Browsing by Author "Chen, YC"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- ItemAnthropogenic perturbations to the atmospheric molybdenum cycle(American Geophysical Union, 2021-01-28) Wong, MY; Rathod, SD; Marino, R; Li, LL; Howarth, RW; Alastuey, A; Alaimo, MG; Barraza, F; Carneiro, MC; Chellam, S; Chen, YC; Cohen, DD; Connelly, D; Dongarra, G; Gómez, D; Hand, JL; Harrison, RM; Hopke, PK; Hueglin, c; Kuang, KW; Lambert, F; Liang, J; Losno, R; Maenhaut, W; Milando, C; Monteiro, MIC; Morera-Gómez, Y; Rodríguez, S; Querol, X; Smichowski, P; Varrica, D; Xiao, YH; Xu, YJ; Mahowald, NMMolybdenum (Mo) is a key cofactor in enzymes used for nitrogen (N) fixation and nitrate reduction, and the low availability of Mo can constrain N inputs, affecting ecosystem productivity. Natural atmospheric Mo aerosolization and deposition from sources such as desert dust, sea-salt spray, and volcanoes can affect ecosystem function across long timescales, but anthropogenic activities such as combustion, motor vehicles, and agricultural dust have accelerated the natural Mo cycle. Here we combined a synthesis of global atmospheric concentration observations and modeling to identify and estimate anthropogenic sources of atmospheric Mo. To project the impact of atmospheric Mo on terrestrial ecosystems, we synthesized soil Mo data and estimated the global distribution of soil Mo using two approaches to calculate turnover times. We estimated global emissions of atmospheric Mo in aerosols (<10 μm in diameter) to be 23 Gg Mo yr−1, with 40%–75% from anthropogenic sources. We approximated that for the top meter of soil, Mo turnover times range between 1,000 and 1,000,000 years. In some industrialized regions, anthropogenic inputs have enhanced Mo deposition 100-fold, lowering the soil Mo turnover time considerably. Our synthesis of global observational data, modeling, and a mass balance comparison with riverine Mo exports suggest that anthropogenic activity has greatly accelerated the Mo cycle, with potential to influence N-limited ecosystems. © 2022 American Geophysical Union
- ItemElectron doping evolution of the anisotropic spin excitations in BaFe(2-x)NixAs2(Americal Physical Society, 2012-07-10) Luo, HQ; Yamani, Z; Chen, YC; Lu, XY; Wang, M; Li, SL; Maier, TA; Danilkin, SA; Adroja, DT; Dai, PCWe use inelastic neutron scattering to systematically investigate the Ni-doping evolution of the low-energy spin excitations in BaFe(2-x)NixAs2 spanning from underdoped antiferromagnet to overdoped superconductor (0.03 <= x <= 0.18). In the undoped state, BaFe2As2 changes from paramagnetic tetragonal phase to orthorhombic antiferromagnetic (AF) phase below about 138 K, where the low-energy (<=similar to 80 meV) spin waves form transversely elongated ellipses in the [H, K] plane of the reciprocal space. Upon Ni doping to suppress the static AF order and induce superconductivity, the c-axis magnetic exchange coupling is rapidly suppressed and the momentum distribution of spin excitations in the [H, K] plane is enlarged in both the transverse and longitudinal directions with respect to the in-plane AF ordering wave vector of the parent compound. As a function of increasing Ni-doping x, the spin excitation widths increase linearly but with a larger rate along the transverse direction. These results are in general agreement with calculations of dynamic susceptibility based on the random phase approximation (RPA) in an itinerant electron picture. For samples near optimal superconductivity at x approximate to 0.1, a neutron spin resonance appears in the superconducting state. Upon further increasing the electron doping to decrease the superconducting transition temperature T-c, the intensity of the low-energy magnetic scattering decreases and vanishes concurrently with vanishing superconductivity in the overdoped side of the superconducting dome. Comparing with the low-energy spin excitations centered at commensurate AF positions for underdoped and optimally doped materials (x <= 0.1), spin excitations in the overdoped side (x = 0.15) form transversely incommensurate spin excitations, consistent with the RPA calculation. Therefore, the itinerant electron approach provides a reasonable description to the low-energy AF spin excitations in BaFe(2-x)NixAs2. © 2012, American Physical Society.