Browsing by Author "Wu, HC"

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    Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements
    (John Wiley & Sons, Inc, 2013-07-25) Hathorne, EC; Gagnon, A; Felis, T; Adkins, J; Asami, R; Boer, W; Caillon, N; Case, D; Cobb, KM; Douville, E; deMenocal, P; Eisenhauer, A; Garbe-Schönberg, D; Geibert, W; Goldstein, S; Hughen, K; Inoue, M; Kawahata, H; Kölling, M; Cornec, FL; Linsley, BK; McGregor, HV; Montagna, P; Nurhati, IS; Quinn, TM; Raddatz, J; Rebaubier, H; Robinson, L; Sadekov, A; Sherrell, R; Sinclair, D; Tudhope, AW; Wei, GJ; Wong, HKY; Wu, HC; You, CF
    The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1. ©2013 American Geophysical Union
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    Magnetic structure and Kondo lattice behavior in CeVGe3: an NMR and neutron scattering study
    (American Physical Society, 2023-09-28) Chaffey, C; Wu, HC; Jin, H; Sherpa, P; Klavins, P; Avdeev, M; Aji, S; Shimodate, R; Nawa, K; Sato, TJ; Taufour, V; Curro, NJ
    We present nuclear magnetic resonance (NMR), neutron diffraction, magnetization, and transport measurements on a single crystal and powder of CeVGe3. This material exhibits heavy fermion behavior at low temperatures, accompanied by antiferromagnetic (AFM) order below 5.8 K. We find that the magnetic structure is incommensurate with AFM helical structure, characterized by a magnetic modulated propagation vector of (0,0,0.49) with in-plane moments rotating around the c axis. The NMR Knight shift and spin-lattice relaxation rate reveal a coherence temperature T∗∼15K, and the presence of significant antiferromagnetic fluctuations reminiscent of the archetypical heavy fermion compound CeRhIn5. We further identify a metamagnetic transition above Hm∼2.5T for magnetic fields perpendicular to c. We speculate that the magnetic structure in this field-induced phase consists of a superposition with both ferromagnetic and antiferromagnetic components, which is consistent with the NMR spectrum in this region of the phase diagram. Our results thus indicate that CeVGe3 is a hexagonal structure analog to tetragonal CeRhIn5. ©2023 American Physical Society.