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1

Synthesis and Structure of (Ca,Sr)-Substituted Lanthanum Manganite  

Microsoft Academic Search

The phase composition and structure of equilibrium LaMnO3-CaMnO3-SrMnO3 samples prepared at 1500C in air are investigated. The results demonstrate that the system contains a broad region of La1 ? x(Ca1 ? ySry)xMnO3 perovskite-like solid solutions in which calcium and strontium cations substitute for lanthanum. The solid solutions have an orthorhombic (Pnma), rhombohedral \\u000a

B. V. Slobodin; E. V. Vladimirova; S. L. Petukhov; L. L. Surat; I. A. Leonidov

2005-01-01

2

Rietveld refinement, electrical properties and magnetic characteristics of Ca-Sr substituted barium hexaferrites  

Microsoft Academic Search

Mtype Ca-Sr substituted barium hexaferrites having compositions BaFe12O19, Ba0.5Ca0.5Fe12O19 and Ba0.5Ca0.25Sr0.25Fe12O19 have been synthesized by commercial solid state reaction method. The effects of doping on structural, dielectric and magnetic properties were systematically investigated. The Rietveld refinement of X-ray powder diffraction data revealed that the samples possess single hexagonal phase with space group P63\\/mmc, with two molecules in the unit cell

Ashima Hooda; Sujata Sanghi; Ashish Agarwal; Reetu Dahiya

3

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

PubMed

The pre-Btzinger complex (preBtC) underlies inspiratory rhythm generation. As a result of network interactions, preBtC neurons burst synchronously to produce rhythmic premotor inspiratory activity. Each inspiratory burst consists of action potentials (APs) on top of a 10- to 20-mV synchronous depolarization lasting 0.3-0.8 s known as inspiratory drive potential. The mechanisms underlying the initiation and termination of the inspiratory burst are unclear, and the role of Ca(2+) is a matter of intense debate. To investigate the role of extracellular Ca(2+) in inspiratory burst initiation and termination, we substituted extracellular Ca(2+) with Sr(2+). We found for the first time an ionic manipulation that significantly interferes with burst termination. In a rhythmically active slice, we current-clamped preBtC neurons (Vm ? -60 mV) while recording integrated hypoglossal nerve (?XIIn) activity as motor output. Substitution of extracellular Ca(2+) with either 1.5 or 2.5 mM Sr(2+) significantly prolonged the duration of inspiratory bursts from 653.4 30.7 ms in control conditions to 981.6 78.5 ms in 1.5 mM Sr(2+) and 2,048.2 448.5 ms in 2.5 mM Sr(2+), with a concomitant increase in decay time and area. Substitution of extracellular Ca(2+) by Sr(2+) is a well-established method to desynchronize neurotransmitter release. Our findings suggest that the increase in inspiratory burst duration is determined by a presynaptic mechanism involving desynchronization of glutamate release within the network. PMID:25429120

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

2015-02-15

4

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

5

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

6

Dielectric and Polarization Studies of Ca Substituted in Bi4SrTi4O15 Ceramics  

Microsoft Academic Search

The processing conditions, microstructure and dielectric properties of strontium bismuth titanate (SBT) were studied by means of Ca substitution in the strontium site referred to hereinafter as SCBT. The mechano-chemical activation method permits one to reduce the particle size of the initial products, so the surface area of the powder is increased, improving in most cases its reactivity.X-ray diffraction analysis

Gagan Anand; A. R. James; P. Sarah

2010-01-01

7

Superconductivity and phases in the MTlSrCaCuO and MTlSrCuO systems with M=Cr, Mo, and W  

Microsoft Academic Search

Cr-, Mo-, or W-substituted TlSrCaCuO and TlSrCuO samples were prepared and investigated by resistance and ac susceptibility measurements and by x-ray diffraction analyses. The results showed that CrTlSrCaCuO, MoTlSrCaCuO, and WTlSrCaCuO systems form a 1212-type phase, but with different Tc: 100K, 70 K, and 50 K, respectively. Some MoTlSrCaCuO samples exhibit weak superconductivity at 100 K. The Ca-free CrTlSrCuO system

Y. F. Li; Z. Z. Sheng; D. O. Pederson

1992-01-01

8

Effect of Cu substitution on magnetic behaviour and electrical properties of bilayered manganite La1.2Sr1.5Ca0.3Mn2O7  

NASA Astrophysics Data System (ADS)

DC magnetization and electrical resistance measurements have been made on 0.5 atomic% Cu substituted bi-layered system La1.2Sr1.5Ca0.3Mn1.99Cu0.01O7 for studying the effect of low level substitution of Cu at Mn site. Rietveld analysis of X-Ray diffraction pattern of the sample confirms the single phase Sr3Ti2O7 type structure. On cooling below room temperature the system shows magnetic orderings ferromagnetic (FM) ordering in ab plane below ~270K and 3D FM ordering below ~45K. Also at an intermediate temperature of ~2i0K there is a signature of another transition which could be attributed to onset of an antiferromagnetic state. Substitution of Cu weakens ferromagnetism and the system shows 96% magnetoresistance (MR) at the field of 8 Tesla. The system remains electrical insulator down to 8K. Resistance versus temperature curves has been fitted following Variable range hopping and semiconducting models. Estimated values of density of states at Fermi energy and of Debye temperature are in reasonably good agreement with those reported for other perovskites. Magnetoresistance versus field curves show hysteresis and discontinuities.

Saxena, A.; Krishnamurthy, A.; Srivastava, B. K.

2015-02-01

9

Cenozoic seawater Sr/Ca evolution  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

10

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

SciTech Connect

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

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

1991-01-01

11

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

SciTech Connect

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

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

1991-12-31

12

Effect of substitution of Fe for Mn on the structural, magnetic properties and magnetocaloric effect of LaNdSrCaMnO3  

NASA Astrophysics Data System (ADS)

We have studied the structural, magnetic and magnetocaloric properties of La0.6Nd0.1Sr0.15Ca0.15Mn1-xFexO3 (LNSCMFex) perovskite samples. The samples were synthesized using the solid-state reaction at high temperature and were analyzed by XRD data based on the Rietveld refinement technique. LNSCMFex samples crystallized in orthorhombic symmetry with Pnma space group. Besides, the curves of magnetization reveals that all samples exhibit a magnetic transition from the paramagnetic to ferromagnetic phase at the Curie temperature TC, which decreases from 327 K to 296 K with the increase of the Fe doping level from x=0 to x=0.1. The thermal evolution of magnetization in the ferromagnetic phase at low temperature varies as T3/2 in accordance with Bloch's law. The magnitude of the isothermal magnetic entropy, (- ? SMmax), at the FM Curie temperature increases from 3.79 J/kg K for x=0 composition to 5.8 J/kg K for x=0.1, under a magnetic field of 5 T. For an applied magnetic field of 5 T, the relative cooling power (RCP) values are found to vary between 173.66 and 231.76 J/kg. These results suggest that these materials could be used as an active magnetic refrigerant around room temperature.

Dhahri, Ja.; Dhahri, A.; Oummezzine, M.; Hlil, E. K.

2015-03-01

13

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

PubMed

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

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

2014-04-01

14

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

NASA Technical Reports Server (NTRS)

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

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

1967-01-01

15

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

PubMed

The mechanism of solar water oxidation by photosystem II (PSII) is of fundamental interest and it is the object of extensive studies both in the past and present. The solar water oxidation reaction of PSII occurs in the oxygen-evolving complex (OEC). The OEC consists of a tetranuclear manganese calcium-oxo (Mn4Ca-oxo) cluster that is surrounded by amino acid residues and inorganic cofactors. The role of the Ca(2+) ion in the water oxidation reaction is one of the most interesting questions that is yet to be answered. In this study, we probe the structural and functional differences induced by metal ion substitution in the Mn4Ca-oxo cluster by substituting the Ca(2+) ion in the OEC by a Sr(2+) ion. We apply two-dimensional (2D) hyperfine sublevel correlation (HYSCORE) spectroscopy to detect weak magnetic interactions between the paramagnetic Mn4Sr-oxo cluster and the surrounding protons in the S2 state of the OEC of Sr(2+)-substituted PSII. We identify three groups of protons that are magnetically interacting with the Mn4Sr-oxo cluster. Using the recently reported 1.9 resolution X-ray structure of the OEC in the S1 state [Umena et al.] and the high-resolution 2D HYSCORE spectroscopy studies of the S2 state of the OEC of Ca(2+)-containing PSII [Milikisiyants et al., Energy Environ. Sci., 2012, 5, 7747], we discuss the assignments of the three groups of protons that are magnetically coupled to the Mn4Sr-oxo cluster. Since hyperfine interactions are highly sensitive to small perturbations in the electronic and geometric structure of paramagnetic centers, a comparison of the 2D HYSCORE spectra of Sr(2+)-substituted and Ca(2+)-containing PSII allows us to draw important conclusions with respect to the structure of the substrate water molecules in the OEC and the role of the Ca(2+) ion in the water oxidation reaction. In addition, for the first time, we determine the experimental value of the spin projection factor for the Mn(III) ion of the Mn4Ca-oxo cluster as ?1 = 1.7 from the assignment of the hyperfine interaction of the paramagnetic cluster with the protons of the D1-His332 residue of PSII. PMID:25167223

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

2014-10-14

16

Are seawater Sr/Ca variations preserved in Quaternary foraminifera?  

SciTech Connect

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

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

1999-11-01

17

Controls on Sr/Ca in benthic foraminifera and implications for seawater Sr/Ca during the late Pleistocene  

NASA Astrophysics Data System (ADS)

Changes in the Sr to Ca ratio of sea water have important implications for the interpretation of past climate. It has proven difficult to interpret Sr/Ca of foraminiferal calcite as a measure of seawater Sr/Ca or as reflecting the influence of deep water carbonate ion saturation (?[CO32-]) on the incorporation of Sr into benthic foraminiferal carbonate. Here, we address this issue by measurements of paired benthic foraminiferal Sr/Ca and B/Ca (a proxy for deep water ?[CO32-]) for core-tops from the global ocean and three down cores at different settings during the Last Glacial-interglacial cycle. These new data suggest a significant control of deep water ?[CO32-] on benthic foraminiferal Sr/Ca, and that down-core shell Sr/Ca variations can be largely accounted for by past deep water ?[CO32-] changes. We conclude that seawater Sr/Ca has likely remained near-constant on glacial-interglacial timescales during the late Pleistocene, in agreement with model results. With due caution, benthic Sr/Ca may be used as an auxiliary proxy for deep water ?[CO32-] if seawater Sr/Ca is constant.

Yu, Jimin; Elderfield, Henry; Jin, Zhangdong; Tomascak, Paul; Rohling, Eelco J.

2014-08-01

18

Effect of Ca on structural and ferroelectric properties of SrBi 2Ta 2O 9 and SrBi 2Nb 2O 9 thin films  

Microsoft Academic Search

In this study, we have improved the remanent polarization of SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) thin films using Ca substitution at Sr-site. SBT and SBN thin films with different concentrations of Ca were deposited on Pt\\/TiO2\\/SiO2\\/Si substrates using pulsed-laser-deposition technique. The lattice parameters was found to be decreased with Ca incorporation and was attributed to the smaller ionic radii of

Rasmi R. Das; P. Bhattacharya; W. Prez; Ram S. Katiyar

2004-01-01

19

Phase formation of R{sub E}-substituted 212-type compounds La{sub 1.6}Sr{sub 0.4}Ca{sub 1{minus}x}R{sub Ex}Cu{sub 2}O{sub 6}  

SciTech Connect

The phase formation and electrical and magnetic properties of R{sub E}-substituted compounds La{sub 1.6}Sr{sub 0.4}Ca{sub 1{minus}x}R{sub Ex}Cu{sub 2}O{sub 6} (R{sub E} = rare-earth elements) were investigated systematically. It was found that all the rare-earth elements (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb) except Ce form 212-type compounds. Their structures were verified by Rietveld structure refinement.

Tao, F.; Liu, G.D.; Che, G.C.; Zhao, Z.X.; Wu, F.; Chen, X.L.; Zhang, Y.Z. [Chinese Academy of Sciences, Beijing (China)] [Chinese Academy of Sciences, Beijing (China)

1998-06-01

20

Measuring Local Gradients of Intra-Mitochondrial [Ca] in Cardiac Myocytes During SR Ca Release  

PubMed Central

Rationale Mitochondrial [Ca2+] ([Ca2+]mito) regulates mitochondrial energy production, provides transient Ca2+buffering under stress and can be involved in cell death. Mitochondria are near the sarcoplasmic reticulum (SR) in cardiac myocytes and evidence for crosstalk exists. However, quantitative measurements of [Ca2+]mito are limited and spatial [Ca2+]mito gradients have not been directly measured. Objective To directly measure local [Ca2+]mito during normal SR Ca release in intact myocytes, and evaluate potential subsarcomeric spatial [Ca2+]mito gradients. Methods and Results We used in-situ calibration of the mitochondrially targeted inverse pericam indicator Mitycam and directly measured [Ca2+]mito during SR Ca2+ release in intact rabbit ventricular myocytes by confocal microscopy. During steady state pacing ?[Ca2+]mito amplitude was 29 3 nM, rising rapidly (similar to cytosolic [Ca2+]i) but declining much more slowly. Taking advantage of the structural periodicity of cardiac sarcomeres, we found that [Ca2+]mito near SR Ca2+ release sites (Z-lines) vs. mid sarcomere (M-line) reached a higher peak amplitude (37 4 vs. 26 4 nM, respectively P < 0.05) which occurred earlier in time. This difference was attributed to ends of mitochondria being physically closer to SR Ca2+ release sites, because the mitochondrial Ca2+ uniporter was homogeneously distributed and elevated [Ca2+] applied laterally did not produce longitudinal [Ca2+]mito gradients. Conclusions We developed methods to measure spatiotemporal [Ca2+]mito gradients quantitatively during excitation-contraction coupling. The amplitude and kinetics of [Ca2+]mito transients differ significantly from those in the cytosol and are higher and faster near the Z- vs. M-line. This approach will help clarify SR-mitochondrial Ca2+ signaling. PMID:23243207

Lu, Xiyuan; Ginsburg, Kenneth S.; Kettlewell, Sarah; Bossuyt, Julie; Smith, Godfrey L.; Bers, Donald M.

2013-01-01

21

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

22

Effect of substitution of Cr on magnetic behavior and electrical transport in bi-layered manganite La 1.2Sr 1.5Ca 0.3Mn 2O 7  

NASA Astrophysics Data System (ADS)

DC magnetization and electrical resistance measurements have been made on four samples in the series La 1.2Sr 1.5Ca 0.3Mn 2-xCr xO 7 corresponding to x = 0, 0.01, 0.03 and 0.05. The systems show onset of 3D ferromagnetic (FM) state in the temperature range 75-90 K Magnetization-temperature measurements in zero field cooling and field cooling modes, made under different external fields show long time evolution of magnetization with time suggestive of FM disorder and high magnetic anisotropy. At two temperatures above the Curie point of 75-90 K, broad discontinuities are seen in the range 260-270 K and 200-220 K. These might be signatures of transitions to FM order in ab plane and to an AFM state, respectively. An alternative explanation for the two higher temperature discontinuities could be in terms of a possible intergrowth in the ab plane reported in bi-layered systems. Insulator-metal transition temperature lies close to Tc but the system with 2.5 atomic percent Cr ( x = 0.05) does not attain metallic state down to 20 K. Estimated values of density of states at Fermi energy and Debye temperature, for the studied compositions, are in reasonably good agreement with those reported in other perovskites.

Saxena, Arpita; Krishnamurthy, Anjali; Srivastava, Bipin K.; Nigam, A. K.

2011-05-01

23

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

NASA Astrophysics Data System (ADS)

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

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

1981-03-01

24

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

25

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

26

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

27

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

28

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

29

Assessment of intra-SR free [Ca] and buffering in rat heart.  

PubMed Central

To measure the free intrasarcoplasmic reticulum [Ca] ([Ca]SR) in isolated rat cardiac microsomes, ventricular tissue was homogenized in the presence of the low-affinity Ca indicator furaptra. Stepwise increases in cuvette [Ca] ([Ca]c) in the presence of ATP caused progressive increases in steady-state intravesicular fluorescence ratio to a maximum (Rmax). Steady-state [Ca]SR/[Ca]c was approximately 7000. Therefore the resting [Ca]SR may approach 700 microM in the rat cardiac myocyte at [Ca]c = 100 nM. The sarcoplasmic reticulum (SR) Ca pump requires a free energy of deltaG approximately 44 kJ x mol(-1) to generate this [Ca] gradient (e.g., approximately 74% of deltaG(ATP)). Total SR 45Ca uptake was also measured in digitonin-permeabilized myocytes as a function of [Ca]c in the absence of precipitating ions. The steady-state SR Ca content at 100 nM [Ca]c was approximately 400 micromol/liter cytosolic volume. Used together, these data allowed evaluation of the in situ SR Ca-buffering properties. The SR Ca-binding site concentration was approximately 14 mM, and Kd(Ca) approximately 0.638 mM [Ca]SR. Images FIGURE 1 PMID:9284319

Shannon, T R; Bers, D M

1997-01-01

30

Improvements of magnetic properties of Sr ferrite magnets by substitutions of La and Co  

SciTech Connect

Recently, it is intensively required to improve the magnetic properties of Sr ferrite magnets in order to decrease the weight of motors used in automobiles and to improve the efficiency of motors used in electric appliances such as air conditioners. The effect of the simultaneous partial substitution of Co{sup 2+} for Fe{sup 3+} and of La{sup 3+} for Sr{sup 2+} ion in Sr ferrite on the magnetic properties of anisotropic Sr ferrite magnets was investigated. It was found that the coercive force of Sr ferrite magnets is increased without significant decrease in residual flux density by La-Co substitution. Temperature coefficients of coercive force were found to be also improved by La-Co substitution.

Ogata, Yasunobu; Kubota, Yutaka; Takami, Takashi; Tokunaga, Masaaki; Shinohara, Tadashi

1999-09-01

31

Shoot Sr concentrations in relation to shoot Ca concentrations and to soil properties  

Microsoft Academic Search

This work was aimed to investigate whether shoot Sr concentrations of plant species are related to respective Ca concentrations and to soil properties and to compare the Sr-Ca observed ratios (OR), defined as the quotient of the ratios Sr\\/Ca in shoots and in the soil solution or in the extractable form, among species and soils. Ten pasture plant species were

D. S. Veresoglou; N. Barbayiannis; T. Matsi; C. Anagnostopoulos; G. C. Zalidis

1996-01-01

32

Luminescence Spectroscopy of Eu-doped (Ca,Sr)TiO{sub 3} Nanocrystals Prepared by Using Sonochemical Method  

SciTech Connect

Perovskite-type compounds (ABO{sub 3}) of (Ca,Sr)TiO{sub 3} doped with trivalent europium (Eu{sup 3+}) were synthesized by sonochemical techniques. Powder X-ray diffraction measurement on (Ca,Sr)TiO{sub 3} were used to identify the perovskite crystal structure. The photoluminescence property in (Ca,Sr)TiO{sub 3} with europium substitution several atoms in the host lattice was also studied. Further, the photoluminescence spectra were taken at room temperature. The structural difference between fourth kinds of doped samples with different heating temperatures accounts for the intensification of the luminescence intensity. The presented measurements monitor the emission wavelengths of the Eu{sup 3+} with emission peaks at 593, 615 and 700 nm. The obtained results were discussed with respect to developed preparation method.

Kurniawan, C. [Chemistry Department of Semarang State University, Jl. Raya Sekaran Semarang (Indonesia); Prijamboedi, B. [Chemistry Department of Bandung Institute of Technology, Jl. Ganesha 10 Bandung (Indonesia)

2010-10-24

33

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

SciTech Connect

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

Stevenson, J.W.; Armstrong, T.R.; Pederson, L.R. [and others

1995-04-01

34

Occurrence of interactions between individual Sr?- and Ca?-effects on maize root and shoot growth and Sr?, Ca? and Mg? contents, and membrane potential: consequences on predicting Sr?-impact.  

PubMed

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

Moyen, Christelle; Roblin, Gabriel

2013-09-15

35

Reactions of Ca and Sr with CH 3X and CF 3X (X ? Br, I). A laser-induced fluorescence study on nascent CaBr, SrBr, and SrI  

Microsoft Academic Search

Continuous-wave laser-induced fluorescence (LIF) spectra have been measured of nascent SrBr, SrI, and CaBr, formed in the reactions of Sr with CH3X and CF3X (X ? Br,I), and of Ca with CH3Br and CF3Br. The bandhead spectra measured for the reactions involving Sr can be attributed to the formation of highly vibrationally excited SrX; for the reaction with CF3I vibrational

F. Keijzer; J. M. Teule; J. Bulthuis; G. J. de Graaff; M. H. Hilgeman; M. H. M. Janssen; E. H. van Kleef; J. J. van Leuken; S. Stolte

1996-01-01

36

Determination of the Bond Lengths in MgCCH, CaCCH and SrCCH  

NASA Astrophysics Data System (ADS)

%High resolution spectra have been analyzed for the tilde{A}2E-tilde{X}2A_1 transition of M-12C12CH, M-12C12CD and M-13C13CH, where M refers to Mg, Ca and Sr. All the molecules except CaCCH have been recorded and analyzed in our laboratory in a laser ablation molecular jet source. The rotational constants extracted from the fits allowed us to calculate accurate bond lengths in MgCCH, CaCCH and SrCCH. This study is of particular interest since it shows how the structure of the molecules evolves as we substitute the alkaline earth atom by another one from the same family. The results showed clear trends in how the molecules account for changes in the mass of the metal atom and how the bond lengths in the ligand CCH are significantly different from the bond lengths in HCCH. Surprisingly, the triple bond between the two carbon atoms happens to be the one that experiences the greatest change. To determine the three bond lengths in a linear four atom molecule, one requires spectral data from three isotopologues of that molecule. By combining information from previously published analyses with new high resolution isotopically substituted spectra, we have determined the bond lengths for MgCCH, CaCCH and SrCCH. In each case, the tilde{A}2?-tilde{X}2?^+ spectra of the M-12C12CH, M-12C12CD and M-13C13CH isotopologues were considered, where M refers to Mg, Ca and Sr. This study is of particular interest since it shows how the structure of this family of molecules evolves as we change the alkaline earth atom attached to the CCH ligand. In MgCCH, the structure of the CCH ligand is nearly the same as it is in acetylene, HCCH. Surprisingly, the bonding in the ligand is quite different from that of acetylene for the two heavier acetylide molecules, with the triple bond between the two carbon atoms experiencing the greatest change. M. Li and J. A. Coxon, J. Mol. Spectrosc. 176 (1996) 206-210 M. J. Dick, P. M. Sheridan, J. -G. Wang and P. F. Bernath, J. Mol. Spectrosc. 233 (2005) 197-202 J. Overend, Trans. Faraday Soc. 56 (1960) 310-314

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

2011-06-01

37

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

38

A study of Sm-substituted SrM magnets sintered using hydrothermally synthesised powders  

NASA Astrophysics Data System (ADS)

Anisotropic SrM magnets with Sm substitution, which is observed to have the largest beneficial effect both on the coercivity and on the inhibition of grain growth at high temperature among the other elements such as La, Nd and Pr, were investigated. The average grain size of the samples decreases with increasing Sm/Sr ratio. All the magnets with Sm additions exhibit a bigger coercivity and remanence than those of the SrM magnet without Sm and the coercivity of the magnets increases with increasing Sm/Sr ratio. EDX quantitative analysis suggests that the solubility of Sm 3+ in the SrM-type structure is very small and that the Sm 3+ preferably goes into SrFeO 3-x, which is probably located around the SrM grain boundaries. The coercivity mechanism of the magnets is nucleation controlled. The formation and the distribution of the SrFeO 3-x phase around the SrM grain boundraies probably provides the inhibition of SrM grain growth, the reduction of the reverse domain nucleation at the grain surface and the isolation of the SrM grains. All these factors would contribute to the improvements of the coercivity of the magnets with Sm additions.

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

2006-03-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

40

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, Jos; Thackeray, Francis; Albarde, Francis

2008-08-01

41

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

42

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

43

Thermal stability of methanol dehydrogenase is altered by the replacement of enzyme-bound Ca2+ with Sr2+.  

PubMed

Methanol dehydrogenase (MEDH) possesses tightly bound Ca2+ in addition to its pyrroloquinoline quinone prosthetic group. Ca2+ was replaced with Sr2+ by growing the host bacterium, Paracoccus denitrificans, in media in which Ca2+ was replaced with Sr2+. At temperatures in the transition region for stability, the rate constants for inactivation of MEDH purified from these cells (Sr-MEDH) were 2-fold lower than those for MEDH. However, Arrhenius plots yielded an activation energy (Ea) of 699 kJ (167 kcal)/mol for MEDH compared with 640 kJ (153 kcal)/mol for Sr-MEDH. Further analysis by transition-state theory yielded values for the activation enthalpy (delta H*) and activation entropy (delta S*) of 696 kJ (166 kcal)/mol and 1.73 kJ (414 cal)/mol per K for MEDH and 637 kJ (152 kcal)/mol and 1.55 kJ (371 cal)/mol per K for Sr-MEDH. The higher rate of inactivation of MEDH than Sr-MEDH at higher temperatures is a consequence of a more favourable net gain in entropy. This positive entropy contribution increases at high temperatures, and reduces the more favourable stability obtained from the enthalpy contribution for the free energy (delta G*) of inactivation. The differences in these thermodynamic data are discussed in relation to the recently determined crystal structure of MEDH as well as 1H electron-nuclear double resonance studies of the influence of Sr2+ substitution on the structure of the pyrroloquinoline quinone-derived radical in MEDH. PMID:7945232

Harris, T K; Davidson, V L

1994-10-01

44

Re-entrant metallicity and magnetoresistance induced by Ce for Sr substitution in SrCoO(3-?).  

PubMed

Cerium for strontium substitution allows an oxygen deficient perovskite Sr(1-x)Ce(x)CoO(3-?) to be stabilized with a cerium solubility limited to x?0.15 (Trofimenko et al 1997 Solid State Ion.100183). For these samples, the magnetic properties depend clearly upon the oxygen content: Sr(0.9)Ce(0.1)CoO(2.74) and Sr(0.9)Ce(0.1)CoO(2.83) are weak and strong ferromagnets (T(C) = 160K), respectively, the maximum ac-magnetic susceptibility of the latter being larger by two orders of magnitude than that of the former. In contrast to other Sr(1-x)L(x)CoO(3-?) series (L = lanthanide, Y(3) or Th(4+)), the electrical resistivity (?) behaviour does not simply reflect the magnetic behaviour. For x = 0.10 the re-entrant ? feature becomes more pronounced whereas the ferromagnetic fraction and cobalt oxidation state increase. This unexpected behaviour could be related to the Ce(3+)/Ce(4+) mixed valency, the 4f localized moment of the Ce(3+) cations interacting with the conduction electrons through a Kondo-like mechanism. It is also found that the increase of oxygen vacancies favours the appearance of magnetoresistance at low T, reaching -50% at 5K in 7T for the Sr(0.95)Ce(0.05)CoO(2.61) sample prepared in a sealed tube. PMID:21690783

Maignan, A; Raveau, B; Hbert, S; Pralong, V; Caignaert, V; Pelloquin, D

2006-05-01

45

The crystal structure and low-magnetic-field properties of the Pb and Ba-doped Bi-Sr-Ca-Cu-O system  

Microsoft Academic Search

The XRD analyses for the Bi-Pb-Sr-Ca-Ba-Cu-O system show that the addition of Ba ions is favourable to the formation of the higher-Tc phase (Tc>100 K), and TEM observations show that the partial substitution of Ba ions for Ca ions induces a change in the crystal microstructure of the higher-Tc phase (Tc>100 K); a new modulation mode with a wavelength of

Mao Zhiqiang; Zeng Xinglin; Yang Li; Wang Yu; Wang Shunxi; Cao Leizhao; Chen Zhaojia; Fan Chenggao; Zhang Yuheng

1991-01-01

46

SR33805, a Ca2+ antagonist with length-dependent Ca2+ -sensitizing properties in cardiac myocytes.  

PubMed

1. This study examined the effects of SR33805, a fantofarone derivative with reported strong Ca(2+) -antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. 2. On intact cells loaded with the Ca(2+)-fluorescent indicator Indo-1, the application of low concentrations of SR33805 enhanced the amplitude of unloaded cell shortening and decreased the duration of cell shortening. Amplitude of the Ca(2+) transient was also decreased. 3. These effects were accompanied with a shortening of the action potential and a dose-dependent blockade of L-type calcium current (IC(50)=2.4 x 10(-8) M). 4. On skinned cardiac cells, the application of a low SR33805 concentration (10(-8) M) induced a significant increase in maximal Ca(2+)-activated force at the two-tested sarcomere lengths (SLs), 1.9 and 2.3 microm. 5. The application of a larger dose of SR33805 (10(-6)-10(-5) M) induced a significant leftward shift of the tension-pCa relation that accounts for Ca(2+)-sensitization of the myofilaments, particularly at 2.3 microm SL. 6. In conclusion, despite its strong Ca(2+)-antagonistic properties SR33805 increases cardiac cell contractile activity as a consequence of its Ca(2+)-sensitizing effects. These effects are attributable to both an increase in the maximal Ca(2+)-activated force and a length-dependent Ca(2+)-sensitization. PMID:12746228

Cazorla, Olivier; Lacampagne, Alain; Fauconnier, Jeremy; Vassort, Guy

2003-05-01

47

Strong biological controls on Sr/Ca ratios in aragonitic marine bivalve shells  

NASA Astrophysics Data System (ADS)

It is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments. Sr/Ca ratios have been successfully used as a temperature proxy in corals and sclerosponges. Previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on Sr/Ca ratios. As many studies have used bivalve growth rates to determine temperature, we tested if Sr/Ca ratios could predict temperature through its relationship with growth rate. Shells from the two species of clams from the same family (veneroidea) studied here, Saxidomus giganteus and Mercenaria mercenaria, show vastly different seasonal Sr/Ca profiles. A strong relationship between average annual Sr/Ca ratios and annual growth rate was found in S. giganteus shells from both Washington (R2 = 0.87) and Alaska (R2 = 0.64), USA, but not in M. mercenaria shells from North Carolina, USA. Furthermore, the Sr/Ca-growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in S. giganteus (R2 = 0.73). Although there were significant positive correlations between Sr/Ca ratios and temperature in S. giganteus shells, the correlations were weak (0.09 < R2 < 0.27), and thus Sr/Ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves. It is clear from this study that Sr/Ca ratios are not under thermodynamic control in either clam species, since thermodynamics predict a negative correlation between Sr/Ca ratios and temperature in aragonite. This points toward dominance of biological processes in the regulation of Sr2+. This is also reflected by the largely differing Sr/Ca partition coefficients (DSr) in these shells (DSr ? 0.25), when compared to inorganic, coral, and sclerosponge studies (DSr ? 1), all of which show a negative dependence of Sr/Ca on temperature. We suggest that caution be taken when using Sr/Ca in any biogenic aragonite as a temperature proxy when the DSr greatly deviates from one, as this indicates the dominance of biological controls on Sr/Ca ratios.

Gillikin, David Paul; Lorrain, Anne; Navez, Jacques; Taylor, James W.; Andr, Luc; Keppens, Eddy; Baeyens, Willy; Dehairs, Frank

2005-05-01

48

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

NASA Astrophysics Data System (ADS)

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. We also report calibration of the Sr/Ca-temperature relationship for three coral species, Porites lobata, Pocillopora eydouxi and Pavona clavus, collected from 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 <0.2C for corals located in tropical oligotrophic waters, and potentially larger for corals located in upwelling areas. Sr/Caanalyses along two different growth axes of a Galapagos Pavona clavus, with annual extension rates of ~6 and 12 mm/y, respectively, indicate an offset of 1-2C, 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.

de Villiers, Stephanie; Shen, Glen T.; Nelson, Bruce K.

1994-01-01

49

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

50

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

PubMed

The influence of magnesium- and strontium-substitutions on injectability and mechanical performance of brushite-forming alpha-TCP cements has been evaluated in the present work. The effects of Mg- and Sr-substitutions on crystalline phase composition and lattice parameters were determined through quantitative X-ray phase analysis and structural Rietveld refinement of the starting calcium phosphate powders and of the hardened cements. A noticeable dependence of injectability on the liquid-to-powder ratio (LPR), smooth plots of extrusion force versus syringe plunger displacement and the absence of filter pressing effects were observed. For LPR values up to 0.36 ml g(-1), the percentage of injectability was always higher and lower for Mg-containing cements and for Sr-containing cements, respectively, while all the pastes could be fully injected for LPR > 0.36 ml g(-1). The hardened cements exhibited relatively high wet compressive strength values (~17-25 MPa) being the Sr- and Mg-containing cements the strongest and the weakest, respectively, holding an interesting promise for uses in trauma surgery such as for filling bone defects and in minimally invasive techniques such as percutaneous vertebroplasty to fill lesions and strengthen the osteoporotic bone. PMID:19851845

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

2010-02-01

51

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

52

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

53

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

54

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

55

Sr \\/ Ca ratios as indicators of varying modes of pelagic carbonate diagenesis in the ooze, chalk and limestone realms  

Microsoft Academic Search

There has been an interest in the application of Sr\\/Ca ratios in pelagic carbonates to reconstruct paleoceanographic conditions such as changes in the oceanic Ca and Sr budgets or calcareous nannoplankton productivity, but the effect of burial diagenesis on primary Sr\\/Ca records has not been sufficiently understood. In order to clearly document Sr\\/Ca records of pelagic carbonates relative to original

Atsushi Ando; Hodaka Kawahata; Takeshi Kakegawa

2006-01-01

56

Ambient Pressure Structural Quantum Critical Point in the Phase Diagram of (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13}.  

PubMed

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

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

2015-03-01

57

Low loss Sr{sub 1-x}Ca{sub x}La{sub 4}Ti{sub 5}O{sub 17} microwave dielectric ceramics  

SciTech Connect

Highlights: {yields} New single phase highly dense (95%) microwave dielectric Sr{sub 1-x}Ca{sub x}La{sub 4}Ti{sub 5}O{sub 17} (0 {<=} x {<=} 1) ceramics were designed and processed. {yields} Theoretical density and molar volume decreased due to the substitution of small Ca{sup 2+} for large Sr{sup 2+}. {yields} As required for microwave dielectric applications, optimum properties (i.e. {epsilon}{sub r} {approx} 53.7, Qf{sub o} {approx} 11,532 GHz and {tau}{sub f} {approx} -1.4 ppm/{sup o}C) were achieved for Sr{sub 0.4}Ca{sub 0.6}La{sub 4}Ti{sub 5}O{sub 17} (x = 0.6). -- Abstract: Microwave dielectric ceramics in the Sr{sub 1-x}Ca{sub x}La{sub 4}Ti{sub 5}O{sub 17} (0 {<=} x {<=} 1) composition series were prepared through a solid state mixed oxide route. All the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1450-1580 {sup o}C. Theoretical density and molar volume decreased due to the substitution of Ca{sup 2+} for Sr{sup 2+} which was associated with a decrease in the dielectric constant ({epsilon}{sub r}) and temperature coefficient of resonant frequency ({tau}{sub f}) but an increase in quality factor, Qf{sub o}. Optimum properties were achieved for Sr{sub 0.4}Ca{sub 0.6}La{sub 4}Ti{sub 5}O{sub 17} which exhibited, {epsilon}{sub r} {approx} 53.7, Qf{sub o} {approx} 11,532 GHz and {tau}{sub f} {approx} -1.4 ppm/{sup o}C.

Iqbal, Yaseen, E-mail: dryaseeniqbal@yahoo.co.uk [Materials Research Laboratory, Institute of Physics and Electronics, University of Peshawar, Post Code 25120 (Pakistan)] [Materials Research Laboratory, Institute of Physics and Electronics, University of Peshawar, Post Code 25120 (Pakistan); Manan, Abdul [Materials Research Laboratory, Institute of Physics and Electronics, University of Peshawar, Post Code 25120 (Pakistan) [Materials Research Laboratory, Institute of Physics and Electronics, University of Peshawar, Post Code 25120 (Pakistan); Department of Materials Science and Engineering, Sir Robert Hadfield Building, University of Sheffield, S1 3JD (United Kingdom); Reaney, I.M., E-mail: I.M.Reaney@sheffield.ac.uk [Department of Materials Science and Engineering, Sir Robert Hadfield Building, University of Sheffield, S1 3JD (United Kingdom)

2011-07-15

58

Low-loss Z-type hexaferrite with Sr-substitution for microwave antenna miniaturization  

Microsoft Academic Search

Magnetic and dielectric properties of conventional ceramics processed 3 Ba(1?x)SrxO 2 CoO 10.4 Fe2O3 (x = 0.1 ? 0.8) hexaferrite were investigated for microwave antenna miniaturization. Sr substitution was used to modulate the high frequency properties of Co2Z materials in this paper. The properties of the materials were characterized by SEM, XRD, Vector Network Analyzer, and so on.

C. C. Xiang; Y. Nie; Z. K. Feng

2011-01-01

59

doi:10.1016/j.gca.2004.03.021 Mg/Ca, Sr/Ca, and stable isotopes in modern and Holocene Protothaca staminea shells from  

E-print Network

doi:10.1016/j.gca.2004.03.021 Mg/Ca, Sr/Ca, and stable isotopes in modern and Holocene Protothaca molluscs deposit their shells, trace elements and stable isotopes sensitive to such shifts in water in a coastal upwelling region. Mg/Ca and Sr/Ca ratios were analyzed by excimer laser ablation

van Geen, Alexander

60

Hydrothermal alteration processes at midocean ridges: Experimental and theoretical constraints from Ca and Sr exchange reactions and Sr isotopic ratios  

NASA Astrophysics Data System (ADS)

Diabase and basalt were reacted with Na-Ca-K-Cl fluids of seawater chlorinity at 375-425C, 375-400 bars, and fluid/rock mass ratios of 0.5-1.0 to assess the role of basalt chemistry and texture on Sr and Ca mobility during high-temperature hydrothermal alteration. An additional experiment, utilizing an 84Sr spiked fluid, was performed to help quantify reaction rates of processes affecting Sr mobility. The experimental results help to constrain reaction processes responsible for the chemistry of hot spring fluids at midocean ridges. Alteration of basalt and diabase is characterized by formation of tremolite-actinolite-smectite-chlorite and clinozoisitic epidote-smectite-chlorite, respectively. Diabase alteration produced dissolved Sr/Ca ratios similar to those observed for ridge crest hot spring fluids, whereas alteration of a mostly crystalline basalt produced significantly lower ratios. This observation supports the premise that the Sr/Ca ratios observed in vent fluids may be produced during deep-seated reaction of the hydrothermal fluids with diabase dikes and/or gabbro at relatively low fluid/rock ratios and suggests that hydrothermal alteration of primary igneous minerals at relatively high temperatures (400C) leads to formation of a mineral with low DSr/Ca, Possibly hydrothermal plagioclase. Results of the 84Sr spiked experiment indicated that only 4% of the Sr in basalt was mobilized after 800 hours of reaction despite the fact that B and Li were nearly quantitatively leached. It is thus suggested that B and Li are good indicators of the amount of fresh rock encountered by fluids, while Sr concentration and isotopic data can be used to estimate the degree of alteration that the Sr-bearing primary minerals have undergone. The degree of alteration of subsurface reservoirs may be estimated by dividing the fluid/rock ratio obtained for highly mobile elements by the fluid/rock ratio obtained from path-integrated Sr isotope and concentration data. Based on this method, for example, it can be estimated that only 5% of the primary Sr-bearing minerals encountered by fluids in the subsurface at EPR 21N are actually converted to secondary phases.

Berndt, Michael E.; Seyfried, William E., Jr.; Beck, J. Warren

1988-05-01

61

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

PubMed Central

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

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

2014-01-01

62

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

63

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

64

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

SciTech Connect

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

Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. [Argonne National Lab., IL (United States); Nash, A.S. [Marquette Univ., Milwaukee, WI (United States)

1992-05-01

65

Thin films of the Bi2Sr2Ca2Cu3O(x) superconductor  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

67

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

SciTech Connect

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

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

2010-03-11

68

Magnetic properties of La-Zn substituted Sr-hexaferrites by self-propagation high-temperature synthesis  

Microsoft Academic Search

The La-Zn substituted SrM-type ferrites with the composition of Sr1-xLaxFe12-xZnxO19(x=0-0.4) were prepared by self-propagating high-temperature synthesis (SHS). The single SrM phase was detected by XRD in the as-received samples by controlling the Fe contents in the reagents. The substitution of La3+ and Zn2+ obviously increased the magnetic properties of the as-prepared samples. The maximum improvements of Br, Hcb and (BH)m

Lishun YOU; Liang QIAO; Jingwu ZHENG; Meiyan JIANG; Liqiang JIANG; Jiawei SHENG

2008-01-01

69

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

70

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 0.510.18to 1.090.14, 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 0.2150.004 to 0.3330.004, with a mean ?88/86Sr of rainwater is 0.2960.01. 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

71

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

72

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

1997-01-01

73

Hole Distribution in (Sr,Ca,Y,La)14Cu24O41 Compounds Studied by X-ray Absorption and Emission Spectroscopy  

NASA Astrophysics Data System (ADS)

The polarization dependence of soft x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) near the O 1s absorption edge was measured on two-leg ladder single-crystalline samples of (Sr,Ca,Y,La)14Cu24O41 (14-24-41). The hole distributions in 14-24-41 compounds are determined by polarization analysis. For samples with less than or equal to 5 holes/chemical formula (c.f.), all holes reside on the edge-shared chain layer. In the case of Sr14-xCaxCu24O41 (6 holes/c.f.), there is approximately one hole on the two-leg ladder layer, with about five holes remaining on the edge-shared chain layer. By Ca substitution for Sr in the Sr14-xCaxCu24O41 samples, 0.3 holes transfer from the edge-shared chain to the two-leg ladder layer. It is possible that some of the holes on the two-leg ladder layer move from the rung sites to the leg sites upon Ca substitution.

Kabasawa, Eiki; Nakamura, Jin; Yamada, Nobuyoshi; Kuroki, Kazuhiko; Yamazaki, Hisashi; Watanabe, Masamitsu; Denlinger, Jonathan D.; Shin, Shik; Perera, Rupert C. C.

2008-03-01

74

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

PubMed

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

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

2012-08-01

75

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

NASA Astrophysics Data System (ADS)

Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB6, SrB6, BaB6 and the ternary hexaborides CaxSr1-xB6, CaxBa1-xB6, SrxBa1-xB6 (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB6 (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process.

Grsoy, M.; Takeda, M.; Albert, B.

2015-01-01

76

(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

77

Strontium calcium ratios (Sr\\/Ca) and strontium isotopic ratios ( 87Sr\\/ 86Sr) of Australopithecus robustus and Homo sp. from Swartkrans  

Microsoft Academic Search

Previous study of the strontium calcium ratio (Sr\\/Ca) of robust australopithecine skeletons from the Transvaal site of Swartkrans indicated that this Pleistocene hominid was an omnivore, suggesting that models for niche differentiation amongst contemporaneous hominids based on trophic level (i.e. Homo sp. = omnivore vs. A. robustus = herbivore) may be incorrect. In this study, we report that relatively elevated

Andrew Sillen; Grant Hall; Richard Armstrong

1995-01-01

78

Superconducting properties of Ca3Ir4Sn13: a ?SR study  

NASA Astrophysics Data System (ADS)

Muon spin relaxation and rotation (?SR) measurements have been performed to study the superconducting properties of Ca3Ir4Sn13. Zero-field ?SR data shows no sign of any magnetic anomaly in Ca3Ir4Sn13 at the superlattice transition temperature, T* or in the superconducting ground state. Transverse-field ?SR measurements in the vortex state provided the temperature dependence of the magnetic penetration depth ?. The dependence of ??2 with temperature is consistent with the existence of a single s-wave energy gap in the superconducting state of Ca3Ir4Sn13 with a gap value of 1.51(5) meV at absolute zero temperature. The magnetic penetration depth at zero temperature ?(0) is 351(4) nm. The ratio ?(0)/kBTc = 2.41(8) indicates that Ca3Ir4Sn13 is a strong-coupling superconductor.

Biswas, P. K.; Amato, A.; Wang, Kefeng; Petrovic, C.; Khasanov, R.; Luetkens, H.; Morenzoni, E.

2014-12-01

79

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

PubMed Central

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

yehaug, Leiv; Loose, Kristian.; Jlle, GuroF.; Re, smund T.; Sjaastad, Ivar; Christensen, Geir; Sejersted, OleM.; Louch, WilliamE.

2013-01-01

80

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

81

Hydrothermal Preparation and Characterization of Ultralong Strontium-Substituted Hydroxyapatite Whiskers Using Acetamide as Homogeneous Precipitation Reagent  

PubMed Central

The ultralong strontium- (Sr-) substituted hydroxyapatite (SrHAp) whiskers were successfully prepared using acetamide as homogeneous precipitation reagent. The effect of the Sr substitution amount on the lattice constants and proliferation of human osteoblast cells (MG-63) was further investigated. The results showed that the SrHAp whiskers with diameter of 0.212??m and ultralong length up to 200??m were obtained and the Sr substitution level could be facilely tailored by regulating the initial molar ratio of Sr/(Sr + Ca) in raw materials. The Sr2+ replaced part of Ca2+ and the lattice constants increased apparently with the increase of the Sr substitution amount. Compared with the pure HAp whiskers, the Sr substitution apparently stimulated the proliferation of MG-63 at certain extracted concentrations. Our study suggested that the obtained SrHAp whiskers might be used as bioactive and mechanical reinforcement materials for hard tissue regeneration applications. PMID:24592192

Xu, Jianqiang; Yang, Yaoqi; Wan, Rong; Zhang, Weibin

2014-01-01

82

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

SciTech Connect

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

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

2007-10-01

83

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

84

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

SciTech Connect

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

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

2009-01-01

85

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

86

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

NASA Astrophysics Data System (ADS)

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

Allison, N.; Finch, A. A.

2002-12-01

87

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

NASA Astrophysics Data System (ADS)

Stable isotope ( 18O/ 16O and 13C/ 12C) 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 ? 18O 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. Ostracode ? 18O values show a gradual increase by 5 between 500 yr BP and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and ? 18O variations (3-4), 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 ? 13C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C 4 (? 13C -12) to CAM (? 13C = -26)-type vegetation over time.

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

1998-10-01

88

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

SciTech Connect

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

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

1999-11-01

89

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

90

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

91

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

92

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

93

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

NASA Astrophysics Data System (ADS)

Analysis of aragonite from sea shells and coral skeletons showed a clear correlation between the strontium and calcium concentrations for these crystals (Sr/Ca ratio) and seawater temperature obtained by satellites and ship readings. In this work we present the results of a study that correlates Sr/Ca ratio with formation temperature of another calcium crystal, the hydroxyapatite (Ca 10(PO 4) 6(OH) 2), main mineral compound of teeth and bones from vertebrates. These animals, independent of its thermoregulation pattern (endothermic or ectothermic) have variations of internal temperature along the body. One interesting application of this work is to differentiate warm-blooded animals from cold-blooded ones just by measuring Sr/Ca ratio in their bones. Bones from a crocodile from Caiman yacare species and two dogs, a poodle and a non defined race, were analyzed using PIXE technique and thick target correction. A 1.78 (18) MeV external proton beam was used in LAMFI-USP with an accumulated charge of about 10 ?C for probing the samples. Emitted X-rays were collected using Si-PIN detectors (140 keV for Fe). As in coral skeletons, the Sr/Ca ratio of animals is lower in the body's warmer parts and higher in colder parts.

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

2008-04-01

94

Claudin-14 regulates renal Ca++ transport in response to CaSR signalling via a novel microRNA pathway  

PubMed Central

The paracellular claudin channel of the thick ascending limb (TAL) of Henle is critical for Ca++ reabsorption in the kidney. Genome-wide association studies (GWASs) have identified claudin-14 associated with hypercalciuric nephrolithiasis. Here, we show that claudin-14 promoter activity and transcript are exclusively localized in the TAL. Under normal dietary condition, claudin-14 proteins are suppressed by two microRNA molecules (miR-9 and miR-374). Both microRNAs directly target the 3?-UTR of claudin-14 mRNA; induce its mRNA decay and translational repression in a synergistic manner. Through physical interaction, claudin-14 blocks the paracellular cation channel made of claudin-16 and -19, critical for Ca++ reabsorption in the TAL. The transcript and protein levels of claudin-14 are upregulated by high Ca++ diet, while downregulated by low Ca++ diet. Claudin-14 knockout animals develop hypermagnesaemia, hypomagnesiuria, and hypocalciuria under high Ca++ dietary condition. MiR-9 and miR-374 transcript levels are regulated by extracellular Ca++ in a reciprocal manner as claudin-14. The Ca++ sensing receptor (CaSR) acts upstream of the microRNA-claudin-14 axis. Together, these data have established a key regulatory role for claudin-14 in renal Ca++ homeostasis. PMID:22373575

Gong, Yongfeng; Renigunta, Vijayaram; Himmerkus, Nina; Zhang, Jiaqi; Renigunta, Aparna; Bleich, Markus; Hou, Jianghui

2012-01-01

95

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

96

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

97

Late Maastrichtian paleoclimatic and paleoceanographic changes inferred from Sr/Ca ratio and stable isotopes  

E-print Network

susceptibility data in hemipelagic sediments that span the last 700 kyr of the Maastrichtian at Elles, TunisiaLate Maastrichtian paleoclimatic and paleoceanographic changes inferred from Sr/Ca ratio and stable between surface and bottom waters). The carbon isotope composition of planktonic foraminifera indicates

Keller, Gerta

98

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

99

Microstructure and properties of Bi-Sr-Ca-Cu-O with nanometer-scale alumina additions.  

SciTech Connect

Al{sub 2}O{sub 3} particles {approx}30 nm is size were added to Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} in a 1:4 molar ratio. For comparison, 0.3 and {approx}3 pm Al{sub 2}O{sub 3} particles were added to separate batches. All materials were partial-melt processed. The Al{sub 2}O{sub 3} reacted during melting to primarily form stable compounds of approximate composition (Sr,Ca){sub 2}AlO{sub 4}. All additions caused slight decreases in the T{sub c} and melting point of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}. The submicrometer Al{sub 2}O{sub 3} additions induced large expansions in magnetic-hysteresis width at 6 K. Electron microscopy examinations strongly suggested that the hysteresis expansion was related to alloying of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} matrix rather than to pinning by volume defects.

Goretta, K. C.

1998-09-11

100

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

NASA Astrophysics Data System (ADS)

The volcano-hydrothermal system of El Chichn 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 Chichn 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 Chichn 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 Chichn 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.; Sols-Pichardo, G.; Rouwet, D.; Bernard-Romero, R. A.

2011-08-01

101

Sr/Ca Sensitivity to Aragonite Saturation in Cultured Coral Measured by NanoSIMS (Invited)  

NASA Astrophysics Data System (ADS)

NanoSIMS was used to identify and compositionally characterize the micron scale region of skeletal growth resulting from a short coral culture experiment. Using this technique we quantify the sensitivity of Sr/Ca, a proxy for temperature, to aragonite saturation (?), 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 sp. were all grown at 25 C but at different and near constant carbonate ion concentrations, from 180 to 400 M (pH of 7.9 to 8.5), yielding a two-fold range in calcification rate. Despite the range of ?s and calcification rates, the average Sr/Ca of nanoSIMS spot measurements corresponding to each condition are within 1.2% (2? std. dev. of the 5 means). Furthermore, the average Sr/Ca measured in this study agrees with two previous coral culture experiments conducted at the same temperature but where ? was not controlled. These results suggest carbonate ion concentration is not a complicating factor to Sr/Ca paleothermometry over this range of ?. Within the framework of a closed system (Rayleigh) model for biomineralization, similar Sr/Ca ratios suggest similar amounts of Rayleigh fractionation. Combined with existing data for low ? conditions, the extent of Rayleigh fractionation is used to test alternative biomineralization models governing the acid-base chemistry of the calcifying fluid. Assuming that coral use alkalinity pumping to increase local calcifying fluid carbonate ion concentration, we try to understand what controls this pumping. Under most conditions, Sr/Ca ratios are consistent with a scenario where calcifying fluid alkalinity increases until reaching a target pH. However, under conditions of very low seawater ?, coral cannot pump enough alkalinity to reach the target pH. Below this threshold value, between approximately 1Sr/Ca sensitivity to ?. This model should improve our understanding of how anthropogenic CO2 will impact coral reefs and can help us better interpret past climate records in coral.

Gagnon, A. C.; Adkins, J. F.; Erez, J.

2010-12-01

102

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

NASA Astrophysics Data System (ADS)

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 22C 28C, the best fitting linear relationships for the two species agree within their respective errors with a maximum deviation less than 0.3C. Our calibration overlaps with the only published calibration for Porites ( deVilliers et al., 1994) but is somewhat less temperature sensitive. The maximum temperature differences for the two calibrations between 21C and 27C are 1.2C. The D-SST relationship calculated using the data of Beck et al. (1992, 1994) and their unpublished seawater data lies between these two calibrations. Our calibration removes some discrepancies previously described in the studies of McCulloch et al. (1994a) on the Great Barrier Reef and of Min et al. (1995) on New Caledonia. We found little growth rate effect on the calibration for P. lutea between 18 mm/yr and 23 mm/yr. We have also monitored the seawater [Sr/Ca] for the entire 1993. The observed variation of 0.033 mmol/mol can cause a temperature artifact of 0.7C and is thus a dominant error in using this new paleo-thermometer. To carry out this experiment, we have developed a microsurgical technique that can be used to sample corals at better than 0.15 mm resolution. The analytical precision should ultimately allow SST reconstruction of better than 0.2C. Furthermore, the insensitivity of the calibration against growth rate variation and species differences suggests a promising future for this new thermometer, in contrast to the pessimism of deVilliers et al. (1995). However, inter-laboratory differences and the question of seawater [Sr/Ca] variation need to be addressed first. We recommend a single SST calibration for the Sr/Ca thermometer on coral Porites: Sr/Ca N = 10.286-0.0514 SST (N: normalized to Hawaii seawater [Sr/Ca] = 8.510 mmol/mol) or D[Sr/Ca] = 1.2077 - 0.006011 SST.

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

1996-10-01

103

A coral sr/ca calibration and replication study of two massive corals from the gulf of mexico  

USGS Publications Warehouse

This study examined the variations in the ratio of strontium-to-calcium (Sr/Ca) for two Atlantic corals (Montastraea faveolata and Siderastrea siderea) from the Dry Tortugas National Park (centered on 24.7??N, 82.8??W) in the Gulf of Mexico. Cores from coral colonies in close proximity (10s of meters) and with the same environmental conditions (i.e., depth and water chemistry) were micro-sampled with approximately monthly resolution and the resulting Sr/Ca variations were calibrated with local sea surface temperature (SST) records. Replication tests for coral Sr/Ca variations found high agreement between intra-colony variations and between individual colonies of S. siderea (a single M. faveolata colony was sampled). Regression analysis of monthly variations in coral Sr/Ca and local SST revealed significant correlation on monthly and inter-annual timescales. Verification of the calibration on different timescales found coral Sr/Ca-SST reconstructions in S. siderea were more accurate than those from M. faveolata, especially on inter-annual timescales. Sr/Ca-SST calibration equations for the two species are significantly different (cf., Sr/Ca=-0.042 SST+10.070, S. siderea; Sr/Ca=-0.027 SST+9.893, M. faveolata). Mean linear extension for M. faveolata is approximately twice that of S. siderea (4.63, 4.31, and 8.31mmyear-1, A1, F1, and B3, respectively); however, seasonal Sr/Ca variability in M. faveolata is less than S. siderea (0.323, 0.353, and 0.254mmolmol-1, A1, F1, and B3, respectively). The reduced slope for M. faveolata is attributed to physical sampling issues associated with complex time-skeletal structure of M. faveolata, i.e., a sampling effect, and not a growth effect since the faster growing M. faveolata has the reduced Sr/Ca variability. ?? 2011 Elsevier B.V.

DeLong, K.L.; Flannery, J.A.; Maupin, C.R.; Poore, R.Z.; Quinn, T.M.

2011-01-01

104

Direct comparison of a Ca+ single-ion clock against a Sr lattice clock to verify the absolute frequency measurement.  

PubMed

Optical frequency comparison of the (40)Ca(+) clock transition ?(Ca)((2)S(1/2-)(2D(5/2), 729 nm) against the (87)Sr optical lattice clock transition ?(Sr) ((1)S(0)-(3)P(0), 698 nm) has resulted in a frequency ratio ?(Ca) / ?(Sr) = 0.957 631 202 358 049 9(2 3). The rapid nature of optical comparison allowed the statistical uncertainty of frequency ratio ?(Ca) / ?(Sr) to reach 1 10(-15) in 1000s and yielded a value consistent with that calculated from separate absolute frequency measurements of ?(Ca) using the International Atomic Time (TAI) link. The total uncertainty of the frequency ratio using optical comparison (free from microwave link uncertainties) is smaller than that obtained using absolute frequency measurement, demonstrating the advantage of optical frequency evaluation. We note that the absolute frequency of (40)Ca(+) we measure deviates from other published values by more than three times our measurement uncertainty. PMID:23037353

Matsubara, Kensuke; Hachisu, Hidekazu; Li, Ying; Nagano, Shigeo; Locke, Clayton; Nogami, Asahiko; Kajita, Masatoshi; Hayasaka, Kazuhiro; Ido, Tetsuya; Hosokawa, Mizuhiko

2012-09-24

105

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 March 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 BP 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 {approximately} {minus}12{per_thousand}) to CAM ({delta}{sup 13}C = {minus}26{per_thousand})-type vegetation over time.

Ingram, B.L. [Univ. of California, Berkeley, CA (United States). Dept. of Geology] [Univ. of California, Berkeley, CA (United States). Dept. of Geology; Deckker, P. de [Australian National Univ., Canberra (Australia). Dept. of Geology] [Australian National Univ., Canberra (Australia). Dept. of Geology; Chivas, A.R. [Univ. of Wollongong, New South Wales (Australia). School of Geoscience] [Univ. of Wollongong, New South Wales (Australia). School of Geoscience; Conrad, M.E. [Lawrence Berkeley National Lab., CA (United States). Center for Isotope Geochemistry] [Lawrence Berkeley National Lab., CA (United States). Center for Isotope Geochemistry; Byrne, A.R. [Univ. of California, Berkeley, CA (United States). Dept. of Geography] [Univ. of California, Berkeley, CA (United States). Dept. of Geography

1998-10-01

106

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

107

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

SciTech Connect

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

Hinton, T.G.

1989-01-01

108

Mssbauer spectrometric study of nonstoichiometric perovskite, A (Co0.8Fe0.2) O3- (A=Ba, Sr, Ca), for oxidative coupling of methane  

NASA Astrophysics Data System (ADS)

Nonstoichiometric perovskites. A(Co0.8Fe0.2)O3-6, were prepared by a pyrolysis of mixed metal citrates, and the catalytic property and structure of these perovskites were investigated. The efficiency of an oxidative coupling of methane increases with the order of Ba. Sr, and Ca substituted in A site and decreases with the amounts of deficient oxygens. The mixed valence of B site ions in the disordering of deficient oxygen is considered to contribute mainly to the oxidative coupling of methane.

Nomura, Kiyoshi; Goda, Takeshi; Ujihira, Yusuke; Hayakawa, Takashi; Takehira, Katsuomi

1992-04-01

109

Structural, electric and magnetic properties of Bi(Pb)?Sr?Ca(Re)?Cu(M)?O vitroceramics  

NASA Astrophysics Data System (ADS)

The effect of the partial substitution of Ca ions by Gd and Eu ions and of Cu ions by elements from 3d group of transition metals on structural, electric and magnetic properties of Bi-vitroceramics from 2223 class was studied by X-ray diffraction, paramagnetic resonance, electric and statical magnetic susceptibility measurements.

Simon, S.; Burzo, E.; Cozar, O.; Barbur, I.; Simon, V.; Ardelean, I.; Pop, V.; Borodi, Gh.

1991-12-01

110

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-SchNberg, Dieter; Brummer, Geert-Jan A.

2013-04-01

111

Involvement of CaSR in hyperglycemia-induced macroangiopathy and related mechanism.  

PubMed

In order to clarify the potential role of calcium sensing receptor (CaSR), a typical G protein coupled receptor (GPCR), in hyperglacemia-induced macroangiopathy, experimental hyperglycemia models in vivo and in vitro were prepared. Firstly, SD rats were divided into control group (n=10) and diabetes group (n=10), and diabetic model was induced via high-fat diet feeding and streptozotocin (STZ, 30 mg/kg) injection. Hydroxyproline level, determined via Choramnie T oxidation method, in vessel wall in diabetic rats was 30% more than that in control group. The gene transcription and expression levels were detected by real-time PCR and Western blotting, respectively. Both of collagen I and III mRNA levels in diabetic aorta were nearly twice those in normal aorta. The cleaved caspase-3 and -9 were elevated 1.5 and 2.5 times respectively in diabetic vascular cells. As compared with controls, mRNA and protein levels of CaSR in aorta were increased by 3 and 1.5 times in diabetes group. The expression levels of Bax as well as pro-apoptotic kinases (phospho-p38 and phosphor-JNK) were also increased 2, 0.5 and 0.5 times respectively in diabetic rats. To further validate the involvement of CaSR in cell apoptosis and explore the potential mechanism, the endothelial cell line (human umbilical vascular endothelial cells, HUVECs) was stimulated with high concentration of glucose (33 mmol/L) to mimic hyperglycemia in vitro. Cell-based assays also showed that the CaSR level and key apoptotic proteins (cleaved caspase-3 and -9, Bax, phospho-p38 and phosphor-JNK) were elevated in response to stimulation, and inhibition of CaSR by using specific inhibitor (NPS-2143, 10 ?mol/L) could protect cells against apoptosis. Our results demonstrated that CaSR might take important part in the development of diabetic macroangiopathy through promoting cell apoptosis induced by hyperglycemia. PMID:25673191

Lu, Jin-Ping; Ren, Jiang-Hua; Chen, Ling; Li, Xia; Chen, Hui-Li

2015-02-01

112

Measurement of the internal magnetic field in the correlated iridates Ca4IrO6, Ca5Ir3O12, Sr3Ir2O7 and Sr2IrO4  

NASA Astrophysics Data System (ADS)

Oxides containing iridium ions display a range of magnetic and conducting properties that depend on the delicate balance between interactions and are controlled, at least in part, by the details of the crystal architecture. We have used muon spin rotation (?SR) to study the local field in four iridium oxides, Ca4IrO6, Ca5Ir3O12, Sr3Ir2O7, and Sr2IrO4, which show contrasting behavior. Our ?SR data on Ca4IrO6 and Ca5Ir3O12 are consistent with conventional antiferromagnetism where quasistatic magnetic order develops below TN=13.85(6) and 7.84(7) K, respectively. A lower internal field is observed for Ca5Ir3O12, as compared to Ca4IrO6, reflecting the presence of both Ir4+ and Ir5+ ions and resulting in a more magnetically dilute structure. Muon precession is only observed over a restricted range of temperature in Sr3Ir2O7, while the Mott insulator Sr2IrO4 displays more complex behavior, with the ?SR signal containing a single, well-resolved precession signal below TN=230 K, which splits into two precession signals at low temperature following a reorientation of the spins in the ordered state.

Franke, I.; Baker, P. J.; Blundell, S. J.; Lancaster, T.; Hayes, W.; Pratt, F. L.; Cao, G.

2011-03-01

113

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

NASA Astrophysics Data System (ADS)

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

Hart, S. R.

2009-12-01

114

Behavior of Bi1.7Pb0.3Sr2Ca2Cu3Ox at high temperature  

Microsoft Academic Search

Carefully prepared and well-characterized Bi1.7Pb0.3 Sr2Ca2Cu3Ox samples were studied by means of differential scanning calorimetry, thermogravimetry, and room and high temperature x-ray diffraction in different atmospheres. It is found that the decomposition of Bi1.7Pb0.3Sr2Ca2Cu3Ox strongly depends on the given conditions. In argon atmosphere, the sample begins to decompose at 850 C, and finally decomposes mainly into Bi2Sr2CuOx, Cu2O, CaO, and

H. Zhang; F. Ritter; T. Frieling; B. Kindler; W. Assmus

1995-01-01

115

Europium substitution into intermetallic phases grown in Ca/Zn flux  

SciTech Connect

Replacement of calcium with europium in the phases Ca{sub 21}Ni{sub 2}Zn{sub 36} and CaNi{sub 2}Zn{sub 3} was attempted to explore the possibility of substitution in metal flux reactions and potential magnetic interactions between closely spaced Eu{sup 2+} ions. Limited substitution occurs when Eu is added to the reaction of nickel in a Ca/Zn flux mixture, up to stoichiometries of Eu{sub 5.8(3)}Ca{sub 15.2(3)}Ni{sub 2}Zn{sub 36} and Eu{sub 0.42(8)}Ca{sub 0.58(8)}Ni{sub 2}Zn{sub 3}. Structural characterization and magnetic susceptibility studies on Eu{sub x}Ca{sub 21-x}Ni{sub 2}Zn{sub 36} phases indicate that the Eu and Ca ions do not form an even solid solution on their sites, but instead segregate in separate regions of the crystals. The europium-rich regions of the samples order ferromagnetically, with T{sub C} dependent on the size of the clusters. If the concentration of Eu in the flux is raised above 20 mol%, a new compound Eu{sub 1.63(1)}Ca{sub 1.37(1)}Ni{sub 2}Zn{sub 3} (Cmcm, a=4.1150(5) A, b=16.948(2) A, c=10.302(1) A, Z=4, R{sub 1}=0.0396) is produced. - Graphical abstract: Exploration of europium substitution into intermetallic compounds grown in Ca/Zn flux has yielded analogs of Eu{sub x}Ca{sub 21-x}Ni{sub 2}Zn{sub 36} with unusual magnetic properties due to segregation of europium in the crystals; high concentrations of Eu in the flux trigger the growth of Eu{sub 1.63(1)}Ca{sub 1.37(1)}Ni{sub 2}Zn{sub 3} with a new structure type.

Stojanovic, Milorad [Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390 (United States); Latturner, Susan E., E-mail: latturne@chem.fsu.ed [Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390 (United States)

2009-08-15

116

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

NASA Astrophysics Data System (ADS)

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

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

2003-11-01

117

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

118

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

Microsoft Academic Search

Rapid accumulation of CaCO 3 is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO 3 , primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota . Gyraulus deflectus and Amnicola integra

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

1981-01-01

119

(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

120

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

121

Photoluminescence property of vanadates M 2V 2O 7 (M: Ba, Sr and Ca)  

Microsoft Academic Search

We investigated the photoluminescent properties including the internal quantum efficiency (?) for the M2V2O7 (M: Ba, Sr, and Ca) as a new vanadate phosphor system. In the M2V2O7, the broad band emission spectra from 400 to 800nm derived from the charge transfer transition in the VO4 tetrahedra were observed. The emission band of these compounds consisted of two maxima Em1

T. Nakajima; M. Isobe; T. Tsuchiya; Y. Ueda; T. Manabe

2010-01-01

122

A contribution to the application of flame photometry on Ca, Sr, Ba and Li  

Microsoft Academic Search

SummaryTest solutions containing Li, Ca, Sr and Ba salts were sprayed into a flame photometer of simple design. The line-to-background\\u000a ratio, the detection limit, interference effects, filter leakage and the form of the standard graphs were investigated. With\\u000a each element readings were made with a series of interference filters of varying central wavelength and with an acetylene-air\\u000a and propane-air flame,

Tj Hollander; A. J. Borgers; C. T. J. Alkemade

1956-01-01

123

A contribution to the application of flame photometry on Ca, Sr, Ba and Li  

Microsoft Academic Search

Summary Test solutions containing Li, Ca, Sr and Ba salts were sprayed into a flame photometer of simple design. The line-to-background ratio, the detection limit, interference effects, filter leakage and the form of the standard graphs were investigated. With each element readings were made with a series of interference filters of varying central wavelength and with an acetylene-air and propane-air

Tj. Hollander; A. J. Borgers; C. T. J. Alkemade

1954-01-01

124

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

125

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 22C ? 28C, the best fitting linear relationships for the two species agree within their respective errors with a maximum deviation less than 0.3C.

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

1996-01-01

126

Gamma-ray shielding properties of CaOSrOB 2O 3 glasses  

Microsoft Academic Search

Mass attenuation coefficients, effective atomic numbers and effective electron densities have been determined experimentally for the glass system xCaO(0.3x)SrO0.7B2O3 at photon energies 511, 662, 1173, and 1332keV. The results are compared with theoretical calculations. In addition, the molar volume of the glasses has been derived from density measurements, and the excess volume has been determined as a function of composition.

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

2005-01-01

127

Superconducting Bi-Ca-Sr-Cu oxide thin films by spray pyrolysis of metal acetates  

Microsoft Academic Search

Superconducting Bi-Ca-Sr-Cu oxide thin films have been prepared on ZrO2-coated silicon (111) wafers by spray pyrolysis of metal acetate precursors followed by rapid annealing to 850 C in air. Resistivity measurements indicate a broad superconducting transition with Tc onset near 90 K and zero resistivity below 60 K. The films are highly oriented with the c axis normal to the

Dale F. Vaslow; Gunter H. Dieckmann; David Dawson Elli; Arthur B. Ellis; D. Scott Holmes; Anthony Lefkow; Mark MacGregor; James E. Nordman; Michael F. Petras; Yifeng Yang

1988-01-01

128

A comprehensive review of the XRD data of the primary and secondary phases present in the BSCCO superconductor system. Part 1: Ca-Sr-Cu oxides  

NASA Astrophysics Data System (ADS)

X-ray powder patterns for the phases in the CaO-SrO-CuO ternary system, along with the corresponding crystal structures, were obtained from the literature and from the Powder Diffraction File (PDF). Available X-ray diffraction (XRD) patterns were compared with each other and, when possible, with a simulated pattern for each phase, yielding a recommended reference pattern. The simulated powder patterns presented here deal with the phases found within the (Ca, Sr)O, (Ca,Sr)2CuO3, (Ca,Sr)14Cu24O41, (Ca,Sr)CuO2, (Ca,Sr)Cu2O3, and (Ca,Sr)Cu2O2 solid solution series and are recommended for the PDF.

Reardon, B. J.; Hubbard, C. R.

1992-01-01

129

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 (110?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

130

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

131

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

132

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

133

Thermoelectric properties and electronic structure of the Zintl phase Sr?In?Sb? and the Ca(5-x)Sr(x)In?Sb? solid solution.  

PubMed

The Zintl phase Sr5In2Sb6 is isostructural with Ca5In2Sb6-a promising thermoelectric material with a peak zT of 0.7 when the carrier concentration is optimized by doping. Density functional calculations for Sr5In2Sb6 reveal a decreased energy gap and decreased valence band effective mass relative to the Ca analog. Chemical bonding analysis using the electron localizability indicator was found to support the Zintl bonding scheme for this structure type. High temperature transport measurements of the complete Ca(5-x)Sr(x)In2Sb6 solid solution were used to investigate the influence of the cation site on the electronic and thermal properties of A5In2Sb6 compounds. Sr was shown to be fully miscible on the Ca site. The higher density of the Sr analog leads to a slight reduction in lattice thermal conductivity relative to Ca5In2Sb6, and, as expected, the solid solution samples have significantly reduced lattice thermal conductivities relative to the end member compounds. PMID:25479002

Zevalkink, Alex; Chanakian, Sevan; Aydemir, Umut; Ormeci, Alim; Pomrehn, Gregory; Bux, Sabah; Fleurial, Jean-Pierre; Snyder, G Jeffrey

2015-01-14

134

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

135

Crystalline phases during the melting of Bi sub 2 Sr sub 2 CaCu sub 2 O sub x  

SciTech Connect

The melting of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} material has been studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in order to study the phases that formed in the high temperature regions. Two distinct phases of (Sr{sub 1-x}Ca{sub x})CuO{sub 2} and (Sr{sub 1-x}Ca{sub x}){sub 2}CuO{sub 3} have been observed in the Bi-rich matrix depending upon quenching temperatures. Crystallization from the melt by fast cooling usually produce the co-existence of Bi (2201) and these Sr-Ca-Cu-O phases. 12 refs., 2 figs.

Xu, Ming; Polonka, J.; Goldman, A.I.; Finnemore, D.K.; Li, Qiang; Laabs, F.C.

1991-01-01

136

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

USGS Publications Warehouse

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

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

2012-01-01

137

Electronic Structure, Chemical Bonding, and Solid-State NMR Spectroscopy of the Digallides of Ca, Sr, and Ba  

Microsoft Academic Search

Combined application of 69,71 Ga NMR spectroscopy and quan- tum mechanical calculations reveals the chemical bonding in the digallides of Ca, Sr, and Ba. An analysis of the electron localization function (ELF) shows honeycomb-like 63 nets of the Ga atoms as the most prominent struc- tural features in SrGa2 and BaGa2 .F or CaGa2 a description of a 3+1-coordi- nated

Frank Haarmann; Katrin Koch; Daniel Grner; Walter Schnelle; Oliver Pecher; Raul Cardoso-Gil; Horst Borrmann; Helge Rosner; Yuri Grin

2009-01-01

138

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 Kubos formula. Experimental data for Bi 2Sr 2CaCu 2O 8+ ? are discussed.

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

2012-02-01

139

Involvement of palmitate/Ca(2+)(Sr(2+))-induced pore in the cycling of ions across the mitochondrial membrane.  

PubMed

The palmitate/Ca(2+)-induced (Pal/Ca(2+)) pore, which is formed due to the unique feature of long-chain saturated fatty acids to bind Ca(2+) with high affinity, has been shown to play an important role in the physiology of mitochondria. The present study demonstrates that the efflux of Ca(2+) from rat liver mitochondria induced by ruthenium red, an inhibitor of the energy-dependent Ca(2+) influx, seems to be partly due to the opening of Pal/Ca(2+) pores. Exogenous Pal stimulates the efflux. Measurements of pH showed that the Ca(2+)-induced alkalization of the mitochondrial matrix increased in the presence of Pal. The influx of Ca(2+) (Sr(2+)) also induced an outflow of K(+) followed by the reuptake of the ion by mitochondria. The outflow was not affected by a K(+)/H(+) exchange blocker, and the reuptake was prevented by an ATP-dependent K(+) channel inhibitor. It was also shown that the addition of Sr(2+) to mitochondria under hypotonic conditions was accompanied by reversible cyclic changes in the membrane potential, the concentrations of Sr(2+) and K(+) and the respiratory rate. The cyclic changes were effectively suppressed by the inhibitors of Ca(2+)-dependent phospholipase A2, and a new Sr(2+) cycle could only be initiated after the previous cycle was finished, indicating a refractory period in the mitochondrial sensitivity to Sr(2+). All of the Ca(2+)- and Sr(2+)-induced effects were observed in the presence of cyclosporin A. This paper discusses a possible role of Pal/Ca(2+) pores in the maintenance of cell ion homeostasis. PMID:25450352

Mironova, Galina D; Saris, Nils-Erik L; Belosludtseva, Natalia V; Agafonov, Alexey V; Elantsev, Alexander B; Belosludtsev, Konstantin N

2015-02-01

140

Effects of Gd substitution on microstructures and low temperature dielectric relaxation behaviors of SrTiO{sub 3} ceramics  

SciTech Connect

In this paper, Sr{sub 1-3x/2}Gd{sub x}TiO{sub 3} ceramics (0.00 {<=} x {<=} 0.05) were prepared from powders obtained by a sol-gel method. X-ray diffraction results showed that the Gd ion substituted Sr site, and the unit cell volume of doped samples decreased with increasing Gd doping concentrations, which was due to the difference between Sr/Gd ionic radii. Moreover, the structural change also led to an increase in the antiferrodistortive transition temperature. Dielectric properties of all samples were investigated over broad temperature and frequency ranges, and four dielectric relaxation behaviors were identified in different samples. It was found that two intrinsic dielectric relaxation behaviors for the pure SrTiO{sub 3} ceramics could be gradually disappeared with increasing Gd doping concentrations, which was ascribed to the change of domain state induced by Sr vacancies. On the other hand, the other two dielectric relaxation behaviors were induced by Gd doping. The relaxation behavior with activation energy in the range of 100-130 meV was originated from oxygen vacancies, while another relaxation behavior with activation energy in the range of 200-230 meV corresponded to the thermal motions of Ti{sup 4+} ions.

Fang Liang; Dong Wen; Zheng Fengang; Shen Mingrong [Jiangsu Key Laboratory of Thin Films and Department of Physics, Soochow University, Suzhou 215006 (China)

2012-08-01

141

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

NASA Astrophysics Data System (ADS)

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

Allison, Nicola; Finch, Adrian A.

2004-05-01

142

Next neighbors effect along the CaSrBa-kermanite join: Long-range vs. short-range structural features  

SciTech Connect

An original approach has been developed herein to explore the correlations between short- and long-range structural properties of solid solutions. X-ray diffraction (XRD) and electronic absorption spectroscopy (EAS) data were combined on a (Ca,Sr,Ba){sub 2}(Mg{sub 0.7}Co{sub 0.3})Si{sub 2}O{sub 7} join to determine average and local distances, respectively. Instead of varying the EAS-active ion concentration along the join, as has commonly been performed in previous studies, the constant replacement of Mg{sup 2+} by a minimal fraction of a similar size cation (Co{sup 2+}) has been used to assess the effects of varying second-nearest neighbor cations (Ca, Sr, Ba) on the local distances of the first shell. A comparison between doped and un-doped series has shown that, although the overall symmetry of the Co-centered T1-site was retained, greater relaxation occurs at the CoO{sub 4} tetrahedra which become increasingly large and more distorted than the MgO{sub 4} tetrahedra. This is indicated by an increase in both the quadratic elongation (?{sub T1}) and the bond angle variance (?{sup 2}{sub T1}) distortion indices, as the whole structure expands due to an increase in size in the second-nearest neighbors. This behavior highlights the effect of the different electronic configurations of Co{sup 2+} (3d{sup 7}) and Mg{sup 2+} (2p{sup 6}) in spite of their very similar ionic size. Furthermore, although the overall symmetry of the Co-centered T1-site is retained, relatively limited (<10 deg) angular variations in OCo{sup 2+}O occur along the solid solution series and large changes are found in molar absorption coefficients showing that EAS Co{sup 2+}-bands are highly sensitive to change in the local structure. - Graphical abstract: Average (MgO) vs. local (CoO{sub local}) tetrahedral bond distances in function of the average X cation radius in the (Ca,Sr,Ba){sub 2}(Mg{sub 0.7}Co{sub 0.3})Si{sub 2}O{sub 7} join. - Highlights: New method to assess short- vs. long-range properties of non-ideal solid solutions. Constant Co{sup 2+}-for-Mg replacement turns the CaSrBa-kermanite join EAS-active. Co?Mg substitution does not produce any alteration in the average structure. Relaxation around Co-tetrahedra scales with second-nearest neighbor cation radius. Different electronic configurations of Co and Mg cause different local structures.

Dondi, Michele [Institute of Science and Technology for Ceramics (ISTECCNR), via Granarolo 64, 48018 Faenza (Italy); Ardit, Matteo, E-mail: rdtmtt@unife.it [Department of Physics and Earth Sciences, University of Ferrara, via Saragat 1, 44100 Ferrara (Italy); Cruciani, Giuseppe [Department of Physics and Earth Sciences, University of Ferrara, via Saragat 1, 44100 Ferrara (Italy)

2013-06-15

143

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

PubMed

The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures. PMID:17654648

Stashans, Arvids; Chamba, Gaston; Pinto, Henry

2008-02-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2015-04-01

145

Photoluminescence property of vanadates M 2V 2O 7 (M: Ba, Sr and Ca)  

NASA Astrophysics Data System (ADS)

We investigated the photoluminescent properties including the internal quantum efficiency ( ?) for the M 2V 2O 7 (M: Ba, Sr, and Ca) as a new vanadate phosphor system. In the M 2V 2O 7, the broad band emission spectra from 400 to 800 nm derived from the charge transfer transition in the VO 4 tetrahedra were observed. The emission band of these compounds consisted of two maxima Em 1 and Em 2 corresponding to 3T1- 1A1 and 3T2- 1A1 transitions, respectively. These two maxima red-shifted with the decreasing ionic radius of M-site, as a result, the luminescent colour was varied from green (M: Ba) to yellowish orange (M: Ca). The ? for the Ba 2V 2O 7, Sr 2V 2O 7 and Ca 2V 2O 7 were 25%, 8% and 0.9%, respectively. This enhancement of ? in the M 2V 2O 7 could be due to following structural features: the stronger V-V and weaker V-M correlations.

Nakajima, T.; Isobe, M.; Tsuchiya, T.; Ueda, Y.; Manabe, T.

2010-10-01

146

Sr-90 Immobilization by Infiltration of a Ca-Citrate-PO{sub 4} Solution into the Hanford 100-N Area Vadose Zone  

SciTech Connect

This project was initiated to develop a strategy for infiltration of a Ca-citrate-PO{sub 4} solution in order to precipitate apatite [Ca{sub 6}(PO{sub 4}){sub 10}(OH){sub 2}] in desired locations in the vadose zone for Sr-90 remediation. Laboratory experiments have demonstrated that infiltration of a Ca-citrate-PO{sub 4} solution into sediments at low and high water saturation results in citrate biodegradation and formation of apatite. The citrate biodegradation rate was relatively uniform, in spite of the spatial variability of sediment microbial biomass, likely because of microbial transport processes that occur during solution infiltration. The precipitate was characterized as hydroxyapatite, and the Sr-90 substitution into apatite was shown to have an incorporation half-life of 5.5 to 16 months. One and two dimensional (1-D and 2-D) laboratory infiltration experiments quantified the spatial distribution of apatite that formed during solution infiltration. Slow infiltration in 2-D experiments at low water saturation show the apatite precipitate concentrated in the upper third of the infiltration zone. More rapid 1-D infiltration studies show the apatite precipitate concentrated at greater depth. (authors)

Szecsody, J.E.; Fruchter, J.S.; Burns, C.A.; Rockhold, M.L.; Oostrom, M.; Williams, M.D.; Vermeul, V.R. [Pacific Northwest National Laboratory, Richland, WA (United States)

2008-07-01

147

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

SciTech Connect

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

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

2008-08-15

148

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

149

Late Maastrichtian paleoclimatic and paleoceanographic changes inferred from Sr\\/Ca ratio and stable isotopes  

Microsoft Academic Search

Milankovitch-scale cycles can be recognized in high-resolution ?13C, ?18O, Sr\\/Ca, mineralogical, and magnetic susceptibility data in hemipelagic sediments that span the last 700 kyr of the Maastrichtian at Elles, Tunisia. Oxygen isotope data reveal three cool periods between 65.50 and 65.55 Ma (21.523.5 m), 65.26 and 65.33 Ma (811 m), and 65.04 and 65.12 Ma (1.54 m), and three warm

D. Stben; U. Kramar; Z. A. Berner; M. Meudt; G. Keller; S. Abramovich; T. Adatte; U. Hambach; W. Stinnesbeck

2003-01-01

150

Flux creep in Bi2Sr2Ca1Cu2O(8+x) single crystals  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

151

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

DOEpatents

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

Shi, Donglu (Chicago, IL)

1992-01-01

152

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

153

Oxygen Surface Exchange Kinetics on Sr-Substituted Lanthanum Manganite and Ferrite Thin-Film Microelectrodes  

E-print Network

The surface oxygen exchange kinetics occurring on dense La0.8Sr0.2MnO3 (65nm thick) and La0.8Sr0.2FeO3 (110nm thick) thin films were investigated by electrochemical impedance spectroscopy (EIS). Rutherford backscattering ...

la O', Gerardo Jose

154

Band Systems of MgCl, CaCl and SrCl  

Microsoft Academic Search

A vibrational analysis has been made of band systems due to MgCl, CaCl and SrCl. There are two systems due to MgCl with nuE*=26,441.5, omega'=474.8 and omega''=447.4 for the more intense system and nuE=25,887.2, omega'=466.9 and omega''=447.4 for the less intense system. CaCl has three extensive systems with nuE=16,093.5, omega'=367.1, omega''=364.5 nuE=16,850.6, omega'=361.0, omega''=364.0 nuE=26,498.9, omega'=336.0, omega''=368.3, respectively. There are

Allan E. Parker

1935-01-01

155

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

NASA Astrophysics Data System (ADS)

AWO 4 (A = Ca, Sr) was prepared from metal salts [Ca(NO 3) 24H 2O or Sr(NO 3) 2], Na 2WO 42H 2O and different moles of cetyltrimethylammonium bromide (CTAB) in water by cyclic microwave irradiation. The structure of AWO 4 was characterized by X-ray diffraction (XRD) and selected area electron diffraction (SAED). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the presence of nanoparticles in clusters with different morphologies; spheres, peaches with notches, dumb-bells and bundles, influenced by CTAB. Six Raman vibrational peaks of scheelite structure were detected at 908, 835, 793, 399, 332 and 210 cm -1 for CaWO 4 and 917, 833, 795, 372, 336 and 192 cm -1 for SrWO 4, which are assigned as ?1(A g), ?3(B g), ?3(E g), ?4(B g), ?2(A g) and ?f.r.(A g), respectively. Fourier transform infrared (FTIR) spectra provided the evidence of W-O stretching vibration in [WO 4] 2- tetrahedrons at 793 cm -1 for CaWO 4 and 807 cm -1 for SrWO 4. The peaks of photoluminescence (PL) spectra were at 428-434 nm for CaWO 4, and 447-451 nm for SrWO 4.

Thongtem, Titipun; Kaowphong, Sulawan; Thongtem, Somchai

2008-09-01

156

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

157

50 MeV Li 3+ irradiation effects on the thermal expansion of Ca 1- xSr xZr 4P 6O 24  

NASA Astrophysics Data System (ADS)

The influence of 50 MeV Li 3+ ion irradiation on the thermal expansion of the low thermal expansion ceramic Ca 1- xSr xZr 4P 6O 24 ( x=0.00, 0.25, 0.50, 0.75 and 1.00) belonging to the sodium zirconium phosphate (NZP) family of ceramics was studied in the temperature range 300-1100 K. The observed changes in XRD, microstructure and thermal expansion are reported. These changes are strongly dependent upon the strontium substitution at calcium sites in the basic structure. The XRD and scanning electron microscope (SEM) studies indicate that the ion irradiation causes amorphization, especially at the grain boundaries. The thermal expansion hysteresis reduces due to Sr substitution and is further reduced upon irradiation. It is suggested that the amorphization due to irradiation helped release of thermal stress and thereby lead to the reduction in the hysteresis in thermal expansion. The composition with x=0.50 having low coefficient of thermal expansion (CTE), low hysteresis and the least thermal expansion anisotropy is least affected by the Li 3+ irradiation and hence may qualify as the radiation resistant material.

Angadi, Basavaraj; Jali, V. M.; Lagare, M. T.; Kini, N. S.; Umarji, A. M.; Kumar, Ravi; Arora, S. K.; Kanjilal, D.

2002-01-01

158

Effect of oxygen concentration on superconductivity of Bi-Sr-Ca-K-Cu-O compounds  

SciTech Connect

In order to study the relation between the oxygen content and superconductivity samples of Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}x}K{sub x}Cu{sub 2}O{sub y} (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were prepared and treated under different conditions. It was found that the superconducting properties are sensitive to the oxygen concentration and the T{sub c,zero} of Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}x}K{sub x}Cu{sub 2}O{sub y} can be shifted over a range of about 22 K by the changing oxygen concentration; no structural difference induced by oxygen were observed. The change in superconducting properties may be the result of a change in Cu average valence state. In addition, the change in superconducting phase with K{sup +} concentration is also studied.

Han Zhiyi; Mao Zhiqiang; Wang Yu; Chen Qun; Zhang Ning; Zhou Zhe; Chao LieZhao; Cheng Zhaojia; Zhou Guien; Zhang Yuheng (Univ. of Science and Technology of China, Anhui (China))

1991-02-01

159

Electrical transport in superconducting BiPbSrCaCuO  

NASA Astrophysics Data System (ADS)

Measurements of the magnetic field and temperature dependent electrical resistance and thermoelectric power of a lead-doped polycrystalline sample of BiPbSrCaCuO are reported. According to the d.c. susceptibility data, the sample shows a major Meissner effect at 110 K with an additional feature at 80 K which indicates the presence of the second phase. Magnetoresistance is muck less sensitive to the fraction of the second phase than are the thermopower measurements that clearly resolve a shoulder-like structure at 80 K. The application of a magnetic field results in a positive contribution to the thermopower, S( B, T), below the Tc of the zero-field superconducting phase transition. Based on an analysis of the S( B, T) in terms of the transport entropy of the vortex motion we find that the data for lead-free ( Tc = 85K) and lead-doped ( Tc = 110K) BiSrCaCuO compounds provide a reasonable estimate of the principal quantum unit {h?}/{2m} of the particle flux.

Gridin, Vladimir V.; Datars, W. R.; Ummat, P. K.

1990-04-01

160

Quasiparticle tunneling in Bi-Sr-Ca-Cu-O thin films  

NASA Astrophysics Data System (ADS)

Tunnel junctions were formed by depositing a thin layer of Al2O3(20 Å) and Al counter electrodes onto sputtered and annealed Bi-Sr-Ca-Cu-O films. Differential conductance spectra displayed low conductivity at low bias, and two pairs of peaks, symmetric with respect to zero bias, which correlate in energy and relative magnitude with the two superconducting Bi-Sr-Ca-Cu-O phases present in the film (110 and 85 K). The measured values of the peak positions and the reduced gap parameter are ?1=18-21 meV(85-K phase), ?2=25-28 meV (110-K phase), 2?/kBTc=5.5+/-0.6 for both phases. The shape of the conductance curves at higher bias is parabolic. This effect can be explained by the presence of a composite barrier. Such a barrier is likely to be the result of insulating or semiconducting grain surfaces in addition to the artificial barrier.

Kussmaul, A.; Moodera, J. S.; Roesler, G. M., Jr.; Tedrow, P. M.

1990-01-01

161

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

162

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

NASA Astrophysics Data System (ADS)

One of the basic data to understand global change and past global changes is the measurement and the reconstruction of temperature of marine water masses. E.g. seawater temperature controls the density of seawater and in combination with salinity is the major driving force for the oceans circulation system. Geochemical investigations on cold-water corals Lophelia pertusa and Desmophyllum cristagalli indicated the potential of these organisms as high-resolution archives of environmental parameters from intermediate and deeper water masses (Adkins and Boyle 1997). Some studies tried to use cold-water corals as a high-resolution archive of temperature and salinity (Smith et al. 2000, 2002; Blamart et al. 2005; Lutringer et al. 2005). However, the fractionation of stable isotopes (delta18O and delta13C) and element ratios (Sr/Ca, Mg/Ca, U/Ca) are strongly influenced by vital effects (Shirai et al. 2005; Cohen et al. 2006), and difficult to interpret. Nevertheless, ongoing studies indicate the potential of a predominant temperature dependent fractionation of distinct isotopes and elements (e.g. Li/Ca, Montagna et al. 2008; U/Ca, Mg/Ca, delta18O, Lpez Correa et al. 2008; delta88/86Sr, Rggeberg et al. 2008). Within the frame of DFG-Project TRISTAN and Palo-TRISTAN (Du 129/37-2 and 37-3) we investigated live-collected specimens of cold-water coral L. pertusa from all along the European continental margin (Northern and mid Norwegian shelves, Skagerrak, Rockall and Porcupine Bank, Galicia Bank, Gulf of Cadiz, Mediterranean Sea). These coral samples grew in waters characterized by temperatures between 6C and 14C. Electron Microprobe investigations along the growth direction of individual coral polyps were applied to determine the relationship between the incorporation of distinct elements (Sr, Ca, Mg, S). Cohen et al. (2006) showed for L. pertusa from the Kosterfjord, Skagerrak, that ~25% of the coral's Sr/Ca ratio is related to temperature, while 75% are influenced by the calcification rate of the organism. However, the Sr/Ca-temperature relation of our L. pertusa specimens suggest, that mean values are more reliable for temperature reconstruction along a larger temperature range than local high-resolution investigations. Additionally, our results plot on same line of Sr/Ca-temperature relationship like tropical corals indicating a similar behaviour of element incorporation during calcification. References: Adkins JF, Boyle EA (1997) Changing atmospheric ?14C and the record of deep water paleoventilation ages. Paleoceanography 12:337-344 Blamart D, Rollion-Bard C, Cuif J-P, Juillet-Leclerc A, Lutringer A, Weering Tv, Henriet J-P (2005) C and O isotopes in a deep-sea coral (Lophelia pertusa) related to skeletal microstructure. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin Heidelberg, p 1005-1020 Cohen AL, Gaetani GA, Lundlv T, Corliss BH, George RY (2006) Compositional variability in a cold-water scleractinian, Lophelia pertusa: New insights into vital effects. Geochemistry, Geophysics, Geosystems 7:Q12004, doi:12010.11029/12006GC001354 Lpez Correa M, Montagna P, Rggeberg A, McCulloch M, Taviani M, Freiwald A (2008) Trace elements and stable isotopes in recent North Atlantic Lophelia pertusa along a latitudal gradient and from fossil Mediterranean sites. ASLO 2008 Summer Meeting, St. John's, Newfoundland & Labrador, Canada, 08.06.-13.06.2008, p. 47 Lutringer A, Blamart D, Frank N, Labeyrie L (2005) Paleotemperatures from deep-sea corals: scale effects. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin, Heidelberg, p 1081-1096 Montagna P, Lpez-Correa M, Rggeberg A, McCulloch M, Rodolfo-Metalpa R, Dullo W-C, Ferrier-Pags C, Freiwald A, Henderson G, Mazzoli C, Russo S, Silenzi S, Taviani M (2008) Coral Li/Ca in micro-structural domains as a temperature proxy. Goldschmidt Conference, Vancouver, British Columbia, Canada Rggeberg A, Fietzke J, Liebetrau V, Eisenhauer A, Dullo W-C, Freiwald A (2008) Stable strontium isot

Rggeberg, Andres; Riethdorf, Jan-Rainer; Raddatz, Jacek; Lpez Correa, Matthias; Montagna, Paolo; Dullo, Wolf-Christian; Freiwald, Andr

2010-05-01

163

Superfast contractions without superfast energetics: ATP usage by SR-Ca2+ pumps and crossbridges in toadfish swimbladder muscle  

PubMed Central

The rate at which an isometrically contracting muscle uses energy is thought to be proportional to its twitch speed. In both slow and fast muscles, however, a constant proportion (25-40 %) of the total energy has been found to be used by SR-Ca2+ pumps and the remainder by crossbridges. We examined whether SR-Ca2+ pumps account for a larger proportion of the energy in the fastest vertebrate muscle known (the toadfish swimbladder), and whether the swimbladder muscle utilizes energy at the superfast rate one would predict from its mechanics.The ATP utilization rates of the SR-Ca2+ pumps and crossbridges were measured using a coupled assay system on fibres skinned with saponin. Surprisingly, despite its superfast twitch speed, the ATP utilization rate of swimbladder was no higher than that of much slower fast-twitch amphibian muscles.The swimbladder achieves tremendous twitch speeds with a modest steady-state ATP utilization rate by employing two mechanisms: having a small number of attached crossbridges and probably utilizing intracellular Ca2+ buffers (parvalbumin) to spread out the time over which Ca2+ pumping can occur.Finally, although the total ATP utilization rate was not as rapid as expected, the relative proportions used by SR-Ca2+ pumps and the crossbridges were similar to other muscles. PMID:10896717

Rome, Lawrence C; Klimov, Andrei A

2000-01-01

164

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

Microsoft Academic Search

Glacialinterglacial variation in the marine Sr\\/Ca ratio has important implications for coral Sr thermometry [J.W. Beck et al., Science 257 (1992) 644647]. A possible variation of 13% was proposed based on ocean models [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 11071118]. 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

165

Cr:LiSr(0.8)Ca(0.2)AlF(6) tunable laser.  

PubMed

A new congruent melting compound intermediate between the solid solutions of LiCaAIF(6) and LiSrAlF(6) is reported. When doped with Cr(3+) ion, the new compound (Cr:LiSr(0.8)Ca(0.2)AlF(6)) has demonstrated roomtemperature lasing in the spectral region from 750 to 950 nm. This material has mechanical properties similarto those of Cr:LiCaAlF(6) and a broadband laser tuning range similar to that of Cr:LiSrAlF(6). Long-pulse, flash-lamp-pumped lasing with 1.25% overall efficiency is reported by using a rod cut from an earlier boule. PMID:19798253

Chai, B H; Lefaucheur, J L; Stalder, M; Bass, M

1992-11-15

166

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

SciTech Connect

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

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

1997-04-01

167

Thermophysical characteristics of Ca1- x Sr x F2 solid-solution Crystals (0 ? x ? 1)  

NASA Astrophysics Data System (ADS)

The thermal conductivity of crystals of a continuous series of isovalent Ca1 - x Sr x F2 solid solutions has been experimentally investigated in the temperature ranges of 50-300 K (0 ? x ? 1) and 54-303 K ( x = 0.743). The concentration dependence k( x) of the thermal conductivity has been revealed for Ca1- x Sr x F2 crystals. It is shown that k > 3 W/(m K) at 300 K for any x. Being extrapolated to the melting temperature range, the phonon mean free path l( T) in Ca0.257Sr0.743F2 crystal approaches to the unit-cell parameter a.

Popov, P. A.; Moiseev, N. V.; Karimov, D. N.; Sorokin, N. I.; Sulyanova, E. A.; Sobolev, B. P.; Konyushkin, V. A.; Fedorov, P. P.

2015-01-01

168

Experimental Determination of Sr partitioning and Ca Isotope Fractionation in the CaSO4-NaCl-H2O system  

NASA Astrophysics Data System (ADS)

Anhydrite and gypsum are important, retrograde soluble minerals in geologic environments including mid ocean ridge hydrothermal systems and saline aquifers. Precipitation and/or dissolution of Ca-sulfate phases may control the distribution of stable Ca isotopes and Sr concentrations between fluids and minerals. Considerable research in the CaCO3-H2O system suggests that stable isotope fractionation of Ca between the dissolve pool and precipitating mineral are primarily controlled by the mineral growth rates. The partitioning of Sr appears to be growth rate dependent as well. We designed a series of hydrothermal precipitation experiments to test the idea that similar rate dependent isotope and trace metal fractionation occurs in the CaSO4-H2O system. Experiments were conducted between 110-160C using a titanium Parr mini bench top reactor. Mixtures of CaCl2, SrCl2 and Na2SO4 were dissolved in water and loaded into a Teflon lined vessel. Sealed experiments were purged with nitrogen gas for approximately 20 minutes to create a CO2-free environment. Experiments were rapidly charged to approximately 250 psi and heated to the desired run temperature. Experiment duration was between 36 and 360 hours. Completed experiments were depressurized and solid run products were recovered by filtration. Fluid samples from the beginning and end of each experiment were preserved for elemental and isotopic measurements. Preliminary results for experiments with CaSO4 supersaturation ~10 have thin needle-like crystals of mixed gypsum-bassanite-anhydrite based on SEM and XRD analysis. Sr distribution coefficients range between 0.48-0.74, greater than published equilibrium values, while D44Ca = 0.7-1.1 per mil, similar to low temperature carbonates.

Brown, S. T.; DePaolo, D. J.

2012-12-01

169

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.; Mller, Wolfgang; Prieto, Manolo

2012-09-01

170

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.; Bhm, Florian; Rickaby, Rosalind E. M.; Wiechert, Uwe; Korte, Christoph

2013-10-01

171

Thermoelectric properties of Al substituted misfit cobaltite Ca3(Co1- x Al x )4O9 at low temperature  

NASA Astrophysics Data System (ADS)

Thermoelectric properties of Al substituted compounds Ca3(Co1- x Al x )4O9 ( x = 0, 0.03, 0.05), prepared by a sol-gel process, have been investigated in the temperature range 305-20 K. The results indicate that after Al substitution for Co in Ca3(Co1- x Al x )4O9, the direct current electrical resistivity and thermopower increase due to the reduction of carrier concentration. Experiments show that Al substitution results in decreased lattice thermal conductivity. The figure of merit of temperature behavior suggests that Ca3(Co0.97Al0.03)4O9 would be a promising candidate thermoelectric material for high-temperature thermoelectric application.

Liu, Yi; Chen, Hong-mei; Hu, Jin-lian; Tang, Xu-bing; Li, Hai-jin; Wang, Wei

2014-07-01

172

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

173

Study on the superconducting composite material formation in the system Bi 2Sr 2CaCu 2O 8+ x/Al-containing phases  

NASA Astrophysics Data System (ADS)

Phase evolution in the Bi?Sr?Ca?Cu?Al?O system was studied. Two Al-containing phases BiSr 1.5Ca 0.5Al 2O z and (Sr 1- xCa x) 3Al 2O 6 ( x = 0.4 - 0.45) were determined to be chemically compatible with Bi 2.18Sr 2CaCu 2O 8+ x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr 1.5Ca 0.5Al 2O z was found to be in equilibrium only with the melt and the (Sr 1- xCa x) 3Al 2O 6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr 1.5Ca 0.5Al 2O z ? (Sr 1- xCa x) 3Al 2O 6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr 1.5Ca 0.5Al 2O z and Bi-2212 + m(Sr 1- xCa x) 3Al 2O 6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr 1.5Ca 0.5Al 2O z phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 ?m) grains of (Sr 1- xCa x) 3Al 2O 6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr 1- xCa x) 3Al 2O 6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content.

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

1997-02-01

174

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)OZn{sup 2+}(S=0)OCo{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

175

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

176

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

177

Synthesis and superconductivity in (Pb,Ti)Sr 2(Ca 1- xR x)Cu 2O z( R= Pr and Tb ) systems  

NASA Astrophysics Data System (ADS)

The (Pb,Ti)-based 1212 compounds ( Pb0.5Ti0.5) Sr2( Ca1-xRx) Cu2Oz ( R= Pr and Tb ) are synthesized to study the effect of Pr and Tb substitution on superconductivity. It is found that for R=Pr, the 1212-phase formation region exists for 0.35-1.0, while for R=Tb, the 1212-phase is obtained in the narrow range of 0.3-0.5. Superconductivity is observed for phases with x=0.35-0.55 for R= Pr and x=0.3 -0.50 for R=Tb. Maximum Tc of 45 and 54 K are observed for R=Pr and Tb, respectively.

Lee, Ho Keun

2000-07-01

178

EFFECT OF ALKALINE EARTH SUBSTITUTION ON ELECTRICAL PROPERTIES OF SrBi4Ti4O15 CERAMICS  

Microsoft Academic Search

Ferroelectric Sr1xCaxBi4Ti4O15 (SCBT-x x = 0.00, 0.20, 0.40, 0.50, 0.70, 0.90 and 1.00) ceramic samples were prepared using the conventional solid-state reaction. The Curie temperature (Tc) increases with Ca doping. The temperature dependence of dielectric loss (tan ?) shows two dielectric anomalies at x = 0.20 while only one dielectric loss peak is found in other cases. The remnant polarization

DAN SHAN; XIAO-FENG QIAN; WEI WANG; XIAO-BING CHEN

2007-01-01

179

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

180

Effects of K doping on structural and superconducting properties of Bi1.5Pb0.5Sr1.8CaCu2O8+? compounds  

NASA Astrophysics Data System (ADS)

Two kinds of potassium doped Bi(Pb)2212 samples are used to investigate the effect of doping the Bi(Pb)2212 ((Bi,Pb)2Sr2CaCu2O8) 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 Bi1.5Pb0.5(Sr1.8-xKx)CaCu2O8+d and Bi1.5Pb0.5Sr1.8CaCu2O8+dKx (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.

2013-12-01

181

First principles studies on the structural, elastic, electronic properties and heats of formation of MgeAE (AE Ca, Sr, Ba) intermetallics  

E-print Network

of states of eight MgeAE (AE ¼ Ca, Sr, Ba) intermetallic compounds. The ob- tained results indicate ¼ Ca, Sr, Ba) systems intermetallic compounds have generated significant interests over the past fewe9] for the eight Mg intermetallic compounds. Moreover, investigations focused on the elastic

Melnik, Roderick

182

New high-pressure Sr-Ca-Cu-O compounds and their superconducting properties  

SciTech Connect

It is shown for (Sr, Ca)[sub 1[minus]y]CuO[sub 2.00+z] (nominal composition) superconductors fabricated under a high pressure of 5 GPa and at 930[degrees]C that, as z increases, the Meissner fraction increases from a few percent to 20% and then starts to decrease. In the X-ray powder diffraction pattern for the sample with the maximum Meissner fraction, it is obvious that the [open quotes]infinite layer[close quotes] structure has been decomposed and a new structure becomes the major phase. It appears that the new structure is the [open quotes]0223[close quotes] structure which consists of rock-salt and the [open quotes]infinite-layer[close quotes] type blocks. This material is likely to be a new superconducting cuprate. 17 refs., 4 figs.

Adachi, Seiji; Yamauchi, H.; Tanaka, Shoji (Superconductivity Research Lab., Tokyo (Japan)); Mori, Nobuo (Univ. of Tokyo (Japan))

1994-02-01

183

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 canunder optimized conditionsbe 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

184

Magnetoresistance in polymer-assisted deposited Sr- and Ca-doped lanthanum manganite films  

NASA Astrophysics Data System (ADS)

We have grown epitaxial films of La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) on single crystalline LaAlO3 substrates by a cost effective polymer-assisted deposition technique. Film crystallinity, microstructure, resistivity, magnetization, and magnetoresistance (MR) were highly dependent on the annealing temperature in the film processing. High negative MR values of -50% (at 305K) and -88% (at 250K) were observed at magnetic field of 5T, for high temperature annealed LSMO and LCMO films, respectively. These results are comparable to those for films grown by pulsed laser deposition and rf sputtering techniques.

Jain, M.; Li, Y.; Hundley, M. F.; Hawley, M.; Maiorov, B.; Campbell, I. H.; Civale, L.; Jia, Q. X.; Shukla, P.; Burrell, A. K.; McCleskey, T. M.

2006-06-01

185

Eliashberg analysis of Bi2Sr2CaCu2O8+? intrinsic tunneling spectra  

NASA Astrophysics Data System (ADS)

Tunneling spectra of Bi2Sr2CaCu2O8+? intrinsic Josephson junctions with different doping are analyzed and reproduced using a d-wave Eliashberg formalism in a wide temperature range below Tc , from which the pairing glue spectral function ?2 F (?) composed of a low-energy resonance peak and a high-energy broad spectrum is obtained. As temperature increases toward Tc , the resonance peak shows continuous decrease both in energy and in height while the broad spectrum slightly increases in height. The calculated coupling constant demonstrates an important role for pairing by the broad spectrum that originates from spin fluctuations. The gap function extracted from the analysis bears a close resemblance to the recent Hubbard and t-J model simulations. We discuss the limitations of the d-wave Eliashberg approach used in our analysis.

Sui, Xiao-Hong; Tang, H.; Zhao, S. P.; Su, Zhao-Bin

2015-04-01

186

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

187

Coupling of exocytosis to depolarization in rat pancreatic islet ?-cells: effects of Ca 2+ , Sr 2+ and Ba 2+ -containing extracellular solutions  

Microsoft Academic Search

Using rat -cells we present evidence that Sr2+ and Ba2+, like Ca2+, support depolarization-induced increases in membrane capacitance which reflect insulin granule exocytosis. Even with identical total charge entry, Sr2+ and Ba2+ are 35 and 20-fold less effective than Ca2+ in supporting release. While exocytosis supported by Sr2+ is graded with cation entry and complete within 250ms of depolarization, exocytosis

David W. Barnett

1995-01-01

188

Occurrence of a strontium hexaferrite field in the CaOSrOFe 2O 3 system  

NASA Astrophysics Data System (ADS)

The phase relations at 1100?C in the system CaO Fe 2O 37 SrO Fe 2O 3Fe 2o 3 were determined by X-ray diffraction analysis and microscopical observation of polished sections of air quenched specimens. In particular, the boundaries of a homogeneous strontium hexaferrite field were determined by metallographic methods.

Lucchini, E.; Slokar, G.

1980-07-01

189

STM Studies of Near-Optimal Doped Bi_2Sr_2CaCu_2O_8 delta  

SciTech Connect

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

Kapitulnik, Aharon

2010-04-05

190

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

PubMed

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

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

2014-04-16

191

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

SciTech Connect

For the nominal composition of Bi(2.27-x)Pb(x)Sr2Ca2Cu3O(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, S.; Majewski, P.; Aldinger, F.

1995-04-01

192

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

193

Effects of Ca and Sr chemical doping on the average superconducting kinetic energy of YBa2Cu3O7-?  

NASA Astrophysics Data System (ADS)

In this brief communication we applied the MZFC(T) and MFCC(T) reversible dc magnetizations to get the average superconducting kinetic energy density, kS(T,B) of YBa2Cu3O7-?, Y0.95Ca0.05Ba2Cu3O7-? and YBa1.75Sr0.25Cu3O7-? ceramic samples with the aim of study the effects of Ca and Sr doping on the kS(T,B). The MZFC(T) and MFCC(T) measurements were performed with a SQUID magnetometer from quantum design to dc magnetic fields up to 50kOe. The determination of the kS(T,B) from reversible dc magnetization is supported by virial theorem of superconductivity [kS(T,B) = MB]. The kS(T,B) results show an common temperature profile for all the samples which is smoothly affected by the magnetic field. On the other hand the kS(T,B) results to T > Tc could not be associated to the pseudogap phenomenon. The Ca doping affects more effectively the kS(T,B) behaviour then Sr doping. A possible explanation to this feature could be associated to the fact that the hole doping promoted by Ca doping depress more considerably the superconducting state and enhances the granular character of the YBa2Cu3O7-? superconductor than the chemical pressure effect promoted by Sr doping.

Vieira, V. N.; Mendona, A. P. A.; Dias, F. T.; Hneda, M. L.; Pureur, P.; Schaf, J.; Mesquita, F.

2015-03-01

194

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

195

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

196

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

SciTech Connect

Ten compounds belonging to the series of oxygen-deficient perovskite oxides Ca2Fe2 xMnxO5 and CaSrFe2 xMnxO5+y, where x = 1/2, 2/3, and 1 and y 0 0.5, were synthesized and investigated with respect to the ordering of oxygen vacancies on both local and long-range length scales and the effect on crystal structure and magnetic properties. For the set with y 0 the oxygen vacancies always order in the long-range sense to form the brownmillerite structure containing alternating layers of octahedrally and tetrahedrally coordinated cations. However, there is a change in symmetry from Pnma to Icmm upon substitution of Sr for one Ca for all x, indicating local Td chain (vacancy) disorder. In the special case of CaSrFeMnO5 the neutron diffraction peaks broaden, indicating only short-range structural order on a length scale of 160 . This reveals a systematic progression from Ca2FeMnO5 (Pnma, well-ordered tetrahedral chains) to CaSrFeMnO5 (Icmm, disordered tetrahedral chains, overall short-range order) to Sr2FeMnO5 (Pm3m, destruction of tetrahedral chains in a long-range sense). Systematic changes occur in the magnetic properties as well. While long-range antiferromagnetic order is preserved, the magnetic transition temperature, Tc, decreases for the same x when Sr substitutes for one Ca. A review of the changes in Tc for the series Ca2Fe2 xMxO5, taking into account the tetrahedral/octahedral site preferences for the various M3+ ions, leads to a partial understanding of the origin of magnetic order in these materials in terms of a layered antiferromagnetic model. While in all cases the preferred magnetic moment direction is (010) at low temperatures, there is a cross over for x = 0.5 to (100) with increasing temperature for both the Ca2Fe2 xMnxO5 and the CaSrFe2 xMnxO5 series. For the y > 0 phases, while a brownmillerite ordering of oxygen vacancies is preserved for the Ca2 phases, a disordered Pm3m cubic perovskite structure is always found when Sr is substituted for one Ca. Long-range magnetic order is also lost, giving way to spin glass or cluster-glass-like behavior below 50 K. For the x = 0.5 phase, neutron pair distribution function (NPDF) studies show a local structure related to brownmillerite ordering of oxygen vacancies. Neutron diffraction data at 3.8 K show a broad magnetic feature, incommensurate with any multiple of the chemical lattice, and with a correlation length (magnetic domain) of 6.7(4) .

Ramezanipour, Farshid [McMaster University; Greedan, John E [McMaster University; Cranswick, Lachlan M.D. [Canadian Neutron Beam Centre, National Research Council, Chalk River Laboratorie; Donaberger, R. L. [National Research Council of Canada; Garlea, Vasile O [ORNL; Siewenie, Joan [Los Alamos National Laboratory (LANL)

2012-01-01

197

SP-SR interneurones: a novel class of neurones of the CA2 region of the hippocampus.  

PubMed

The CA2 region of the hippocampus has distinctive properties and inputs and may be linked with the pathology of specific psychiatric and neurological disorders. It is, therefore, important to understand CA2 circuitry and its involvement in the circuitry of the hippocampus. Properties of CA2 basket cells have been reported. However, other classes of CA2 interneurones with cell bodies located in stratum pyramidale remained to be described. In this study, the unusual axonal arbors of a novel subclass of dendrite-preferring CA2 interneurones whose somata are located in the pyramidal cell layer was revealed following intracellular recordings and biocytin labeling. One to four apical dendrites emerged from the soma, branched in stratum radiatum (SR) forming a tuft, but rarely penetrated stratum lacunosum-moleculare (SLM). One or two basal dendrites branched close to the soma, the branches extended through stratum oriens (SO) and often reached the alveus. Unlike CA2 bistratified cells, the axons of these cells arborized almost exclusively in SR with few, if any, branches extending to stratum pyramidale (SP), SO, or SLM. These interneurones again, unlike bistratified cells, were immunonegative for parvalbumin and cholecystokinin. Electrophysiologically, they were similar to some CA2 basket and bistratified cells in that they presented a "sag" in response to hyperpolarizing current injections and displayed spike frequency adaptation. They targeted the apical dendrites of neighboring CA2 pyramidal cells and received inputs from them. PMID:22431345

Mercer, Audrey; Botcher, Nicola A; Eastlake, Karen; Thomson, Alex M

2012-08-01

198

Transition metal substituted SrTiO3 perovskite oxides as promising functional materials for oxygen sensor  

NASA Astrophysics Data System (ADS)

Modern industries employ several gases as process fluids. Leakage of these gases in the operating area could lead to undesirable consequences. Even in chemical industries, which use large quantities of inert gases in confined areas, accidental leakage of these process gases would result in the reduction of oxygen partial pressure in atmospheric air. For instance, large amounts of gaseous nitrogen and argon are used in pharmaceutical industries, gas filling/bottling plants, operating area of Fast Breeder reactors, etc. Fall of concentration of oxygen in air below 17% could lead to life risk (Asphyxiation) of the working personnel that has to be checked well in advance. Further, when the leaking gas is of explosive nature, its damage potential would be very high if its concentration level in air increases beyond its lower explosive limit. Surveillance of the ambient within these industries at the critical areas and also in the environment around them for oxygen therefore becomes highly essential. Sensitive and selective gas sensors made of advanced materials are required to meet this demand of monitoring environmental pollution. The perovskite class of oxides (ABO3) is chemically stable even at high temperatures and can tolerate large levels of dopants without phase transformations. The electronic properties of this parent functional material can be tailored by adding appropriate dopants that exhibit different valence states. Aliovalent transition metal substituted SrTiO3 perovskites are good mixed ionic and electronic conductors and potential candidates for sensing oxygen at percentage level exploiting their oxygen pressure dependent electrical conductivity. This paper presents the preparation, study of electrical conductivity and oxygen-sensing characteristics of iron and cobalt substituted SrTiO3.

Misra, Sunasira

2012-07-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

200

High oxygen pressure single crystal growth of highly Ca-doped spin ladder compound Sr 14- xCa xCu 24O 41 ( x>12)  

NASA Astrophysics Data System (ADS)

Large size high-quality Ca-doped Sr 14- xCa xCu 24O 41 ( x=12.2, 12.6 and 13) spin ladder superconducting single crystals were grown using a modified mirror floating zone furnace with oxygen pressure up to 35 bar. The qualities of the as-grown single crystals were confirmed by polarized optical microscopy, neutron diffraction and X-ray diffraction methods. The sample compositions and homogeneity were measured using micro-X-ray fluorescence spectroscopy. The lattice parameters of each sample have been refined using the Rietveld method. The oxygen stoichiometry measurements which were performed by hydrogen reduction/thermogravimetry method show that all the three samples are slightly oxygen deficient even though high oxygen pressure was applied during growth. The high oxygen pressure is indispensible for growing highly Ca-doped Sr 14- xCa xCu 24O 41 single crystals. The susceptibility was measured along c-axis for all three compositions, fitting well with the one dimensional dimer model, consistent with the reported values of undoped Sr 14Cu 24O 41 parent compounds.

Deng, Guochu; Radheep, D. Mohan; Thiyagarajan, R.; Pomjakushina, Ekaterina; Wang, Shuang; Nikseresht, Neda; Arumugam, S.; Conder, Kazimierz

2011-07-01

201

Superconducting Bi-Sr-Ca-Cu-O films prepared by DC magnetron sputtering on new polycrystalline substrates  

Microsoft Academic Search

Superconducting thin films of Bi-Sr-Ca-Cu-O have been deposited for the first time onto several new stabilized binary oxide solid solution systems:MgO:CaO, MgO: ZrO2, ZrO2:Y2O3, and ZrO2:CaO. The films were grown at substrate temperatures of up to 750 degrees C. Immediately after deposition on polished substrates the films were crystalline and had quite a low room temperature resistivity; they developed superconductivity

M. R. Namin; B. H. Blott

1991-01-01

202

Effects of Mn substitution on the thermoelectric properties of the electron-doped perovskite Sr1-xLaxTiO3  

NASA Astrophysics Data System (ADS)

We have tried to improve the n-type thermoelectric properties of the electron- doped Perovskite Sr1-xLaxTiO3 by a Mn substitution. The 1 ~ 2 % Mn substitution enhances the Seebeck coefficient (S) and reduces the thermal conductivity (?) by about 50 % at room temperature (RT) without largely increasing the resistivity for the 5 % electron-doped SrTiO3. Consequently, the power factor at RT keeps a large value comparable to that of Bi2Te3 and the dimensionless figure-of-merits at RT increases twofold by the slight Mn substitution. Such a large reduction of ? at RT is perhaps due to the effect of Jahn-Teller active Mn3+ ions, around which dynamical local lattice distortion may occur.

Okuda, T.; Hata, H.; Eto, T.; Nishina, K.; Kuwahara, H.; Nakamura, M.; Kajimoto, R.

2014-12-01

203

Structure and magnetism of rare-earth-substituted Ca{sub 3}Co{sub 2}O{sub 6}  

SciTech Connect

Yttrium- and rare-earth-substituted derivatives of Ca{sub 3-} {sub v}R{sub v} Co{sub 2}O{sub 6} (R =Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu) have been synthesized and structurally characterized by powder X-ray and neutron diffraction. All phases adopt the K{sub 4}CdCl{sub 6}-type structure with space group R3-barc), in which the trivalent R {sup 3+} substituents randomly occupy the Ca{sup 2+} site. The homogeneity range of Ca{sub 3-} {sub v}R{sub v} Co{sub 2}O{sub 6} extends to v{approx}0.90 for the substituents concerned. A significant increase in the Co2-O distances within the trigonal-prismatic Co2O{sub 6} co-ordination polyhedra upon introduction of R {sup 3+} confirms that extra electrons from the R {sup 3+}-for-Ca{sup 2+} substitution exclusively enter the Co2 site of the quasi-one-dimensional Ca{sub 3-} {sub v}R{sub v} Co{sub 2}O{sub 6} structure, thereby formally reducing its oxidation state. This is furthermore supported by magnetic susceptibility and low-temperature neutron diffraction measurements. The long-range ferrimagnetic ordering temperature is reduced upon R substitution and appears to vanish for v>{approx}0.30. - Graphical abstract: Yttrium- and rare-earth-substituted derivatives of Ca{sub 3-} {sub v}R{sub v} Co{sub 2}O{sub 6} have been synthesized. A significant increase in the Co2-O distances within the trigonal-prismatic Co{sub 2}O{sub 6} coordination polyhedra confirms that extra electrons from the R {sup 3+}-for-Ca{sup 2+} substitution enter the Co2 site, thereby formally reducing its valence state. The long-range ferrimagnetic ordering of the parent Ca{sub 3}Co{sub 2}O{sub 6} phase vanishes at v>{approx}0.30 in Ca{sub 3-} {sub v}R{sub v} Co{sub 2}O{sub 6}.

Hervoches, Charles H. [Institute for Energy Technology, P.O. Box 40, N-2027 Kjeller (Norway)], E-mail: Charles.Hervoches@ife.no; Fjellvag, Helmer [Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); Kjekshus, Arne [Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); Fredenborg, Vivian Miksch [Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo (Norway); Hauback, Bjorn C. [Institute for Energy Technology, P.O. Box 40, N-2027 Kjeller (Norway)

2007-02-15

204

First principles calculations of hyperfine parameters on the Ca manganite with substitutional Cd-modeling of a PAC experiment  

NASA Astrophysics Data System (ADS)

The APW+lo (augmented plane waves+local orbitals) method of density functional theory, as implemented in the Wien2k code, is applied to calculate the electric field gradient of manganites. We report the first principles calculations on CaMnO3, and modeling of a perturbed angular correlation experiment with implanted Cd111m isotope. To model the experiment we additionally calculate in CaCdxMnO3, where we substitute Cd at the Ca site. Increasing Cd dilution is done with the use of supercells. We find that the experimental CaMnO3 low-temperature value Vzz?610-21 V/m2 is reproduced, when optimizing internal parameters. The analysis of the EFG tensor at the Ca atoms, with different electric field gradients at inequivalent positions, reveals that the convergence of the calculations is obtained.

Gonalves, J. N.; Haas, H.; Lopes, A. M. L.; Amaral, V. S.; Correia, J. G.

2010-05-01

205

Dielectric and Nonohmic Properties of CaCu3Ti4O12/SrTiO3 Ceramics  

NASA Astrophysics Data System (ADS)

In this work, (1 - x)CaCu3Ti4O12- xSrTiO3 [(1 - x)CCTO/ xST, x = 0% to 2%] ceramic samples were prepared by the solid-state reaction method. The dielectric and electrical properties of CaCu3Ti4O12 (CCTO) and CaCu3Ti4O12/SrTiO3 (CCTO/ST) ceramics were investigated. The results show that a small amount of Sr2+ can enter the lattice of CCTO. The mean grain size of the ceramic samples increased greatly for x = 0.5% and then decreased for x = 0.75% to 2%. ST addition and Sr2+ preferential occupancy in CCTO grains should be responsible for the change of the microstructure. Interestingly, the dielectric constant ( ?) of the 0.5% ST-added sample increased significantly while the dielectric loss (tan ?) remained low. With further increase of the ST content, the ? and tan ? values of the CCTO ceramics decreased monotonically while the nonlinear current-voltage properties were significantly enhanced. The change in the potential barrier height is thought to be the main cause for the opposite behaviors in the dielectric properties and nonohmic characteristics.

Xue, Renzhong; Liu, Dewei; Chen, Zhenping; Dai, Haiyang; Chen, Jing; Zhao, Gaoyang

2015-04-01

206

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

PubMed

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

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

2012-03-12

207

The deposition of strontium-substituted hydroxyapatite coatings.  

PubMed

Strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interest recently as strontium (Sr) has been shown to have the dual benefit of promoting bone formation and reducing bone resorption, in vivo. In this work, SrHA coatings were deposited onto polycrystalline titanium surfaces using radio frequency (RF) magnetron co-sputtering and compared to those deposited from HA alone. In particular, the influence of different levels of Sr-substitution of the sputtering targets (5 and 13% Sr-substituted HA targets) on the properties of the deposited coatings produced at a low discharge power level (150W) were investigated using FTIR, XPS, XRD, ToFSIMS and AFM techniques (both before and after annealing at 500C). The results show that Sr could be successfully incorporated into the HA lattice to form SrHA coatings and that they contained no other impurities. However, the coating produced from the 13% Sr-substituted target had a higher Ca+Sr/P ratio (1.950.14) and Sr content when compared to the coating produced from the 5% Sr-substituted target (1.580.20). The deposition rate also decreased with increasing Sr content of the sputtering targets. Furthermore, as the Sr content of the coatings increased, so did the preferred 002 orientation of the coating along with increased surface roughness and heterogeneity of the surface features. Therefore, this study has shown that RF magnetron sputtering offers a means to control attendant properties of Sr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surface topography. PMID:25631262

Boyd, Adrian R; Rutledge, L; Randolph, L D; Mutreja, I; Meenan, B J

2015-02-01

208

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

209

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 Amde 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?) (0.65C), 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 0.6C is observed in the twentieth century coral Sr/Ca-SST record.

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

2007-12-01

210

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

PubMed Central

Tumor necrosis factor alpha (TNF?) and its receptor TNFR1 play a central role in the development of colitis-associated colon cancer. To understand a role for the extracellular calcium-sensing receptor (CaSR) and its non-canonical Wnt mediators, Wnt5a/Ror2, we used reductionistic systems. We added lipopolysaccharide (LPS) to mouse peritoneal macrophages, RAW264.7 cells, a murine macrophage cell line, and 18Co colonic myofibroblasts, to stimulate TNF? secretion and then activated endogenous CaSR. CaSR activation inhibited TNF? secretion, which in RAW264.7 cells knockdown of CaSR by short-interfering RNA (siRNA) duplex reversed. LPS-stimulated NF?B promoter activity in RAW264.7 cells was inhibited by CaSR activation with Ca2+ or other polyvalent CaSR agonists. Reducing CaSR expression with siRNA duplex prevented this inhibition. Following LPS addition to CaSRHEK cells or RAW264.7 macrophages, CaSR stimulation deneddylated Cullin1. Wnt5a added to HT-29 cells which overexpressed Ror2 or T84 monolayers treated with 3?mM Ca2+ reduced TNFR1 protein expression ?70%. TNF?/INF? addition to high resistance T84 monolayers reduced transepithelial resistance 50% within 4?h. CaSR activation (3?mM Ca2+) together with rhWnt5a (200?ng/ml) prevented this reduction while Wnt3a addition had no effect. LPS-stimulated TNF? secretion from RAW264.7 cells was not effected by rhWnt5a but increased 10-fold by Wnt3a. Together our results suggest that following LPS challenge, CaSR activation will inhibit NF?B activity and reduce TNF? secretion from macrophages and stroma while Wnt5a/Ror2 engagement on intestinal epithelia reduces TNFR1 expression, allowing TNF? signaling to be titrated. Our results also suggest that canonical Wnt signaling may enhance TLR4 stimulation of TNF? secretion from murine macrophages. PMID:21603229

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

2010-01-01

211

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 AePtCd systems. Cubic Ca6Pt8Cd16 (Fm-3m, Z = 4, a = 13.513(1) ) 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 , c ? 4.47 ) 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 PtCd and PdSb 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, CaCd versus ErPd.

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

2013-02-18

212

Cluster chemistry in electron-poor Ae-Pt-Cd systems (Ae = Ca, Sr, Ba): (Sr,Ba)Pt2Cd4, Ca6Pt8Cd16, and its known antitype Er6Pd16Sb8.  

PubMed

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) ) 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 , c ? 4.47 ) 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. PMID:23418724

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

2013-03-01

213

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

214

Measurement of the mass attenuation coefficients and electron densities for BiPbSrCaCuO superconductor at different energies  

Microsoft Academic Search

The mass attenuation coefficients for Bi, Pb, Sr, Ca, Cu metals, Bi2O3, PbO, SrCO3, CaO, CuO compounds and solid-state forms of Bi1.7Pb0.3Sr2Ca2Cu3O10 superconductor were determined at 57.5, 65.2, 77.1, 87.3, 94.6, 122 and 136keV energies. The samples were irradiated using a 57Co point source emitted 122 and 136keV ?-ray energies. The X-ray energies were obtained using secondary targets such as

U. evik; H. Baltas

2007-01-01

215

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

Microsoft Academic Search

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

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

1991-01-01

216

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

PubMed

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

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

2012-01-01

217

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

USGS Publications Warehouse

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 150180 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.

2013-01-01

218

Optical properties of superconducting Bi2Sr2CaCu2O8  

NASA Astrophysics Data System (ADS)

A fundamental optical study was performed on superconducting Bi2Sr2CaCu2O8 by using a high-accuracy universal polarimeter (HAUP). As this crystal is strongly linearly dichroic, we developed the extended HAUP theory which includes the treatments of the optical dichroisms. After having determined the optical nature of the crystal, we applied the extended HAUP method to a thin (001) plate specimen with light traveling to the front and rear directions in the specimen. These two experiments permitted us to separate the reciprocal and nonreciprocal optical effects. No sign of the nonreciprocal effects was found in the HAUP transmission experiment. A gyration tensor component g33 takes place suddenly at Tc (90 K), increases with decreasing temperature, and reaches 1.8710-4 (36/mm of rotatory power) at 15 K. A steep change of birefringence ?n with temperature also occurs below Tc. From the behaviors of g33 and ?n with temperature, it can be concluded that the crystal undergoes a second-order phase transition at Tc into an optically active class. The crystal manifests large linear dichroism, i.e., ?m=-2.210-2.

Kobayashi, J.; Asahi, T.; Sakurai, M.; Takahashi, M.; Okubo, K.; Enomoto, Y.

1996-05-01

219

Evidence of rainfall variations in Southern Brazil from trace element ratios (Mg/Ca and Sr/Ca) in a  

E-print Network

precipitation in the vadose zone of the cave system is the main factor affecting the incorporation of Mg and Sr, especially ice volume buildup in the northern hemisphere, played an important role for monsoon rainfall inten

Massachusetts at Amherst, University of

220

Sr/Ca and Mg/Ca Heterogeneity Across Individual Foram Tests as Revealed by Ion Microprobe Analysis  

NASA Astrophysics Data System (ADS)

Many benthic foraminifera live for >= 1 year and the chemistry of individual tests may preserve information on seawater temperature changes over this time. Microanalysis of individual tests is complicated by the combination of thin test walls and the presence of surface contaminants, not held within the carbonate structure. We optimised conditions for the analysis of Mg and Sr in the benthic foraminifera Ammonia batavus, by ion microprobe. The use of field and contrast apertures restricted the size of the analysed area to ~10 ?m and reduced the effects of sample contamination. Sr concentrations were unaffected by any contamination encountered and Mg could be determined provided checks were made for silicate contamination using Al, Si and K intensities. Measured Mg and Sr concentrations were in reasonable agreement with previously reported values. Mn was present at a level too low to permit clean analysis, even at very low levels of contamination. Significant variations in Sr concentrations occurred within individual test chambers and may reflect the juxtapositioning of calcite of different ages as the test is deposited. Significant variations in Mg and Sr concentrations occurred between test chambers. Sr increased in concentration in the outermost (most recently deposited) parts of the test. This may reflect an increase in test calcification rate coincident with increases in bottom water temperature or food availability. The development of this method provides a valuable tool for investigating geochemical variations across individual foraminifera tests.

Austin, W. E.; Allison, N.

2002-12-01

221

In situ, rf plasma deposition of Bi2Sr2Ca2Cu3Ox thin films at atmospheric pressure  

NASA Astrophysics Data System (ADS)

Superconducting Bi2Sr2Ca2Cu3Ox thin films have been prepared in situ at atmospheric pressure by an inductively coupled, argon-oxygen rf plasma. This high Tc phase has been achieved by exposing the grown film, in situ, to the same argon-oxygen plasma used for the deposition of the film. No post-annealing steps are required. Bi2Sr2Ca2Cu3Ox films with critical temperatures of 100 K and critical current densities of 1105 A/cm2 at 77 K and zero field have been obtained at a deposition rate of 100-200 /min. The films are mirror smooth with very few particulates and pinholes. Control of the substrate heater temperature is critical as high-quality films grow only in a narrow temperature range. The effect of plasma treatment and substrate heater temperature is discussed.

Shah, A.; Patel, S.; Narumi, E.; Shaw, D. T.

1993-05-01

222

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

223

Orientation Control of (Sr,Ca)2NaNb5O15 Ceramics by Spin-Forming-Extended Method  

NASA Astrophysics Data System (ADS)

Using a spin-forming-extended method, which is one of the template grain growth methods, one-directional grain-orientation control was performed in (Sr,Ca)2NaNb5O15 (SCNN) ceramics. Rod like templates were prepared by the one-step flux method using the mixed salts of KCl and NaCl. In order to obtain the SCNN templates with a high aspect ratio, the two-step flux method in which Sr0.95Ca0.05Nb2O6 powder is utilized as the precursor was also examined. From these templates, the rectangular samples with c-axis orientation in the thickness direction were fabricated. The textured samples with an orientation factor of 0.9 and a remnant polarization of 7.4 C/cm2 were obtained using the resulting templates from the two-step flux method.

Ishii, Keisuke; Hashizume, Emi; Tashiro, Shinjiro

2012-09-01

224

Electron-phonon superconductivity in APt3P (A=Sr, Ca, La) compounds: From weak to strong coupling  

NASA Astrophysics Data System (ADS)

We study the newly discovered Pt phosphides APt3P (A=Sr, Ca, La) [T. Takayama , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.237001 108, 237001 (2012)] using first-principles calculations and Migdal-Eliashberg theory. Given the remarkable agreement with the experiment, we exclude the charge-density wave scenario proposed by previous first-principles calculations, and give conclusive answers concerning the superconducting state in these materials. The pairing increases from La to Ca and Sr due to changes in the electron-phonon matrix elements and low-frequency phonons. Although we find that all three compounds are well described by conventional s-wave superconductivity and spin-orbit coupling of Pt plays a marginal role, we show that it could be possible to tune the structure from centrosymmetric to noncentrosymmetric opening new perspectives towards the understanding of unconventional superconductivity.

Subedi, Alaska; Ortenzi, Luciano; Boeri, Lilia

2013-04-01

225

Epitaxial thin films of ATiO(3-x)H(x) (A = Ba, Sr, Ca) with metallic conductivity.  

PubMed

Epitaxial thin films of titanium perovskite oxyhydride ATiO(3-x)H(x) (A = Ba, Sr, Ca) were prepared by CaH(2) reduction of epitaxial ATiO(3) thin films deposited on a (LaAlO(3))(0.3)(SrAl(0.5)Ta(0.5)O(3))(0.7) substrate. Secondary ion mass spectroscopy detected a substantial amount and uniform distribution of hydride within the film. SrTiO(3)/LSAT thin film hydridized at 530 C for 1 day had hydride concentration of 4.0 10(21) atoms/cm(3) (i.e., SrTiO(2.75)H(0.25)). The electric resistivity of all the ATiO(3-x)H(x) films exhibited metallic (positive) temperature dependence, as opposed to negative as in BaTiO(3-x)H(x) powder, revealing that ATiO(3-x)H(x) are intrinsically metallic, with high conductivity of 10(2)-10(4) S/cm. Treatment with D(2) gas results in hydride/deuteride exchange of the films; these films should be valuable in further studies on hydride diffusion kinetics. Combined with the materials' inherent high electronic conductivity, new mixed electron/hydride ion conductors may also be possible. PMID:22563869

Yajima, Takeshi; Kitada, Atsushi; Kobayashi, Yoji; Sakaguchi, Tatsunori; Bouilly, Guillaume; Kasahara, Shigeru; Terashima, Takahito; Takano, Mikio; Kageyama, Hiroshi

2012-05-30

226

Interaction between endoplasmic/sarcoplasmic reticulum stress (ER/SR stress), mitochondrial signaling and Ca2+ regulation in airway smooth muscle (ASM)1  

PubMed Central

Airway inflammation is a key aspect of diseases such as asthma. Several inflammatory cytokines (e.g., TNF? and IL-13) increase cytosolic Ca2+ ([Ca2+]cyt) responses to agonist stimulation and Ca2+ sensitivity of force generation, thereby enhancing airway smooth muscle (ASM) contractility (hyper-reactive state). Inflammation also induces ASM proliferation and remodeling (synthetic state). In normal ASM, the transient elevation of [Ca2+]cyt induced by agonists leads to a transient increase in mitochondrial Ca2+ ([Ca2+]mito) that may be important in matching ATP production with ATP consumption. In human ASM (hASM) exposed to TNF? and IL-13, the transient increase in [Ca2+]mito is blunted despite enhanced [Ca2+]cyt responses. We also found that TNF? and IL-13 induce reactive oxidant species (ROS) formation and endoplasmic/sarcoplasmic reticulum (ER/SR) stress (unfolded protein response) in hASM. ER/SR stress in hASM is associated with disruption of mitochondrial coupling with the ER/SR membrane, which relates to reduced mitofusin 2 (Mfn2) expression. Thus, in hASM it appears that TNF? and IL-13 result in ROS formation leading to ER/SR stress, reduced Mfn2 expression, disruption of mitochondrionER/SR coupling, decreased mitochondrial Ca2+ buffering, mitochondrial fragmentation, and increased cell proliferation. PMID:25506723

Delmotte, Philippe; Sieck, Gary C.

2015-01-01

227

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

228

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

229

Investigation of possible half-metallic antiferromagnets on double perovskites LaABB'O6 (A=Ca,Sr,Ba; B,B'=transition elements)  

NASA Astrophysics Data System (ADS)

We thoroughly investigated all the possible (C229=406) candidates of half-metallic (HM) antiferromagnet (AFM) with the structure LaSrBB'O6, where BB' pairs are any combination of two 3d, 4d, and 5d transition elements. Sr was also replaced by Ca or Ba whenever HM-AFM was found and similar calculation was performed in order to probe more possibilities. We have found that LaAWXO6, where A =Ca,Sr,Ba and X =Tc,Re are potential candidates of HM-AFM. Among those HM-AFM candidates, LaAWReO6 (A =Sr,Ba) are rather robust than others for the structural optimization. Including previous Wang and Guo's work in 2006 and this work, we believe that we have found all possible HM-AFM candidates for double perovskites structure LaABB'O6 (A =Ca,Sr,Ba and B ,B'=transition elements).

Chen, S. H.; Xiao, Z. R.; Liu, Y. P.; Wang, Y. K.

2010-11-01

230

Standard enthalpies of formation of Sr 2CuO 3 and Ca 2CuO 3  

Microsoft Academic Search

The enthalpies of reactions between alkaline-earth cuprates M2CuO3 (M=Ca, Sr) and hydrochloric acid were measured in a hermetic swinging calorimeter at 298.15K. The M2CuO3 samples were prepared by solid-phase synthesis from calcium or strontium carbonate and copper oxide and characterized by X-ray powder diffraction, EDX and wet analysis. The standard enthalpies of formation obtained for the cuprates, ?14314kJmol?1 for Ca2CuO3

A. S. Monayenkova; A. A. Popova; L. A. Tiphlova; Y. V. Gorushkina; A. V. Tsoi; I. P. Romanova; V. A. Alyoshin

2005-01-01

231

A tetragonal to orthorhombic phase transition in Bi 2Sr 2CaCu 2O x  

Microsoft Academic Search

Bi2Sr2CaCu2Ox superconductor was studied in situ by high temperature X-ray diffraction, differential scanning calorimetry (DSC), and thermogravimetry (TG). It is discovered that there is a tetragonal to orthorhombic phase transition at about 600C in the sample. Careful high temperature X-ray diffraction and thermal analysis reveal that the phase transition in a sample with a higher value of Tc (89 K)

H. Zhang; Q. R. Feng; Y. Zhao; F. Ritter; W. Sun; T. Frieling; W. Assmus

1995-01-01

232

Geological note: Authigenic Sr?Ba?Ca carbonate minerals in coals of the Hunter Valley, New South Wales  

Microsoft Academic Search

Strontianite (SrCO3), witherite (BaCO3) and alstonite (CaBa[CO3]2) were among the range of epigenetic coal cleat\\/fracture carbonates identified within the Wittingham Coal Measures, Jerrys Plains Subgroup in the Hunter Valley. Three stages of diagenetic cement development, all related to basin evolution, are postulated. Material for the development of the various carbonates was derived from: basinal pore fluids, surrounding rock and organic

P. J. Tarabbia

1994-01-01

233

Mechanical Properties of Textured Bi 2 Sr 2 CaCu 2 O 8+d High-Temperature Superconductors  

Microsoft Academic Search

The mechanical properties of Bi2Sr2CaCu2O8+d fibers pro- duced via laser-induced directional solidification at differ- ent growth rates were determined through longitudinal and transverse tension tests, as well as flexure tests. In addition, polished sections of as-received fibers and the fracture sur- faces of the broken samples were examined using scanning electron microscopy to elucidate the relationship between the microstructure and

Jose Ygnacio Pastor; Pedro Poza; Javier LLorca

1999-01-01

234

Magnetic relaxation in the 110 K superconducting phase in Bi-Sr-Ca-Cu-O thin films  

NASA Technical Reports Server (NTRS)

We have investigated the time dependence of remnant moment decay in a highly oriented, nearly single high T(sub c) phase Bi-Sr-Ca-Cu-O thin film. A strictly logarithmic time dependence was observed over a 20 K temperature range for observation intervals of 2000 seconds. The normalized decay rate exhibits a peak around 14 K and has a relatively weak magnetic field dependence. These data are then compared with existing data on the YBCO and Eu-based superconductors.

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

1991-01-01

235

A new single crystal growth method of (Bi,Pb) 2Sr 2CaCu 2O z superconductor  

Microsoft Academic Search

A new method was developed to elaborate (Bi,Pb)2Sr2CaCu2Ox (Pb-2212) single crystals. The new process makes use of a progressive increase of the oxygen chemical potential in gaseous phase at a constant temperature 875C below the incongruent melting temperature (T=884C) of the Pb-2212. The composition of this crystal is homogeneous and very close to the stoichiometric composition. Structure characterization of a

M. Mansori; H Faqir; P Satre; A Bendriss; Y Syono; A Sebaoun

1999-01-01

236

Study of Crystal Structure and Physical Properties of the Compound Bi-Pb-Sr-Ca-Ba-Cu-O  

Microsoft Academic Search

With the aid of transmission electron microscopy, the phenomenon of additional superstructure along bar {b} direction was observed for a sample of Bi1.7Pb0.3Sr2Ca1.8Ba0.2Cu3Oy, and two kinds of modulation mode along b axis was found to coexist in this sample. The images of SEM showed that the addition of Ba ions improved the property of two-dimensional growth. The results of XRD

Mao Zhiqiang; Huang Sunli; Wang Yu; Cheng Zhaojia; Yang Li; Fan Chenggao; Zhou Guien; Zhang Yuheng

1991-01-01

237

Thermodynamic Properties of CaNdAlO 4 -SrNdAlO 4 Solid Solutions  

Microsoft Academic Search

The structural and thermodynamic properties of CaNdAlO4-SrNdAlO4 solid solutions are studied at 1673 K by x-ray diffraction and high-temperature calorimetry. The lattice parameters and unit-cell volume of the solid solutions are shown to vary linearly with composition. The measured heats of solid solution are used to evaluate the enthalpies of formation from the constituent oxides and constituent elements and the

L. N. Komissarova; M. A. Ryumin; G. Ya. Pushkina; G. V. Zimina; A. V. Novoselov; A. Pajaczkowska; M. A. Borik; A. L. Ilinskii

2005-01-01

238

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

239

Electronic band structures and photovoltaic properties of MWO{sub 4} (M=Zn, Mg, Ca, Sr) compounds  

SciTech Connect

Divalent metal tungstates, MWO{sub 4}, with wolframite (M=Zn and Mg) and scheelite (M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO{sub 4} and MgWO{sub 4}) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO{sub 4} and SrWO{sub 4}), which was attributed to their enhanced electron transfer resulting from their appropriate band positions. - Graphical abstract: The electronic band structures of divalent metal tungstates are described from the combination of experimental results and theoretical calculations, and their electronic structure-dependent photovoltaic performances are also studied. Highlights: > MWO{sub 4} compounds with wolframite (M=Zn and Mg) and scheelite structure (M=Ca and Sr) were prepared. > Their electronic band structures were investigated by the calculations and the measurements. > Their photovoltaic properties were determined by the crystal and electronic structures.

Kim, Dong Wook, E-mail: dong0414@snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Cho, In-Sun [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 (United States); Shin, Seong Sik [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Lee, Sangwook [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Noh, Tae Hoon; Kim, Dong Hoe [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Jung, Hyun Suk [School of Advanced Materials Engineering, Kookmin University, Seoul 136-702 (Korea, Republic of); Hong, Kug Sun, E-mail: kshongss@plaza.snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of)

2011-08-15

240

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

241

Migratory life history of European eel Anguilla anguilla from freshwater regions of the River Asi, southern Turkey and their high otolith Sr:Ca ratios.  

PubMed

Otolith Sr:Ca ratios from 32 of 34 European eel Anguilla anguilla collected from three freshwater sites in the River Asi, southern Turkey, indicated that they were resident in fresh water without apparent exposure to salt water since the elver stage. The Sr:Ca ratio criterion indicative of residence in fresh water was more than twice that of values from other European countries. Otolith Sr:Ca ratios of A. anguilla from fresh waters can vary among regions, possibly reflecting regional-specific water chemistry. Hence, the use of Sr:Ca ratios determined in one region to interpret results from a different region might lead to misclassification of migratory life-history types. PMID:21366578

Lin, Y-J; Yalin-zdilek, S; Iizuka, Y; Gm?, A; Tzeng, W-N

2011-03-01

242

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

USGS Publications Warehouse

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

Takesue, R.K.; VanGeen, A.

2004-01-01

243

Synthesis and crystal structure of nanocrystalline phase: Ca 1- xM xZr 4P 6O 24 (M = Sr, Ba and x = 0.0-1.0)  

NASA Astrophysics Data System (ADS)

The structure of strontium and barium substituted nano crystalline calcium zirconium phosphate (CZP) was determined on the basis of crystal data of solid solutions. It was found that upto 2.42 mol % of strontium and 1.62 mol % of barium could be loaded into CZP formulations without significant changes of the three-dimensional framework structure. The crystal chemistry of Ca 1- xM xZr 4P 6O 24 (M = Sr, Ba and x = 0.0-1.0) phases has been investigated using General Structure Analysis System (GSAS) programming. The Sr and Ba substituted CZP phases crystallize in the space group R-3 and Z = 6. Powder diffraction data have been subjected to Rietveld refinement to arrive at a satisfactory structural convergence of R-factors. The unit cell volume and polyhedral (ZrO 6 and PO 4) distortion increases with rise in the size and mole % of loaded cation in the CZP matrix. The PO 4 stretching and bending vibrations in the Infra red (IR) region have been assigned. SEM, TEM and EDAX analysis provide evidence of Sr and Ba in the matrix.

Rashmi, Chourasia; Shrivastava, O. P.

2011-02-01

244

Color point tuning for (Sr,Ca,Ba)Si2O2N2:Eu2+ for white light LEDs  

Microsoft Academic Search

Color point tuning is an important challenge for improving white light LEDs. In this paper, the\\u000apossibilities of color tuning with the efficient LED phosphor Sr1-x-y-zCaxBaySi2O2N2:Euz\\u000a2+ (0 e x, y e\\u000a1; 0.005 e z e 0.16) are investigated. The emission color can be tuned in two ways: by changing Eu2+\\u000aconcentration and by substitution of the host lattice

Volker Bachmann; R. C Ronda; A. Meijerink; O. Oeckler; W. Schnick

2009-01-01

245

Growth and characterization of (Bi, Pb)2Sr2Ca2Cu3Ox single Shaoyan Chu and Michael E. McHenry  

E-print Network

grown using a fused-salt reaction of Bi2O3, PbO, SrCl2, CaCl2, CuCl, and KNO3 in a KCl flux solutions,3 a novel fused-salt reaction procedure was de- veloped to grow BSCCO superconductors. High-purity single crystals of Bi-2201 or Bi-2212 were prepared by the reaction of Bi2O3, SrCl2, CaCl2, and Cu

McHenry, Michael E.

246

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.

Jeff Tepper

247

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

248

Voltage clamp methods for the study of membrane currents and SR Ca2+ release in adult skeletal muscle fibres  

PubMed Central

Skeletal muscle excitation-contraction (E-C)1 coupling is a process composed of multiple sequential stages, by which an action potential triggers sarcoplasmic reticulum (SR)2 Ca2+ release and subsequent contractile activation. The various steps in the E-C coupling process in skeletal muscle can be studied using different techniques. The simultaneous recordings of sarcolemmal electrical signals and the accompanying elevation in myoplasmic Ca2+, due to depolarization-initiated SR Ca2+ release in skeletal muscle fibres, have been useful to obtain a better understanding of muscle function. In studying the origin and mechanism of voltage dependency of E-C coupling a variety of different techniques have been used to control the voltage in adult skeletal fibres. Pioneering work in muscles isolated from amphibians or crustaceans used microelectrodes or high resistance gap techniques to manipulate the voltage in the muscle fibres. The development of the patch clamp technique and its variant, the whole-cell clamp configuration that facilitates the manipulation of the intracellular environment, allowed the use of the voltage clamp techniques in different cell types, including skeletal muscle fibres. The aim of this article is to present an historical perspective of the voltage clamp methods used to study skeletal muscle E-C coupling as well as to describe the current status of using the whole-cell patch clamp technique in studies in which the electrical and Ca2+ signalling properties of mouse skeletal muscle membranes are being investigated. PMID:22306655

Hernndez-Ochoa, Erick O.; Schneider, Martin F.

2012-01-01

249

Thermochemical behavior and transport properties of Pr-substituted SrTiO3 as potential solid oxide fuel cell anode  

NASA Astrophysics Data System (ADS)

Phase composition, structural stability, electrical properties, thermochemical expansion and redox behavior of Pr-substituted SrTiO3 were assessed for potential application in solid oxide fuel cell anodes. XRD analysis confirms formation of single-phase perovskite-like Sr1-xPrxTiO3? and Sr1-1.5xPrxTiO3? (x=0.02-0.30) ceramics under both oxidizing and reducing conditions, although microstructural studies indicate minor precipitation of TiO2 in reduced Sr-deficient ceramics with high Pr content. XPS analysis in combination with XRD suggests that Pr cations substitute into strontium sublattice in mixed 4+/3+ oxidation state and are essentially insoluble in titanium sublattice. Reduction at elevated temperatures results in 2-3 orders of magnitude increase of n-type electronic conductivity with respect to oxidized materials. Thermogravimetric and electrical studies demonstrate however very slow reduction kinetics at temperatures below 1273K associated with nearly frozen equilibrium in cation sublattice and low oxygen vacancy concentration in oxidized materials. Electrical behavior is discussed in conjunction with defect chemistry of donor-doped strontium titanate. All oxidized and reduced materials exhibit moderate thermal expansion coefficients, compatible with that of common solid electrolytes, and a small contribution of chemical expansion on reduction.

Yaremchenko, A. A.; Patrcio, S. G.; Frade, J. R.

2014-01-01

250

Processing for both high-{Tc} and high-J{sub c} (Tl,Pb,Bi)(Sr,Ba){sub 2}Ca{sub 2}Cu{sub 3}O{sub 9} superconducting tapes  

SciTech Connect

The authors have found an efficient and highly reproducible method for the preparation of the homogeneous Tl-1223 powders by the partial substitution of Ba{sup 2+} into the Sr{sup 2+} sites in the (Tl{sub 0.6}Pb{sub 0.2}Bi{sub 0.2})(Sr{sub 2{minus}x}Ba{sub x})Ca{sub 2}Cu{sub 3}O{sub 9} system. Superconducting tapes (sheathed in silver) based on the titled system have been fabricated by using the powder-in-tube (PIT) method. Typical critical temperatures ({Tc}) of around 120 K and transport critical current densities (J{sub c}) of about 1.05 {times} 10{sup 4} A/cm{sup 2} at 77 K in a zero magnetic field have been routinely obtained on short lengths ({approximately}3 cm) of the sintered Tl-1223 tapes after rolling. Moreover, a prototype superconducting (Tl,Pb,Bi)(Sr,Ba){sub 2}Ca{sub 2}Cu3O{sub 9} magnet (with three pancake coils, each containing four 3 m lengths of rolled tapes) generated field of 240 G at 77 K was obtained.

Liu, R.S.; Wu, S.F.; Tai, C.H.; Shy, D.S. [Industrial Technology Research Inst., Hsinchu (Taiwan, Province of China). Materials Research Labs.

1994-12-31

251

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

252

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

253

Electrical transport and superconductivity in the Al 2O 3-Bi 2Sr 1.8Ca 1.2Cu 2O y and MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y composites  

NASA Astrophysics Data System (ADS)

We have measured the resistivities ? of Al 2O 3-Bi 2Sr 1.8Ca 1.2Cu 2O y and MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y composites with the nominal Bi 2Sr 1.8Ca 1.2Cu 2O y volume fraction, ? 2212, ranging from 0.15 to 1.00. For the Al 2O 3-Bi 2Sr 1.8Ca 1.2Cu 2O y composites, we find for the samples with ? 2212?0.6 that the superconducting transition temperature, Tc, is not disturbed by the addition of Al 2O 3. For ? 2212<0.3, no zero-resistivity state is observed. For the MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y composites, Tc is barely disturbed for the samples with ? 2212?0.7. No superconducting state is observed for the samples with ? 2212<0.35. The variation of ?(300 K) with ? 2212 indicates a three-dimensional percolating Bi-Sr-Ca-Cu-O matrix occurring at ? 2212?0.19 and ?0.15 in Al 2O 3-Bi 2Sr 1.8Ca 1.2 Cu 2O y and MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y, respectively. Both resistivity and magnetization measurements suggest that the reactions of Bi 2Sr 1.8Ca 1.2Cu 2O y with MgO are weaker than with Al 2O 3.

Lin, J. J.; Lin, W. Y.; Tsui, R. F.

1993-06-01

254

Doping dependence of the O 1{ital s} core-level photoemission in Bi-Sr-Ca-Cu-O superconductors  

SciTech Connect

The O 1{ital s} core level of three different Bi-Sr-Ca-Cu-O superconductors has been studied by means of high-resolution x-ray-photoelectron spectroscopy (XPS) and x-ray-absorption spectroscopy (XAS). The O 1{ital s} XPS spectra could be decomposed into three components that were unambiguously assigned to the emission from the three different oxide layers in the crystal structure. These are, in order of increasing binding energy, Cu-O{sub 2}, Sr-O, and Bi-O. Furthermore, the component assigned to the Cu-O{sub 2} layers exhibits a shift which depends on the hole doping as monitored by the XAS spectra. {copyright} {ital 1996 The American Physical Society.}

Qvarford, M. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden)] [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden); Soederholm, S. [Materials Physics, Department of Physics, Royal Institute of Technology, S-100 44 Stockholm (Sweden)] [Materials Physics, Department of Physics, Royal Institute of Technology, S-100 44 Stockholm (Sweden); Chiaia, G.; Nyholm, R.; Andersen, J.N.; Lindau, I. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden)] [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund (Sweden); Karlsson, U.O. [Materials Physics, Department of Physics, Royal Institute of Technology, S-100 44 Stockholm (Sweden)] [Materials Physics, Department of Physics, Royal Institute of Technology, S-100 44 Stockholm (Sweden); Leonyuk, L. [Department of Geology, Moscow State University, 119 899 Moscow (Russia)] [Department of Geology, Moscow State University, 119 899 Moscow (Russia); Nilsson, A.; Martensson, N. [Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala (Sweden)] [Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala (Sweden)

1996-06-01

255

Phase and microstructure evolution in the process of the composite Bi-2212-(Sr, Ca)3 Al2 O6 glass-ceramics formation  

NASA Astrophysics Data System (ADS)

Devitrification of glass with a cation ratio corresponding to the composition {Bi2.1Sr2CaCu2Ox+0.4Sr1.7Ca1.3Al2O6} was studied. At temperatures below 600 C, the phases crystallized in the order Bi-2201, Cu2O, CaO, (Sr,Ca)3Bi2O6, while Al ions concentrated in the remaining glass. Above 600 C, Bi-2212 and (Sr,Ca)3Al2O6 formed simultaneously, so that at 750 C, the two-phase composite Bi-2212-(Sr,Ca)3Al2O6 was obtained that contained grains of the aluminate phase 0.03-0.3 m in size. The Al-rich phase surplus increased the stability of the glass and accelerated Bi-2212 phase formation, while development of superconductivity in Bi-2212 was slowed down. It was shown that composite glass-ceramics with bulk superconductivity could be obtained at temperatures above 850 C.

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

1999-08-01

256

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 (SiO2P2O5CaONa2O) with 0100% 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 37C 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 compositionstructureproperty 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

257

The series Bi2Sr2Ca(n-1) Cu(n)O(2n+4) (1 less than or equal to n less than or equal to 5): Phase stability and superconducting properties  

NASA Technical Reports Server (NTRS)

Phase relations at 850 and 870 C, melting transitions in air, oxygen, and helium were studied for Bi(2.1)Sr(1.9) CuO6 and for the Bi2Sr2Ca(n-1) Cu(n)O(2n+4) for n = 1, 2, 3, 4, 5, and infinity (CaCuO2). Up to 870 C, the n = 2 composition resides in the compatibility tetrahedron bounded by Bi(2+x)(Sr,Ca)(3-y) Cu2O8, (Sr,Ca)14 Cu24O41, Ca2CuO3, and a Bi-Sr-Ca-O phase. The n is greater than or equal to 3 compositions reside in the compatibility tetrahedron Bi(2+x)(Sr,Ca)(3-y) Cu2O8 - (Sr,Ca)14 Cu24O41 - Ca2CuO3 - CuO up to 850 C. However, Bi(2+x)Sr(4-y) Cu3O10 forms for n is greater than or equal to 3 after extended heating at 870 C. Bi(2+x)Sr(2-y) CuO6 and Bi(2+x)(Sr,Ca)(3-y) Cu2O8 melt in air at 914 C and 895 C respectively. During melting, all of the compositions studied lose 1 to 2 percent by weight of oxygen from the reduction of copper. Bi(2+x)Sr(2-y) CuO6, Bi(2+n)(Sr,Ca)(3-y) Cu2O8, and Bi(2+x)(Sr,Ca)(4-y) Cu3O10 exhibit crystallographic alignment in a magnetic field, with the c-axes orienting parallel to the field.

Deguire, Mark R.; Bansal, Narottam P.; Farrell, David E.; Finan, Valerie; Kim, Cheol J.; Hills, Bethanie J.; Allen, Christopher J.

1989-01-01

258

Electronic structure, chemical bonding, and solid-state NMR spectroscopy of the digallides of Ca, Sr, and Ba.  

PubMed

Combined application of (69,71)Ga NMR spectroscopy and quantum mechanical calculations reveals the chemical bonding in the digallides of Ca, Sr, and Ba. An analysis of the electron localization function (ELF) shows honeycomb-like 6(3) nets of the Ga atoms as the most prominent structural features in SrGa(2) and BaGa(2). For CaGa(2) a description of a 3+1-coordinated Ga atom is revealed by the ELF and by an analysis of interatomic distances. The NMR spectroscopic signal shift is mainly due to the Knight shift and is almost equal for the investigated digallides, whereas the anisotropy of the signal shift decreases with the radius of the alkaline-earth metals. Calculated and observed values of the electric field gradient (EFG) are in good agreement for CaGa(2) and BaGa(2) but differ by about 21 % for SrGa(2) indicating structural instability. Better agreement is achieved by considering a puckering of the Ga layers. For BaGa(2) an instability of the structure is indicated by a peak in the density of states at the Fermi level, which is shifted to lower energies when taking puckering of the Ga layers into account. Both structural modifications are confirmed by crystallographic information. The Fermi velocity of the electrons is strongly anisotropic and is largest in the (001) plane of the crystal structure. This results in an alignment of the crystallites with the [001] axis perpendicular to the magnetic field as observed in (69,71)Ga NMR spectroscopy and magnetic susceptibility experiments. The electron transport is predominantly mediated by the Ga-Ga p(x)- and p(y)-like electrons in the (001) plane. The specific heat capacity of BaGa(2) was determined and indicated the absence of phase transitions between 1.8 and 320 K. PMID:19123208

Haarmann, Frank; Koch, Katrin; Grner, Daniel; Schnelle, Walter; Pecher, Oliver; Cardoso-Gil, Raul; Borrmann, Horst; Rosner, Helge; Grin, Yuri

2009-01-01

259

Structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba)  

NASA Astrophysics Data System (ADS)

The structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba) in the cubic (B1, B2 and B3) phases and in the wurtzite (B4) phase are investigated using density functional theory calculations as implemented in VASP code. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are computed. The calculated lattice parameters are in good agreement with the experimental and the other available theoretical results. Electronic structure reveals that all the five alkaline earth metal oxides exhibit semiconducting behavior at zero pressure. The estimated band gaps for the stable wurtzite phase of BeO is 7.2 eV and for the stable cubic NaCl phases of MgO, CaO, SrO and BaO are 4.436 eV, 4.166 eV, 4.013 eV, and 2.274 eV respectively. A pressure induced structural phase transition occurs from wurtzite (B4) to NaCl (B1) phase in BeO at 112.1 GPa and from NaCl (B1) to CsCl (B2) phase in MgO at 514.9 GPa, in CaO at 61.3 GPa, in SrO at 42 GPa and in BaO at 14.5 GPa. The elastic constants are computed at zero and elevated pressures for the B4 and B1 phases for BeO and for the B1 and B2 phases in the case of the other oxides in order to investigate their mechanical stability, anisotropy and hardness. The sound velocities and the Debye temperatures are calculated for all the oxides using the computed elastic constants.

Cinthia, A. Jemmy; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Iyakutti, K.

2015-04-01

260

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

261

Photoluminescence property of A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] phosphors.  

PubMed

A new efficient phosphor, A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] has been synthesized by the solid-state method at high temperature. X-ray diffraction analysis confirmed the formation of the compound. Photoluminescence excitation measurements show that the phosphor can be efficiently excited by near-ultraviolet light from 300 nm to 400 nm to realize emission covering the 397-647 nm region of visible spectrum. Therefore, newly synthesized novel phosphor may be useful as green-emitting phosphor in solid-state lighting. PMID:22961920

Singh, Roshani; Dhoble, S J

2013-01-01

262

Fabrication and physical properties of DC SQUIDs using Bi(Pb)SrCaCuO thin films  

NASA Astrophysics Data System (ADS)

The fabrication and physical properties of DC SQUIDs using Bi(Pb)SrCaCuO thin films are reported. The total Josephson critical current of DC SQUIDs with different microbridge widths (0.5-12?m) ranges from 8 ?A to 5 mA. The observed quantum interference pattern under an applied magnetic filed is largely deformed and a discussion based on the multiple interference effect is given. The measured voltage modulation depth is found to be smaller than the calculated value. The Josephson critical current exhibits a (1- T/ Trmc) n dependence on temperature where n=1-2.5.

Wen, Zhongmin; Iguchi, Ienari

1990-06-01

263

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

264

Phenomenological approach to the superconducting gap of Bi 2Sr 2CaCu 2O 8+ ?  

NASA Astrophysics Data System (ADS)

A self-consistent gap equation is modified for purely two-dimensional d symmetry singlet Cooper-pairs, and numerically solved by introducing a phenomenological pair interaction potential. It is found that the calculations including the pair interaction potential well reproduce the temperature dependence of the normalized superconducting gap of Bi 2Sr 2CaCu 2O 8+ ? and showed that the present calculations are consistent with the condition of the free energy minimum. It is pointed out that the attractive pair interaction potential introduced here may be related to the spin-exchange interaction on a spin singlet state.

Kitamura, Michihide; Irie, Akinobu; Oya, Gin-ichiro

2005-07-01

265

Structural, electrical, dielectric and magnetic properties of Gd-Sn substituted Sr-hexaferrite synthesized by sol-gel combustion method  

NASA Astrophysics Data System (ADS)

The effect of Gd-Sn substitution on the structural, electrical and magnetic properties of Sr1-xGdx Fe12-ySny O19 (where x=0.00, 0.025, 0.05, 0.075, 0.1) and (y=0.00, 0.25, 0.5, 0.75, 1) prepared by the sol-gel combustion method has been investigated. The XRD analysis shows the presence of Fe2O3 phase at higher substitution. The average crystallite size obtained lies between 19-42 nm which is beneficial in obtaining suitable signal-to-noise ratio in high density recording media. The FTIR spectra of annealed samples of SrFe12O19, Sr0.95Gd0.05 Fe11.5Sn0.5O19 show that strontium hexaferrite nanoparticles have been synthesized successfully. DC electrical resistivity shows metal-to-semiconductor transition with temperature. The value of transition temperature increases with dopant content. Room temperature dc resistivity and energy of activation decreases while drift mobility increases on increasing the dopant concentration. The magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) decreases with increasing the dopant concentration.

Ashiq, Muhammad Naeem; Shakoor, Sajeela; Najam-ul-Haq, Muhammad; Warsi, Muhammad Farooq; Ali, Irshad; Shakir, Imran

2015-01-01

266

Electronic study of Al substituted La0.7Ca0.3MnO3 using photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

Polycrystalline samples of La0.7Ca0.3Mn1-XAlXO3 (X=0, 0.05, 0.15) are prepared using solid state reaction route. Photoemission spectroscopy measurements were performed on these samples to investigate their electronic properties. Al shows 3+ oxidation state in both Al doped samples while no effect of Al doping is found on the core level spectrum of La 4d and Ca 2p orbitals and they were found in 3+ and 2+ oxidation state respectively in all the samples . Mn 2p core level photoemission measurements indicates that for 5% Al doped sample (lower doping) Al ions replaces the Mn3+ ions while they substitute Mn4+ in 15 % Al doped sample ((higher doping).

Phase, D. M.; Kumar, Manish; Wadikar, A. D.; Choudhary, R. J.

2014-04-01

267

Substitution of H- for O- and H- emissions of 12CaO7Al2O3  

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

268

Synthesis, structure and chemical bonding of CaFe{sub 2?x}Rh{sub x}Si{sub 2} (x=0, 1.32, and 2) and SrCo{sub 2}Si{sub 2}  

SciTech Connect

The finding of superconductivity in Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2} put the attention on the investigation of compounds that crystallize with ThCr{sub 2}Si{sub 2} structure type such as AT{sub 2}X{sub 2} (A=alkali/alkaline earth/rare earth element; T=transition metal and X=element of the 1315th group). In this context the silicides CaFe{sub 2}Si{sub 2}, CaFe{sub 0.68(6)}Rh{sub 1.32(6)}Si{sub 2}, CaRh{sub 2}Si{sub 2} and SrCo{sub 2}Si{sub 2} have been synthesized by reaction of the elements under an argon atmosphere. Single crystals were obtained by special heat treatment in welded niobium/tantalum ampoules. The compounds were investigated by means of powder and single crystal X-ray diffraction. All compounds crystallize in the ThCr{sub 2}Si{sub 2}-type structure with space group I4/mmm (No. 139): a=3.939(1) , c=10.185(1) , R{sub 1}=0.045, 85 F{sup 2} values, 8 variable parameters for CaFe{sub 2}Si{sub 2}; a=4.0590(2) , c=9.9390(8) , R{sub 1}=0.030, 90 F{sup 2} values, 10 variable parameters for CaFe{sub 0.68(6)}Rh{sub 1.32(6)}Si{sub 2}; a=4.0695(1) , c=9.9841(3) , R{sub 1}=0.031, 114 F{sup 2} values, 9 variable parameters for CaRh{sub 2}Si{sub 2}; and a=3.974(1) , c=10.395(1) , R{sub 1}=0.036, 95 F{sup 2} values, 8 variable parameters for SrCo{sub 2}Si{sub 2}. The structure of SrCo{sub 2}Si{sub 2} contains isolated [Co{sub 2}Si{sub 2}]{sup 2?} 2D-layers in the ab-plane whereas in CaFe{sub 2?x}Rh{sub x}Si{sub 2} the [T{sub 2}Si{sub 2}] layers (T=Fe and Rh) are interconnected along the c-axis via Si3Si bonds resulting in a three-dimentional (3D) [T{sub 2}Si{sub 2}]{sup 2?} polyanions and therefore belong to the so-called collapsed form of the ThCr{sub 2}Si{sub 2}-type structure. The SrCo{sub 2}Si{sub 2} and CaRh{sub 2}Si{sub 2} are isoelectronic to the parent 122 ironpnictide superconductors AeFe{sub 2}As{sub 2} (Ae=alkaline earth elements), whereas CaFe{sub 2}Si{sub 2} is a full substituted variant (As/Si) of CaFe{sub 2}As{sub 2}. The crystal chemistry and chemical bonding in the title compounds are discussed in terms of LMTO band structure calculations and a topological analysis using the Electron Localization Function (ELF). - Graphical abstract: The SrCo{sub 2}Si{sub 2} and CaFe{sub 2?x}Rh{sub x}Si{sub 2} (x==0, 1.32, and 2) crystallize in the ThCr{sub 2}Si{sub 2}-type. The structure of SrCo{sub 2}Si{sub 2} contains isolated [Co{sub 2}Si{sub 2}]{sup 2?} layers in the ab-plane, whereas the [T{sub 2}Si{sub 2}] layers in CaFe{sub 2?x}Rh{sub x}Si{sub 2} are interconnected along the c-axis via Si3Si bonds resulting in a [T{sub 2}Si{sub 2}]{sup 2?} network. - Highlights: Synthesis and structure of ternary silicides SrCo{sub 2}Si{sub 2} and CaFe{sub 2?x}Rh{sub x}Si{sub 2} (x=0, 1.32, and 2). The SrCo{sub 2}Si{sub 2} and CaRh{sub 2}Si{sub 2} are isoelectronic to the parent 122 ironpnictide superconductors AeFe{sub 2}As{sub 2}. CaFe{sub 2}Si{sub 2} is a full substituted variant (As/Si) of superconductor CaFe{sub 2}As{sub 2}. The title compounds demonstrate the tunable Si3Si distances.

Hlukhyy, Viktor, E-mail: viktor.hlukhyy@lrz.tu-muenchen.de; Hoffmann, Andrea V.; Fssler, Thomas F.

2013-07-15

269

Reconstructing 20th Century SST 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 focused on coral conservation, analytical expense, and time constraints. Coral Sr/Ca reproducibility through the 20th century was investigated using three intra-colony and three inter-colony coral records, from the reefs offshore of the Amde Island, New Caledonia. The coral Sr/Ca signal is highly reproducible; the average absolute offset between coeval monthly Sr/Ca determinations between any two coral Sr/Ca time series is 0.036 mmol/mol (~0.65 C), which is <2x 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 (r = -0.95, -0.56, respectively, p < 0.05, n = 304) for the period 1967 to 1992 and monthly 1 gridded SST data product (r = -0.95, -0.53, respectively, p < 0.05, n = 1198) for the period 1900 to 1999. The coral Sr/Ca-SST reconstruction exhibits decadal-scale fluctuations that exceed those observed in the gridded SST time series, which may reflect true differences between the SST at a shallow reef site and those averaged over a 1-grid box or they may reflect inadequacies in the methodology used to create the gridded SST product when few observations are available. A warming trend of ~0.65 C is observed in the coral Sr/Ca-SST record, which is consistent with estimates of warming of the tropical surface oceans over the 20th century. Monthly coral Sr/Ca records and a seasonally resolved coral ?18O record from this site share variance in the later half of the 20th century, but not in the early 20th century, suggestive of a change in seawater ?18O. The 20th century trend in the coral ?18O record is consistent with a 20th century freshening of surface seawater at Amde.

Delong, K. L.; Quinn, T. M.; Taylor, F. W.

2006-12-01

270

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

271

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

272

Doping effect in layer structured SrBi2Nb2O9 ferroelectrics Yun Wu, Mike J. Forbess, Seana Seraji, Steven J. Limmer, Tammy P. Chou, Carolyn  

E-print Network

is Bi2Am 1BmOm 3 , where A Bi, Pb, Na, K, Sr, Ca, Ba, rare earths; B Ti, Nb, Ta, Fe, Mo, W, Cr; and m 1 SBN , ferroelectrics. Substitution in both the A site Sr2 by Ca2 and Ba2 and B site Nb5 by V5 up to 30 on the doping effect on the improvement of physical properties in BLSFs. Millan et al. reported the substitution

Cao, Guozhong

273

Electronic, magnetic and structural properties of A {sub 2}VMoO{sub 6} perovskites (A=Ca, Sr)  

SciTech Connect

The perovskites Sr{sub 2}VMoO{sub 6} and Ca{sub 2}VMoO{sub 6} have been synthesized by liquid-mix technique in citrate melts, and their electronic, magnetic and structural properties have been investigated. No signs of V/Mo ordering are seen by synchrotron X-ray powder diffraction, but despite the chemical disorder both oxides are highly conductive and Pauli paramagnetic. Electrical conductivities of these solid solutions are comparable or higher than those reported for polycrystalline AMoO{sub 3} end members. It is suggested that the delocalized metallic conductivity of these compounds with two different transition-metal atoms implies valence equilibrium between the degenerate oxidation-state couples V{sup 4+}Mo{sup 4+} and V{sup 3+}Mo{sup 5+}. - Graphical abstract: Unit cell of Ca(V{sub 0.5}Mo{sub 0.5})O{sub 3}.

Karen, P. [Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern N-0315, Oslo (Norway)]. E-mail: pavel.karen@kjemi.uio.no; Moodenbaugh, A.R. [Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973-5000 (United States); Goldberger, J. [Department of Chemistry, Ohio State University, 100 West 18th Avenue, Columbus, OH 43210-1185 (United States); Santhosh, P.N. [Department of Chemistry, Ohio State University, 100 West 18th Avenue, Columbus, OH 43210-1185 (United States); Woodward, P.M. [Department of Chemistry, Ohio State University, 100 West 18th Avenue, Columbus, OH 43210-1185 (United States)

2006-07-15

274

Tropical Atlantic SSTS at the Last Glacial Maximum derived from Sr/Ca ratios of fossil coral  

NASA Astrophysics Data System (ADS)

The sensitivity of the tropics to climate change is a particularly controversial issue in paleoclimatology. At the heart of this controversy are disagreements amongst different proxy datasets regarding the amplitude of glacial-interglacial changes in temperature, particularly at the sea surface. Data obtained from the aragonitic skeletons of massive reef corals have contributed in no small measure to the debate, yielding LGM and deglacial SSTs 5-6C cooler than today (Guilderson et al., 1994; McCulloch et al., 1999; Correge et al., 2004), that imply a high sensitivity of Earth's climate to changes in boundary conditions (Crowley, 2000). We used SIMS ion microprobe to analyze Sr/Ca ratios of small pieces of Montastrea coral retrieved from a Barbados drillcore (Guilderson et al., 2001). U/Th dates place the samples between 22 and 24 kyr BP. Localized areas of dissolution and re-growth of secondary (diagenetic) aragonite crystals were identified at centers of septa. Sr/Ca ratios of these crystals were higher than Sr/Ca ratios of original coral crystals preserved in adjacent fasciculi and yielded relatively cooler derived SSTs. The original coral crystals, recognized by their size and orientation, were selectively targeted for analysis using a 20 micron-diameter sample spot. Our calibration study using modern corals from Bermuda, St Croix (USVI) and Barbados indicates that Montastrea Sr/Ca is strongly correlated with SST and with annual extension (growth) rate (Saenger et al., 2006). Growth rate of the fossil corals was determined from measurement of daily growth bands identified in petrographic thin-sections. Application of a growth-dependent Sr/Ca-T calibration yielded Barbados SSTs that were, on average, 2.5C cooler than today during the LGM and ~1C cooler than today during Heinrich Event 2. Our LGM SSTs are consistent with the original CLIMAP estimates (CLIMAP, 1976) and with more recent Mg/Ca-based SSTs derived from calcitic foraminifera in the Caribbean (Schmidt et al., 2004). References: CLIMAP Project members (1976) The surface of the ice-age Earth, Science, 191(4232), 1131-1137. Correge T, Gagan MK, Beck JW, Burr GS, Cabioch G, Le Cornec F (2004) Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dryas event, Nature, (6986) 927-928 Crowley TJ (2000) CLIMAP SSTs re-revisited, Climate Dynamics, 16, 241-255 Guilderson TP, Fairbanks RG, Rubenstone JL (1994) Tropical temperature variations since 20,000 years ago: modulating interhemspheric climate change, Science, 263:663-665. Guilderson TP, Fairbanks RG, Rubenstone JL (2001) Tropical Atoantic coral oxygen isotopes: glacial- interglacial sea surface temperatures and climate change, Marine Geology, 172, 75-89 McCulloch MT, Tudhope AW, Esat TM, Mortimer GE, Chappell J, Pillans B, Chivas, AR, Omura A (1999) Coral record of equatorial sea-surface temperatures during the pen-ultimate deglaciation at Huon Peninsula, Science, 283, 202-204 Saenger CP, Cohen AL, Oppo D, Hubbard D (2006) Tropical North Atlantic Coral-Based Sea Surface Temperature and Salinity Reconstructions From the Little Ice Age and Early Holocene. Abstract, Fall AGU.

Cohen, A. L.; Saenger, C. P.

2006-12-01

275

The G Allele of CaSR R990G Polymorphism Increases Susceptibility to Urolithiasis and Hypercalciuria: Evidences from a Comprehensive Meta-Analysis  

PubMed Central

Background. The calcium-sensing receptor gene (CaSR) is a candidate to explain urolithiasis. A number of case-control studies were conducted to investigate associations between CaSR polymorphisms with risks of hypercalciuria and urolithiasis in humans. But the results were still inconsistent. Methods. A meta-analysis was performed to address this issue. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to estimate the strength of associations between CaSR polymorphisms and the risk of urolithiasis. The pooled standardized mean difference (SMD) with 95% CI was used for the meta-analysis of CaSR polymorphisms and urine calcium concentration. Results. For urolithiasis association, the SS genotype of A986S polymorphism was a risk factor for urolithiasis in Asians and PHPT patients, but a protective factor in Caucasians. The GG genotype of R990 polymorphism was associated with an increased risk of urolithiasis, especially in Caucasians and healthy population. Regarding urine calcium concentration association, individuals with the G allele had a higher level of urine calcium than the noncarriers. Conclusions. This meta-analysis revealed that the G allele of CaSR R990G polymorphism increases susceptibility to urolithiasis and hypercalciuria. The A986S and Q1011E polymorphisms were associated with urolithiasis and hypercalciuria in specific populations. PMID:25705702

Liu, Kang; Wang, Xiaolan; Ye, Jiaxin; Qin, Chao; Shao, Pengfei; Zhang, Wei; Li, Jie; Yin, Changjun

2015-01-01

276

Measurement of RyR permeability reveals a role of calsequestrin in termination of SR Ca2+ release in skeletal muscle  

PubMed Central

The mechanisms that terminate Ca2+ release from the sarcoplasmic reticulum are not fully understood. D4cpv-Casq1 (Sztretye et al. 2011. J. Gen. Physiol. doi:10.1085/jgp.201010591) was used in mouse skeletal muscle cells under voltage clamp to measure free Ca2+ concentration inside the sarcoplasmic reticulum (SR), [Ca2+]SR, simultaneously with that in the cytosol, [Ca2+]c, during the response to long-lasting depolarization of the plasma membrane. The ratio of Ca2+ release flux (derived from [Ca2+]c(t)) over the gradient that drives it (essentially equal to [Ca2+]SR) provided directly, for the first time, a dynamic measure of the permeability to Ca2+ of the releasing SR membrane. During maximal depolarization, flux rapidly rises to a peak and then decays. Before 0.5 s, [Ca2+]SR stabilized at ?35% of its resting level; depletion was therefore incomplete. By 0.4 s of depolarization, the measured permeability decayed to ?10% of maximum, indicating ryanodine receptor channel closure. Inactivation of the t tubule voltage sensor was immeasurably small by this time and thus not a significant factor in channel closure. In cells of mice null for Casq1, permeability did not decrease in the same way, indicating that calsequestrin (Casq) is essential in the mechanism of channel closure and termination of Ca2+ release. The absence of this mechanism explains why the total amount of calcium releasable by depolarization is not greatly reduced in Casq-null muscle (Royer et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.201010454). When the fast buffer BAPTA was introduced in the cytosol, release flux became more intense, and the SR emptied earlier. The consequent reduction in permeability accelerated as well, reaching comparable decay at earlier times but comparable levels of depletion. This observation indicates that [Ca2+]SR, sensed by Casq and transmitted to the channels presumably via connecting proteins, is determinant to cause the closure that terminates Ca2+ release. PMID:21788611

Sztretye, Monika; Yi, Jianxun; Figueroa, Lourdes; Zhou, Jingsong; Royer, Leandro; Allen, Paul; Brum, Gustavo; Ros, Eduardo

2011-01-01

277

Influence of tungsten substitution and oxygen deficiency on the thermoelectric properties of CaMnO3-?  

NASA Astrophysics Data System (ADS)

Polycrystalline tungsten-substituted CaMn1-xWxO3-? (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; Saucke, Gesine; Dbeli, Max; Shkabko, Andrey; Sagarna, Leyre; Karvonen, Lassi; Weidenkaff, Anke

2013-12-01

278

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, berlandstrasse 129, CH-8600 Dbendorf (Switzerland); Dbeli, Max [Ion Beam Physics, Schafmattstrasse 20, ETH Hnggerberg, Swiss Federal Institute of Technology, CH-8093 Zrich (Switzerland); Weidenkaff, Anke [Laboratory for Solid State Chemistry and Catalysis, Empa, Swiss Federal Laboratories for Materials Science and Technology, berlandstrasse 129, CH-8600 Dbendorf (Switzerland); Materials Chemistry, Institute for Materials Science, University of Stuttgart, Heisenbergstr. 3, DE-70569 Stuttgart (Germany)

2013-12-28

279

Crystal and chemical anisotropy effects in AE2ZnN2, (AE=Ca, Sr, Ba) from ab initio  

NASA Astrophysics Data System (ADS)

In the tetragonal ternary nitrides AE2ZnN2 (AE=Ca, Sr, Ba), Zn has a rare linear coordination with nitrogen (N-Zn-N) along the c axis and N is located in an AE5Zn-like octahedron. Such features lead to original anisotropic crystal and chemical bond effects addressed herein with DFT-GGA based methods accounting for the cohesive energies, the energy volume equations of state EOS, the elastic constants and the properties of chemical bonding. Along AE=Ca, Sr, Ba an increasing overall compressibility under hydrostatic pressure is inferred from the respective EOS's, but the elastic constants Cij exhibit highly anisotropic features with large magnitudes of C33 along the tetragonal c axis versus smaller C11=C22 along a, b. Decreasing C33-C11 along the title compounds signals decreasing anisotropy. The three ternaries are calculated as small gap insulators in agreement with experimental results of conductivity. The chemical bonding characterizes strong Zn-N bonds versus weaker AE-N thus reflecting the crystal anisotropy.

Matar, Samir F.; Etourneau, Jean; Ouaini, Nam

2015-01-01

280

Evidence for Local Moment Magnetism in Superconducting Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

We have used inelastic neutron scattering to measure the dynamic spin susceptibility in optimally-doped Bi2Sr2CaCu2O8+? (Tc = 91 K). Four crystals with a total mass of 19 g were measured on the MAPS spectrometer at ISIS for temperatures of 10 K and 100 K. We have been able to identify the magnetic excitations in the energy range 20-90 meV. The magnetic nature of the scattering has been confirmed with spin-polarization analysis on IN22 at the ILL. While we see temperature-dependent changes for energies around 40 meV that are consistent with earlier studies, we find that the Q-integrated signal shows a much weaker variation with temperature. The absolute magnetic cross section is quite comparable to that of spin fluctuations in stripe ordered La1.875Ba0.125CuO4. As the magnetism in the latter system has been shown to have a dominant contribution from local moments [1], we argue that the same must be true for Bi2Sr2CaCu2O8+?. [1] M. Huecker et al., Phys. Rev. B (accepted); cond-mat/0503417v3.

Tranquada, John; Xu, G. Y.; Gu, G. D.; Huecker, M.; Fauque, B.; Perring, T. G.; Stock, C.; Regnault, L.-P.

2009-03-01

281

Microwave Dielectric Properties of A2P2O7 (A = Ca, Sr, Ba; Mg, Zn, Mn)  

NASA Astrophysics Data System (ADS)

Microwave dielectric properties of A2P2O7 (A = Ca, Sr, Ba, Mn, Mg, Ba) ceramic materials were investigated by a network analyzer at the frequency of 10 GHz. It was found that A2P2O7 ceramics could be sintered at relatively lower temperature below 1150C, although the thortveitite type series, Mn2P2O7, ?-Mg2P2O7 and ?-Zn2P2O7 with smaller ionic radii of A cations were hard to sinter to full density. The dielectric constant of A2P2O7 is lower than 10. The Q f value increased according to the sequence of ?-Ba2P2O7, ?-Sr2P2O7 and ?-Ca2P2O7 in dichromatic type series, and the sequence of Mn2P2O7, ?-Mg2P2O7 and ?-Zn2P2O7 in thortveitite type series, respectively. The temperature coefficient of resonant frequency ?f for all samples exhibits negative value. Larger ?f for ?-Zn2P2O7, ?-Mg2P2O7 and ?-Ba2P2O7 is mainly due to their reversible phase transformations. The microwave dielectric properties were discussed from the point view of bond valence.

Bian, Jian-jiang; Kim, Dong-Wan; Hong, Kug Sun

2004-06-01

282

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

SciTech Connect

The thermal expansion behavior and mechanism of A-site-deficient lanthanum manganite perovskites, La{sub 1{minus}x}MnO{sub 3} (0 < x {le} 0.1), and alkaline earth metal (AE)-doped lanthanum manganite perovskites, La{sub 1{minus}x}AE{sub x}MnO{sub 3} (AE = Ca and Sr, 0 {le} x {le} 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 up to 20 mol % and with increasing Sr content up to 10 mol %, and then increased. During the thermal cycle measurement, the La{sub 1{minus}x}MnO{sub 3} (0 {le} x {le} 0.1) perovskite samples and the La{sub 1{minus}x}AE{sub x}MnO{sub 3} perovskites (0 {le} x {le} 0.3) shrank, while no anomalous shrinkage behavior was observed for the La{sub 0.6}AE{sub 0.4}MnO{sub 3} samples. From the results of high-temperature X-ray diffraction analysis, no dependency of cell volume of the perovskites on aging time at selected temperatures and on thermal cycles was observed.

Mori, Masashi; Hiei, Yoshiko; Sammes, N.M.; Tompsett, G.A.

2000-04-01

283

Structure, solvation, and dynamics of Mg?, Ca?, Sr?, and Ba? complexes with 3-hydroxyflavone and perchlorate anion in acetonitrile medium: a molecular dynamics simulation study.  

PubMed

Molecular dynamics simulations of complexes of Mg(2+), Ca(2+), Sr(2+), and Ba(2+) with 3-hydroxyflavone (flavonol, 3HF) and ClO?? in acetonitrile were performed. The united atoms force field model was proposed for the 3HF molecule using the results of DFT quantum chemical calculations. 3HF was interpreted as a rigid molecule with two internal degrees of freedom, i.e., rotation of the phenyl ring and of the OH group with respect to the chromone moiety. The interatomic radial distribution functions showed that interaction of the cations with flavonol occurs via the carbonyl group of 3HF and it is accompanied with substitution of one of the acetonitrile molecules in the cations' first solvation shells. Formation of the cation-3HF complexes does not have significant impact on the rotation of the phenyl ring with respect to the chromone moiety. However, the orientation of the flavonol's OH-group is more sensitive to the interaction with doubly charged cations. When complex with Mg(2+) is formed, the OH-group turns out of the plane of the chromone moiety that leads to rupture of intramolecular H-bond in the ligand molecule. Complexation of Ca(2+), Sr(2+), and BaClO?? with 3HF produces two structures with different OH-positions, as in the free flavonol with the intramolecular H-bond and as in the complex with Mg(2+) with disrupted H-bonding. It was shown that additional stabilization of the [MgClO4(3HF)](+) and [BaClO4(3HF)](+) complexes is determined by strong affinity of perchlorate anion to interact with flavonol via intracomplex hydrogen bond between an oxygen atom of the anion and the hydrogen atom of the 3-hydroxyl group. Noticeable difference in the values of the self-diffusion coefficients for Kt(2+) from one side and ClO??, 3HF, and AN in the cations' coordination shell from another side implies quite weak interaction between cation, anion, and ligands in the investigated complexes. PMID:24852544

Agieienko, Vira N; Kolesnik, Yaroslav V; Kalugin, Oleg N

2014-05-21

284

Thermal exposure effects on the in vitro degradation and mechanical properties of Mg-Sr and Mg-Ca-Sr biodegradable implant alloys and the role of the microstructure.  

PubMed

Magnesium is an attractive biodegradable material for medical applications due to its non-toxicity, low density and good mechanical properties. The fast degradation rate of magnesium can be tailored using alloy design. The combined addition of Sr and Ca results in a good combination of mechanical and corrosion properties; the alloy compositions with the best performance are Mg-0.5Sr and Mg-0.3Sr-0.3Ca. In this study, we investigated an important effect, namely thermal treatment (at 400 C), on alloy properties. The bio-corrosion of the alloys was analyzed via in vitro corrosion tests in simulated body fluid (SBF); the mechanical properties were studied through tensile, compression and three-point bending tests in two alloy conditions, as-cast and heat-treated. We showed that 8h of heat treatment increases the corrosion rate of Mg-0.5Sr very rapidly and decreases its mechanical strength. The same treatment does not significantly change the properties of Mg-0.3Sr-0.3Ca. An in-depth microstructural investigation via transmission electron microscopy, scanning electron microscopy, electron probe micro-analysis and X-ray diffraction elucidated the effects of the thermal exposure. Microstructural characterization revealed that Mg-0.3Sr-0.3Ca has a new intermetallic phase that is stable after 8h of thermal treatment. Longer thermal exposure (24h) leads to the dissolution of this phase and to its gradual transformation to the equilibrium phase Mg17Sr2, as well as to a loss of mechanical and corrosion properties. The ternary alloy shows better thermal stability than the binary alloy, but the manufacturing processes should aim to not exceed exposure to high temperatures (400 C) for prolonged periods (over 24 h). PMID:25491955

Bornapour, M; Celikin, M; Pekguleryuz, M

2015-01-01

285

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 (65N, 23W) and the Azores (38N, 26W) (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

286

The influence of heat-treatment on microstructure and magnetic properties of rare-earth substituted SrFe 12O 19  

Microsoft Academic Search

Rare-earth substituted strontium ferrite nanopowders SrFe12?xRxO19 (R=La, Gd and Er; x=0.2, 0.5 and 1) were prepared by solgel-autocombustion method and subsequent heat treatments. The results of X-ray diffraction measurements showed the M-type hexagonal structure. Magnetic properties, such as specific saturation magnetization Ms, specific remanent magnetization ?r and coercivity Hc, as well as microstructure depend on the heat-treatment conditions (temperature and

N. Rezlescu; C. Doroftei; E. Rezlescu; P. D. Popa

2008-01-01

287

Ca and 87/86 Sr isotopes as tracers of silicate weathering in small  

E-print Network

and Rb/Sr ratios from thosein the sediment up to the values observed in the soils. In the volcanic area@usgs.gov We present calciumstable isotope and strontium radiogenic isotope datafor soils and sediments developed on volcanic and igneousrocks forming small catchments in the Massif Central (France

Paris-Sud XI, Université de

288

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

289

Spin gap in the zigzag spin-1/2 chain cuprate Sr(0.9)Ca(0.1)CuO(2).  

PubMed

We report a comparative study of (63)Cu nuclear magnetic resonance spin lattice relaxation rates T(1)(-1) on undoped SrCuO(2) and Ca-doped Sr(0.9)Ca(0.1)CuO(2) spin chain compounds. A temperature independent T(1)(-1) is observed for SrCuO(2) as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T(1)(-1) for T<90 K in the Ca-doped sample evidencing the opening of a spin gap. The data analysis within the J(1)-J(2) Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J(2)-exchange coupling as a possible cause of the spin gap. PMID:21797568

Hammerath, F; Nishimoto, S; Grafe, H-J; Wolter, A U B; Kataev, V; Ribeiro, P; Hess, C; Drechsler, S-L; Bchner, B

2011-07-01

290

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

291

Low-temperature reduction of brownmillerite CaFeO2.5 in LaAlO3/CaFeO2.5 heterostructures made on SrTiO3.  

PubMed

When LaAlO3/CaFeO2.5 thin-film heterostructures made on SrTiO3 were annealed with CaH2 at low temperatures below 300 C, the brownmillerite CaFeO2.5 layer was reduced to CaFeO2 with an infinite-layer structure while both the LaAlO3 capping layer and the SrTiO3 substrate remained intact. The reduction behaviour strongly depends on the lattice matching of LaAlO3 to CaFeO2.5, suggesting that oxygen ions migrate through the coherently grown LaAlO3 layer of the heterostructure predominantly in the out-of-plane direction. The structural defects near the interface in the relaxed-structure LaAlO3 capping layer prevent the oxygen ions from migrating. PMID:25134664

Murakami, Noriaki; Kan, Daisuke; Ichikawa, Noriya; Shimakawa, Yuichi

2014-10-21

292

Crystal structure and magnetic properties of Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy  

SciTech Connect

Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A{sup 2+} results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe{sup 4+} ruled out by Mssbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi{sub 0.8}Ba{sub 0.2}FeO{sub 3} sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

Rangi, Manisha; Agarwal, Ashish, E-mail: aagju@yahoo.com; Sanghi, Sujata [Department of Applied Physics, Guru Jambheshwar University of Science and Technology, Hisar-125001 (Haryana) India (India); Singh, Ripandeep; Meena, S. S.; Das, A. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai-400 085 (India)

2014-08-15

293

Crystal structure and magnetic properties of Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy  

NASA Astrophysics Data System (ADS)

Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A2+ results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe4+ ruled out by Mssbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi0.8Ba0.2FeO3 sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

Rangi, Manisha; Agarwal, Ashish; Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.

2014-08-01

294

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 25C 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

295

Strontium in coral aragonite: 3. Sr coordination and geochemistry in relation to skeletal architecture  

NASA Astrophysics Data System (ADS)

Use of the coral Sr palaeothermometer assumes that the Sr in coral skeletons is substituted randomly for Ca in the aragonite structure. The presence of Sr in additional phases e.g., strontianite, or the non random distribution of Sr across metal sites in aragonite, would complicate the Sr/Ca-sea surface temperature relationship. We have used Sr K-edge microEXAFS (extended X-ray absorption fine structure) to determine the structural state of Sr across selected microvolumes of four coral skeletons ( Porites lobata, Acropora palmata, Pavona clavus, and Montastrea annularis). We used a 5 3 ?m beam to analyse specific areas of the coral skeletal architecture, i.e., centres of calcification, fasciculi, and dissepiments. All EXAFS analyses refine, within error, to an ideally substituted Sr in aragonite, and we found no evidence of strontianite or partly ordered structural states. Anisotropy in the first shell responses results from the fact that the analysed microvolumes are not necessarily averaged for the responses of all crystal orientations in the aragonite. Although secondary ion mass spectrometry confirmed that Sr/Ca composition can vary substantially between skeletal components, we find no evidence for any contrast in Sr structural state. Sr heterogeneity may result from kinetic effects, reflecting complex disequilibrium processes during crystal precipitation, or biological effects, resulting from variations in the composition of the calcifying fluid which are biologically mediated.

Allison, Nicola; Finch, Adrian A.; Newville, Matthew; Sutton, Stephen R.

2005-08-01

296

A high-resolution Sr/Ca and [delta][sup 18]O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Nino  

SciTech Connect

A high-resolution (near weekly) Sr/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period of 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the [delta][sup 18]O value of seawater. Using the Sr/Ca temperature calibration of De Villiers et al., the Sr/Ca records exhibit seasonally controlled cyclical SST (sea surface temperature) variations of from [approximately] 21 to [approximately] 28[degrees]C. During the very strong El Nino of 1982-1983, the Sr/CA systematics indicate a sharp drop in the winter SST to [approximately] 18.5[degrees]C. This represents a temperature anomaly of -3[degrees]C which is approximately twice that given by the [delta][sup 18]O variations, suggesting an [approximately] x2 amplification of the anomaly by the Sr/Ca system, possibly due to the increasing dominance of inorganically controlled aragonite-seawater fractionation. The oxygen isotope systematics show the combined effects of both temperature and changing seawater [delta][sup 18]O values, the latter reflecting the influx of [sup 18]O-depleted runoff during periods of high rainfall. Due to the extremely low ([approximately] 10[sup [minus]3]) Sr and Ca contents of river runoff relative to seawater, it is possible to use the Sr/Ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the [delta][sup 18]O value of seawater. Using this approach it is possible to quantitatively reproduce the volume of runoff from the Burdekin River during the periods of major flooding that occurred in early 1979 and 1981. The results of this study demonstrate that the combined use of high-resolution Sr/Ca and [delta][sup 18]O systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate.

McCulloch, M.T.; Gagan, M.K.; Mortimer, G.E.; Chivas, A.R. (Australian National Univ., Canberra (Australia)); Isdale, P.J. (Australian Institute of Marine Science, Queensland (Australia))

1994-06-01

297

Chemical bonding study in Ca substituted Y 2BaNiO 5 by analysis of charge density distribution  

NASA Astrophysics Data System (ADS)

Y 2BaNiO 5, along with its Ca-substituted analog Y 2- xCa xBaNiO 5 (0< x?0.33), displays peculiar physical properties related to the presence of linear chains of NiO 6 octahedra. These compounds can be considered prototypical Haldane systems and one-dimensional Heisenberg antiferromagnets. In this work, we investigate how the presence of calcium influences the electronic charge distribution and the bond character of these octahedra. The electron density map ?( r) is derived from powder X-ray diffraction patterns with a novel procedure based upon a correlative use of two methods: Maximum Entropy Method (MEM) and Whole Powder Profile Fitting (WPPF). We compute the Laplacian ? 2?( r) at the Bader critical point of the M-O bond; this quantity is shown to be directly related to structural parameters and their dependence upon composition. In particular, the substantial contraction of NiO 6 octahedra with increasing Ca content is related to an Ni-O bond which becomes more ionic as x increases up to x=0.24. On the other hand, covalency becomes stronger above x=0.24, particularly along some Ba-O bonds. Computation of the Shannon entropies confirms the existence of a singularity of the x=0.24 composition, which is a threshold for the re-arrangement of the crystal structure.

Merli, Marcello; Capsoni, Doretta; Bini, Marcella; Massarotti, Vincenzo

2002-01-01

298

Effects of A1 site occupation on dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics  

NASA Astrophysics Data System (ADS)

Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tetragonal tungsten bronzes are investigated. The Sr4CaCeTi3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr4CaEuTi3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca2+ and Eu3+ could lead to the uneven distribution of Ca2+ and Eu3+ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarizationelectric field (PE) curves are evaluated at room temperature and both of them show hysteresis loops. Sr4CaCeTi3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current densityelectric field (JE) curves are measured at room temperature with a largest leakage current density of ~ 10?6 A/cm2, indicating that their leakage currents are rather low.

Fang, Yu-Jiao; Gong, Gao-Shang; Gebru, Zerihun; Yuan, Song-Liu

2014-12-01

299

Thermoelectric properties and electronic structure of the Zintl phase Sr5In2Sb6 and the Ca5?xSrxIn2Sb6 solid solution  

NASA Astrophysics Data System (ADS)

The Zintl phase Sr5In2Sb6 is isostructural with Ca5In2Sb6a promising thermoelectric material with a peak zT of 0.7 when the carrier concentration is optimized by doping. Density functional calculations for Sr5In2Sb6 reveal a decreased energy gap and decreased valence band effective mass relative to the Ca analog. Chemical bonding analysis using the electron localizability indicator was found to support the Zintl bonding scheme for this structure type. High temperature transport measurements of the complete Ca5?xSrxIn2Sb6 solid solution were used to investigate the influence of the cation site on the electronic and thermal properties of A5In2Sb6 compounds. Sr was shown to be fully miscible on the Ca site. The higher density of the Sr analog leads to a slight reduction in lattice thermal conductivity relative to Ca5In2Sb6, and, as expected, the solid solution samples have significantly reduced lattice thermal conductivities relative to the end member compounds.

Zevalkink, Alex; Chenakian, Sevan; Aydemir, Umut; Ormeci, Alim; Pomrehn, Gregory; Bux, Sabah; Fleurial, Jean-Pierre; Snyder, G. Jeffrey

2015-01-01

300

Behavioral migration diversity of the Yangtze River Japanese Eel, Anguilla japonica, based on otolith Sr/Ca ratios.  

PubMed

The Yangtze River estuary is the main production area of Anguilla japonica in China, as well as the only existing fishery area for adult eels. Japanese eels are distributed in the main rivers and many tributaries from the Yangtze River estuary to the upper Jinsha River, which extend to nearly 3 000 km. However, their migration behaviors remain relatively unknown. We analyzed the biological characteristics of 153 specimens of silver eels collected from the Jingjiang section of Yangtze River (31(o)30'N, 120(o)42'E) between September and November, 2008, and tested the sagittal Sr/Ca ratios of 27 specimens. Among the 153 specimens examined, 85 were female and 68 were male, which translated to a female-male ratio of 1 : 0.8. The ages of the female specimens ranged from 3 to 7 a (average 5.52) with an average total length (TL) of (669 80) mm, average body weight (BW) of (555 229)g, average condition factor of 1.77 0.22, and average gonad somatic index (GSI) of 1.32 0.31. The ages of the males ranged from 3 to 5 a (average:4.38) with an average TL of (518 51) mm, average BW of (234 76) g, average condition factor of 1.62 0.18, and average GSI of 0.21 0.11. All biological parameters of females were significantly larger than those of the male specimens (P<0.05). According to the average Sr/Ca ratio (7.99 1.05) 10(-3) of the elver mark of sagitta, 17 individuals (62.96%) were river eels and 10 individuals (37.04%) were estuarine eels. Of 16 females, 13 individuals (81.25%) were river eels and 3 were estuarine eels, while of 11 males, 36.36% were river eels and 63.64% were estuarine eels. The analysis on Sr/Ca ratios for every growth layer group (GLG) indicated there were no significant differences between second-age males and females. However, significant differences were observed between the third-age, fourth-age, and migration-age male and female specimens. This was likely related to the fact that second-age eels of both sexes stay in the same inhabitation waters; however, as they grow older, they move to different areas. PMID:21842541

Guo, Hong-Yi; Zheng, Yi; Tang, Wen-Qiao; Shen, Hao; Wei, Kai; Xie, Zheng-Li; Tsukamoto, Katsumi

2011-08-01

301

Towards a high thermoelectric performance in rare-earth substituted SrTiO3: effects provided by strongly-reducing sintering conditions.  

PubMed

Donor-substituted strontium titanate ceramics demonstrate one of the most promising performances among n-type oxide thermoelectrics. Here we report a marked improvement of the thermoelectric properties in rare-earth substituted titanates Sr0.9R0.1TiO3? (R = La, Ce, Pr, Nd, Sm, Gd, Dy, Y) to achieve maximal ZT values of as high as 0.42 at 1190 K < T < 1225 K, prepared via a conventional solid state route followed by sintering under strongly reducing conditions (10%H2-90%N2, 1773 K). As a result of complex defect chemistry, both electrical and thermal properties were found to be dependent on the nature of the rare-earth cation and exhibit an apparent correlation with the unit cell size. High power factors of 1350-1550 ?W m(-1) K(-2) at 400-550 K were observed for R = Nd, Sm, Pr and Y, being among the largest reported so far for n-type conducting bulk-ceramic SrTiO3-based materials. Attractive ZT values at high temperatures arise primarily from low thermal conductivity, which, in turn, stem from effective phonon scattering in oxygen-deficient perovskite layers formed upon reduction. The results suggest that highly-reducing conditions are essential and should be employed, whenever possible, in other related micro/nanostructural engineering approaches to suppress the thermal conductivity in target titanate-based ceramics. PMID:25377924

Kovalevsky, A V; Yaremchenko, A A; Populoh, S; Thiel, P; Fagg, D P; Weidenkaff, A; Frade, J R

2014-12-28

302

Protective effect of antioxidants against sarcoplasmic reticulum (SR) oxidation by Fenton reaction, however without prevention of Ca-pump activity.  

PubMed

The Ca(2+)-ATPase of the sarcoplasmic reticulum (SERCA) of rabbit skeletal muscle was oxidized by Fe2+/H2O2/ascorbic acid (AA), a system which generates HO(.) radicals according to the Fenton reaction: (Fe2(+)+H2O2-->HO(.)+OH(-)+Fe(3+)) under conditions similar to the pathological state of inflammation. Under these conditions, when hydroxyl-radicals and/or ferryl-radicals are generated, a 50% decrease of the SERCA activity was observed, a significant decrease of SH groups and an increase of protein carbonyl groups and lipid peroxidation were identified. Two new bands, time dependent in density, appeared in the SERCA protein electrophoresis after incubation with the Fenton system (at approximately 50 and 75kDa), probably due to structural changes as supported also by trypsin digestion. Immunoblotting of DNPH derivatized protein bound carbonyls detected a time dependent increase after incubation of SERCA with the Fenton system. Trolox and the pyridoindole stobadine (50microM) protected SR against oxidation induced via the Fenton system by preventing SH group oxidation and lipid peroxidation. Pycnogenol((R)) and EGb761 (40microg/ml) protected SERCA in addition against protein bound carbonyl formation. In spite of the antioxidant effects, trolox and stobadine were not able to prevent a decrease in the SERCA Ca(2+)-ATPase activity. Pycnogenol and EGb761 even enhanced the decrease of the Ca(2+)-ATPase activity induced by the Fenton system, probably by secondary oxidative reactions. PMID:18692562

Voss, Peter; Engels, Martina; Strosova, Miriam; Grune, Tilman; Horakova, Lubica

2008-10-01

303

Arsenate Substitution in Hydroxylapatite: Structural Characterization of the Ca5(PxAs1-xO4)3OH Solid Solution  

SciTech Connect

Arsenate (As{sup 5+}) substitution in the hydroxylapatite structure was examined using a combination of crystallographic and spectroscopic techniques. Samples of hydroxylapatite, the As{sup 5+}-substituted analog (synthetic johnbaumite), and five intermediate compositions were synthesized from solution. Synchrotron X-ray diffraction data show that all samples are single-phase, confirming complete substitution. No evidence is found for lowering of symmetry below P6{sub 3}/m. Rietveld structure refinements show progressive expansion of the unit cell with increasing As substitution, which can be accounted for primarily by an average expansion of the tetrahedral site. Sizes of Ca polyhedra show little variation as a result of As substitution. NMR results show no evidence for local clustering of PO{sub 4} tetrahedra. EXAFS confirms that the size of As-centered tetrahedra remains constant across the solid-solution series.

Lee, Y.; Stephens, P; Tang, Y; Li, W; Phillips, B; Parise, J; Reeder, R

2009-01-01

304

Heat capacity proportional to T2 induced by Ru substitution in CaCu3(Ti4-xRux)O12 (x?0.5)  

NASA Astrophysics Data System (ADS)

The effect of Ru substitution for Ti on the ground-state properties of three-dimensional antiferromagnet (AF) CaCu3Ti4O12 is studied by means of magnetic susceptibility and heat-capacity measurements. A small amount of Ru substituted for Ti suppresses AF long-range order and induces a new intermediate state with T2 -proportional heat capacity, which shows a clear contrast to a simple spin-dilution effect demonstrated by the Zn substitution for Cu. Ru substitution also creates a finite density of state at the Fermi level while keeping nominal valence of Cu ions to be 2+ , which is essential to a novel insulator-to-metal crossover driven by an isovalent substitution of Ru4+ for Ti4+ .

Tsukada, I.; Kammuri, R.; Kida, T.; Yoshii, S.; Takeuchi, T.; Hagiwara, M.; Iwakawa, M.; Kobayashi, W.; Terasaki, I.

2009-02-01

305

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

306

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

307

Itinerant-to-localized electron transition in CaRu{sub 1{minus}{ital x}}Sn{sub {ital x}}O{sub 3} and SrRu{sub 1{minus}{ital x}}Pb{sub {ital x}}O{sub 3}  

SciTech Connect

SrRuO{sub 3} and CaRuO{sub 3} are perovskites with an orthorhombic distortion and are believed to have a narrow itinerant band. SrRuO{sub 3} is the only known ferromagnetic conductor in 4{ital d} transition-metal oxides, while CaRuO{sub 3} is a paramagnetic conductor. Substituting Pb and Sn for Ru in SrRuO{sub 3} and CaRuO{sub 3}, respectively, preserves the crystal structure, while removing electrons from the 4{ital d} band, resulting in an itinerant-to-localized electron transition and also substantially altering the magnetic coupling, giving rise to a new magnetically ordered phase. In particular, it appears that the paramagnetic CaRuO{sub 3} is on the verge of magnetic ordering and readily evolves into a magnetically ordered phase when slightly doped with Sn (4{endash}10{percent}). Such an ordered phase is not stable and disappears when Sn concentration is higher than 10{percent}. On the other hand, the Curie temperature ({ital T}{sub {ital C}}=165 K) of SrRuO{sub 3} seems to be sensitive to Pb doping, and increases to 210 K when the Pb concentration in the compound is higher than 30{percent}. For both SrRuO{sub 3} and CaRuO{sub 3} the transition to the magnetic state is accompanied by an itinerant-to-localized electron transition due to the 4{ital d}-electron depletion. These results are based on measurements of magnetic susceptibility and electrical resistivity. This study reveals striking observations which underscore the importance of the interplay between the conduction band and (anti)ferromagnetism. {copyright} {ital 1996 The American Physical Society.}

Cao, G.; McCall, S.; Bolivar, J.; Shepard, M.; Freibert, F.; Henning, P.; Crow, J.E. [National High Magnetic Field Laboratory, Tallahassee, Florida 32306 (United States)] [National High Magnetic Field Laboratory, Tallahassee, Florida 32306 (United States); Yuen, T. [Temple University, Philadelphia, Pennsylvania 19122 (United States)] [Temple University, Philadelphia, Pennsylvania 19122 (United States)

1996-12-01

308

Combined effects of transition metal (Ni and Rh) substitution and annealing/quenching on the physical properties of CaFe2As2  

NASA Astrophysics Data System (ADS)

We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T =Ni, Rh substitution (x) on the physical properties of Ca(Fe1-xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co substitution. Ni substitution, which brings one more extra electron per substituted atom and suppresses the c-lattice parameter at roughly the same rate as Co substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as that found for Co substitution, but the parameter range for superconductivity has been shrunk (roughly by a factor of 2). This result is similar to what is found when Co- and Ni-substituted BaFe2As2 are compared. On the other hand, Rh substitution, which brings the same amount of extra electrons as does Co substitution, but suppresses the c-lattice parameter more rapidly, has a different phase diagram. The collapsed tetragonal phase exists much more pervasively, to the exclusion of the normal, paramagnetic, tetragonal phase. The range of antiferromagnetic/orthorhombic phase space is noticeably reduced, and the superconducting region is substantially suppressed, essentially truncated by the collapsed tetragonal phase. In addition, we found that whereas for Co substitution there was no difference between phase diagrams for samples annealed for 1 or 7 days, for Ni and Rh substitutions a second, reversible effect of annealing was revealed by 7-day anneals.

Ran, S.; Bud'ko, S. L.; Straszheim, W. E.; Canfield, P. C.

2014-08-01

309

Synthesis and Structure of CaBiO 2Cl and SrBiO 2Cl: New Distorted Variants of the Sillen X1 Structure  

Microsoft Academic Search

Two new layered oxyhalides,MBiO2Cl (M=Ca, Sr), have been synthesized and characterized. Both are derived from the ideal Sillen X1 structure type, being composed of fluorite-like [MBiO2]+layers separated by single Cl?layers. However, deviations from the idealized tetragonal structure due to cation site ordering lead to two different super structures being formed. The structure of CaBiO2Cl has been solvedab initioand refined from

Susan M. Fray; Christopher J. Milne; Philip Lightfoot

1997-01-01

310

The influence of selected metals (Mg, Ca, Sr and Ba) on the electronic system of the p-halogenobenzoic acids  

NASA Astrophysics Data System (ADS)

The assignment of the vibrational spectra of p-halogenobenzoic acid complexes with Mg, Ca, Sr and Ba is proposed. The influence of the metals on the electronic system of p-halogenobenzoic acids is the topic of study. The biggest differences in wavenumber of selected bands dependent on metal ion occurred within the spectral range: 1604-1612, 1550-1520, 1440-1410, 1302-1243, 1100-1090 and 875-865 cm -1. The influence of halogen (F, Cl, Br and I) on the electronic system of complexes was also investigated. The effect of halogen was mostly seen within the spectral range: 1610-1580, 1546-1540, 1183-1164, 1019-849 and 688-681 cm -1. The main factor responsible for the changes in the vibrational structure of the molecules was the ionic potential.

Koczo?, P.; Mo?cibroda, P.; Dobrosz-Teperek, K.; Lewandowski, W.

2001-05-01

311

A tetragonal to orthorhombic phase transition in Bi 2Sr 2CaCu 2O x  

NASA Astrophysics Data System (ADS)

Bi 2Sr 2CaCu 2O x superconductor was studied in situ by high temperature X-ray diffraction, differential scanning calorimetry (DSC), and thermogravimetry (TG). It is discovered that there is a tetragonal to orthorhombic phase transition at about 600C in the sample. Careful high temperature X-ray diffraction and thermal analysis reveal that the phase transition in a sample with a higher value of T c (89 K) is very obvious, but in a sample with a lower value of T c (65 K) is hardly observed. By comparing this phase transition and the orthorhombic to tetragonal transition in YBa 2Cu 3O y system, some difference and similarity among Bi-system and Y-system superconductors are obtained.

Zhang, H.; Feng, Q. R.; Zhao, Y.; Ritter, F.; Sun, W.; Frieling, T.; Assmus, W.

1995-09-01

312

Superconductivity on a Crossover Phenomenon of SpinLadder System SrCa13Cu24O41 Single Crystals  

NASA Astrophysics Data System (ADS)

Electrical resistivity and alternating current susceptibility measurements were performed for the spinladder compound SrCa13Cu24O41 under hydrostatic pressure up to 8 GPa. The superconducting transition was observed below TC = 14.7 K at pressures above 2 GPa. By using high-quality single crystals, the bulk superconductivity with a volume fraction of 50% and temperature quadratic behavior of the normal state resistivity were observed above 3.7 GPa. They suggest that a strong interladder interaction induces the bulk superconductivity and transforms the system into a Fermi-liquid-like state. The optimal pressure was in a crossover region and the highest TC was observed without going through the bulk superconducting state. Our results suggest that the superconducting state on the crossover phenomenon presents the feature of the doped two-leg spinladder system because the spin gap was observed in this compound.

Hisada, Akihiko; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Fujiwara, Naoki; Deng, Guochu; Pomjakushina, Ekaterina; Conder, Kazimierz; Mohan Radheep, Dinadhayalane; Thiyagarajan, Raman; Esakkimuthu, Sankaran; Arumugam, Sonachalam

2014-07-01

313

High pressure induced spin state crossover in Sr2CaYCo4O10.5  

NASA Astrophysics Data System (ADS)

The layered cobaltite Sr2CaYCo4O10.5 with formal average cobalt oxidation state close to 3+ has been studied as functions of both temperature and pressure up to 4 GPa by neutron powder diffraction (NPD). The crystal structure is shown to have tetragonal symmetry (space group I4/mmm; 2ap 2ap 4ap superstructure), and the magnetic structure at ambient pressure is found to be G-type antiferromagnetic with TN close to 310 K. The magnetic moments within the CoO6 octahedral layers and anion-deficient CoO4.5 layers are 1.2?B and 2.8?B, respectively. At 25 K, and applied pressure of 3.5 GPa is sufficient to completely suppress a long-range magnetic order. This result is interpreted in terms of a pressure-induced high-to-low spin state crossover of the Co3+ ions.

Sikolenko, V.; Troyanchuk, I.; Bushinsky, M.; Efimov, V.; Keller, L.; White, J. S.; Schilling, F. R.; Schorr, S.

2015-02-01

314

Relaxor behavior of ferroelectric Ca0.22Sr0.12Ba0.66Nb2O6  

NASA Astrophysics Data System (ADS)

The relaxor behavior of tetragonal tungsten bronze uniaxial relaxor ferroelectric calcium strontium barium niobate (Ca0.22Sr0.12Ba0.66Nb2O6 or CSBN-22) single crystal was studied by measuring elastic constants and thermal expansion with the aid of resonant ultrasound spectroscopy and dilatometry, respectively, in the temperature range 300 K-1503 K. Thermal expansion yields evidence of the Burns temperature TB and the intermediate characteristic temperature T*, which was also supported by the temperature evolutions of the elastic constants cij. CSBN-22 was found to be 2%-3% elastically stiffer than CBN-28. The presented results open the perspective to understand the relaxor behavior of CSBN.

Shekhar Pandey, Chandra; Schreuer, Jrgen; Burianek, Manfred; Mhlberg, Manfred

2013-01-01

315

Magnetic Anomaly of La1?xMxFeO3 (M = Ca, Sr, and Ba) around 100 K  

NASA Astrophysics Data System (ADS)

A magnetic anomaly has been found around 100 K in La1?xMxFeO3 (M = Ca, Sr, and Ba) and Pr1?xSrxFeO3 with 0.05 ? x ? 0.4; the spontaneous magnetization of the weak ferromagnet increases below about 100 K after cooling in a magnetic field. We propose a model in which Fe4+ ions populated by doped holes preferentially occupy one magnetic sublattice of the antiferromagnetic structure in LaFeO3 and PrFeO3 as a result of charge ordering, which induces an inequality between the sublattice magnetizations and modifies the system from the antiferromagnet to a ferrimagnet. The magnetization below the magnetic anomaly temperature is explained as that of a weak ferromagnet with the canted sublattice magnetizations of the ferrimagnet.

Nakamae, Yuki; Ishida, Shu; Takemura, Wataru; Ohno, Masatoshi; Okada, Akimasa; Mitsui, Toshihiro; Kobayashi, Yoshihiko; Nakamura, Jin; Asai, Kichizo

2014-06-01

316

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

317

Preparation of Bi-Sr-Ca-Cu-O whiskers from an amorphous matrix in the presence of oxide dopants  

SciTech Connect

Attempts to prepare single crystals of bismuth-containing superconductors of the Bi{sub 2}Sr{sub 2}Ca{sub n-1}Cu{sub n}O{sub 2n+4} (n=1-3) series met serious difficulties, including high growth anisotropy, the close stability ranges of the members of the series, their incongruent melting, the volatility of some components, and slow crystallization kinetics. Whisker growth puts some additional requirements on the amorphous initial state, fixed temperature gradient, and oxygen flow. The low growth rate makes it difficult to prepare long whiskers, which are necessary for solving fundamental and technological problems. This field has been studied extensively by several research teams. In this work, the authors found that whisker growth is accelerated by doping the initial melt with some oxides or their mixtures. The principles for selecting the dopants are stated. A model for whisker growth in the dopant-oxide matrix is proposed.

Os`kina, T.E.; Kozlovskii, V.F.; Tret`yakov, Y.D. [Moscow State Univ. (Russian Federation)

1995-09-01

318

Composite to Tilted Vortex Lattice Transition in Bi2Sr2CaCu2O8+? in Oblique Fields  

NASA Astrophysics Data System (ADS)

Precision measurements of the vortex phase diagram in single crystals of the layered superconductor Bi2Sr2CaCu2O8+? in oblique magnetic fields confirm the existence of a second phase transition, in addition to the usual first-order vortex-lattice melting line Hm(T). The transition has a strong first-order character, is accompanied by strong hysteresis, and intersects the melting line in a tricritical point (Hm?, Hcr?). Its field dependence and the changing character of the melting line at the tricritical point strongly suggest that the ground state for magnetic fields closely aligned with the superconducting layers is a lattice of uniformly tilted vortex lines.

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

2006-12-01

319

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 (145C). 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

320

Fourfold Structure of Vortex-Core States in Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

We present a detailed study of vortex-core spectroscopy in slightly overdoped Bi2Sr2CaCu2O8+? using a low-temperature scanning tunneling microscope. Inside the vortex core, we observe a fourfold symmetric modulation of the local density of states with an energy-independent period of (4.30.3)a0. Furthermore, we demonstrate that this square modulation is related to the vortex-core states which are located at 6meV. Since the core-state energy is proportional to the superconducting gap magnitude ?p, our results strongly suggest the existence of a direct relation between the superconducting state and the local electronic modulations in the vortex core.

Levy, Giorgio; Kugler, Martin; Manuel, Alfred A.; Fischer, ystein; Li, Ming

2005-12-01

321

Benthic Foraminiferal Mg/Ca and Sr/Ca Presented Under Varying Population Densities on the Southeastern United States Continental Shelf  

NASA Astrophysics Data System (ADS)

Unraveling the inherent variabilities in benthic foraminiferal Mg/Ca and other trace elements will help produce a more refined temperature proxy for benthic foraminiferal calcification temperature. To date, proxy signature variability in field samples has been attributed to microhabitat and poorly understood vital effects. Vital effects such as food supply, calcification rate, metabolic rate, may influence microhabitat chemistry or foraminiferal shell chemistry, but are difficult to measure. However, easily measurable benthic population densities and abundances are likely to be driven by food supply, and may also be controlled by foraminiferal calcification or metabolic rates. Mg/Ca and Sr/Ca from live core-top benthic foraminfera were investigated to test whether vital effect factors, as reflected by faunal abundance and diversity, influence foraminiferal element/calcium ratios. Foraminiferal element/calcium ratios are presented along with corresponding abundances and species diversities of cores collected in 2001, 2005, and 2006 from the shallow-slope environ of the Charleston Bump (31 55'N, 79 11'W; ~220m water depth; temp range: 9.4-11.2 C; calcite saturation state: 2.29- 2.73). Overall total foraminiferal population densities increased by 6 fold in the more recent years (2001, n=350, 6.1 individuals/cm3; 2005, n>2300, 40 individuals/cm3; 2006, n>1900, 33.6 individuals/cm3). If a correlation exists between benthic foraminiferal population densities and element/calcium ratios, then this may suggest that biological processes can affect foraminiferal element/calcium shell chemistry. Funded by NSF OCE9911654, OCE0351029, and OCE 0437366.

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

2006-12-01

322

Nanosized Cr2O3 as pinning center in (Bi,Pb)-Sr-Ca-Cu-O superconductor tapes  

NASA Astrophysics Data System (ADS)

Nanosized Cr2O3 (6 nm) has been introduced into (Bi,Pb)-Sr-Ca-Cu-O/Ag tapes fabricated by the powderin-tube method. The starting powder with composition (Bi,Pb)2Sr2Ca2Cu3O10(Cr2O3)0.05 was prepared by the solid state reaction method. The superconductor tapes with thickness of about 0.3 mm and length about 2 cm were heated at 845C for 96, 144, 192 and 240 h. The samples were characterized by the four point probe electrical measurements, X-ray powder diffraction method and scanning electron microscopy. The transport critical current density, Jc was measured from 30 to 65 K using the 1 ?/cm criterion. The highest Jc was obtained for the tape heated for 240 h with Jc = 1700 A/cm2 at 30 K. XRD patterns showed that the samples consisted of the 2212 and 2223 phase. SEM micrographs showed the plat-like structure. The role of nano-Cr2O3 in the superconductor system is discussed. The size of the nanoparticle (R) was larger than the coherence length, ? but smaller than the penetration depth, ?(?< R

Lee, G. H.; Abd-Shukor, R.

2013-05-01

323

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

324

Experimental demonstration of hybrid improper ferroelectricity and the presence of abundant charged walls in (Ca,Sr)3Ti2O7 crystals  

NASA Astrophysics Data System (ADS)

On the basis of successful first-principles predictions of new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Using trilinear coupling of two types of octahedron rotation, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the RuddlesdenPopper compounds (Ca3Ti2O7, Ca3Mn2O7 and (Ca/Sr/Ba)3(Sn/Zr/Ge)2O7). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in bulk crystals of Ca3Ti2O7, as well as Sr-doped Ca3Ti2O7. Furthermore, (Ca, Sr)3Ti2O7 is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit a conduction difference of two orders of magnitude. These discoveries provide new research opportunities, not only for new stable ferroelectrics of RuddlesdenPopper compounds, but also for meandering conducting domain walls formed by planar polarization.

Oh, Yoon Seok; Luo, Xuan; Huang, Fei-Ting; Wang, Yazhong; Cheong, Sang-Wook

2015-04-01

325

Experimental demonstration of hybrid improper ferroelectricity and the presence of abundant charged walls in (Ca,Sr)3Ti2O7 crystals.  

PubMed

On the basis of successful first-principles predictions of new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Using trilinear coupling of two types of octahedron rotation, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden-Popper compounds (Ca3Ti2O7, Ca3Mn2O7 and (Ca/Sr/Ba)3(Sn/Zr/Ge)2O7). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in bulk crystals of Ca3Ti2O7, as well as Sr-doped Ca3Ti2O7. Furthermore, (Ca, Sr)3Ti2O7 is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit a conduction difference of two orders of magnitude. These discoveries provide new research opportunities, not only for new stable ferroelectrics of Ruddlesden-Popper compounds, but also for meandering conducting domain walls formed by planar polarization. PMID:25581628

Oh, Yoon Seok; Luo, Xuan; Huang, Fei-Ting; Wang, Yazhong; Cheong, Sang-Wook

2015-04-01

326

Effect of La{sup 3+} substitution with Gd{sup 3+} on the resistive switching properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films  

SciTech Connect

This study demonstrated that the resistive switching voltage of perovskite manganite material could be controlled by A-site cation substitution in A MnO{sub 3} perovskite manganite structure. A partial substitution of La{sup 3+} in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} with smaller cation Gd{sup 3+} induced A-site vacancy of the largest Sr{sup 2+} cation with surface segregation of SrO{sub y} due to ionic size mismatch, and the induced vacancies reduced migration energy barrier. The operating voltage decreased from 3.5?V to 2.5?V due to a favorable condition for electrochemical migration and redox of oxygen ions. Moreover, surface-segregated SrO{sub y} was enhanced with Gd-substitution and the SrO{sub y} reduced Schottky-like barrier height and resistive switching ratio from the potential drop and screening effect. The relationship between A-site vacancy generation resulting in surface segregation of SrO{sub y} and resistive switching behavior was also investigated by energy resolved x-ray photoelectron spectroscopy, O 1s near edge x-ray absorption spectroscopy, and current voltage measurement.

Lee, Hong-Sub; Park, Chang-Sun; Park, Hyung-Ho, E-mail: hhpark@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749 (Korea, Republic of)

2014-05-12

327

Bulk vortex matter in Bi2Sr2CaCu2O8+ using Corbinol disk contacts Y. M. Wang,* M. S. Fuhrer,  

E-print Network

Bulk vortex matter in Bi2Sr2CaCu2O8+ using Corbinol disk contacts Y. M. Wang,* M. S. Fuhrer, and A disk contact geometry. This Corbino disk contact geometry allows us to measure true bulk vortex between our measurements and others measurements using the conventional four-probe contact geometry, which

Rubloff, Gary W.

328

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

E-print Network

Microstructure 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 and fatigue-free and lead-free nature, Aurivillius bismuth-layer structure compounds BLSCs are widely used

Cao, Wenwu

329

Eu and Dy activated (Sr0.90Ca0.10)3(PO4)2 phosphors for near- UV LED  

NASA Astrophysics Data System (ADS)

The new efficient trivalent Eu and Dy activated (Sr0.90Ca0.10)3(PO4)2 phosphors were prepared by the conventional solid state method. X-ray powder diffraction analysis confirmed the formation of (Sr0.90Ca0.10)3(PO4)2 host lattice. The Eu3+ PL emission spectrum was observed in (Sr0.90Ca0.10)3(PO4)2 phosphors at 590 (orange) and 614 nm (red) region, the spectrum due to 5D0-7F1 and 5D0-7F2 transitions at near UV excitation, respectively. (Sr0.90Ca0.10)3(PO4)2: Dy3+ excited by 350 nm near-ultraviolet (NUV) light, the phosphors show an efficient blue and yellow band emissions, which originates from the 4F9/2-6H15/2 and 4F9/2-6H13/2 transitions of Dy3+ ion, respectively. The excitation spectra of the phosphors are broadband extending from 340 to 400 nm, which are characteristics of NUV excited LED. The investigated prepared phosphors are suitable for a NUV excited LED.

Shinde, K. N.; Dhoble, S. J.

2015-02-01

330

NUCLEAR THERMODYNAMIC DATABASE O-U-Zr-Fe-Cr-Ni-Ag-In-B-C-Ba-La-Ru-Sr-Al-Ca-Mg-Si  

E-print Network

NUCLEAR THERMODYNAMIC DATABASE « NUCLEA » O-U-Zr-Fe-Cr-Ni-Ag-In-B-C-Ba-La-Ru-Sr-Al-Ca-Mg-Si + Ar - TVA : FR 91 304 441 090 #12;NUCLEA Nuclear Thermodynamic Database Version 2007-01 developed March 1996 on the legal protection of databases. Extraction and/or re-utilization of the whole

Paris-Sud XI, Université de

331

Pressure Dependence of Flux Dynamics in Bi2Sr2CaCu2O8+ M. P. Raphael, M. E. Reeves, C. Kendziora, and E. F. Skelton  

E-print Network

Pressure Dependence of Flux Dynamics in Bi2Sr2CaCu2O8+ M. P. Raphael, M. E. Reeves, C. Kendziora are presented in this paper which were obtained using a new technique for measuring the pressure dependence of pressure on flux motion. Pressure changes the atomic interplanar spacing, and hence the interplanar

Reeves, Mark E.

332

Effect of Ca substitution on some physical properties of nano-structured and bulk Ni-ferrite samples  

NASA Astrophysics Data System (ADS)

Nanoparticles of Ni1-xCaxFe2O4 (x=0.0, 0.02, 0.04, 0.06 and 0.10) were prepared by citrate precursor method. A part of these samples was sintered at 600 C for 2 h in order to keep the particles within the nano-size while the other part was sintered at 1000 C to let the particles to grow to the bulk size. The effect of Ca2+ ion substitution in nickel ferrite on some structural, magnetic, electrical and thermal properties was investigated. All samples were characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). A two probe method was used to measure the dc electrical conductivity whereas the photoacoustic (PA) technique was used to determine the thermal diffusivity of the samples. To interpret different experimental results for nano and bulk samples some cation distributions were assumed based on the VSM and XRD data. These suggested cation distributions give logical explanations for other experimental results such as the observed values of the absorption bands in FTIR spectra and the dc conductivity results. Finally, in the thermal measurements it was found that increasing the Ca2+ ion content causes a decrease in the thermal diffusivity of both nano and bulk samples. The explanation of this behavior is ascribed to the phonon-phonon scattering.

Assar, S. T.; Abosheiasha, H. F.

2015-01-01

333

Synthesis of Dy3+ and Ce3+ activated Sr6BP5O20 and Ca6BP5O20 borophosphate phosphors  

NASA Astrophysics Data System (ADS)

In this paper we report the modified solid state synthesis of Dy and Ce activated Sr6BP5O20, Ca6BP5O20 and (CaXSr(1-X))6BP5O20 phosphors. The prepared phosphors were characterized by the x-ray powder diffraction and photoluminescence techniques. The PL excitation spectra showed the excitation peaks ranging from 300 to 400 nm due to the 4f ? 4f transitions of Dy3+ ions. This mercury-free excitation is useful for solid state lighting and light-emitting diode (LED). The PL emission spectrum of Dy3+ ion under 348 nm excitation was observed at 483 nm (blue) due to 4F9/2 ? 6 H15/2 transitions. Other emissions were observed at 576 nm (yellow) due to 4F9/2 ? 6H13/2 transitions and 670 nm (red) due to 4F9/2 ? 6 H11/2 transitions in prepared borophosphate phosphor. Dy activated Ca6BP5O20 phosphor showed intense emission as compared with Sr6BP5O20 phosphors which have been reported in this paper. From these characteristics, Dy activated Sr6BP5O20, Ca6BP5O20 and (CaXSr(1-X))6BP5O20 phosphors are one of the candidates for the white LED. The PL emission spectra of Ce3+ ion in the Sr6BP5O20, Ca6BP5O20 and (CaXSr(1-X))6BP5O20 phosphors in the UV region under broad band excitation at around 247 nm are presented for the scintillation application.

Kharabe, V. R.; Dhoble, S. J.; Moharil, S. V.

2008-10-01

334

SR Ca 2+ store refilla key factor in cardiac pacemaking  

Microsoft Academic Search

This study presents a theoretical analysis of the role of store Ca2+ uptake on sinoatrial node (SAN) cell pacemaking. Two mechanisms have been shown to be involved in SAN pacemaking, these being: 1) the membrane oscillator model where rhythm generation is based on the interaction of voltage-dependent membrane ion channels and, 2) the store oscillator model where cyclical release of

Mohammad S. Imtiaz; Pierre-Yves von der Weid; Derek R. Laver; Dirk F. van Helden

2010-01-01

335

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

Microsoft Academic Search

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)

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

1998-01-01

336

Reconstructing changes in seep activity by means of pore water and solid phase Sr\\/Ca and Mg\\/Ca ratios in pockmark sediments of the Northern Congo Fan  

Microsoft Academic Search

This study focuses on the vertical distribution of authigenic carbonates (aragonite and high Mg-calcite) in the form of finely disseminated precipitates as well as massive carbonate concretions present in and above gas hydrate bearing sediments of the Northern Congo Fan. Analyses of Ca, Mg, Sr and Ba in pore water, bulk sediments and authigenic carbonates were carried out on gravity

K. Nthen; S. Kasten

2011-01-01

337

Phase transitions and equations of state of alkaline earth fluorides CaF2 , SrF2 , and BaF2 to Mbar pressures  

NASA Astrophysics Data System (ADS)

Phase transitions and equations of state of the alkaline earth fluorides CaF2 , SrF2 , and BaF2 were examined by static compression to pressures as high as 146 GPa. Angle-dispersive x-ray diffraction experiments were performed on polycrystalline samples in the laser-heated diamond-anvil cell. We confirmed that at pressures less than 10 GPa all three materials undergo a phase transition from the cubic (Fm3m) fluorite structure to the orthorhombic (Pnam) cotunnite-type structure. This work has characterized an additional phase transition in CaF2 and SrF2 : these materials were observed to transform to a hexagonal (P63/mmc) Ni2In -type structure between 63-79 GPa and 28-29 GPa, respectively, upon laser heating. For SrF2 , the Ni2In -type phase was confirmed by Rietveld refinement. Volumes were determined as a function of pressure for all high-pressure phases and fit to the third-order Birch-Murnaghan equation of state. For CaF2 and SrF2 , the fluorite-cotunnite transition results in a volume decrease of 8-10% , while the bulk modulus of the cotunnite-type phase is the same or less than that of the fluorite phase within uncertainty. For all three fluorides, the volume reduction associated with the further transition to the Ni2In -type phase is 5% . The percentage increase in the bulk modulus (?K) across the transition is greater when the cation is smaller. While for BaF2 , ?K is 10-30% , ?K values for SrF2 and CaF2 are 45-65% and 20-40% . Although shock data for CaF2 have been interpreted to show a transition to a highly incompressible phase above 100 GPa, this is not consistent with our static equation of state data.

Dorfman, Susannah M.; Jiang, Fuming; Mao, Zhu; Kubo, Atsushi; Meng, Yue; Prakapenka, Vitali B.; Duffy, Thomas S.

2010-05-01

338

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

NASA Astrophysics Data System (ADS)

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 2-type structure ( Pnma, Z=4, a=8.108(2), 8.124(2), 8.421(2), 8.509(2) ; b=4.944(1), 4.949(1), 5.168(1), 5.189(1) ; c=9.170(2), 9.184(2), 9.685(2), 9.740(2) , 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 2Si 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 Ae2Tt analogues.

Liu, Shengfeng; Corbett, John D.

2006-03-01

339

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

340

Phase transitions in Ca{sub 3}(BN{sub 2}){sub 2} and Sr{sub 3}(BN{sub 2}){sub 2}  

SciTech Connect

{alpha}-Ca{sub 3}(BN{sub 2}){sub 2} crystallizes in the cubic system (space group: Im3-bar m) with one type of calcium ions disordered over 78 of equivalent (8c) positions. An ordered low-temperature phase ({beta}-Ca{sub 3}(BN{sub 2}){sub 2}) was prepared and found to crystallize in the orthorhombic system (space group: Cmca) with lattice parameters: a=1024.18(2)pm, b=732.43(2)pm, and c=2091.60(4)pm. Structure refinements on the basis of X-ray powder data have revealed that orthorhombic {beta}-Ca{sub 3}(BN{sub 2}){sub 2} corresponds to an ordered super-structure of cubic {alpha}-Ca{sub 3}(BN{sub 2}){sub 2}. The space group Cmca assigned for {beta}-Ca{sub 3}(BN{sub 2}){sub 2} is derived from Im3-bar m by a group-subgroup relationship. DSC measurements and temperature-dependent in situ X-ray powder diffraction studies showed reversible phase transitions between {beta}- and {alpha}-Ca{sub 3}(BN{sub 2}){sub 2} with transition temperatures between 215 and 240 deg. C. The structure Sr{sub 3}(BN{sub 2}){sub 2} was reported isotypic with {alpha}-Ca{sub 3}(BN{sub 2}){sub 2} (Im3-bar m) with one type of strontium ions being disordered over 12 of equivalent (2c) positions. In addition, a primitive (Pm3-bar m) structure has been reported for Sr{sub 3}(BN{sub 2}){sub 2}. Phase stability studies on Sr{sub 3}(BN{sub 2}){sub 2} revealed a phase transition between a primitive and a body-centred lattice around 820 deg. C. The experiments showed that both previously published structures are correct and can be assigned as {alpha}-Sr{sub 3}(BN{sub 2}){sub 2} (Im3-bar m, high-temperature phase), and {beta}-Sr{sub 3}(BN{sub 2}){sub 2} (Pm3-bar m, low-temperature phase). A comparison of Ca{sub 3}(BN{sub 2}){sub 2} and Sr{sub 3}(BN{sub 2}){sub 2} phases reveals that the different types of cation disordering present in both of the cubic {alpha}-phases (Im3-bar m) have a directing influence on the formation of two distinct (orthorhombic and cubic) low-temperature phases.

Haeberlen, Marco [Abteilung fuer Festkoerperchemie und Theoretische Anorganische Chemie, Institut fuer Anorganische Chemie, Eberhard-Karls-Universitaet, Auf der Morgenstelle 18, D-72076 Tuebingen (Germany); Glaser, Jochen [Abteilung fuer Festkoerperchemie und Theoretische Anorganische Chemie, Institut fuer Anorganische Chemie, Eberhard-Karls-Universitaet, Auf der Morgenstelle 18, D-72076 Tuebingen (Germany); Meyer, H.-Juergen [Abteilung fuer Festkoerperchemie und Theoretische Anorganische Chemie, Institut fuer Anorganische Chemie, Eberhard-Karls-Universitaet, Auf der Morgenstelle 18, D-72076 Tuebingen (Germany)]. E-mail: juergen.meyer@uni-tuebingen.de

2005-05-15

341

Synthesis and structure of new bismuth containing oxychlorides: BiSr 3O 3Cl 3 and BiCa 3O 3Cl 3  

NASA Astrophysics Data System (ADS)

A new bismuth strontium oxychloride BiSr 3O 3Cl 3 has been synthesized and structurally characterized from single crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma (#62) with a=6.687(2) , b=11.4618(8) , c=11.565(2) , V=886,4(3) 3, and Z=4. From the formula weight of 626.20, the density is calculated to be 4.693 g/cm 3. The structure of BiSr 3O 3Cl 3 can be described as a layered structure arranged in sequence Cl/Sr-O/Bi-Sr-O-Cl/Sr-O/Cl along the b axis. The Bi-Sr-O-Cl layer is unique among all the known bismuth oxyhalides in that oxygen and halide are mixed in one layer. Two types of Sr atom and one type of Bi atom are found. Strontium of the Sr-O layer is coordinated by three O atoms with Sr-O distances ranging from 2.404(7) to 2.557(6) and by five Cl atoms with Sr-Cl distances from 3.010(2) to 3.394(3) . Strontium of the Bi-Sr-O-Cl layer is coordinated to three oxygen atoms with Sr-O distances in the range of 2.419(8) to 2.505(6) and to six chlorine atoms with Sr-Cl distances in the range 2.922(3) to 3.796(4) . The Bi atom is coordinated by three O atoms and two Cl atoms with Bi-O bond lengths ranging from 2.062(8) to 2.071(6) and Bi-Cl bond lengths of 3.472(3) . The isostructural compound BiCa 3O 3Cl 3 was also synthesized; the cell dimensions from single crystal data are a=6.383(3) , b=10.803(3) , and c=11.422(3) .

Huang, Jinfan; Sleight, Arthur W.

1992-01-01

342

Heterobimetallic Complexes with MIII-(?-OH)-MII Cores (MIII = Fe, Mn, Ga; MII = Ca, Sr, and Ba): Structural, Kinetic, and Redox Properties  

PubMed Central

The effects of redox-inactive metal ions on dioxygen activation were explored using a new FeII complex containing a tripodal ligand with 3 sulfonamido groups. This iron complex exhibited a faster initial rate for the reduction of O2 than its MnII analog. Increases in initial rates were also observed in the presence of group 2 metal ions for both the FeII and MnII complexes, which followed the trend NMe4+ < BaII < CaII = SrII. These studies led to the isolation of heterobimetallic complexes containing FeIII-(?-OH)-MII cores (MII = Ca, Sr, and Ba) and one with a [SrII(OH)MnIII]+ motif. The analogous [CaII(OH)GaIII]+ complex was also prepared and its solid state molecular structure is nearly identical to that of the [CaII(OH)FeIII]+ system. Nuclear magnetic resonance studies indicated that the diamagnetic [CaII(OH)GaIII]+ complex retained its structure in solution. Electrochemical measurements on the heterobimetallic systems revealed similar one-electron reduction potentials for the [CaII(OH)FeIII]+ and [SrII(OH)FeIII]+ complexes, which were more positive than the potential observed for [BaII(OH)FeIII]+. Similar results were obtained for the heterobimetallic MnII complexes. These findings suggest that Lewis acidity is not the only factor to consider when evaluating the effects of group 2 ions on redox processes, including those within the oxygen-evolving complex of Photosystem II. PMID:24058726

Park, Young Jun; Cook, Sarah A.; Sickerman, Nathaniel S.; Sano, Yohei; Ziller, Joseph W.

2013-01-01

343

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

344

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

345

Oxygen vacancy-mediated room-temperature ferromagnetism in insulating cobalt-substituted SrTiO3 epitaxially integrated with silicon  

NASA Astrophysics Data System (ADS)

Room-temperature ferromagnetic insulating behavior is demonstrated in cobalt-substituted SrTiO3 grown on silicon. Ferromagnetism is exhibited by films with a composition of 30-40% cobalt. Measurements of stoichiometry by x-ray photoelectron spectroscopy indicate Co replacing Ti with the concomitant creation of an approximately equal number of oxygen vacancies as the cobalt ions. First-principles modeling of this system shows that the observed local magnetic moment originates from a cobalt-oxygen vacancy complex with Co in the +2 valence state. The calculations also confirm the insulating nature of the material. The ability to deposit a room-temperature ferromagnetic insulator onto silicon may be useful for certain spintronics applications such as spin filters for spin-injection contacts.

Posadas, Agham B.; Mitra, Chandrima; Lin, Chungwei; Dhamdhere, Ajit; Smith, David J.; Tsoi, Maxim; Demkov, Alexander A.

2013-04-01

346

Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlatticesA designed playground for honeycomb physics  

NASA Astrophysics Data System (ADS)

We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

2015-04-01

347

Chemical Diffusion in the Bi, Sr, Ca, Cu/O System: The Kinetics and Mechanism of the Solid-State Synthesis of a Single-Phase "2212" Material  

NASA Astrophysics Data System (ADS)

Monodimensional (chemical) diffusion measurements have been used to find a clean solid-state path to a pure Bi-Sr-Ca-Cu-O superconductor with two-layer structure, i.e., a suitable sequence of solid-state reactions such that each step gives a single-phase product. When starting from carbonate precursors of CaO and SrO plus Bi 2O 3 and CuO, the critical point of a reaction path of this kind is an appropriate choice of the external conditions of temperature, oxygen partial pressure, and cation molecularities, which must be different from the ideal "2212" values. The results show that a clean solid-state synthesis of a single-phase two-layer material is achieved by reacting at 750C under P(O 2) = 10 -3 atm the Sr 14Cu 24O 41 phase and the ternary solid solution with monoclinic symmetry and cation molecularity near 0.376:0.082:0.543 (Ca:Sr:Bi).

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

1995-05-01

348

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

349

Gd substituted NiCa ferrite/poly vinyl alcohol nanocomposite  

NASA Astrophysics Data System (ADS)

Magnetic nanocomposite material composed of poly vinyl alcohol encapsulated Ni 0.2Ca 0.8Gd 0.08Fe 1.92O 4 was synthesized by a two step chemical method including sol-gel combustion and solvent casting technique. The obtained samples were characterized by powder X-ray diffraction; transmission electron microscopy and Fourier transform infrared spectroscopy. The results of spectroanalysis pointed towards the existence of a considerably feasible interaction between the polymer chain and the ferrite particles. The dc magnetization measurements divulged that both pristine and the nanocomposite samples under applied magnetic field exhibit no hysteretic behavior at room temperature, symptomatic of the superparamagnetic behavior. The departure of field cooled and zero field cooled curves in the moment-versus-temperature plot further confirmed the room temperature superparamagnetic behavior. The extrapolation of the slope of the curves to M=0 imparted the average value of Curie temperature at 323 K (50 C) for both the samples, suggestive of the efficacy of the material for finding application in self controlled hyperthermia.

Prasad, Arun S.; Dolia, S. N.

2012-03-01

350

Antiferroelectric phase transition in (Sr1- xCax)TiO3 (0.12<x?0.40): I. Dielectric studies  

NASA Astrophysics Data System (ADS)

Results of a detailed dielectric study of phase transition in Sr1-xCaxTiO3 in the composition range 0.18?x?0.40 are reported. It is shown that the temperatures T'm and T''m corresponding to the peaks in the real (?'(T)) and imaginary (?''(T)) parts of the dielectric constant, respectively, are not only coincident but also frequency independent, suggesting that these anomalies are due to a thermodynamic phase transition and not a dipole glass/relaxor ferroelectric transition. The Curie-Weiss temperature, as determined from the ?'(T) data above the transition temperature, is found to be negative. Using Landau theory considerations, the negative Curie-Weiss temperature is interpreted in terms of an antiferroelectric phase transition. It is proposed that the smearing of the ?'(T) data in the composition range 0.016?x?0.12 reported by Bednorz and Muller is due to the frustration introduced by the antiferroelectric interactions caused by Ca2+ substitution and the ferroelectric interactions of the SrTiO3 matrix.

Ranjan, Rajeev; Pandey, Dhananjai

2001-05-01

351

Selective substitution of vanadium for molybdenum in Sr2(Fe1-xVx)MoO6 double perovskites  

Microsoft Academic Search

The crystal and magnetic structures of Sr2(Fe1-xVx)MoO6 (0.03<=x<=0.1) compounds are refined by alternately using X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) data collected at room temperature. The refinement results reveal that the V atoms selectively occupy the Mo sites instead of the Fe sites for x<=0.1. The 3d\\/4d cation ordering decreases with the increase of the V content.

Q. Zhang; G. H. Rao; Q. Huang; X. M. Feng; Z. W. Ouyang; G. Y. Liu; B. H. Toby; J. K. Liang

2006-01-01

352

Selective substitution of vanadium for molybdenum in Sr 2(Fe 1? x V x )MoO 6 double perovskites  

Microsoft Academic Search

The crystal and magnetic structures of Sr2(Fe1?xVx)MoO6 (0.03?x?0.1) compounds are refined by alternately using X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) data collected at room temperature. The refinement results reveal that the V atoms selectively occupy the Mo sites instead of the Fe sites for x?0.1. The 3d\\/4d cation ordering decreases with the increase of the V content.

Q. Zhang; G. H.. Rao; Q. Huang; X. M. Feng; Z. W. Ouyang; G. Y. Liu; B. H. Toby; J. K. Liang

2006-01-01

353

Transformation of AeIn4 Indides (Ae = Ba, Sr) into an AeAu2In2 Structure Type Through Gold Substitution  

SciTech Connect

The title compounds were prepared from the elements by high-temperature solid-state synthesis techniques. X-ray structural analyses shows that BaAu{sub 2}In{sub 2} (1) and SrAu{sub 2}In{sub 2} (2) crystallize in a new orthorhombic structure, Pnma, Z = 4 (a = 8.755(2), 8.530(2) {angstrom}; b = 4.712(1), 4.598(1) {angstrom}; c = 12.368(3), 12.283(4) {angstrom}, respectively). Gold substitutes for 50% of the indium atoms in the tetragonal BaIn{sub 4} and monoclinic SrIn{sub 4} parents to give this new and more flexible orthorhombic structure. The Ae atoms in this structure are contained within chains of hexagonal prisms built of alternating In and Au that have additional augmenting atoms around their waists from further condensation of parallel displaced chains. The driving forces for these structural changes are in part the shorter Au-In distances (2.72 and 2.69 {angstrom}) relative to d(In-In) in the parents, presumably because of relativistic contractions with Au. Generalities about such centered prismatic building blocks and their condensation modes in these and related phases are described. Band structure calculations (EHTB) demonstrate that the two compounds are metallic, which is confirmed by measurements of the resistivity of 1 and the magnetic susceptibilities of both.

Dai, Jing-Cao; Corbett, John D.

2007-04-17

354

Regional variation in otolith Sr:Ca ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes.  

PubMed

Otolith Sr:Ca ratios of the African longfinned eel Anguilla mossambica and giant mottled eel Anguilla marmorata from nine freshwater sites in four rivers of South Africa were analysed to reconstruct their migratory life histories between freshwater and saltwater habitats. For A. mossambica, the Sr:Ca ratios in the otolith edge differed significantly among rivers and had large effect sizes, but did not differ among sites within a river. Otolith Sr:Ca ratios did not differ among rivers for A. marmorata. When rivers were pooled, the edge Sr:Ca ratios of A. mossambica were not significantly different from those of A. marmorata. According to the river-specific critical Sr:Ca ratio distinguishing freshwater from saltwater residence, most A. mossambica and A. marmorata had saltwater habitat experience after settlement in fresh water. This was primarily during their elver stage or early in the yellow eel stage. During the middle and late yellow eel stage, freshwater residency was preferred and only sporadic visits were made to saltwater habitats. The data also suggest that regional variations in otolith Sr:Ca ratios affect the critical Sr:Ca value and are a challenge for the reconstruction of migratory life histories that should be explicitly considered to avoid bias and uncertainty. PMID:22803718

Lin, Y-J; Jessop, B M; Weyl, O L F; Iizuka, Y; Lin, S-H; Tzeng, W-N; Sun, C-L

2012-07-01

355

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

356

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

357

Absence of long-range magnetic order in the La1.4Sr0.8Ca0.8Mn2O7 bilayered manganite.  

PubMed

This paper presents the results of a high-resolution neutron diffraction and magnetometry investigation on the optimally doped (x = 0.3) La(1.4)Sr(0.8)Ca(0.8)Mn(2)O(7) bilayered manganite. In particular, two samples with different oxygen contents have been studied to put in prominence the role of the Mn average valence states at fixed cation concentration. The results show, for the first time, the absence of long-range magnetic order in this optimally doped manganite when the A-site of the structure is doped with equal proportions of isovalent Ca and Sr. This holds for both samples, which present different lattice effects with T, thus suggesting the primary role of cation disorder as the source of the lack of long-range order. The presence, for both samples, of defined insulating- to metallic-like transitions suggests that the transport properties are not linked to the evolution of long-range order and that two-dimensional spin ordering in the layers of the perovskite blocks may be sufficient to "assist" the hole hopping. A possible reason for the suppression of magnetic order induced by the Ca doping is a size effect coupled to the cation size mismatch between the Sr and Ca ions. PMID:16942078

Malavasi, Lorenzo; Mozzati, Maria Cristina; Pomjakushin, Vladimir; Tealdi, Cristina; Azzoni, Carlo Bruno; Flor, Giorgio

2006-09-01

358

Pulsed laser deposition of strontium-substituted hydroxyapatite coatings  

NASA Astrophysics Data System (ADS)

The growing evidence of the beneficial role of strontium in bone has increased the interest of developing strontium-containing biomaterials for medical applications, and specifically biocompatible coatings that can be deposited on metallic implants to benefit from their load-bearing capabilities. In this work, strontium-substituted hydroxyapatite (Sr-HA) coatings have been fabricated by pulsed laser deposition (PLD) from initial targets obtained after mixing and compacting commercial HA and SrCO3 powders in different proportions. The films thus fabricated were then structurally, morphologically and chemically characterized using scanning electron microscopy, optical profilometry, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The macroscopic morphology of the films presented in all cases equivalent spherical shaped aggregates of typical calcium phosphate coatings. The results reveal, however, the incorporation of Sr2+ and carbonate groups in the coatings as a function of the SrCO3 content in the ablation target, being the incorporation of Sr2+ a linear phenomenon that is accompanied by a similarly linear withdrawal of Ca2+. The role of Sr2+ in the modification of the HA structure and a possible mechanism of substitution of Sr2+ atoms in place of Ca2+ atoms are discussed.

Pereiro, I.; Rodrguez-Valencia, C.; Serra, C.; Solla, E. L.; Serra, J.; Gonzlez, P.

2012-09-01

359

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

360

Pressure dependence of the superconducting critical temperature of the Tl0.5Pb0.5Sr2Ca1 xYxCu2O7 system  

E-print Network

Pressure dependence of the superconducting critical temperature of the Tl0.5Pb0.5Sr2Ca1 xYxCu2O7 of the superconducting transition temperature Tc of Tl0.5Pb0.5Sr2Ca1 xYxCu2O7 for x 0.0, 0.1, 0.2, and 0.35 has been down to liquid helium tem- peratures. At room temperature 300 K TlSr2CaCu2O7 has a resistivity of 7.2 m

Wijngaarden, Rinke J.

361

ab-plane optical spectra of iodine-intercalated Bi1.9Pb0.1Sr2CaCu2O8 : Normal and superconducting properties  

E-print Network

ab-plane optical spectra of iodine-intercalated Bi1.9Pb0.1Sr2CaCu2O8 : Normal and superconducting of an iodine-intercalated Bi1.9Pb0.1Sr2CaCu2O8 single crystal in the 80­40 000 cm 1 10 meV­5 eV frequency range and at temperatures between 10 and 300 K. As compared to the iodine-free Bi2Sr2CaCu2O8 , we find that the visible

Tanner, David B.

362

A ?SR study of the ruthenium perovskites ACu3Ru4O12 with A = Ca, Pr, Nd  

NASA Astrophysics Data System (ADS)

The metallic ruthenium perovskites ACu3Ru4O12 with A = Ca, Pr,Nd were investigated by zero field (ZF) and weak transverse field (TF) muon spin rotation/relaxation (?SR) spectroscopy. The ZF spectra for CaCu3Ru4O12 show pure static Gaussian Kubo-Toyabe relaxation arising from the interaction between the muon spin and the nuclear moments of the Cu ions. This confirms that no atomic magnetic moment exists. A sudden increase of the lattice parameter a when heating above ~150 K had previously been detected by neutron diffraction. The root mean square field at the muon site Brms was found to be 0.15 mT independent of temperature, in particular around 150 K. Also, no change of spectral parameters is seen in the weak TF data in that temperature range. Those findings imply that the structural change around 150 K takes place without noticeably shifting atomic positions. The spectra for PrCu3Ru4O12 and NdCu3Ru4O12 are dominated by the interaction with the dynamic rare earth moments. The analysis requires the use of the electron-nuclear double relaxation formalism. The electronic part shows simple exponential relaxation typical for a paramagnet. It features, with reducing the temperature a steep increase of paramagnetic relaxation rate as is characteristic for an approach to a magnetic spin freezing transition from above. That result suggests that the magnetic ground states of PrCu3Ru4O12 and NdCu3Ru4O12 are spin frozen states, although bulk magnetic data give no direct evidence in that direction.

Kalvius, G. M.; Hartmann, O.; Gnther, A.; Krimmel, A.; Loidl, A.; Wppling, R.; Sedlak, K.; Scheuermann, R.

2014-12-01

363

Geometry-dependent penetration fields in superconducting Bi2Sr2CaCu2O8+? platelets  

SciTech Connect

Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation does not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in H{sub p}. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.

By: Curran, P. J.; Clem, J. R.; Bending, S. J.; Tsuchiya, Y.; Tamegai, T.

2010-10-01

364

Geometry-dependent penetration fields of superconducting Bi2Sr2CaCu2O8+? platelets  

SciTech Connect

Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation does not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in Hp. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.

Curran, P. J.; Clem, J. R.; Bending, S. J.; Tsuchiya, Y.; Tamegai, T.

2010-10-01

365

Heat Capacity of Zn and Ni Doped Bi_2Sr_2CaCu_2O8 Single Crystals  

NASA Astrophysics Data System (ADS)

The consequences of low non-magnetic and magnetic impurity doping were studied in Bi-2212 single crystals by means of the experimental resistivity, magnetization, heat capacity and thermal conductivity. The effect of the impurities includes, but it is not restricted to, a suppression of the superconducting transition temperature T_C. The heat capacity of Zn (0.3 %) and Ni (0-2.4 %) doped Bi_2Sr_2CaCu_2O8 crystals prepared by the floating solvent traveling zone method has been measured between 0.050 and 2 K in zero and applied magnetic fields up to several tesla. Both pure and doped samples display identical low-temperature nuclear Schottky anomaly tail at T <= 200 mK. The difference between specific heat of the Ni-doped sample and that of the pure Bi-2212 is a broad peak centered at about 1K, with an entropy associated with this feature of about 0.08 J/mol-K or 20% of full Rln (2S+1) spin entropy of Ni impurities (assuming S=1). Freezing of magnetic impurities may be related to observation of a second low-temperature transition in several of the Ni-doped samples.(R. Movshovich et al., preprint. Also A.V. Balatsky et al., preprint.) R. Movshovich et al., preprint

Jaime, M.; Movshovich, R.; Sarrao, J.; Yoshizaki, R.

1998-03-01

366

Initial magnetization and coupling nature of the high-Tc grains in Bi-Pb-Sr-Ca-Cu-O  

NASA Astrophysics Data System (ADS)

The coupling between grains was studied through low-field (<100 Oe) initial magnetization M(H) on bulk samples of Bi-Pb-Sr-Ca-Cu-O with a single high-Tc (110 K) phase prepared under different sintering times ts. The M(H) shows a variation with changing ts due to the weak links between grains and its behavior is characterized by three threshold fields: HB1, HB2, and HB3. The first flux entry into the sample along the grain boundaries due to flux creep occurs at HB1, much lower than H?c1 (~7 Oe at 77 K, ~15 Oe at 0 K) for H? c axis determined from the c-axis-oriented tape with Jc=5400 A/cm2 (77 K, H=0). Between HB1 and HB2, M(H) deviates from a straight line due to shielding of the sample volume; between HB2 and HB3 it falls on the Meissner line, an effect ascribed to electrically decoupled grains. The first flux entry into the grains themselves occurs at HB3, above which M(H) is governed by the intragrain magnetic properties of an Abrikosov lattice. Prolonged sintering improves the weak links between the grains and suppresses both the flux creep at the grain boundaries and the electrical decoupling between grains, which opens transport current paths and leads to the rise in Tc(?=0).

Oota, A.; Noji, H.; Ohba, K.

1991-05-01

367

Direct imaging of hot spot 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) are a promising source of coherent continuous-wave terahertz radiation. When electrical power is applied to these devices, it is thought that 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 from Bi-2212 stacks. In order to better understand these hot spots, we have performed a thermal imaging study of BSCCO stacks which generate approximately 50 microwatts of radiation power at 0.59 THz. Utilizing the temperature-dependent 612nm fluorescence line of Eu^3+, we are able to directly measure the temperature distribution at the top surface of these stacks with a resolution of +/- 1K. The images 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, Timothy; Gray, Ken; Koshelev, Alexei; Kwok, Wai-Kwong; Welp, Ulrich; Vlasko-Vlasov, Vitalii; Kadowaki, Kazuo; Minami, Hidetoshi

2013-03-01

368

X-ray topography of Ca 0.5Sr 0.5NdAlO 4 single crystal  

NASA Astrophysics Data System (ADS)

A Ca 0.5Sr 0.5NdAlO 4 single crystal grown by the Czochralski method in the [1 0 0] direction was investigated by means of conventional projection X-ray topography, and by means of synchrotron white beam and monochromatic beam topography. The topographic investigation revealed growth striations with strong black diffraction contrasts distributed periodically in the form of concentric rings, and a significant number of resolved defects. Some of these defects seem to be associated with precipitates, while others form linear diffraction contrasts located perpendicularly to the striation stripes. The last category of defects can be somehow associated with dislocations, but provides much more intense and complex diffraction contrast that can be expected for individual dislocations. A significant lattice deformation associated with striation was revealed with some of the synchrotron topographic methods, particularly back-reflection white beam topography with fine mesh placed behind the crystal and transmission synchrotron section topography, where a characteristic bending of the section image was observed. The transmission section topographs provided also good visibility of segregation fringes in the plane intersected by the beam, corresponding to the subsequent positions of the growth surface.

Malinowska, A.; Lefeld-Sosnowska, M.; Wieteska, K.; Wierzchowski, W.; Graeff, W.; Pajaczkowska, A.

2008-07-01

369

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

370

Harmonic frequency mixing in Bi2Sr2CaCu2O8+X intrinsic Josephson junctions  

NASA Astrophysics Data System (ADS)

In a c-axis junction stack (10 ?m10 ?m in a-b plane) patterned on a Bi2Sr2CaCu2O8+X single crystal, we performed harmonic mixings between a 100 GHz signal and up to the 98th harmonic of a local oscillator at about 1 GHz. The dependence of PIF on V, where PIF is the mixing output at the intermediate frequency and V is the dc voltage across the junction stack, was strongly affected by the local oscillator power levels. For low values of local oscillator power, the optimum operation point where PIF became maximum was around zero bias, and typical multi-branch structure of PIF vs V curves were observed. For high values of local oscillator power, the optimum operation point moved to the high-voltage region. In both cases, interesting oscillations occurred on the PIF vs V curves. Our experimental results led us to believe that intrinsic Josephson junctions can be good candidates for high frequency applications and the harmonic mixing may be a useful probe to investigate plasma phenomena in the layered superconductors.

Wang, H. B.; Aruga, Y.; Tachiki, T.; Mizugaki, Y.; Chen, J.; Nakajima, K.; Yamashita, T.; Wu, P. H.

1999-10-01

371

Sr Incorporation and Calcium Isotopic Fractionation during Calcium Carbonate Precipitation  

NASA Astrophysics Data System (ADS)

Element substitution and calcium isotopic fractionation can provide information about the mechanisms of CaCO3 precipitation, precipitation rates, temperatures and solution chemistry. In the present study precipitation experiments for the formation of the CaCO3 polymorphs: calcite, aragonite and vaterite were carried out. Calcium carbonates are formed at various Mg/Ca ratios or in presence of polyaspartic acid at temperatures between 5 and 40? C at pH 8.3 by using an advanced CO2-diffusion technique (Tang et al., 2008). The results indicate elevated Sr distribution coefficients (DSr) during calcite and vaterite formation at increasing precipitation rates, whereas DSr-values decrease only slightly with increasing rate during the formation of aragonite. 44Ca/40Ca fractionation increases for aragonite and calcite formation as precipitation rates increase. Preliminary results show less calcium isotopic fractionation for vaterite compared to calcite and aragonite. However, 44?40CaCaCO3(s)-Ca(aq)-values for the three modifications indicate an inverse correlation with DSr. Respective mechanisms and proposed models are discussed. Reference Tang J., Khler S.J., and Dietzel M. (2008) Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic calcite formation: I. Sr in corporation, Geochimica et Cosmochimica Acta, 72, 3718-3732.

Niedermayr, A.; Dietzel, M.; Khler, S. J.; Bhm, F.; Kisakurek, B.; Eisenhauer, A.

2009-04-01

372

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

373

Stepwise behavior of vortex-lattice melting transition in tilted magnetic fields in single crystals of Bi(2)Sr(2)CaCu(2)O(8 + delta).  

PubMed

The vortex-lattice melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) single crystals was studied using in-plane resistivity measurements in magnetic fields tilted away from the c axis to the ab plane. In order to avoid the surface barrier effect which hinders the melting transition in the conventional transport measurements, we used the Corbino geometry of electric contacts. The complete H(c) - H(ab) phase diagram of the melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) is obtained for the first time. The c-axis melting field component H(c)(melt) exhibits the novel, stepwise dependence on the in-plane magnetic fields H(ab) which is discussed on the basis of the crossing vortex-lattice structure. The peculiar resistance behavior observed near the ab plane suggests the change of phase transition character from first to second order. PMID:11177965

Mirkovi?, J; Savel'ev, S E; Sugahara, E; Kadowaki, K

2001-01-29

374

Investigations of defect structure and EPR parameters for tetragonal Nd3+ centers in AWO4 (A=Ca, Sr, Pb) crystals by superposition model analysis  

NASA Astrophysics Data System (ADS)

The characteristics of the local environment around the paramagnetic centers formed by the Nd3+ ions doped into three tungstate crystals (CaWO4, SrWO4 and PbWO4) are investigated by using superposition model analysis. The inter-relation between the electronic and molecular structures of Nd3+ ion in a tetragonal (S4 symmetry) ligand field has been established by a complete diagonalization (of energy matrix) method. The local lattice distortions in the vicinity of the impurity ion Nd3+ have been derived and the local distortion angles ??=-1.69, -1.13, and -1.48 are obtained for Nd3+ in CaWO4, SrWO4 and PbWO4, respectively. The calculated EPR parameters are in good agreement with the experimental values. On the basis of this, the links between EPR g-factors and the local structure as well as crystal field parameters are studied.

Li, Hui; Kuang, Xiao-Yu; Mao, Ai-Jie; Wang, Zhen-Hua

2014-07-01

375

Evaluating Sea Surface Temperature Variability Using Replicated Porites lobata Coral Sr/Ca Records From Clipperton Atoll (1994-1894AD)  

NASA Astrophysics Data System (ADS)

The fidelity of coral Sr/Ca as a tracer of water temperature was assessed at monthly resolution in cores from three coral colonies of Porites lobata at Clipperton Atoll (10 18'N, 109 13'W) in the eastern Pacific. Significant linear relationships were found between individual cores and instrumental sea surface temperature (SST) for the 20-year calibration period of 1994-1974 (R2= 0.55, 0.52, and 0.49; P < 0.001) with similar slopes ranging from 0.065 to 0.069 mmol/mol/ C but with slightly different y-intercept values (11.19, 11.02, and 11.15). The 3-core composite average increased the regression to instrumental SST (R2= 0.66) with a slope of 0.068 mmol/mol/ C and y-intercept of 11.12. Correlations of monthly Sr/Ca data between cores was high (core 2B vs. 6A from 1994 to 1942, R= 0.69; core 2B vs. 4B from 1994 to ~1934, R=0.44) with the exception of a 10-year section of growth in one coral. SEM images and skeletal ?18O and ?13C revealed nothing anomalous about this interval. Inter-colony comparison of calcification rates displayed poor reproducibility and does not appear to exert a significant influence on skeletal Sr/Ca. The composite Clipperton Sr/Ca record (without data from the anomalous interval) exhibits interannual fluctuations highly correlated with the El Nio Southern Oscillation (ENSO) that are in phase with observed gridded SST record (Global Ice and Sea Surface Temperature Ver. 2.2 (GISST)). Despite the greater amplitude of annual and interannual variability in the composite Sr/Ca-SST record relative to gridded SST, the overall similar ENSO frequency and periodicity attests to the high degree of reproducibility of this temperature proxy at Clipperton. Our coral derived SST record shows dampened ENSO-band variability in the 1920s-1940s during the well- documented "ENSO quiet period". Examination of only the boreal spring data in the composite Sr/Ca record and in Clipperton ?18Oseawater record (using coral skeletal ?18O and Sr/Ca data from 1994-1894) indicates reduced interannual spring SST variability and greater interannual ?18Oseawater variability from 1925 to mid 1940s. These observations support change in freshwater flux in the region and imply anomalous variations in the Intertropical Convergence Zone during the ENSO quite period. An observed warming trend of 1C since 1976 may have been related to the 1976 Cold Event and subsequent interdecadal climate shift of the Pacific Ocean. These results highlight the need to replicate records in coral-based paleoclimatology, but also support the conclusion reached by many studies for SST driven Sr/Ca variability in rapidly growing Porites corals.

Wu, H. C.; Linsley, B. K.; Schrag, D. P.

2009-05-01

376

Luminescent Nitridophosphates CaP2 N4 :Eu(2+) , SrP2 N4 :Eu(2+) , BaP2 N4 :Eu(2+) , and BaSr2 P6 N12 :Eu(2.).  

PubMed

Nitridophosphates MP2 N4 :Eu(2+) (M=Ca, Sr, Ba) and BaSr2 P6 N12 :Eu(2+) have been synthesized at elevated pressures and 1100-1300?C starting from the corresponding azides and P3 N5 with EuCl2 as dopant. Addition of NH4 Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single-crystal X-ray diffraction data (CaP2 N4 :Eu(2+) (P63 , no.?173), a=16.847(2), c=7.8592(16)?, V=1931.7(6)?(3) , Z=24, 2033 observed reflections, 176 refined parameters, wR2 =0.096). Upon excitation by UV light, luminescence due to parity-allowed 4f(6) ((7) F)5d(1) ?4f(7) ((8) S7/2 ) transition was observed in the orange (CaP2 N4 :Eu(2+) , ?max =575?nm), green (SrP2 N4 :Eu(2+) , ?max =529?nm), and blue regions of the visible spectrum (BaSr2 P6 N12 :Eu(2+) and BaP2 N4 :Eu(2+) , ?max =450 and 460?nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline-earth ions. The corresponding full width at half maximum values (2240-2460?cm(-1) ) are comparable to those of other known Eu(2+) -doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba3 P5 N10 Br:Eu(2+) , this investigation represents the first report on the luminescence of Eu(2+) -doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu(2+) -doped nitridophosphates may have the potential to be further developed into efficient light-emitting diode phosphors. PMID:25765825

Pucher, Florian J; Marchuk, Alexey; Schmidt, Peter J; Wiechert, Detlef; Schnick, Wolfgang

2015-04-20

377

An EXAFS study on Bi 2Sr 2Ca 1-xPr xCu 2O 8-? single crystal using polarized synchrotron radiation  

NASA Astrophysics Data System (ADS)

We have made polarization dependent Extended X-ray Absorption Fine Structure (EXAFS) measurements on a Bi 2Sr 2Ca 1-xPr xCu 2O 8-? single crystal in the E// a, E// b and E// a^45 orientations. The results on Cu-K edge and Pr L III edge EXAFS have been discussed to explain the quenching of superconductivity due to the presence of Pr cation as it was known to destruct the superconductivity by disturbing the local environment around Ca.

Dalela, S.; Dalela, B.; D, Neena; Alvi, P. A.

2011-03-01

378

Magnetic and transport properties of single-crystal Ca2RuO4: Relationship to superconducting Sr2RuO4  

Microsoft Academic Search

Ca2RuO4, which has the single-layer tetragonal K2NiF4 structure, shows nonmetallic behavior for T<300 K unlike its isostructural counterpart, Sr2RuO4, which is metallic for all T<1300 K and which undergoes a superconducting transition temperature below T=1.35 K, possibly with p-wave spin pairing. Magnetization, electrical-resistivity, and heat-capacity data for single-crystal Ca2RuO4 are presented. An antiferromagnetic transition is identified at TN=110 K in

G. Cao; S. McCall; M. Shepard; J. E. Crow; R. P. Guertin

1997-01-01

379

Formation of superconducting Bi sub 2-y Pb sub y Sr sub 2 Ca sub 2 Cu sub 3 O sub x from coprecipitated oxalates  

SciTech Connect

The conditions for the coprecipitation of Bi{sup 3+}, Pb{sup 2+}, Ca{sup 2+} as oxalates are reported. These oxalates were used as precursors for the formation of Bi{sub 2-y}Pb{sub y}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconducting ceramics. The behavior of the oxalates upon heat treatment was studied by thermogravimetry. Both the oxalates and the superconducting oxides were analyzed and characterized by atomic absorption spectroscopy and by X-ray diffraction.

Bernhard, K.; Gritzner, G.; Wang, Xianzhong; Baeuerle, D. (Johannes Kepler Universitaet Linz (Austria))

1990-06-01

380

Neutron diffraction, specific heat and ?SR study of the spin-chain compounds Ca 2+ x Y 2? x Cu 5O 10  

Microsoft Academic Search

We report on neutron diffraction, specific heat and ?SR studies of the edge-sharing spin-chain compound Ca2+xY2?xCu5O10. At small and intermediate hole doping (x<1) the ordered Cu moment decreases rapidly. Above x=1 the long-range magnetic order disappears. The magnetic system develops into a state, where a spin-chain regime and static magnetic configurations formed by the residual spins coexist. Near x=2 the

V. Kargl; A. Mirmelstein; P. Bni; D. Sheptyakov; A. Amato; S. Kazakov; J. Karpinski; A. Erb

2004-01-01

381

Numerical results on two-body and (two + three)-body lattice dynamics of CaF2, SrF2, and BaF2  

Microsoft Academic Search

Utilizing semiempirical two-body and (two + three)-body force fields, respectively, two distinct sets of shell-model calculations are reported on the crystal dynamics of CaF2, SrF2, and BaF2. The central force computations cover longwave properties, dispersion curves, specific heat, and thermal expansion. Also included are numerical results for mean square amplitudes as calculated conventionally and, in addition, by a new computational

1973-01-01

382

Ab initio prediction of the structural, electronic, elastic and thermodynamic properties of the tetragonal ternary intermetallics XCu2Si2 (X = Ca, Sr)  

NASA Astrophysics Data System (ADS)

Structural parameters, electronic structure, elastic constants and thermodynamic properties of the tetragonal ternary intermetallics CaCu2Si2 and SrCu2Si2 are investigated theoretically for the first time using the plane-wave ultra-soft pseudopotential method based on the density functional theory. The calculated equilibrium structural parameters agree well with the existing experimental data. Pressure dependence of the structural parameters is also explored. Analysis of the band structure, total and site-projected l-decomposed densities of states and valence charge distributions reveals the conducting character of both considered materials with a mixture of ionic-covalent chemical bonding character. Pressure dependences of the single-crystal elastic constants C ij for CaCu2Si2 and SrCu2Si2 are explored. The elastic wave velocities propagating along the principal crystallographic directions are numerically estimated. The elastic anisotropy is estimated and further illustrated by 3D-direction-dependent of the Young's modulus. A set of some macroscopic elastic moduli, including the bulk, Young's and shear moduli, Poisson's coefficient, average elastic wave velocities and Debye temperature, were calculated for polycrystalline CaCu2Si2 and SrCu2Si2 from the C ij via the Voigt-Reuss-Hill approximations. Through the quasiharmonic Debye model, which takes into account the phonon effects, the temperature and pressure dependencies of the bulk modulus, unit cell volume, volume thermal expansion coefficient, Debye temperature and volume constant and pressure constant heat capacities of CaCu2Si2 and SrCu2Si2 are explored systematically in the ranges of 0-40 GPa and 0-1400 K.

Reffas, Mounir; Bouhemadou, Abdelmadjid; Haddadi, Khelifa; Bin-Omran, Saad; Louail, Layachi

2014-12-01

383

Weak links within a Bi sub 2 Sr sub 2 Ca sub 1 Cu sub 2 O sub x single crystal by magnetizaion and dirct optical observations  

SciTech Connect

We have performed magnetic susceptibility and direct optical High Contrast Magnetic Flux (HICOM) observations on a single crystal of Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub x}. Low temperature pinning and high temperature flux creep have been observed by HICOM. The results suggest that the breakdown of flux pinning may occur gradually with temperature and may exhibit spatial variation related to sample inhomogeneities. 4 refs., 2 figs.

Willis, J.O. (Los Alamos National Lab., NM (United States)); Nakamura, N.; Gotoh, S.; Takamuku, K.; Koshizuka, N.; Tanaka, S. (Superconductivity Research Lab., Tokyo (Japan))

1991-01-01

384

Vortex line pinning in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals with columnar defects  

SciTech Connect

The ac transmittivity of heavy-ion irradiated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals shows a sharp cusp as function of the dc field orientation with respect to the columnar defects. This unambiguously demonstrates the connected nature of vortices in these samples. In contrast, the irreversibility line does not reveal a cusp.

van der Beek, C.J.; Vinokur, V.M.; Crabtree, G.W. [Argonne National Lab., IL (United States); Schmidt, B.; Konczykowski, M. [CEA-Ecole Polytechnique, 91 - Palaiseau (France). Lab. d`Etudes des Solides Irradies

1994-05-01

385

Dielectric investigation of M IIM IV(PO 4) 2 double orthophosphates (M II = Ca, Sr, Ba, Pb; M IV = Ti, Zr, Hf, Ge, Sn)  

Microsoft Academic Search

MIIMIV(PO4)2 (MII=Ca, Sr, Ba, Pb; MIV=Ti, Zr, Hf, Ge, Sn) ceramics were prepared by solid state reaction method and consolidated by spark plasma sintering in order to study their electrical properties. The dielectric study performed at room temperature was aimed to determine the basic electrical properties of these compounds. MaxwellWagner polarization contributions, which are active at low frequencies cause a

Florin Tudorache; Karin Popa; Liliana Mitoseriu; Nicoleta Lupu; Damien Bregiroux; Gilles Wallez

2011-01-01

386

Multiple flux-flow branches and phase transition of Josephson fluxon lattice in intrinsic Bi2Sr2CaCu2O8+x stacked Josephson junctions  

Microsoft Academic Search

We experimentally study the c-axis current-voltage characteristics (IVCs) of small area Bi2Sr2CaCu2O8+x mesas containing only a few intrinsic stacked Josephson junctions (SJJs). In a magnetic field, H, parallel to the ab-plane, a Josephson flux-flow branch (FFB) appears in the IVCs. The FFB consists of multiple closely spaced but distinct sub-branches and exhibit a well defined Fiske step structure. When normalised

V. M. Krasnov; N. Mros; A. Yurgens; D. Winker

1999-01-01

387

Use of microsatellite DNA and otolith Sr:Ca ratios to infer genetic relationships and migration history of four morphotypes of Rhinogobius sp. OR  

Microsoft Academic Search

The genetic diversity and relationship among four morphotypes of Rhinogobius sp. OR, Gobiidae (T?shoku, Shinjiko, Gi-t?shoku, and Shimahire) were investigated with seven microsatellite DNA loci,\\u000a and amphidromy of these morphotypes was verified by strontium (Sr) and calcium (Ca) deposition in the otolith. Samples of\\u000a T?shoku, Shinjiko, Gi-t?shoku, and Shimahire were collected from, respectively, three, three, two, and four locations\\u000a in

Kenichi Ohara; Momoko Hotta; Daisuke Takahashi; Takashi Asahida; Hitoshi Ida; Tetsuya Umino

2009-01-01

388

Thermal decomposition study of [MCu(C 3H 2O 4) 2(H 2O) n ] phases (M is Ca ( n = 3), Sr and Ba ( n = 4))  

Microsoft Academic Search

Three new compounds with the general formula [MCu(C3H2O4)2(H2O)n] (M is Ca (n = 3), Sr and Ba (n = 4)) have been synthesized and characterized by analytical and infrared techniques. X-ray diffraction methods have shown that all the complexes have orthorhombic unit cells. Thermal decomposition of these compounds using TGA-DSC and DTA techniques involves three consecutive steps: dehydration, ligand pyrolysis

M. Insausti; I. Gil de Muro; L. Lorente; T. Rojo; E. H. Bocanegra; M. I. Arriortua

1996-01-01

389

Synthesis and crystal structure of MCu(edta)·4HO: Molecular precursors for MCuO (M = Ca, Sr, Ba)  

Microsoft Academic Search

The compounds MCu(edta)·4HO (edta = ethylenediaminetetraacetic acid; M = Ca, Sr, Ba) have been synthesized and characterized by analytical and spectroscopic techniques. The structures of the strontium and barium complexes have been determined by X-ray diffraction methods. Both compounds are isostructural and crystallize in the monoclinic system, space group P2\\/c, with four formula weights in a cell measuring a =

M. Insausti; L. Lezama; R. Cortes; T. Rojo; J. L. Pizarro; E. H. Bocanegra; M. I. Arriortua

1994-01-01

390

Physical properties of the doped manganites Ln0.5M0.5Mno3 (Ln = Pr, La; M = Sr, Ca, Ba)  

Microsoft Academic Search

We present the structural, magnetic and electrical properties of some manganese oxides such as Ln0.5M0.5MnO3 (Ln = La, Pr and M = Ca, Sr, Ba) in which the average ionic radius of the A site cation is varied while keeping the Mn\\/Mn ratio fixed to 1. All the studied samples have a perovskite structure with rhombohedral or orthorhombic distortion.

K. Guidara; J. Dhahri; E. Dhahri

2000-01-01

391

Tropical sea Surface Temperature and Salinity Variability During Deglaciation Inferred From A new Tahitian Coral Oxygen Isotope and Sr/Ca Record  

NASA Astrophysics Data System (ADS)

We investigate tropical sea surface temperature (SST) variability during the last deglaciation from a subfossil Porites coral. Since this species is still growing in the same location today, this analysis allows for a direct comparison between modern and prehistoric behavior as deglaciation proceeded. The coral sample was recovered during IODP Leg 310 drilling of offshore fossil reefs (sample 310 11A 6R 1W 27,0-40,0). Stratigraphic evidence and mean ?18O values suggest that the coral grew as sea level began to rise just following the last glacial maximum; these inferences will be confirmed with U-series dating now in progress. Exploration for diagenetic features using SEM and thin sections has allowed us to identify the parts of the coral slab most suitable for paleoclimate analysis. To reconstruct sea surface conditions during this time, we measured ?18O and Sr/Ca at 0.5mm resolution; annual density banding indicates that our record spans roughly 15 years with an annual growth rate of 9-15 mm/yr. Mean oxygen isotope values fall about 2 heavier than a modern coral from neighboring Moorea. Assuming an ice volume correction of 0.8-1.0, our ?18O results suggest that cooler SSTs were probably accompanied by regional seawater ?18O increases, as a paleotemperature interpretation of the isotopic results yields values around 5- 6C, larger than expected. Modern Sr/Ca calibration data are planned to allow us to use Sr/Ca to partition the temperature and seawater isotope components of this signal, and replication of both Sr/Ca and ?18O will allow us to assess additional uncertainties. The annual cycle of coral ?18O is comparable or slightly reduced from the modern, although differences in site exposure may partly account for the difference we observe. We will compare our temperature inferences with additional data and with coupled model results.

Coppola, A. I.; Cole, J.; Barnett, H.; Tudhope, A. W.; Ault, T. R.

2007-12-01

392

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

393

Microstructure and superconductivity in a new superconductor series - (Tl,Pb)1Sr2Ca(n-1)Cu(n)O(2n+3-delta)  

Microsoft Academic Search

The procedure for synthesizing the first two menmbers of the new superconductor series, (Tl,Pb)1Sr2Ca(n-1)Cu(n)O(2n+3-delta), with n values equal to 1 and 2, is described together with the superconducting properties of these compounds. The detailed atomic-level microstructures of these compounds were determined and computer simulated with structural models. It was found that the value of Tc increased with n and the

J. C. Barry; B. L. Ramakrishna; Renu Sharma; Z. Iqbal; H. Eckhardt

1989-01-01

394

Effects of La3+ substitution on the magnetic properties of double perovskites A2FeMoO6 (A=Ca and Ba)  

Microsoft Academic Search

We have studied effects of the partial substitution of La3+ for A2+ on the magnetic properties of double perovskites A2FeMoO6 (A=Ca and Ba). Polycrystalline A2-xLaxFeMoO6 (0?x?0.3) samples have been prepared by the conventional solid-state reaction in a stream of 5% H2\\/Ar gas. The X-ray data indicate that A=Ca is monoclinic with the space group P21\\/n and A=Ba is cubic with

H. Han; H. M. Yang; W. Y. Lee; S. B. Kim; C. S. Kim; B. W. Lee

2003-01-01

395

Modified texture and high temperature transport properties of doubly substituted Ba xAg yCa 2.8Co 4O 9 thermoelectric oxide  

NASA Astrophysics Data System (ADS)

Doubly substituted polycrystalline compound bulk samples of Ba xAg yCa 2.8Co 4O 9 were prepared via citrate acid sol-gel method followed by spark plasma sintering. The phase composition, orientation, texture and high temperature electrical properties were systematically investigated. The results showed that the orientation and the texture could be modified by altering ratio of Ba to Ag. The resistivity and the Seebeck coefficient of substituted samples were decreased by decreasing Ba/Ag ratio except for that of Ba 0.1Ag 0.1Ca 2.8Co 4O 9 sample with lowest electrical resistivity (7.2 m? cm at 973 K), moderately high Seebeck coefficient (172 ?V/K at 973 K) and improved power factor (0.42 mW/mK 2 at 973 K).

Zhang, F. P.; Lu, Q. M.; Zhang, J. X.

2009-08-01