Browsing by Author "Kobayashi, Y"

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    Differentiating between the d13C signature from environmental conditions and SOM cycling in eastern Australian peat sediments
    (Australasian Quaternary Association (AQUA), 2021-07-08) Forbes, MS; Cohen, TJ; Marx, SK; Sherborne-Higgins, B; Cadd, H; Francke, A; Cendón, DI; Peterson, MA; Mooney, SD; Constantine, M; Boesl, F; Kobayashi, Y; Mazumder, D
    The analysis of stable carbon isotopes is commonly used in Quaternary science to reconstruct the environmental conditions and vegetation contributions to sedimentary sequences. However, the measured d13C signature of the total organic matter (OM) pool can also reflect other complexities within depositional environments. The peats of the Thirlmere Lakes system in the southern section of the Blue Mountains World Heritage Area provides an excellent opportunity to closely scrutinise such d13C dynamics. These deposits are rich in TOC (20-40%) meaning analytical techniques such as 13C-NMR, used to characterise the OM pool, can be applied effectively. Furthermore, the identification of several peat units deposited over the last ~130 ka allows for temporal comparisons. d13C values determined for a 7 m sediment sequence from Lake Couridjah representing both the MIS 1 and MIS 5e interglacial periods vary by up to 4 to 6‰. These trends were subsequently identified in two other sediment sequences (Lake Baraba and Lake Werri Berri) proximal to Lake Couridjah. Initially we interpreted our results as reflecting a C3 dominated vegetation environment with MIS 1 wetter than MIS 5e, following the established relationship between water stress and d13C enrichment. However, spectral analysis of the OM pool indicates that d13C is driven by changing OM dynamics rather than large changes in environmental conditions. In these environments, the greater presence of carbohydrates (i.e. cellulose) in MIS 1 result in more depleted d13C values. In contrast, the MIS 5e peat is dominated by relative inert OM C fractions including charcoal and lipids (such as leaf waxes), which influences environmental proxies such as C/N. Thus, it is likely that the older MIS 5e peat is a more decomposed version of the active MIS 1 peat, and thus differentiating environmental conditions between the two using d13C alone is not particularly illuminating. To overcome this, we describe the d13C values for a coarse charcoal and high temperature hydrogen pyrolysis fractions, modern vegetation, catchment POC and DOC, and n-alkanes composition and generate catchment carbon models for both MIS 1 and MIS5e. Finally comparing the size of the OM pools of both interglacial deposits can provide useful information in estimating the carbon storage capacity of peat deposits in eastern Australia over these time scales. © The Authors.
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    Differentiating between the d13C signature from environmental conditions and SOM cycling in eastern Australian peat sediments
    (Australasian Environmental Isotope Conference, 2022-11-14) Forbes, MS; Cohen, TJ; Marx, SK; Sherborne-Higgins, B; Cadd, H; Francke, A; Cendón, DI; Peterson, MA; Mooney, SD; Constantine, M; Boesl, F; Kobayashi, Y; Mazumder, D
    The analysis of stable carbon isotopes is commonly used in Quaternary science to reconstruct the environmental conditions and vegetation contributions to sedimentary sequences. However, the measured d13C signature of the total organic matter (OM) pool can also reflect other complexities within depositional environments. The peats of the Thirlmere Lakes system in the southern section of the Blue Mountains World Heritage Area provides an excellent opportunity to closely scrutinise such d13C dynamics. These deposits are rich in TOC (20-40%) meaning analytical techniques such as 13C-NMR, used to characterise the OM pool, can be applied effectively. Furthermore, the identification of several peat units deposited over the last ~130 ka allows for temporal comparisons. d13C values determined for a 7 m sediment sequence from Lake Couridjah representing both the MIS 1 and MIS 5e interglacial periods vary by up to 4 to 6‰. These trends were subsequently identified in two other sediment sequences (Lake Baraba and Lake Werri Berri) proximal to Lake Couridjah. Initially we interpreted our results as reflecting a C3 dominated vegetation environment with MIS 1 wetter than MIS 5e, following the established relationship between water stress and d13C enrichment. However, spectral analysis of the OM pool indicates that d13C is driven by changing OM dynamics rather than large changes in environmental conditions. In these environments, the greater presence of carbohydrates (i.e. cellulose) in MIS 1 result in more depleted d13C values. In contrast, the MIS 5e peat is dominated by relative inert OM C fractions including charcoal and lipids (such as leaf waxes), which influences environmental proxies such as C/N. Thus, it is likely that the older MIS 5e peat is a more decomposed version of the active MIS 1 peat, and thus differentiating environmental conditions between the two using d13C alone is not particularly illuminating. To overcome this, we describe the d13C values for a coarse charcoal and high temperature hydrogen pyrolysis fractions, modern vegetation, catchment POC and DOC, and n-alkanes composition and generate catchment carbon models for both MIS 1 and MIS5e. Finally comparing the size of the OM pools of both interglacial deposits can provide useful information in estimating the carbon storage capacity of peat deposits in eastern Australia over these time scales.
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    Direct synthesis of chromium perovskite oxyhydride with a high magnetic-transition temperature
    (Wiley Online Library, 2014-09-22) Tassel, C; Goto, Y; Kuno, Y; Hester, JR; Green, MA; Kobayashi, Y; Kageyama, H
    We report a novel oxyhydride SrCrO2H directly synthesized by a high-pressure high-temperature method. Powder neutron and synchrotron X-ray diffraction revealed that this compound adopts the ideal cubic perovskite structure equation image with O2−/H− disorder. Surprisingly, despite the non-bonding nature between Cr 3d t2g orbitals and the H 1s orbital, it exhibits G-type spin ordering at TN≈380 K, which is higher than that of RCrO3 (R=rare earth) and any chromium oxides. The enhanced TN in SrCrO2H with four Cr-O-Cr bonds in comparison with RCr3+O3 with six Cr-O-Cr bonds is reasonably explained by the tolerance factor. The present result offers an effective strategy to tune octahedral tilting in perovskites and to improve physical and chemical properties through mixed anion chemistry. © 2014, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    Impact of lanthanoid substitution on the structural and physical properties of an infinite-layer iron oxide
    (American Chemical Society, 2016-11-01) Yamamoto, T; Ohkubo, H; Tassel, C; Hayashi, N; Kawasaki, S; Okada, T; Yagi, T; Hester, JR; Avdeev, M; Kobayashi, Y; Kageyama, H
    The effect of lanthanoid (Ln = Nd, Sm, Ho) substitution on the structural and physical properties of the infinite-layer iron oxide SrFeO2 was investigated by X-ray diffraction (XRD) at ambient and high pressure, neutron diffraction, and 57Fe Mössbauer spectroscopy. Ln for Sr substituted samples up to ∼30% were synthesized by topochemical reduction using CaH2. While the introduction of the smaller Ln3+ ion reduces the a axis as expected, we found an unusual expansion of the c axis as well as the volume. Rietveld refinements along with pair distribution function analysis revealed the incorporation of oxygen atoms between FeO2 layers with a charge-compensated composition of (Sr1–xLnx)FeO2+x/2, which accounts for the failed electron doping to the FeO2 layer. The incorporated partial apical oxygen or the pyramidal coordination induces incoherent buckling of the FeO2 sheet, leading to a significant reduction of the Néel temperature. High-pressure XRD experiments for (Sr0.75Ho0.25)FeO2.125 suggest a possible stabilization of an intermediate spin state in comparison with SrFeO2, revealing a certain contribution of the in-plane Fe–O distance to the pressure-induced transition. © 2016 American Chemical Society
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    Isotopic and modelling studies of food web structure in wet and dry conditions, Yanga wetlands NSW, Australia
    (CSIRO, 2010-05-11) Mazumder, D; Johansen, MP; Saintilan, N; Iles, J; Knowles, L; Kobayashi, Y; Wen, L
    Floodplain wetlands provide habitat for a diverse range of aquatic biota, as well as performing other important ecosystem functions such as transformation of nutrients, providing breeding and nursery grounds for numerous species. Overall productivity and biodiversity of floodplain wetlands are closely linked with water availability, and in particular to the reliable reoccurrence of water inflows. Alteration of wetland inflow and outflow regimes can greatly impact the functioning of food-webs through biodiversity loss, diversion of energy flow and ecosystem functionality. In the present study stable isotope ratios (δ13C and δ15N) of primary producers, sediment organic matter (SOM) and a variety of invertebrate and fish species are used to gain better understanding of the food-web relations at various waterholes in wetter and drier conditions in Yanga National Park, in the lower Murrumbidgee floodplain. Mass-balance mixing models were used to examine relative food source contributions to consumer diet. We also employed probabilistic simulation software to better understand trends of trophic positions, diet shifts and varying contributions from sources to consumers in waterholes of the Yanga wetlands. We compared δ13C and δ15N data from wetter (greater surface water area and depth) conditions in February, with data from the drier (smaller surface water area an depth) conditions in August. The data indicated contraction in the trophic position of Hypseleotris spp. (carp guudgeon) in August consistent with shrinking waterholes where species were forced into competing for overlapping, and a more limited variety, of food sources. In particular the endemic Hypseleotris spp. appears to be forced into greater competition with the exotic C. carpio (carp). Data also indicated that energy source of consumer species varied with changing water levels among all waterholes. The drier (August) δ13C values for fish and insects were typically shifted ~1-3‰ lower than the corresponding wetter (February) values. These shifts appear to correspond to depletion in the δ13C algal values, and appear to indicate a greater proportional contribution of δ13C from algae to the δ13C in consumers. This study provides δ13C and δ15N values for endemic and exotic aquatic species in Australian semi-arid wetlands. It provides modelling results indicating shifts in energy source and trophic position relative to water fluctuations and indicates increased competition among similar species that may adversely impact endemic species populations.
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    Isotopic studies of food-web properties in Yanga wetlands, NSW Australia
    (Australasian Environmental Isotope Conference, 2009-12-03) Mazumder, D; Johansen, MP; Kobayashi, Y; Iles, J; Saintilan, N; Knowles, L; Hollins, SE
    Floodplain wetlands provide habitats for a diverse range of species of terrestrial and aquatic biota, and perform important ecosystem functions. Overall productivity and biodiversity of floodplain wetlands is closely linked with water availability and environmental stability. Alternation flow regimes is a major threat to the functioning of food-webs and is responsible for a wide range of ecological responses, including biodiversity loss [1] diversion of energy flow [2] and is suspected to have influenced ecosystem functionality. Changes in land use, flow regulation and diversion for water resources, coupled with climate change have altered energy flow dynamics and structure of aquatic food webs. In the present study stable isotope ratios (δ13C and δ15N) of primary producers, sediment organic matter (SOM) and a variety of invertebrate and fish species are used to gain an understanding of the source of energy and trophic positions for aquatic species at various swamps in the Yanga National Park, lower Murrumbidgee River. A mass balance mixing model [3] was used to determine the fraction of food sources contributing to consumer diet. We also employed probabilistic simulation software (GoldSim) to better understand trends of trophic positions, dietary shifts and varying contributions from sources to consumers in swamps of the Yanga wetlands. We found that energy source varies between swamps in close proximity (in relative contribution of algae). Some trophic links are unaffected by this change (Fig.1) while for others a threshold may be crossed when diet shifts from predominantly benthic organic matter to algae. Over time food chain length is diminished as the floodplain wetland dries, drawing predators into competition. Natural systems are complex and highly variable thereby presenting difficulties and challenges for their effective management. Understanding the variability of the food web properties is important for effective management of the wetlands.
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    Oxyhydrides of (Ca,Sr,Ba)TiO3 perovskite solid solutions
    (American Chemical Society, 2012-11-05) Sakaguchi, T; Kobayashi, Y; Yajima, T; Ohkura, M; Tassel, C; Takeiri, F; Mitsuoka, S; Ohkubo, H; Yamamoto, T; Kim, JE; Tsuji, N; Fujihara, A; Matsushita, Y; Hester, JR; Avdeev, M; Ohoyama, K; Kageyama, H
    The oxyhydride solid solutions (Ca,Sr)TiO3-xHx and (Sr,Ba)TiO3-xHx have been prepared by reducing the corresponding ATiO(3) oxides with calcium hydride. Under the reaction conditions examined, a hydride content of x = 0.1-0.3 was obtained for all compositions. Compared to our previous result with BaTiO3-xHx, the larger particle size in this study (20-30 mu m vs 170 nm) resulted in a somewhat lower hydride amount despite prolonged reaction times. We examined changes in cell volume, octahedral tilt angle, and site occupancy of different anion sites after conversion to oxyhydrides; it appears that these oxyhydrides fit the geometrical descriptions typical for regular ABO(3) perovskites quite well. The hydrogen release temperature, previously shown to be indicative of the hydride exchange temperature, however, does not scale linearly with the A-site composition, indicating a potential effect of chemical randomness. © 2012, American Chemical Society.
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    Superconductivity in BaTi2Sb2O with a d1 square lattice
    (Physical Society of Japan, 2012-10-01) Yajima, T; Nakano, K; Takeiri, F; Ono, T; Hosokoshi, Y; Matsushita, Y; Hester, JR; Kobayashi, Y; Kageyama, H
    We prepared a new two-dimensional oxyantimonide, BaTi(2)Sb(2)O, which shows a superconducting transition at 1.2 K, representing the first superconductivity in a system with Ti(3+) (d(1)) in a square lattice. The TiO(2)Sb(4) mixed anionic coordination stabilizes a unique half-filled Ti d(xy) orbital configuration in Ti(2)O plane, which is analogous to Cu(2+) (d(9)) in the high-T(c) superconductors. A charge density wave (CDW)- or spin density wave (SDW)-like anomaly appears at 50 K, which is significantly reduced compared with 200 K for the isostructural and non-superconducting BaTi(2)As(2)O. © 2012, Physical Society of Japan
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    Synthesis and physical properties of the new oxybismuthides BaTi2Bi2O and (SrF)2Ti2Bi2O with a d1 square net
    (Physical Society of Japan, 2012-12-11) Yajima, T; Nakano, K; Takeiri, F; Hester, JR; Yamamoto, T; Kobayashi, Y; Tsuji, N; Kim, J; Fujiwara, A; Kageyama, H
    We have recently reported the d(1) square-lattice compound BaTi(2)Sb(2)O, which shows superconductivity at T(c) = 1.2K coexisting with a charge- or spin-density wave (CDW/SDW) state. Here, we successfully prepared two new oxybismuthides, BaTi(2)Bi(2)O and (SrF)(2)Ti(2)Bi(2)O, as the first Pn = Bi compounds in the ATi(2)Pn(2)O family. The CDW/SDW state disappeared for both compounds, presumably owing to the considerable interaction between the Ti-3d and Bi-6s orbitals. The complete suppression of the CDW/SDW instability resulted in an enhanced T(c) of 4.6 K for BaTi(2)Bi(2)O. However, (SrF)(2)Ti(2)Bi(2)O exhibits no superconductivity, suggesting the importance of the interlayer interaction for superconductivity. © 2012, Physical Society of Japan
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    T-c enhancement by aliovalent anionic substitution in superconducting BaTi2(Sb1-xSnx)2O
    (Physical Society Japan, 2013-07-01) Nakano, K; Yajima, T; Takeiri, F; Green, MA; Hester, JR; Kobayashi, Y; Kageyama, H
    BaTi2Sb2O is a T-c = 1.2 K superconductor with a d(1) square lattice, and isovalent Bi substitution for Sb can increase its T-c to 4.6 K (BaTi2Bi2O), accompanied by the complete suppression of charge density wave (CDW) or spin density wave (SDW) transition. In the present study, we demonstrate that aliovalent Sn substitution (hole doping) also increases T-c up to 2.5 K for BaTi2(Sb0.7Sn0.3)(2)O, while suppressing CDW/SDW transition only slightly. The overall electronic phase diagram of BaTi2(Sb, Sn)(2)O is qualitatively similar to that of cation-substituted (hole-doped) (Ba,Na)Ti2Sb2O, but quantitative differences such as in T-c are observed, which is discussed in terms of Ti-Pn hybridization and chemical disorder. © 2013, Physical Society of Japan