Complementary Observables for the Determination of |Vub| in Inclusive Semileptonic B Decays

The determination of |Vub| from inclusive semileptonic B decays is limited by uncertainties in modelling the decay distributions in b->ulnu transitions. The largest uncertainties arise from the limited knowledge of the appropriate b quark mass and Fermi momentum to use in the parameterization of the shape function. This paper presents a new method in which these shape function parameters are constrained by the same data used to measure |Vub|. The method requires measurements of the momenta of both the charged lepton and the neutrino in semileptonic B decays. From these quantities two complementary observables can be constructed, one for discriminating between b->ulnu transitions and background and the other for constraining the shape function. Using this technique the uncertainties in |Vub| from the shape function may be significantly reduced.Comment: 8 pages, 3 figure

Advective timescales and pathways of Agulhas leakage

Current research indicates an increase in Agulhas leakage for the past and coming decades. This change potentially alters the strength of the Atlantic meridional overturning circulation, in particular, through advection of positive density anomalies into the North Atlantic. To explore the fate of Agulhas leakage, results from a Lagrangian analysis were evaluated, with virtual floats advected within an eddy-permitting ocean model (ORCA025). A considerable fraction of Agulhas leakage reached the subtropical North Atlantic: of a mean Agulhas leakage transport of 15.3 Sv entering the South Atlantic, 9.7, 7.7, and 6.1 Sv crossed sections at 6 degrees S, 6 degrees N, and 26 degrees N, respectively. The most probable transit time of leakage to reach the respective latitudes is one to two decades. We suggest that changes in Agulhas leakage could manifest in the Gulf Stream regime most probably within two decades. These results were supported by an eddy-resolving implementation of the ocean model (INALT01

Oxidation state of iron in hydrous phono-tephritic melts

The oxidation state of iron in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed H2O-CO2 fluids was experimentally studied at 1200 and 1250{degree sign}C and pressures from 50 to 500 MPa. The oxygen fugacity (fO2) varied from NNO-2.9 to NNO+2.6 in logfO2, relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The iron redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the Fe2+/ΣFe ratio of mg-sized samples within ±0.03 (2σ). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The Fe2+/ΣFe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on Fe2+/ΣFe at given fO2 was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of iron was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower Fe2+/ΣFe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher K2O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in ΣFeO (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between logfO2 and Fe3+/Fe2+ for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as H2O or K2O, on the redox state of iron in silicate melts

A warming climate will make Australian soil a net emitter of atmospheric CO2

Understanding the change in soil organic carbon (C) stock in a warmer climate and the effect of current land management on that stock is critical for soil and environmental conservation and climate policy. By simulation modeling, we predicted changes in Australia’s soil organic C stock from 2010 to 2100. These vary from losses of 0.014–0.077 t C ha−1 year−1 between 2020 and 2045 and 0.013–0.047 t C ha−1 year−1 between 2070 and 2100, under increasing emissions of greenhouse gases and temperature. Thus, Australian soil will be a net emitter of CO2. Depending on the future socio-economic conditions, we predict that croplands will accrue as much as 0.19 t C ha−1 year−1 between 2020 and 2045 due to their management, but accrual will decrease with warming and increased emissions by 2070–2100. The gains will be too small to counteract the losses of C from the larger areas of rangelands and coastal regions that are more sensitive to a warmer climate. In principle, prudent management of the rangelands, for example, improving grazing management and regenerating biodiverse, endemic native plant communities, could sequester more C and mitigate the loss; in practice, it may be more difficult, requiring innovation, interdisciplinary science, cultural awareness and effective policie

Synthesis of cobalt ferrite nanoparticles by constant pH co-precipitation and their high catalytic activity in CO oxidation

A series of cobalt ferrite samples were synthesized from a metal nitrate solution at constant pH between 9 and 12 by the controlled co-precipitation method without any surfactant. Cobalt and iron nitrates and sodium hydroxide base were simultaneously dosed so that the pH was precisely controlled during co-precipitation. The samples were characterized by PXRD, SEM, TEM, BET, and TPR. Careful analysis of typical PXRD peak profiles suggested the presence of two different variants of cobalt ferrite, a nano-scale material giving rise to broad peak tails and a more crystalline material leading to a sharper central profile. Rietveld refinement could be used to quantify the relative amount of both nano and crystalline fractions in these samples indicating that their relative abundance can be controlled by the co-precipitation pH. TEM analysis further proved the presence of both crystalline and nanocrystalline region in the samples. The average crystallite size of the cobalt ferrite nanocrystallites was 4–5 nm. These samples exhibit high BET surface area, in the order of 200 m2 g-1. The samples were tested for catalytic performance in the CO oxidation reaction. The surface area, reduction behavior, and catalytic performance of ferrites were dependent on the relative amount of both the crystalline and nanocrystalline phases

Viscosity of andesite melts and its implication for magma mixing prior to Unzen 1991-1995 eruption

The viscosity of an iron-bearing melt with composition similar to Unzen andesite was determined experimentally in the high (109-1010.5 Pa·s) and low (5-1000 Pa·s) viscosity range using a parallel plate viscometer and the falling sphere method, respectively. Falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 K and 200 to 2000 MPa. Creep experiments were performed in the temperature range of 747 - 845 K at 300 MPa. The water content of the melt varies from nominally dry to 6.2 wt% H2O. The Fe2+/Fetot ratio was determined for each sample in the quenched glass using a colorimetric method. Pressure has minor influence on the viscosity compared with the effect of temperature, water content (main compositional parameter controlling the viscosity) or with the Fe2+/Fetot ratio (especially important at low water content of the melt). Based on our new viscosity data and literature data with measured Fe2+/Fetot ratio we propose a new empirical equation to estimate the viscosity η (in Pa·s) of andesitic melts as a function of temperature T (in K), water content w (in wt%) and Fe2+/Fetot ratio. The derived relationship reproduces the experimental data (87 in total) in the viscosity range from 100.5 to 1013 Pa·s with a 1σ standard deviation of 0.17 log units. However, application of this calculation model is limited to Fe2+/Fetot>0.3 and to temperatures above Tg. Moreover, in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements. The viscosity data are used to interpret mixing processes in the Unzen magma chamber prior to 1991-1995 eruption. We demonstrate that the viscosities of the rhyolite and andesite melts from the two end-member magmas are nearly identical prior and during mixing, enabling efficient magma mixing

Probing Low Energy Neutrino Backgrounds with Neutrino Capture on Beta Decaying Nuclei

We study the interaction of low energy neutrinos on nuclei that spontaneously undergo beta decay showing that the product of the cross section times neutrino velocity takes values as high as 10^{-42} cm^2 c for some specific nuclei that decay via allowed transitions. The absence of energy threshold and the value of the cross section single out these processes as a promising though very demanding approach for future experiments aimed at a direct detection of low energy neutrino backgrounds such as the cosmological relic neutrinos.Comment: Includes a discussion of local relic neutrino density effect on neutrino capture rate. Accepted for publication in JCA

Oxidation state of iron in hydrous phono-tephritic melts

The oxidation state of iron in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed H2O-CO2 fluids was experimentally studied at 1200 and 1250{degree sign}C and pressures from 50 to 500 MPa. The oxygen fugacity (fO2) varied from NNO-2.9 to NNO+2.6 in logfO2, relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The iron redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the Fe2+/ΣFe ratio of mg-sized samples within ±0.03 (2σ). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The Fe2+/ΣFe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on Fe2+/ΣFe at given fO2 was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of iron was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower Fe2+/ΣFe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher K2O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in ΣFeO (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between logfO2 and Fe3+/Fe2+ for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as H2O or K2O, on the redox state of iron in silicate melts