Origin and evolution of the elements: edited by Andrew McWilliam and Michael Rauch     

Marc Rayet 《Meteoritics & planetary science》2005,40(2):331-332

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Fate of dissolved aluminum in the oceans     

Marc Stoffyn  Fred T. Mackenzie 《Marine Chemistry》1982,11(2):105-127

Vertical profiles of dissolved Al in the Atlantic Ocean and Mediterranean Sea are presented. Although dissolved Al appears to be involved in the biochemical cycle of elements, Al does not behave solely as a nutrient within the oceans. Physico-chemical processes (i.e. adsorption and/or chemical precipitation) control the concentration and distribution of Al_aq within the deep waters.A tentative mass balance model of Al_aq in the oceanic system is proposed that takes into account all of the presently known fluxes of Al_aq to and through the oceans. To maintain the deep waters of the ocean at steady state, it is necessary to include in the model, processes that remove Al_aq from these waters. Thus, model calculations support the conclusions drawn from observations that physico-chemical processes remove Al_aq from deep waters. Finally, the proposed model is compatible with the concept that the entire oceanic system is at steady state with respect to dissolved Al.  相似文献   

Planetary Perturbers in Debris Disks     

Kuchner  Marc J. 《Earth, Moon, and Planets》2003,92(1-4):435-445

Neptune dominates the dynamics of the Kuiper Belt. By examining images of debris disks around other stars, we may be able to infer what kinds of planets shape the outer edges of other planetary systems. The last few years have seen a burst of progress in the modeling of azimuthal structures in debris disks created by planetary perturbers; new models incorporate planets on substantially eccentric orbits. I review this recent progress in debris disk dynamics and discuss the Kuiper Belt as a key example.  相似文献   

Constraining dark energy from the abundance of weak gravitational lenses     

Nevin N. Weinberg  Marc Kamionkowski 《Monthly notices of the Royal Astronomical Society》2003,341(1):251-262

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Atmospheric boundary-layer structure observed during a haze event due to forest-fire smoke   总被引：1，自引：0，他引：1  

Markus?PahlowEmail author  Jan?Kleissl  Marc?B.?Parlange 《Boundary-Layer Meteorology》2005,114(1):53-70

During a haze event in Baltimore, U.S.A. from July 6 to 8, 2002, smoke from forest fires in the Québec region (Canada), degraded air quality and impacted upon local climate, decreasing solar radiation and air temperature. The smoke particles in and above the atmospheric boundary layer (ABL) served as a tracer and provided a unique opportunity to investigate the ABL structure, especially entrainment. Elastic backscatter lidar measurements taken during the haze event distinctly reveal the downward sweeps (or wisps) of smoke-laden air from the free atmosphere into the ABL. Visualisations of mechanisms such as dry convection, the entrainment process, detrainment, coherent entrainment structures, and mixing inside the ABL, are presented. Thermals overshooting at the ABL top are shown to create disturbances in the form of gravity waves in the free atmosphere aloft, as evidenced by a corresponding ripple structure at the bottom of the smoke layer. Lidar data, aerosol ground-based measurements and supporting meteorological data are used to link free atmosphere, mixed-layer and ground-level aerosols. During the peak period of the haze event (July 7, 2002), the correlation between time series of elastic backscatter lidar data within the mixed layer and the scattering coefficient from a nephelometer at ground level was found to be high (R=0.96 for z =324 m, and R=0.89 for z=504 m). Ground-level aerosol concentration was at a maximum about 2 h after the smoke layer intersected with the growing ABL, confirming that the wisps do not initially reach the ground.  相似文献   

Vertical distribution of trace elements in the surface waters offshore Nova Scotia     

Marc Stoffyn 《Estuarine, Coastal and Shelf Science》1984,18(4):433-445

Concentrations of the trace elements Fe, Al, Mn, Cu, Cd, Zn and Ni were measured in shallow vertical profiles (maximum depth 500 m) off the Scotian Shelf in the western North Atlantic. The distributions of the trace elements show variations with depth, the most consistent of which are for Fe and Zn. A minimum concentration near the surface followed by an increase with depth is attributed to in situ mechanisms.  相似文献   

Li and B isotopic variations in an Allende CAI: Evidence for the in situ decay of short-lived Be and for the possible presence of the short-lived nuclide Be in the early solar system     

Marc Chaussidon  François Robert 《Geochimica et cosmochimica acta》2006,70(1):224-245

The concentrations and isotopic compositions of lithium, beryllium, and boron, analyzed in situ by ion microprobe in 66 spots of a type B1 Ca-Al-rich inclusion (CAI 3529-41) from the Allende meteorite, are reported. Large variations are observed for both the Li and the B isotopic ratios with ⁷Li/⁶Li ranging from 9.2 ± 0.22 to 12.22 ± 0.43 (a ≈250‰ range in δ⁷Li values) and ¹⁰B/¹¹B ranging from 0.2468 ± 0.0057 to 0.4189 ± 0.0493 (a 410‰ range in δ¹¹B values). The very low Li concentrations (<1 ppb) observed in several anorthite and fassaite grains require that a correction for the contribution of spallogenic Li produced during irradiation of the Allende meteoroid by galactic cosmic rays (GCR) be made (after this correction ⁷Li/⁶Li ranges from 9.2 ± 0.22 to 13.44 ± 0.56, i.e., a ≈350‰ range in δ⁷Li values). In 3529-41, the ¹⁰B/¹¹B ratios are positively correlated with ⁹Be/¹¹B in a manner indicating the in situ decay of short-lived ¹⁰Be (half-life = 1.5 Ma) with a ¹⁰Be/⁹Be ratio at the time of formation of the CAI of 8.8 ± 0.6 × 10⁻⁴, which is in agreement with previous findings [McKeegan, K.D., Chaussidon, M., Robert, F., 2000. Incorporation of short-lived ¹⁰Be in a calcium-aluminum-rich inclusion from the Allende meteorite. Science289, 1334-1337]. The present detailed investigation demonstrates that only minor perturbations of the ¹⁰Be-¹⁰B system are present in 3529-41, contrary to the ²⁶Al/²⁶Mg system for which numerous examples of isotopic redistribution following crystallization were observed [Podosek, F.A., Zinner, E.K., MacPherson, G.J., Lundberg, L.L., Brannon, J.C., Fahey, A.J., 1991. Correlated study of initial ⁸⁷Sr/⁸⁶Sr and Al-Mg systematics and petrologic properties in a suite of refractory inclusions from the Allende meteorite. Geochim. Cosmochim. Acta55, 1083-1110]. Petrographically based criteria were developed to identify within the 66 analyzed spots in 3529-41, those where post-magmatic perturbation of the Li and Be distributions occurred. Li and Be concentrations measured in different analytical spots are compared with those predicted by using experimentally determined partition coefficients according to a model of closed-system crystallization of the CAI melt. These criteria show that 56% of the spots in melilite, 38% in anorthite, and 8% in fassaite suffered post-crystallization perturbations of Li and/or Be distributions. In the remaining spots, which do not show obvious indication of redistribution of Li or Be, the ⁷Li/⁶Li isotopic variations (corrected for GCR exposure) are positively correlated with⁹Be/⁶Li suggesting the in situ decay of now-extinct ⁷Be. The derived isochron implies that at the time of its formation, the CAI melt had a ⁷Be/⁹Be ratio of 0.0061 ± 0.0013 and a ⁷Li/⁶Li ratio of 11.49 ± 0.13. In contrast, all the spots in 3529-41, which do show evidence for post-magmatic redistribution of Li and Be, have relatively constant ⁷Li/⁶Li, averaging 11.72 ± 0.56, which is consistent with mass balance calculations for Li isotopic homogenization in the CAI after the decay of ⁷Be. The incorporation of live ⁷Be in 3529-41 requires, because of the very short half-life of this nuclide (53 days), that it be produced essentially contemporaneously with the formation of the CAI. Therefore, the irradiation processes responsible for production of ⁷Be must have occurred within the solar accretion disk. Calculations developed in the framework of the x-wind model [Gounelle, M., Shu, F.H., Shang, H., Glassgold, A.E., Rehm, E.K., Lee, T., 2004. The origin of short-lived radionuclides and early Solar System irradiation (abstract). Lunar Planet. Sci.35, 1829] reproduce the ⁷Be and ¹⁰Be abundances observed in 3529-41. The correlated presence of ⁷Be and ¹⁰Be in 3529-41 is thus a strong argument that ¹⁰Be, which is observed rather ubiquitously in CAIs, is also a product of irradiation in the early solar system, as might be a significant fraction of other short-lived radionuclides observed in early solar system materials.  相似文献   

A Comparison between WCS and OPeNDAP for Making Model Results and Data Products Available through the Internet     

Fedor Baart  Gerben de Boer  Wim de Haas  Gennadii Donchyts  Marc Philippart  Mark van Koningsveld  Maarten Plieger 《Transactions in GIS》2012,16(2):249-265

Numerical models produce output with a large number of variables, grid cells and time steps. The same applies to algorithms that produce gridded datasets from sparse or abundant raw data. Further use of the resulting data products has been challenging, especially for dissemination outside the institute of origin. Due to the gradually increasing size of data products, simply downloading copies of them is becoming impossible. A gradual transition from traditional download methods to web services is therefore observed. Web services allow for on‐the‐fly access to subsets of data that were hitherto considered as indivisible granules. Here we compare the most mature candidates to serve gridded data through the web: the Open‐source Project for a Network Data Access Protocol (OPeNDAP) and Web Coverage Service (WCS) protocols. In the framework of the new Dutch National Model and Data Centre (NMDC.eu) a distributed data storage has been created by coupling OPeNDAP servers. A WCS service layer is provided for the same data. This allows us to compare OPeNDAP and WCS. Using several use cases, we compare the usability, performance and features of the two protocols.  相似文献   

Freshwater geographies: Experimenting with knowing and doing geography differently   总被引：1，自引：0，他引：1  

Brendon Blue  Claire Gregory  Kiely McFarlane  Marc Tadaki  Petra van Limburg‐Meijer  Nick Lewis 《New Zealand geographer》2012,68(1):62-66

The fair and effective governance of freshwater is an increasingly prominent issue in New Zealand. Emerging from a complex of cultural, economic and biophysical narratives, freshwater geographies are multiple, varied and increasingly acknowledged as worthy of interdisciplinary scrutiny. In this commentary, we reflect on a series of generative spaces that we – as group of postgraduate geographers (plus supporting staff) – created to engage with the multiplicity of freshwater meanings both within and beyond the academy. Through this evolving epistemic‐political project, we significantly reframed our own understandings about what freshwater ‘is’ and how it ought to be governed. By pursuing a deeper understanding of how the world gets made, we expand our ability to know and make it differently.  相似文献   

Subgrid-Scale Dynamics of Water Vapour, Heat, and Momentum over a Lake     

Nikki Vercauteren  Elie Bou-Zeid  Marc B. Parlange  Ulrich Lemmin  Hendrik Huwald  John Selker  Charles Meneveau 《Boundary-Layer Meteorology》2008,128(2):205-228

We examine the dynamics of turbulence subgrid (or sub-filter) scales over a lake surface and the implications for large-eddy simulations (LES) of the atmospheric boundary layer. The analysis is based on measurements obtained during the Lake-Atmosphere Turbulent EXchange (LATEX) field campaign (August–October, 2006) over Lake Geneva, Switzerland. Wind velocity, temperature and humidity profiles were measured at 20 Hz using a vertical array of four sonic anemometers and open-path gas analyzers. The results indicate that the observed subgrid-scale statistics are very similar to those observed over land surfaces, suggesting that the effect of the lake waves on surface-layer turbulence during LATEX is small. The measurements allowed, for the first time, the study of subgrid-scale turbulent transport of water vapour, which is found to be well correlated with the transport of heat, suggesting that the subgrid-scale modelling of the two scalars may be coupled to save computational resources during LES.  相似文献