and (3) the luminescent transition of the excited impurity. The emission and absorption for publication 14 January 1993) The phosphors of alkali-earth sulfides SrS:Eu, (x=0.05 and 0.10 mole per mole spectroscopy. The CaS:Eu phosphors were found to be stabilized against atmospheric water vapor and carbon

Oh, Se-Jung

347

Dipole Polarizability of Alkali-Metal (Na, K, Rb) - Alkaline-Earth-Metal (Ca,Sr) Polar molecules - Prospects of Alignment  

E-print Network

Electronic open-shell ground-state properties of selected alkali-metal (AM) - alkaline-earth-metal (AEM) polar molecules are investigated. We determine potential energy curves of the 2{\\Sigma}+ ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes (23Na, 39K, 85Rb) - (40Ca, 88Sr) are compared with available theoretical and experimental results. The variation of the permanent dipole moment (PDM), average dipole polarizability, and polarizability anisotropy with internuclear distance is determined using finite-field perturbation theory at the CCSD(T) level. Owing to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u., RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for alignment and orientation in combined intense laser and external static electric fields.

Gopakumar, Geetha; Hada, Masahiko; Kajita, Masatoshi

2014-01-01

348

Elastic(properties(and(surface(damage(resistance(of(nitrogen3rich((Ca,Sr)3Si3 O3N(glasses!  

E-print Network

, while the thermal expansion coefficient ( ) [11] decreases. The increase of elastic moduli was reported1 Elastic(properties(and(surface(damage(resistance(of(nitrogen3rich((Ca,Sr)3Si3 O3N´s modulus, shear modulus, bulk modulus and Poisson´s ratio were determined by means of ultrasonic echography

Boyer, Edmond

349

Microstructure and ferroelectric properties of MnO2-doped bismuth-layer ,,Ca,Sr...Bi4Ti4O15 ceramics  

E-print Network

inside the grains, which hinders domain-wall movements. The reduction of domain-wall mobility producesMicrostructure and ferroelectric properties of MnO2-doped bismuth-layer ,,Ca,Sr...Bi4Ti4O15 September 2005 We have studied the microstructures and ferroelectric properties of MnO2-doped bismuth

Cao, Wenwu

350

Effect of aluminium phosphate gel on whole-body retention of simultaneously administered 226 Ra, 85 Sr and 47 Ca in mice  

Microsoft Academic Search

Résumé L'administration presque simultanée d'un gel de phosphate d'alumine et de226RaCl2 réduit de 800 fois l'absorption intestinale du226Ra chez la souris. La charge corporelle en85Sr et47Ca est réduite d'environ 10 resp. 3 fois.

D. Keslev; S. Van Puymbroeck; O. Van der Borght

1972-01-01

351

Abstract--We have successfully manufactured and tested prototypes of a mechanically stabilized Bi2Sr2Ca1Cu2Ox  

E-print Network

Sr2Ca1Cu2Ox (Bi-2212) 6-on-1 cable-in-conduit (CIC). The superconducting wire in the cable testing of the first batch of cable that used an earlier generation of Bi-2212 wire and stainless steel tubing for the outer sheath [5,6]. The cable made for the test coils described here uses an improved wire

McIntyre, Peter

352

Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO3)2-Ca (HCO3)2-CO2-H2O solutions  

USGS Publications Warehouse

Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated non-stoichiometric solutions of Sr(HCO3)2 and Ca(HCO3)2 at 25??C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO3)2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HCO3)2 solutions and 0-4 layers thick in Ca(HCO3)2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO3)2 and Ca(HCO3)2 solutions, respectively. In Sr(HCO3)2 solutions, the XPS signal from the outer ~ 60 A?? on aragonite indicates a composition of 16 mol% SrCO3 after only 2 min of contact, and 14-18 mol% SrCO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO3 after 2 min of contact with Ca(HCO3)2 solution, and is 34-39 mol% CaCO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer ~25 A?? (as much as 26 mol% SrCO3 on aragonite and 44 mol% CaCO3 on strontianite). The results indicate rapid formation of a solid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition of the bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component ((Sr(HCO3)2)) than in solutions spiked with the more soluble component (Ca(HCO3)2), an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a non-stoichiometric surface reactive zone significantly decreases dissolution rates. ?? 1992.

Plummer, L. N.; Busenberg, E.; Glynn, P. D.; Blum, A. E.

1992-01-01

353

Crystal growth of Bi2CaSr2Cu2O8+x superconductors  

E-print Network

. The phase responsible for superconductivity had the composition Laz ?Ba?Cu04 ?, where x&0. 2 and y is small and the compound has a structure siriiilar to potassium nickel fluoride [1]. Chu et ufi [2] demonstrated that the T, could be raised up to 52. 5K... by subject- ing lanthanum compound to a pressure of approximately 1. 2 Kbar. This was then simulated by substitution of a. smaller ion for lanthanum. In early 1987 iA'u et al. [3] discovered superconductivity at nearly 90K in Y-Ba-Cu-O. This invention had...

Hannan, Masud

2012-06-07

354

Synthesis, structure, and properties of four ternary compounds: CaSrTt, Tt=Si, Ge, Sn, Pb  

SciTech Connect

The title compounds were synthesized and characterized by structural measurements and electronic structure calculations. Single-crystal X-ray diffraction analyses established that they all have the orthorhombic inverse-PbCl{sub 2}-type structure (Pnma, Z=4, a=8.108(2), 8.124(2), 8.421(2), 8.509(2)A; b=4.944(1), 4.949(1), 5.168(1), 5.189(1)A; c=9.170(2), 9.184(2), 9.685(2), 9.740(2)A, respectively). The tetrel (Tt) atoms are situated in tricapped trigonal prisms of ordered Sr and Ca atoms in which the smaller Ca atoms play a distinctive role. The structure is distinguishable from the Co{sub 2}Si type by its more nearly ideal 6+3 (TCTP) environment about Tt rather than a higher coordination by cations. Other representations of the two structural types are also considered. Electronic band structure calculations suggest that the compounds are semiconductors, in agreement with literature data on their Ae{sub 2}Tt analogues.

Liu Shengfeng [Ames Laboratory, Department of Chemistry, Iowa State University, Ames, Iowa 50010 (United States); Corbett, John D. [Ames Laboratory, Department of Chemistry, Iowa State University, Ames, Iowa 50010 (United States)]. E-mail: jcorbett@iastate.edu

2006-03-15

355

Synthesis and electrical properties of (Pb,Co)Sr2(Y,Ca)Cu2Oz  

NASA Astrophysics Data System (ADS)

One of related materials to high-temperature superconductors (HTSC's) with nominal compositions of (Pb0.5Co0.5)Sr2(Y1xCax)Cu2Oz (x=0?0.6) is synthesized and characterized. All samples are nearly single-phase, and its crystal structure is likely to be so-called “1-2-1-2” type which is one of typical structures of HTSC's. Electrical resistivity is decreased as x increases. While superconductivity is not observed at temperatures between room-temperature and 20 K for all samples, temperature dependence of the resistivity exhibits metallic behavior down to 150 K for x=0.5. Phase formation and transport behavior are discussed focusing on mixed valence-state of Co2+ and Co3+.

Tashiro, T.; Maeda, T.; Abe, R.; Takechi, S.; Takahashi, T.; Haruta, M.; Horii, S.

356

Oceanographic variability in the South Pacific Convergence Zone region over the last 210 years from multi-site coral Sr/Ca records  

NASA Astrophysics Data System (ADS)

the South Pacific Convergence Zone (SPCZ), the variability in a sub-seasonally resolved microatoll Porites colony Sr/Ca record from Tonga and a previously published high-resolution record from Fiji are strongly influenced by sea surface temperature (SST) over the calibration period from 1981 to 2004 (R2 = 0.67-0.68). However, the Sr/Ca-derived SST correlation to instrumental SST decreases back in time. The lower frequency secular trend (~1°C) and decadal-scale (~2-3°C) modes in Sr/Ca-derived SST are almost two times larger than that observed in instrumental SST. The coral Sr/Ca records suggest that local effects on SST generate larger amplitude variability than gridded SST products indicate. Reconstructed ?18O of seawater (?18Osw) at these sites correlate with instrumental sea surface salinity (SSS; r = 0.64-0.67) but not local precipitation (r = -0.10 to -0.22) demonstrating that the advection and mixing of different salinity water masses may be the predominant control on ?18Osw in this region. The Sr/Ca records indicate SST warming over the last 100 years and appears to be related to the expansion of the western Pacific warm pool (WPWP) including an increasing rate of expansion in the last ~20 years. The reconstructed ?18Osw over the last 100 years also shows surface water freshening across the SPCZ. The warming and freshening of the surface ocean in our study area suggests that the SPCZ has been shifting (expanding) southeast, possibly related to the southward shift and intensification of the South Pacific gyre over the last 50 years in response to strengthened westerly winds.

Wu, Henry C.; Linsley, Braddock K.; Dassié, Emilie P.; Schiraldi, Benedetto; Demenocal, Peter B.

2013-05-01

357

Magnetothermoelectric power of Pr0.5Sr0.5MnO3 with Ru substitution at the Mn site  

NASA Astrophysics Data System (ADS)

The effects of Ru substitution at the Mn site for the manganite series of Pr0.5Sr0.5Mn1- xRuxO3 (0.0?x?0.1) have been studied using magnetothermoelectric power (TEP) along with resistivity and magnetization. Systematic changes of TEP were observed with variation of Ru concentration: suppression of the large negative peak at low temperatures, decrease of curvature with TC enhancement at intermediate temperatures, and increase of the value of TEP at high temperatures. These changes of TEP with Ru substitution and an applied magnetic field are analyzed in terms of broad-band metallic transport (T<170 K), magnon scattering processes (170 KTC). From these results, it was found that the ferromagnetism is more strongly induced by Ru substitution than by an applied magnetic field, suggesting the important role of the Ru d orbitals in the charge transport of the Mn3+-O-Mn4+ network.

Kim, J. S.; Kim, D. C.; McIntosh, G. C.; Chu, S. W.; Park, Y. W.; Kim, B. J.; Kim, Y. C.; Maignan, A.; Raveau, B.

2002-12-01

358

Structural and electronic effects of Sr substitution for Ba in Y(Ba1-xSrx)2Cu3Ow at varying w  

NASA Astrophysics Data System (ADS)

To unveil the structural mechanisms associated with Tc variations induced by either mechanical or chemical pressure, samples of the Y(Ba1-xSrx)2Cu3Ow system with x<=0,0.02,0.1,0.25,0.35,0.5,0.625,0.75,1, as well as those with x=0.5 and w=6.685,6.80,6.96,6.98, have been prepared and characterized. Characterization includes crystal structural refinements based on powder neutron diffraction data taken at room temperature, electron microscopy for detecting a possible Ba/Sr ordering, and resistive and magnetic measurements of the superconducting transition. The effects of Sr substitution on the structural parameters are equivalent to those of a pressure of approximately 10 GPa/x. The main difference is the thickness of the superconducting block CuO2-Y-CuO2, which increases with increasing x and decreases with increasing pressure. As a consequence of the displacement of O4 from the (0,12,0) to the (x,12,0) position, the Ba/Sr-O4 distance decreases with increasing Sr content. At constant w, Tc decreases at the rate of 20 K/x. For x>0, the maximum of Tc occurs at a value of w higher than for x=0. For x=0.5 the thickness of the superconducting block increases with increasing w and consequently with increasing Tc. This indicates that, at least in this system, the thickness of the superconducting block is not the key parameter controlling Tc. The stress of the Ba/Sr and the Y sites, estimated from the bond valence sums (BVSs), decreases with increasing x. For x=0.5, the BVS values are almost equal to the formal values of 2+ and 3+, respectively. The average BVS of Cu1 and Cu2 increases with increasing x. However, this does not correspond to a real increase because the total charge of the Cu cations, as determined by iodometric titration or neutron diffraction, remains constant with x. Our analysis of the structural data suggests that the relaxation of the Ba/Sr layer hinders the charge transfer from Cu1 to Cu2, which accounts for the decrease of Tc with increasing x.

Licci, F.; Gauzzi, A.; Marezio, M.; Radaelli, G. P.; Masini, R.; Chaillout-Bougerol, C.

1998-12-01

359

High-mobility group box 1 (HMGB1) impaired cardiac excitation-contraction coupling by enhancing the sarcoplasmic reticulum (SR) Ca(2+) leak through TLR4-ROS signaling in cardiomyocytes.  

PubMed

High-mobility group box 1 (HMGB1) is a proinflammatory mediator playing an important role in the pathogenesis of cardiac dysfunction in many diseases. In this study, we explored the effects of HMGB1 on Ca(2+) handling and cellular contractility in cardiomyocytes to seek for the mechanisms underlying HMGB1-induced cardiac dysfunction. Our results show that HMGB1 increased the frequency of Ca(2+) sparks, reduced the sarcoplasmic reticulum (SR) Ca(2+) content, and decreased the amplitude of systolic Ca(2+) transient and myocyte contractility in dose-dependent manners in adult rat ventricular myocytes. Inhibiting high-frequent Ca(2+) sparks with tetracaine largely inhibited the alterations of SR load and Ca(2+) transient. Blocking Toll-like receptor 4 (TLR4) with TAK-242 or knockdown of TLR4 by RNA interference remarkably inhibited HMGB1 induced high-frequent Ca(2+) sparks and restored the SR Ca(2+) content. Concomitantly, the amplitude of systolic Ca(2+) transient and myocyte contractility had significantly increased. Furthermore, HMGB1 increased the level of intracellular reactive oxygen species (ROS) and consequently enhanced oxidative stress and CaMKII-activated phosphorylation (pSer2814) in ryanodine receptor 2 (RyR2). TAK-242 pretreatment significantly decreased intracellular ROS levels and oxidative stress and hyperphosphorylation in RyR2, similar to the effects of antioxidant MnTBAP. Consistently, MnTBAP normalized HMGB1-impaired Ca(2+) handling and myocyte contractility. Taken together, our findings suggest that HMGB1 enhances Ca(2+) spark-mediated SR Ca(2+) leak through TLR4-ROS signaling pathway, which causes partial depletion of SR Ca(2+) content and hence decreases systolic Ca(2+) transient and myocyte contractility. Prevention of SR Ca(2+) leak may be an effective therapeutic strategy for the treatment of cardiac dysfunction related to HMGB1 overproduction. PMID:24937603

Zhang, Cuicui; Mo, Miaohua; Ding, Wenwen; Liu, Wenjuan; Yan, Dewen; Deng, Jianxin; Luo, Xinping; Liu, Jie

2014-09-01

360

Rolled-up tubes and cantilevers by releasing SrRuO3-Pr0.7Ca0.3MnO3 nanomembranes  

PubMed Central

Three-dimensional micro-objects are fabricated by the controlled release of inherently strained SrRuO3/Pr0.7Ca0.3MnO3/SrRuO3 nanometer-sized trilayers from SrTiO3(001) substrates. Freestanding cantilevers and rolled-up microtubes with a diameter of 6 to 8 ?m are demonstrated. The etching behavior of the SrRuO3 film is investigated, and a selectivity of 1:9,100 with respect to the SrTiO3 substrate is found. The initial and final strain states of the rolled-up oxide layers are studied by X-ray diffraction on an ensemble of tubes. Relaxation of the sandwiched Pr0.7Ca0.3MnO3 layer towards its bulk lattice parameter is observed as the major driving force for the roll-up of the trilayers. Finally, ?-diffraction experiments reveal that a single object can represent the ensemble proving a good homogeneity of the rolled-up tubes. PACS: 81.07.-b; 68.60.-p; 68.37.Lp; 81.16.Dn. PMID:22151894

2011-01-01

361

Bi-Sr-Ca-Cu-O thin films grown by flash evaporation and pulsed laser deposition  

E-print Network

hours (c) Annealed at 825oC for 3 hours??????? 52 19 (a) SEM micrograph of as-grown film, grown at 725oC (b) AFM image of the above film (c) AFM image of the film, annealed at 835oC for 1 hour??????????????????????... 54 20 AFM analysis of BSCCO thin..., and has not yet been achieved. These superconductors have a crystal structure commonly known as the modified perovskite structure. The family of perovskite materials has the generic formula ABO3. The designation ?perovskite? originates from the mineral Ca...

Ganapathy Subramanian, Santhana

2004-09-30

362

Superconducting ceramics in the Bi1.5SrCaCu2O sub x system by melt quenching technique  

NASA Technical Reports Server (NTRS)

Bi sub 1.5 SrCaCu sub 2 O sub x has been prepared in the glassy state by rapid quenching of the melt. The kinetics of crystallization of various phases in the glass have been evaluated by a variable heating rate differential scanning calorimetry method. The formation various phases on thermal treatments of the glass has been investigated by powder X-ray diffraction and electrical resistivity measurements. Heating at 450 C formed Bi sub 2 Sr sub 2 CuO sub 6, which disappeared on further heating at 765 C, where Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 formed. Prolonged heating at 845 C resulted in the formation of a small amount of a phase with T sub c onset of approx. 108 K, believed to be Bi sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub 10. This specimen showed zero resistivity at 54 K. The glass ceramic approach could offer several advantages in the fabrication of the high-T sub c superconductors in desired practical shapes such as continuous fibers, wires, tapes, etc.

Bansal, Narottam P.; Deguire, Mark R.

1989-01-01

363

Morphology and Properties of (Ba, Sr, Ca) Titanates Synthesized by Microwave-Assisted Hydrothermal Method  

NASA Astrophysics Data System (ADS)

Ba1-xCaxTiO3, Ba1-xSrxTiO3 and Sr1-xCaxTiO3 (x = 0, 0.25, 0.50, 0.75 and 1) nanoparticles were synthesized using the microwave-assisted hydrothermal method. Samples were prepared for 40 minutes at 140°C under a pressure of 3 MPa using an adapted domestic microwave oven. The samples were characterized by X-Ray diffraction (XRD), scanning electron microscopy (FE-SEM), and Raman, photoluminescence (PL) and ultraviolet-visible (UV-Vis) spectroscopies. XRD data show that ceramic powders have crystalline phases associated with a short-range structural disorder. This structural disorder is confirmed by Raman spectral bands indicating multi-phonon processes and the presence of defects or impurities. Such defects account for a broad band in the photoluminescence spectrum in the green light (460 nm) region for all samples. Gap energy variation, obtained from UV-Vis spectra, suggest a non-uniform band structure of these titanates in accordance with the PL results. The morphology of each sample is changed with doping and varies from a spherical to cubic appearance for energy minimization.

Souza, A. E.; Santos, G. T. A.; Silva, R. A.; Moreira, M. L.; Volante, D. P.; Teixeira, S. R.; Longo, E.

2011-10-01

364

Magnetoresistance and Low Field Microwave Absorption in Nanostructured LaSr(Ca)MnO Films  

NASA Astrophysics Data System (ADS)

High magnetic fields and narrow temperature windows for colossal magnetoresistance (CMR) present daunting limitations for applications. Limitations could be overcome by modifying CMR materials via nanostructuring. Nanostructured films of lanthanum strontium(calcium) manganite precursors were electrochemically deposited on silver and various porous carbon substrates, and followed by rapid (ca. 10 s at 900 C) or anodic (at 600 mV vs SCE) oxidation. X-ray diffraction, x-ray fluorescence and scanning electron microscopy techniques were used to establish the formation and composition of the hole doped perovskite structure, and the microstructure of the films. The results of temperature-dependent ac resistance and low field microwave measurements as a function of magnetic field down to below a few hundred gauss and as a function of microstructure, will be presented. Preliminary results on the electrochemical formation and evaluation of the electron doped TlMnO pyrochlore CMR material will also be discussed.

Bleiweiss, M.; Datta, T.; Owens, F.; Iqbal, Z.

1998-03-01

365

Metal organic chemical vapor deposition growth of epitaxial SrRuO 3 and CaRuO 3 thin films with different orientations as the bottom electrode for epitaxial ferroelectric thin film  

Microsoft Academic Search

70nm-thick (100)c, (110)c and (111)c-oriented epitaxial SrRuO3 and CaRuO3 thin films were grown on (100), (110) and (111)SrTiO3 substrates, respectively, by metal organic chemical vapor deposition (MOCVD) at 750°C. Thickness fringes were observed for the (100)c- and (110)c-oriented SrRuO3 films, suggesting a smooth surface for the film and the film-substrate interface. (111)c-oriented SrRuO3 and CaRuO3 films showed a rough surface

Hiroshi Funakubo; Takahiro Oikawa; Noriyuki Higashi; Keisuke Saito

2002-01-01

366

Melt processing of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} superconductor in oxygen and argon atmospheres  

SciTech Connect

Solidification and subsequent annealing of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O{sub 2} and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi{sub 2}Sr{sub 3-x}Ca{sub x}O{sub y} and Cu{sub 2}O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi{sub 2.15}Sr{sub 2}Ca{sub 0.85}Cu{sub 2}O{sub y}.

Holesinger, T.G.; Miller, D.J. [Argonne National Lab., IL (United States); Chumbley, L.S. [Ames Lab., IA (United States)

1992-08-01

367

Melt processing of the Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] superconductor in oxygen and argon atmospheres  

SciTech Connect

Solidification and subsequent annealing of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O[sub 2] and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi[sub 2]Sr[sub 3-x]Ca[sub x]O[sub y] and Cu[sub 2]O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi[sub 2.15]Sr[sub 2]Ca[sub 0.85]Cu[sub 2]O[sub y].

Holesinger, T.G.; Miller, D.J. (Argonne National Lab., IL (United States)); Chumbley, L.S. (Ames Lab., IA (United States))

1992-08-01

368

Sr/Ca sensitivity to aragonite saturation state in cultured subsamples from a single colony of coral: Mechanism of biomineralization during ocean acidification  

NASA Astrophysics Data System (ADS)

Using a new and rapid NanoSIMS-based method, we quantified the sensitivity of skeletal Sr/Ca in coral to the aragonite saturation state of seawater (?SW). Skeletal Sr/Ca is a common proxy for temperature while ?SW is a parameter that varied in the past ocean and is predicted to change with continued ocean acidification. Five adult branches of the surface coral Stylophora pistillata were grown at different ?SW from 2.7 to 4.9 (pH of 7.9-8.5) but at a constant temperature of 25 °C. Despite a large range of growth parameters and a twofold range in calcification rates, the average skeletal Sr/Ca of coral exposed to each condition are within 1.2% of each other (2? std. dev. of the 5 means). Furthermore, the average skeletal Sr/Ca measured in this study agrees with the results of two previous coral culture experiments conducted at the same temperature but where ?SW was not controlled. These results suggest that aragonite saturation has little or no influence on Sr/Ca paleothermometry over the range of ?SW investigated. Combined with existing data for low ?SW conditions, our results were used to elucidate the mechanisms controlling calcifying fluid acid-base chemistry during coral biomineralization. Assuming that coral drive precipitation through alkalinity pumping, our data suggest that this pumping occurs until the calcifying fluid reaches a target pH. Below a threshold ?SW bounded by 1 < ?SW < 2.4, however, coral do not pump enough alkalinity to reach the target pH and instead pump a maximal but finite amount of alkalinity. In this low ?SW regime, calcifying fluid pH is expected to decrease with ?SW. The interplay between these two alkalinity pumping regimes and external seawater composition explain the full range of observed Sr/Ca sensitivity to ?SW and suggest that surface coral may become increasingly sensitive to ocean acidification below a threshold ?SW bounded by 1 < ?SW < 2.4.

Gagnon, Alexander C.; Adkins, Jess F.; Erez, Jonathan; Eiler, John M.; Guan, Yunbin

2013-03-01

369

Generalized Grüneisen parameters and the low temperature thermal expansion of high-Tc superconductor Bi2Sr2CaCu2O8  

NASA Astrophysics Data System (ADS)

The anisotropy of low temperature thermal expansion of Bi2Sr2CaCu2O8 (Bi 2212) is analysed theoretically using quasiharmonic theory of thermal expansion. Vibrational anharmonicity as determined by the generalized Grüneisen parameters (GPs) ?'j and ?''j of the various normal mode frequencies of the lattice has been studied. ?'j refers to change in frequencies due to a uniform areal strain perpendicular to the c-axis and ?''j to the change in frequencies due to a uniform areal strain along the c-axis of the Bi 2212 crystal. The generalized GPs are calculated using the second-order elastic constants (SOECs) and third-order elastic constants (TOECs). The SOECs and TOECs are calculated using deformation theory. The strain energy density ? is estimated by taking into account the interactions of nine nearest neighbours of each atom in the unit cell of Bi 2212. The energy density thus obtained is compared with the strain-dependent lattice energy from the continuum model approximation to obtain the complete set of non-vanishing SOECs and TOECs of Bi2Sr2CaCu2O8. Generally, ?''j exhibits higher values than ?'j. Thus the crystal is more anharmonic along the c-axis than in the ab-plane. The longitudinal acoustic mode ?3'' is the most anisotropic of all the mode gammas. The transverse acoustic mode ?1' attains negative values from ? = 25° to 55°, where ? is the angle made by the direction of wave propagation with the c-axis of the crystal Bi2Sr2CaCu2O8. The low temperature limit of the effective Grüneisen functions ?(0). Hence the discrepancy in the vibrational anharmonicity along the c-axis and along the CuO2 plane persists even at low temperatures. The low temperature limit of the volume lattice thermal expansion ?L is calculated from mode Grüneisen gammas. ?L has been obtained as 4.2 for Bi2Sr2CaCu2O8. The low temperature limit ?L is positive and therefore, we expect the volume lattice thermal expansion to be positive down to absolute zero in Bi2Sr2CaCu2O8. At low temperatures, the acoustic wave velocities in high-Tc superconductors increase their value due to the freezing out of optical phonons. This can be a reason for the higher value of the low temperature limit of Grüneisen gammas in Bi2Sr2CaCu2O8.

Jayachandran, K. P.; Menon, C. S.

2002-01-01

370

Effect of electron correlation in Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3}: Density functional calculation  

SciTech Connect

We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr{sup 4+}-Ru{sup 4+} hybridization is responsible for the high Curie temperature T{sub C} in SrRu{sub 1-x}Cr{sub x}O{sub 3}, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu{sub 1-x}Cr{sub x}O{sub 3} clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted Ca-based compounds as compared to the Sr-based systems shows that the hybridization mechanism is not relevant for these compounds. The bigger exchange splitting of Ru 4d and Cr 3d at the Fermi level with Ru{sup 4+,5+} and Cr{sup 3+,4+} orbital occupancies of CaRu{sub 0.75}Cr{sub 0.25}O{sub 3} in the LSDA+U calculation, compared with that of the LSDA calculation, shows that repulsion between electrons tend to keep the localized spins from overlapping. The low screening of the Ru t{sub 2g} electrons increases T{sub C} in the Ca-based systems, which is consistent with the both high Ru exchange splitting and magnetic moment. The insulating behavior of the high Cr-doped systems can be explained by considering the Ru{sup 4+}+Cr{sup 4+{yields}}Ru{sup 5+}+Cr{sup 3+} charge transfer. - Graphical Abstract: We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using different ab-initio calculation such as LSDA and LSDA+U approximation. The antiferromagnetic hybridization of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The LSDA+U calculation for the more distorted Cr impurity doped Ca-based ruthenate compounds as compared to the Sr-based systems shows repulsion between electrons, which tends to keep the localized spins from overlapping.

Hadipour, H. [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Akhavan, M., E-mail: akhavan@sharif.ed [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of)

2010-07-15

371

Infrared and millimeter wave detection using thin films of Pb doped BiSrCaCuO superconductor  

NASA Astrophysics Data System (ADS)

Thin film detectors made of CuO superconductors were developed in our laboratory. This article reports details of the fabrication and testing of Pb doped BiSrCaCuO detectors. The detector comprises a film sensor housed in a small cryostat with built-in bias supply and temperature control circuitry. The film sensor was first deposited by magnetron rf sputtering and then crystallized under a rapid thermal annealing process. The characteristics of the response of the detector under millimeter wave and infrared illumination were investigated. The millimeter wave response exhibited a Josephson component with a D(*) approximately 10(exp 8) - 10(exp 9) cm.Hz(exp (1/2))/W in the wavelength range of 3 - 8 mm. The transient response to short pulses indicated a time constant tau less than or equal to 10 ns for this component. The response to laser pulses was thermal in origin and inherently compressible, preventing saturation of the detector electronics to intense beams. The wide band characteristic of the responses at both infrared and millimeter wavelengths could be confirmed. The damage threshold of the film sensor was shown to exceed 10 mJ / sq cm per 3 ns pulse. The possible use of these detectors for threat detection and the optimization of their figure of merit are discussed.

Phong, L. Ngo

1995-01-01

372

Transport properties of Tl-Ba/Sr-Ca-Cu-O metal sheated superconducting tapes in magnetic fields  

SciTech Connect

This paper reports on Ag or Au sheathed tapes with a Tl-Ba/Sr-Ca-Cu-O core fabricated by a drawing-rolling and subsequent pressing method. The tape prepared at an optimized condition yielded a transport J{sub c} of 15,900 A/cm{sup 2} at 77 K in the absence of magnetic field, and 1,100 A/cm{sup 2} in a magnetic field of 1 T. The enhancement of J{sub c} in a magnetic field was thought to be caused by an improved junction between grains and an unintentional introduction of a pinning center from various defects and unknown crystal phases. A 67-turn-pancake coil was made from a 10 m long, 0.14 mm thick and 2.5 mm width Ag sheathed tape, which was capable of at least a 7 A critical current at 77 K in the absence of magnetic field. The coil generated up to a maximum magnetic field of 103 Gauss (a coil current of 3.0 A) without resistivity in liquid nitrogen.

Aihara, K.; Okada, M.; Matsumoto, T.; Matsuda, S. (Hitachi Research Lab., Hitachi, Ltd., 4026 Kuji, Hitachi, Ibaraki 319-12 (JP)); Hosono, F.; Seido, M. (Metal Research Lab., Hitachi Cable Ltd., 3550 Kidamari, Tautiura, Ibaraki 300 (JP))

1991-03-01

373

Magnetic relaxation of highly textured Bi2Sr2CaCu2O8+? polycrystalline fibres  

NASA Astrophysics Data System (ADS)

The magnetic relaxation of Bi2Sr2CaCu2O8+? superconducting highly textured polycrystalline materials (fibres) grown by laser induced floating zone melting methods have been studied using ac susceptibility and de magnetisation techniques, Effective pinning energies, Ueff, have been derived for a wide range of current densities, J, and magnetic fields both parallel and perpendicular to the fibre axis. In agreement with the microstructure Ueff,(J)>Ueff,?J and approximately follows for both orientations the phenomenology observed on single crystals for c-axis parallel fields. Near the irreversibility line Ueff is J independent, expressed as: Ueff(T,B)=Ueff(O K, 1 T)B-0.5(1 - T/Tc). Moreover, both Ueff,(J) and Ueff,?(J) values are higher than analogous Ueff,c values on single crystals. Accordingly, for a given temperature the irreversibility line appears at larger fields, about ten times for fields perpendicular to the fibre axis and even higher in the parallel case. A careful analysis of the pinning energy distributions in fibres has been undertaken showing the presence of a high energy shoulder, absent in unirradiated single crystals.

Angurel, L. A.; Martínez, E.; Díez, J. C.; Lera, F.; Navarro, R.

1996-02-01

374

Magnetic relaxation of highly textured Bi 2Sr 2CaCu 2O 8+? polycrystalline fibres  

NASA Astrophysics Data System (ADS)

The magnetic relaxation of Bi 2Sr 2CaCu 2O 8+? superconducting highly textured polycrystalline materials (fibres) grown by laser induced floating zone melting methods have been studied using ac susceptibility and dc magnetisation techniques. Effective pinning energies, Ueff, have been derived for a wide range of current densities, J, and magnetic fields both parallel and perpendicular to the fibre axis. In agreement with the microstructure Ueff, ?( J) > Ueff,? ( J) and approximately follows for both orientations the phenomenology observed on single crystals for c-axis parallel fields. Near the irreversibility line Ueff is J independent, expressed as: Ueff( T, B) = Ueff(0 K, 1 T) B-0.5 (1 - T/ Tc). Moreover, both Ueff,?( J) and Ueff,? ( J) values are higher than analogous Ueff, c values on single crystals. Accordingly, for a given temperature the irreversibility line appears at larger fields, about ten times for fields perpendicular to the fibre axis and even higher in the parallel case. A careful analysis of the pinning energy distributions in fibres has been undertaken showing the presence of a high energy shoulder, absent in unirradiated single crystals.

Martínez, E.; Angurel, L. A.; Díez, J. C.; Lera, F.; Navarro, R.

375

Fabrication of Bi 2Sr 2Ca 1Cu 2O x superconductor using metallic substrate tape clad with Ag  

NASA Astrophysics Data System (ADS)

With the intentions of the reduction of material cost and the improvement of mechanical properties, Ag/Ni and Ag/Stainless Steel (SUS) clad tapes were prepared as substrate materials for the fabrication of Bi 2Sr 2Ca 1Cu 2O x (Bi-2212) superconducting tape. Bi-2212 formed on the Ag/Ni clad tape with a 10 ?m Ag layer thickness showed good superconducting properties of Tc=88 K and Jc (4.2 K, 10 T)=1.7×10 5 A/cm 2, comparable to those of Bi-2212 tape fabricated using pure Ag tape. However, Bi-2212 formed on the Ag/Ni clad tape with a 5 ?m Ag layer thickness showed deteriorated properties due to the transfer of Cu and Ni across the Ag layer. The Ag/SUS clad tape did not work as a substrate material, because the Ag layer was eroded, forming many holes, and hence could not prevent a severe reaction between Bi-2212 and SUS. The Jc of the Bi-2212/Ag/Ni tape started to degrade at ?=0.2-0.3% in the bending test. A tensile test indicated that the Ag/Ni clad tape had about three times larger yield strength than pure Ag tape. From these results, it is expected that the Bi-2212/Ag/Ni tape has a much improved stress tolerance over the conventional Bi-2212/Ag tape.

Nemoto, Y.; Fujii, H.; Kitaguchi, H.; Kumakura, H.; Togano, K.; Shima, K.

2001-02-01

376

Composite superconducting wires obtained by high-rate tinning in molten Bi-Pb-Sr-Ca-Cu-O system  

NASA Technical Reports Server (NTRS)

Long lengths of metal superconductor composites were prepared by passing a copper wire through the bismuth based molten oxide system at a constant speed. The key to successful composite preparation is the high pulling speed involved, which permits minimization of the severe interaction between the unbuffered metal surface and the oxide melt. Depending on the temperature of the melt and the pulling speed, a coating with different thickness and microstructure appeared. The nonannealed thick coatings contained a Bi2(Sr,Ca)2Cu1O6 phase as a major component. After relatively short time annealing at 800 C, both resistivity and initial magnetization versus temperature measurements show superconducting transitions beginning in the 110 to 115 K region. The effects of annealing and composition on obtained results are discussed. This method of manufacture led to the fabrication of wire with a copper core in a dense covering with uniform thickness of about h approximately equal to 5 to 50 microns. Composite wires with h approximately equal to 10 microns (h/d approximately equal to 0.1) sustained bending on a 15 mm radius frame without cracking during flexing.

Grosav, A. D.; Konopko, L. A.; Leporda, N. I.

1991-01-01

377

Influence of pelletization pressure on magnetic susceptibility samples of ceramics Bi (Pb)-Sr-Ca-Cu-O  

NASA Astrophysics Data System (ADS)

The influence of pelletization pressing 100-500 MPa on the quality of the samples from Bi 1.7Pb 0.3Sr 2Ca 2.5Cu 3.5O 10+ ? superconducting transition was investigated. Samples which were pelletized at 100, 200, 300 MPa increased weight by an uncontrollable diffusion of elements from a filling. Obviously, these elements form additive phases on borders of grains, what is possible to conclude from the dependence ??- T. The weight of samples pressed at pressure 400 and 500 MPa practically does not change at sintering. These samples after sintering within 250 h have a rather precise superconducting transition from a magnetic susceptibility. XRD shows that the phase structure of samples differs insignificantly-after sintering time 250 h samples consist basically of a phase 2223. The powder of the same composition annealed also within 250 h without a filling by results of XRD consists of approximately equal amounts of phases 2223 and 2212.

Fradina, I. A.; Alekseev, A. F.; Gridasova, T. Ja.; Morozov, V. V.; Jurchenko, D. O.

1999-01-01

378

Ternary CaCu{sub 4}P{sub 2}-type pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb)  

SciTech Connect

Four ternary pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb) were prepared by reactions of the elements at 850 Degree-Sign C and their crystal structures were determined from single-crystal X-ray diffraction studies. These silver-containing pnictides AAg{sub 4}Pn{sub 2} adopt the trigonal CaCu{sub 4}P{sub 2}-type structure (Pearson symbol hR21, space group R3-bar m, Z=3; a=4.5555(6) A, c=24.041(3) A for SrAg{sub 4}As{sub 2}; a=4.5352(2) A, c=23.7221(11) A for EuAg{sub 4}As{sub 2}; a=4.7404(4) A, c=25.029(2) A for SrAg{sub 4}Sb{sub 2}; a=4.7239(3) A, c=24.689(2) A for EuAg{sub 4}Sb{sub 2}), which can be derived from the trigonal CaAl{sub 2}Si{sub 2}-type structure of the isoelectronic zinc-containing pnictides AZn{sub 2}Pn{sub 2} by insertion of additional Ag atoms into trigonal planar sites within [M{sub 2}Pn{sub 2}]{sup 2-} slabs built up of edge-sharing tetrahedra. Band structure calculations on SrAg{sub 4}As{sub 2} and SrAg{sub 4}Sb{sub 2} revealed that these charge-balanced Zintl phases actually exhibit no gap at the Fermi level and are predicted to be semimetals. - Graphical abstract: SrAg{sub 4}As{sub 2} and related pnictides adopt a CaCu{sub 4}P{sub 2}-type structure in which additional Ag atoms enter trigonal planar sites within slabs built from edge-sharing tetrahedra. Highlights: Black-Right-Pointing-Pointer AAg{sub 4}Pn{sub 2} are the first Ag-containing members of the CaCu{sub 4}P{sub 2}-type structure. Black-Right-Pointing-Pointer Ag atoms are stuffed in trigonal planar sites within CaAl{sub 2}Si{sub 2}-type slabs. Black-Right-Pointing-Pointer Ag-Ag bonding develops through attractive d{sup 10}-d{sup 10} interactions.

Stoyko, Stanislav S.; Khatun, Mansura; Scott Mullen, C. [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Mar, Arthur, E-mail: arthur.mar@ualberta.ca [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada)

2012-08-15

379

XANES and EXAFS studies on a new superconducting intercalation compound, AgIBi2Sr2CaCu2Oy  

NASA Astrophysics Data System (ADS)

A new superconducting intercalation compound, AgIBi2Sr2CaCu2Oy, in which the basal spacing is increased by 7.352 Å, has been prepared from the mixture of polycrystalline Bi2Sr2CaCu2Oy and Ag powder under iodine vapor at 190 °C in an ambient atmosphere. The X-ray absorption studies on I LI- and Ag K-edges indicate that there is no charge-transfer between the intercalated guest species, AgI and host layer. A slight Tc depression (?Tc ~ 13K) upon AgI intercalation is, therefore, probably due to the weakening of interlayer coupling, but the hole donation to the host upon oxygen intercalation may not be excluded.

Choy, J.-H.; Kim, D.-K.; Park, N.-G.; Kim, D.-H.; Hwang, S.-J.; Hwang, S.-H.; Hur, N. H.

1994-12-01

380

Magnetocapacitance of La1-xCaxMnO3/SrTiO3: Nb junctions with different Ca contents  

NASA Astrophysics Data System (ADS)

Manganite-based heterojunctions La1-xCaxMnO3/SrTiO3: Nb (0.5 wt. %) with x = 0.2, 0.3, 0.375, 0.4, 0.5, 0.6, and 0.7 have been fabricated, and the lattice constants of La1-xCaxMnO3 films are experimentally studied. The capacitance characteristics of those junctions under a magnetic field have been investigated. Obvious magnetocapacitance was observed in La0.7Ca0.3MnO3/Nb-SrTiO3 p-n junction near the Curie temperature (TC) of La0.7Ca0.3MnO3 at 0.75 T. The result can be explained by phase separation. This study demonstrates the remarkable tunability of the capacitance for phase separated manganite heterojunctions, which may lead to some potential applications.

Fu, X. N.; Yu, Q. X.; Gao, Q. Q.; Chen, B.

2012-01-01

381

Synthesis, structures and phase transitions in the double perovskites Sr{sub 2-x}Ca{sub x}CrNbO{sub 6}  

SciTech Connect

The synthesis and crystal structures of nine members of the rock-salt ordered double perovskites Sr{sub 2-x}Ca{sub x}CrNbO{sub 6} is presented. The crystal structures of the end members of the series Sr{sub 2}CrNbO{sub 6} and Ca{sub 2}CrNbO{sub 6} were refined using powder neutron diffraction data and are cubic in Fm3-bar m and monoclinic in P2{sub 1}/n, respectively, in both cases there being considerable anti-site Cr-Nb mixing. Variable temperature and/or composition studies suggest a direct first-order P2{sub 1}/n to Fm3-bar m transition, a suggestion supported by selected area electron diffraction studies.

Cheah, Melina C.L. [School of Chemistry, University of Sydney, Sydney, NSW 2006 Australia (Australia); Kennedy, Brendan J. [School of Chemistry, University of Sydney, Sydney, NSW 2006 Australia (Australia)]. E-mail: kennedyb@chem.usyd.edu.au; Withers, Ray L. [Research School of Chemistry, Australian National University, Canberra ACT 2600 (Australia); Yonemura, Masao [Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573 (Japan); Kamiyama, Takashi [Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573 (Japan)

2006-08-15

382

Chemical diffusion of water in the double perovskites Ba 4Ca 2Nb 2O 11 and Sr 6Ta 2O 11  

Microsoft Academic Search

The mechanism and kinetics of water incorporation in the double perovskites ??4Ca2Nb2O11 and Sr6Ta2O11 has been investigated (T=300÷500 °C and aH2O=1·10?3÷2.2·10?2). The formation of hydration products Ba4Ca2Nb2O11·xH2O and Sr6Ta2O11·xH2O (0.2

I. Animitsa; A. Neiman; N. Kochetova; D. Korona; A. Sharafutdinov

2006-01-01

383

Role of Zr-Co substitution at iron site on structural, magnetic and electrical properties of Sr-hexaferrites nanomaterials synthesized by the sol-gel combustion method  

NASA Astrophysics Data System (ADS)

The sol-gel auto-combustion technique has been employed to synthesize the M-type Sr-hexaferrites nanomaterials substituted with binary mixture of zirconium and cobalt at the iron site. The phase purity of the samples is confirmed by X-ray diffraction analysis and the crystallite size is found in the range of 31-45 nm. The scanning electron microscopic analysis also confirms that the particles are in nanosize (25-50 nm). The magnetic parameters like saturation magnetization, remanence, squareness ratio and the coercivity are calculated from the hysteresis loops. The values of saturation magnetization and remanence increase with the increase in Zr-Co content up to x=0.4 while the coercivity decreases continuously with the substituents. The squareness ratio is above 0.5 which indicates that the samples are in single magnetic domain. The room temperature DC electrical resistivity is measured by the two point probe method and is found to increase with Zr-Co content up to the substitution level of x=0.6. These materials can be used in microwave devices as these devices require highly resistive materials with low eddy current losses.

Naeem Ashiq, Muhammad; Fahad Ehsan, Muhammad; Javed Iqbal, Muhammad; Najam-ul-Haq, Muhammad

2013-04-01

384

Structural characterisation of the perovskite series Sr 0.9? x Ca x Ce 0.1MnO 3: Influence of the Jahn–Teller effect  

Microsoft Academic Search

Fifteen perovskite-type compounds Sr0.9?xCaxCe0.1MnO3, x=0–0.9 in steps as fine as 0.05, have been synthesised by solid state methods, and the room temperature structures characterised using X-ray synchrotron powder diffraction. At low Ca contents (x?0.45) the structures are tetragonal in space group I4\\/mcm and at high Ca contents (x?0.55) the compounds are orthorhombic in space group Pbnm. At room temperature these

Brendan J. Kennedy; Jimmy Ting; Qingdi Zhou; Zhaoming Zhang; Motohide Matsuda; Michihiro Miyake

2009-01-01

385

Superconductivity up to 114 K in the Bi-Al-Ca-Sr-Cu-O compound system without rare-earth elements  

NASA Technical Reports Server (NTRS)

Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements. Pressure has only a slight positive effect on T(c). These observations provide an extra material base for the study of the mechanism of high-temperature superconductivity and also the prospect of reduced material cost for future applications of superconductivity.

Chu, C. W.; Bechtold, J.; Gao, L.; Hor, P. H.; Huang, Z. J.

1988-01-01

386

Infrared spectra, Raman spectra, microwave dielectric properties and simulation for effective permittivity of temperature stable ceramics AMoO4-TiO2 (A = Ca, Sr).  

PubMed

In this work, temperature stable microwave dielectric materials (1 - x)AMoO(4)-xTiO(2) (A = Ca, Sr) were prepared by a solid state reaction method. The phase composition, sintering behaviors, microstructures, microwave dielectric properties, effective permittivity and vibrational phonon modes were investigated. The X-ray diffraction pattern and scanning electron microscope analysis indicated that the AMoO(4) (A = Ca, Sr) phase could coexist with the TiO(2) phase. The effective dielectric constants of the AMoO(4)-TiO(2) composites were calculated by the finite element method (FEM), compared with the measured values and the numerical results obtained by the classical mixing rules. The correlation between the dielectric properties and the crystal structures were studied using IR and Raman spectroscopy. The infrared spectra were analyzed using the classical harmonic oscillator model, and revealed that the external vibration modes of AMoO(4) (A = Ca, Sr) had the most significant influence on the dielectric constant. The Raman spectra showed that there were strong interactions in the [MoO(4)] tetrahedron due to the sharp and intense Raman modes. Finally, the low-firing (900 °C) microwave dielectric ceramics were obtained with 3 wt% H(3)BO(3)-CuO addition (BCu), and they possess good microwave dielectric properties with ?(r) = 10.6-13, high Q×f values (40?700-72?050 GHz), and near-zero temperature coefficients of resonant frequency (TCF or ?(f) values). These results also show that (1 - x)AMoO(4)-xTiO(2)-BCu (A = Ca, Sr) ceramics are good candidates for microwave electronic device applications. PMID:23124534

Guo, Jing; Zhou, Di; Wang, Lu; Wang, Hong; Shao, Tao; Qi, Ze M; Yao, Xi

2013-02-01

387

Fabrication and characteristics of the joint properties in (Bi,Pb)2Sr2Ca2Cu3Ox closed double pancake coil  

Microsoft Academic Search

We fabricated two superconducting closed coils and evaluated the joint resistance of the coils by a field decay technique at 77 K. In the process (Bi, Pb)2Sr2Ca2Cu3Ox\\/Ag tape was wound in the form of double-pancake coils, and the ends of the tape were joined to each other by a resistive-joint method. Joint resistance of the coils was evaluated as a

Jung Ho Kim; Seok Hern Jang; Kyu Tae Kim; Jun Hyung Lim; Jinho Joo; Seyong Choi; Wansoo Nah

2004-01-01

388

Superconducting thick films from combined heat treatment of mixtures of YBaCuO and BiPbSrCaCuO  

Microsoft Academic Search

Attention is given to the development of new high-Tc superconducting compounds, starting from mixtures of two high-Tc superconductors, namely, YBaCuO and BiPbSrCaCuO. The composition of the elements is varied in order to study the behavior of the different combined systems, with their resistance-temperature response and the width of the superconducting transition taken into account. It is shown that the mixing

J. Marfaing; Y. Wang; V. Wadhawan; C. Boulesteix; J. P. Sorbier; P. Odier

1992-01-01

389

Strongly enhanced diamagnetism and the vortex-Nernst effect in Bi2Sr2CaCu2O8+x  

Microsoft Academic Search

The magnetization of the Bi2Sr2CaCu2O8+delta (Bi-2212) cuprates has been measured using high-resolution cantilever magnetometer. In underdoped Bi-2212, the fluctuation-induced diamagnetism onsets at temperatures much higher than the critical temperature Tc0. Both the temperature and field dependence of the diamagnetic signals closely match the vortex-Nernst effect measured on the same sample. These new results strongly support the previous finding of the

Yayu Wang; Lu Li; Mike Naughton; Genda Gu; S. Uchida; Nai-Phuan Ong

2005-01-01

390

Microstructural and optical characterization of CaWO 4 and SrWO 4 thin films prepared by a chemical solution method  

Microsoft Academic Search

Stoichiometric CaWO4 and SrWO4 thin films were synthesized using a chemical solution processing, the so-called polymeric precursor method. In this soft chemical method, soluble precursors such as strontium carbonate, calcium carbonate and tungstic acid, as starting materials, were mixed in an aqueous solution. The thin films were deposited on glass substrates by means of the spinning technique. The surface morphology

M. A. M. A Maurera; A. G Souza; L. E. B Soledade; F. M Pontes; E Longo; E. R Leite; J. A Varela

2004-01-01

391

Generalized Grüneisen parameters and the low temperature thermal expansion of high-Tc superconductor Bi2Sr2CaCu2O8  

Microsoft Academic Search

The anisotropy of low temperature thermal expansion of Bi2Sr2CaCu2O8 (Bi 2212) is analysed theoretically using quasiharmonic theory of thermal expansion. Vibrational anharmonicity as determined by the generalized Grüneisen parameters (GPs) gamma'j and gamma''j of the various normal mode frequencies of the lattice has been studied. gamma'j refers to change in frequencies due to a uniform areal strain perpendicular to the

K. P. Jayachandran; C. S. Menon

2002-01-01

392

Lazulite and Ba, Sr, Ca, K-rich phosphates–sulphates in quartz veins from metaquartzites of Tribe? Mountains, Western Carpathians, Slovakia: Compositional variations and evolution  

Microsoft Academic Search

The phosphate–sulphate mineralization occurs in quartz veins in Lower Triassic metaquartzites of the Tribe? Mts., Central Western Carpathians, Slovakia. The mineralization comprises of lazulite, Ba, Sr, Ca, K-rich phosphates–sulphates and barite in an association with muscovite, hematite, locally rutile, zircon, chlorite and tourmaline. The most widespread lazulite forms up to 10 cm large pale to deep blue aggregates in massive quartz.

Pavel Uher; Tomáš Mikuš; Rastislav Milovský; Adrian Biron; Ján Spisiak; Jozef Lipka; Ján Jahn

2009-01-01

393

Hydration Energies and Structures of Alkaline Earth Metal Ions, M2+ (H2O)n, n = 5-7, M = Mg, Ca, Sr, and Ba  

PubMed Central

The evaporation of water from hydrated alkaline earth metal ions, produced by electrospray ionization, was studied in a Fourier transform mass spectrometer. Zero-pressure-limit dissociation rate constants for loss of a single water molecule from the hydrated divalent metal ions, M2+(H2O)n (M = Mg, Ca, and Sr for n = 5–7, and M = Ba for n = 4–7), are measured as a function of temperature using blackbody infrared radiative dissociation. From these values, zero-pressure-limit Arrhenius parameters are obtained. By modeling the dissociation kinetics using a master equation formalism, threshold dissociation energies (Eo) are determined. These reactions should have a negligible reverse activation barrier; therefore, Eo values should be approximately equal to the binding energy or hydration enthalpy at 0 K. For the hepta- and hexahydrated ions at low temperature, binding energies follow the trend expected on the basis of ionic radii: Mg > Ca > Sr > Ba. For the hexahydrated ions at high temperature, binding energies follow the order Ca > Mg > Sr > Ba. The same order is observed for the pentahydrated ions. Collisional dissociation experiments on the tetrahydrated species result in relative dissociation rates that directly correlate with the size of the metals. These results indicate the presence of two isomers for hexahydrated magnesium ions: a low-temperature isomer in which the six water molecules are located in the first solvation shell, and a high-temperature isomer with the most likely structure corresponding to four water molecules in the inner shell and two water molecules in the second shell. These results also indicate that the pentahydrated magnesium ions have a structure with four water molecules in the first solvation shell and one in the outer shell. The dissociation kinetics for the hexa- and pentahydrated clusters of Ca2+, Sr2+, and Ba2+ are consistent with structures in which all the water molecules are located in the first solvation shell. PMID:16429612

Rodriguez-Cruz, Sandra E.; Jockusch, Rebecca A.

2005-01-01

394

The crystal chemistry of the alkaline-earth apatites A10(PO4)6CuxOy(H)z (A = Ca, Sr and Ba)  

Microsoft Academic Search

6(PO4)6CuxOy(H)z (A = Ca, Sr and Ba) was investigated by powder X-ray (PXRD) and neutron diffraction (PND) and X-ray photoelectron spectroscopy (XPS). The refined crystal structures confirmed earlier X-ray diffraction studies that showed copper resides in the apatite channels and additionally, located hydrogen. For all materials copper is primarily divalent (Cu 2+ ) but in the calcium and strontium analogues

Tom Baikie; S. Madhavi; Kevin Blake; T. J. Whitea; Margaret Elcombe; T. J. White

2009-01-01

395

Angular dependence of high field magnetization fluctuation of two-dimensional Bi 2Sr 2CaCu 2O 8 single crystals  

NASA Astrophysics Data System (ADS)

We report reversible magnetization data and the scaling for the magnetization obtained for magnetic fields ( H) applied at various tilt angles ? of the dc magnetic field with respect to the c axis in a single crystal of Bi 2Sr 2CaCu 2O 8. Our data show the crossover of the magnetization below the superconducting onset temperature, which indicates a dominant vortex fluctuation.

Landínez Téllez, D. A.; Calero, J. M.; Albino Aguiar, J.; Roa-Rojas, J.

2004-08-01

396

Effect of SR load and pH regulatory mechanisms on stretch-dependent Ca(2+) entry during the slow force response.  

PubMed

When cardiac muscle is stretched, there is an initial inotropic response that coincides with the stretch followed by a slower increase in twitch force that develops over several minutes (the "slow force response", or SFR). Unlike the initial response to stretch, the SFR is produced by an increase in Ca(2+) transient amplitude, but the cellular mechanisms that give rise to the increased transients are still debated. We have examined the relationship between the SFR, intracellular [Ca(2+)] and the inotropic state of right ventricular trabeculae from rat hearts at 37°C. The magnitude of the SFR varied with [Ca(2+)]o and stimulation frequency, so that the SFR was greatest for conditions associated with a reduced SR Ca(2+) content. The SFR was not blocked by the AT1 receptor blocker losartan, but was reduced by SN-6, an inhibitor of reverse mode Na(+)/Ca(2+)-exchange (NCX). The Na(+)/H(+)-exchange (NHE) inhibitor HOE642 had no effect in HCO3(-)-buffered solutions, but blocked 50% of the SFR in HCO3(-)-free solution. Inhibition of HCO3(-) transport by DIDS increased the SFR and made it sensitive to HOE642. The addition of cross-bridge cycle inhibitors (20mM BDM or 20?M blebbistatin) to the superfusate reduced the SFR as monitored by changes in Ca(2+). In HCO3(-)-free conditions, the SFR was associated with a slow acidification that was inhibited by BDM, and by stopping electrical stimulation. These results can be explained by stretch increasing metabolic demand and stimulating Na(+) entry via both NHE and the Na(+)/HCO3(-) transporters. This mechanism provides a novel link between inotropic state and stretch, as well as a way for the cell to compensate for increased acid load. The feedback mechanism between force and Ca(2+) transient amplitude that we describe is also limited by the degree of SR Ca(2+) load. PMID:23880608

Shen, Xin; Cannell, Mark B; Ward, Marie-Louise

2013-10-01

397

Effects of ionic products from silicon-substituted hydroxyapatite on the rat brain activity: Morris water maze studies and long term potentiation in hippocampal CA1  

Microsoft Academic Search

This study sets to examine the effects of ionic products from silicon-substituted hydroxyapatite (Si-HA) on brain activity in Wistar rats. Animals were treated intraperitoneally with leaching liquor of Si-HA once a day for 2weeks. Morris water maze (MWM) test was employed to evaluate the spatial memory. The long term potentiation (LTP) of synaptic responses in the CA1 area was recorded.

Yi-Yi Wang; Ning Li; Jie Huang; Zhuo Yang; Tao Zhang

2011-01-01

398

Color tunable and thermally stable luminescence of Tb{sup 3+} doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors  

SciTech Connect

Highlights: ? Lowest spin-allowed and spin-forbidden f–d transitions locate at 250 and 280 nm. ? Cross relaxation shortens lifetime of {sup 5}D{sub 3} level, while that of {sup 5}D{sub 4} are unaffected. ? Cross-relaxation can explain concentration quenching of the {sup 5}D{sub 3} emission. ? Dipole–quadrupole interaction is responsible for the non-radiative relaxation. ? Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tb{sup 3+} is thermally stable and color tunable phosphor. -- Abstract: Tb{sup 3+} ions activated Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors were synthesized using a solid state reaction method. The phase impurity was checked by XRD. The photoluminescence (PL) excitation spectrum, emission spectra at room and high temperature, decay curves of samples with different Tb{sup 3+} ions concentration were studied in detail. Cross-relaxation and the Inokuti–Hirayama model were used to analyze the experimental results. Li{sub 4}SrCa(SiO{sub 4}){sub 2}:xTb{sup 3+} are thermally stable and color tunable phosphors.

Zhang, Xinmin, E-mail: zhangxinminam@yahoo.com [College of Materials Science and Engineering, Central South University of Forestry and Technology, Changsha 410004 (China)] [College of Materials Science and Engineering, Central South University of Forestry and Technology, Changsha 410004 (China); Seo, Hyo Jin, E-mail: hjseo@pknu.ac.kr [Department of Physics, Pukyong National University, 599-1, Daeyeon 3-Dong, Nam-Gu,, Busan 608-737 (Korea, Republic of)

2012-08-15

399

Strong anisotropy of Dirac cones in SrMnBi2 and CaMnBi2 revealed by angle-resolved photoemission spectroscopy.  

PubMed

The Dirac materials, such as graphene and three-dimensional topological insulators, have attracted much attention because they exhibit novel quantum phenomena with their low energy electrons governed by the relativistic Dirac equations. One particular interest is to generate Dirac cone anisotropy so that the electrons can propagate differently from one direction to the other, creating an additional tunability for new properties and applications. While various theoretical approaches have been proposed to make the isotropic Dirac cones of graphene into anisotropic ones, it has not yet been met with success. There are also some theoretical predictions and/or experimental indications of anisotropic Dirac cone in novel topological insulators and AMnBi2 (A = Sr and Ca) but more experimental investigations are needed. Here we report systematic high resolution angle-resolved photoemission measurements that have provided direct evidence on the existence of strongly anisotropic Dirac cones in SrMnBi2 and CaMnBi2. Distinct behaviors of the Dirac cones between SrMnBi2 and Ca