The R Coronae Borealis stars: carbon abundances from forbidden carbon lines     

Gajendra Pandey  David L. Lambert  N. Kameswara Rao  Bengt Gustafsson  Nils Ryde  David Yong 《Monthly notices of the Royal Astronomical Society》2004,353(1):143-152

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Towards a consistent geochemical model for prediction of uranium(VI) removal from groundwater by ferrihydrite     

Jon Petter Gustafsson  Ellinor Dässman  Mattias Bäckström 《Applied Geochemistry》2009

Uranium(VI), which is often elevated in granitoidic groundwaters, is known to adsorb strongly to Fe (hydr)oxides under certain conditions. This process can be used in water treatment to remove U(VI). To develop a consistent geochemical model for U(VI) adsorption to ferrihydrite, batch experiments were performed and previous data sets reviewed to optimize a set of surface complexation constants using the 3-plane CD-MUSIC model. To consider the effect of dissolved organic matter (DOM) on U(VI) speciation, new parameters for the Stockholm Humic Model (SHM) were optimized using previously published data. The model, which was constrained from available X-ray absorption fine structure (EXAFS) spectroscopy evidence, fitted the data well when the surface sites were divided into low- and high-affinity binding sites. Application of the model concept to other published data sets revealed differences in the reactivity of different ferrihydrites towards U(VI). Use of the optimized SHM parameters for U(VI)-DOM complexation showed that this process is important for U(VI) speciation at low pH. However in neutral to alkaline waters with substantial carbonate present, Ca–U–CO₃ complexes predominate. The calibrated geochemical model was used to simulate U(VI) adsorption to ferrihydrite for a hypothetical groundwater in the presence of several competitive ions. The results showed that U(VI) adsorption was strong between pH 5 and 8. Also near the calcite saturation limit, where U(VI) adsorption was weakest according to the model, the adsorption percentage was predicted to be >80%. Hence U(VI) adsorption to ferrihydrite-containing sorbents may be used as a method to bring down U(VI) concentrations to acceptable levels in groundwater.  相似文献   

Time-dependent modeling of the Baltic entrance area. 2. Water and salt exchange of the Baltic Sea     

Bo G. Gustafsson 《Estuaries and Coasts》2000,23(2):253-266

A time-dependent model for stratification and circulation within the Baltic entrance area (Gustafsson 2000) is tested against observed salinities for the period 1961–1993. Although the Baltic Sea is one of the largest estuarine systems on earth, this model could be applicable to smaller estuarine systems and embayments with tidal exchange. The seasonal cycle of freshwater flux across the sill area does not follow the seasonal cycle of freshwater supply to the Baltic Sea. The seasonal variation of the flux is a combined effect of the seasonal variation in freshwater supply, in Baltic mean sea level, and in dispersion of salt across the sills. The seasonal variation in dispersion of salt is due to the seasonal cycle of sea level variability. The model is used to predict the inflow of high saline water to the Baltic Sea. The resulting inflow time-series is consistent with variations in the deep-water salinity and temperature in the deeper parts of the Baltic Sea. A comparison with previous estimates of the magnitude of major Baltic inflows shows that the model is able to reproduce the characteristics fairly well although the magnitude of the flows of water and salt appears lower than other estimates. It is shown that a climatic change that increases the wind mixing does not significantly change the major inflows. Both increased amplitudes of sea level variations in the Kattegat and decreased freshwater supply to the Baltic Sea substantially increase the magnitude of the inflows. It is shown that deep-water renewal in the Baltic Sea is obstructed during years with high freshwater supply even if the sea level forcing is favorable to a major inflow.  相似文献   

Gasdynamics of Detached Shells Around Carbon Stars With Variable Mass Loss     

A.V. Myasnikov  N.A. Belov  B. Gustafsson  K. Eriksson 《Astrophysics and Space Science》2000,274(1-2):231-241

Gasdynamic features of detached shells around carbon stars with variable mass loss rate are investigated in detail numerically. It is shown that a shell is unstable and also, 2D perturbations are less developed that 3D ones. The structure of perturbed flows corresponding to different evolution scenarios is compared. The results obtained seem to be promising for interpretation of observations, in particular, the recently obtained detailed data of TT Cyg. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Simultaneous measurements of black carbon and PM2.5, CO,and NO x variability at a locally polluted urban location in India     

S. Tiwari  D. S. Bisht  A. K. Srivastava  Örjan Gustafsson 《Natural Hazards》2015,75(1):813-829

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Estimation of winter leaf area index and sky view fraction for snow modelling in boreal coniferous forests: consequences on snow mass and energy balance     

Sirpa Rasmus  David Gustafsson  Harri Koivusalo  Ari Laurén  Achim Grelle  Olli‐Kalle Kauppinen  Ola Lagnvall  Anders Lindroth  Kai Rasmus  Magnus Svensson  Per Weslien 《水文研究》2013,27(20):2876-2891

Leaf area index (LAI) and canopy coverage are important parameters when modelling snow process in coniferous forests, controlling interception and transmitting radiation. Estimates of LAI and sky view factor show large variability depending on the estimation method used, and it is not clear how this is reflected in the calculated snow processes beneath the canopy. In this study, the winter LAI and sky view fraction were estimated using different optical and biomass‐based approximations in several boreal coniferous forest stands in Fennoscandia with different stand density, age and site latitude. The biomass‐based estimate of LAI derived from forest inventory data was close to the values derived from the optical measurements at most sites, suggesting that forest inventory data can be used as input to snow hydrological modelling. Heterogeneity of tree species and site fertility, as well as edge effects between different forest compartments, caused differences in the LAI estimates at some sites. A snow energy and mass balance model (SNOWPACK) was applied to detect how the differences in the estimated values of the winter LAI and sky view fraction were reflected in simulated snow processes. In the simulations, an increase in LAI and a decrease in sky view fraction changed the snow surface energy balance by decreasing shortwave radiation input and increasing longwave radiation input. Changes in LAI and sky view fraction affected directly snow accumulation through altered throughfall fraction and indirectly snowmelt through the changed surface energy balance. Changes in LAI and sky view fraction had a greater impact on mean incoming radiation beneath the canopy than on other energy fluxes. Snowmelt was affected more than snow accumulation. The effect of canopy parameters on evaporation loss from intercepted snow was comparable with the effect of variation in governing meteorological variables such as precipitation intensity and air temperature. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The role of social networks in natural resource governance: What relational patterns make a difference?   总被引：1，自引：0，他引：1  

rjan Bodin  Beatrice I. Crona 《Global Environmental Change》2009,19(3):366-374

Resent research has identified the existence of social networks as a common and important denominator in cases where different stakeholders have come together to effectively deal with natural resource problems and dilemmas. It has even been shown that social networks can be more important than the existence of formal institutions for effective enforcement and compliance with environmental regulations. However, all social networks are not created equal. On the contrary, the structural pattern of relations (i.e. the topology) of a social network can have significant impact on how actors actually behave. This clearly has implications for actors’ abilities to manage environmental challenges. This review aims to add more precision to initial insights and pending hypotheses about the positive impacts of social networks on governance processes and outcomes, by reviewing and synthesizing empirically based literature explicitly studying structural characteristics of social networks in natural resource governance settings. It is shown that significant differences in governance processes and outcomes can be expected among networks experiencing structural differences in terms of density of relations, degree of cohesiveness, subgroup interconnectivity, and degree of network centralization. Furthermore, the review shows that none of these structural characteristics present a monotonically increasing positive effect on processes of importance for resource governance, and that favoring one characteristic likely occurs at the expense of another. Thus, assessing the most favorable level and mix of different network characteristics, where most of the positive governance effects are obtained while undesired effects are minimized, presents a key research and governance challenge.  相似文献   

Phosphorus recycling and burial in Baltic Sea sediments with contrasting redox conditions   总被引：6，自引：0，他引：6  

Haydon P. Mort  Bo G. Gustafsson 《Geochimica et cosmochimica acta》2010,74(4):1350-6783

In this study, redox-dependent phosphorus (P) recycling and burial at 6 sites in the Baltic Sea is investigated using a combination of porewater and sediment analyses and sediment age dating (²¹⁰Pb and ¹³⁷Cs). We focus on sites in the Kattegat, Danish Straits and Baltic Proper where present-day bottom water redox conditions range from fully oxygenated and seasonally hypoxic to almost permanently anoxic and sulfidic. Strong surface enrichments of Fe-oxide bound P are observed at oxic and seasonally hypoxic sites but not in the anoxic basins. Reductive dissolution of Fe-oxides and release of the associated P supports higher sediment-water exchange of PO₄ at hypoxic sites (up to ∼800 μmol P m⁻² d⁻¹) than in the anoxic basins. This confirms that Fe-bound P in surface sediments in the Baltic acts as a major internal source of P during seasonal hypoxia, as suggested previously from water column studies. Most burial of P takes place as organic P. We find no evidence for significant authigenic Ca-P formation or biogenic Ca-P burial. The lack of major inorganic P burial sinks makes the Baltic Sea very sensitive to the feedback loop between increased hypoxia, enhanced regeneration of P and increased primary productivity. Historical records of bottom water oxygen at two sites (Bornholm, Northern Gotland) show a decline over the past century and are accompanied by a rise in values for typical sediment proxies for anoxia (total sulfur, molybdenum and organic C/P ratios). While sediment reactive P concentrations in anoxic basins are equal to or higher than at oxic sites, burial rates of P at hypoxic and anoxic sites are up to 20 times lower because of lower sedimentation rates. Nevertheless, burial of reactive P in both hypoxic and anoxic areas is significant because of their large surface area and should be accounted for in budgets and models for the Baltic Sea.  相似文献   

Near surface climate in an urban vegetated park and its surroundings   总被引：1，自引：0，他引：1  

C. Jansson  P.-E. Jansson  D. Gustafsson 《Theoretical and Applied Climatology》2007,89(3-4):185-193

Summary Near surface climate was observed through temperature profiling from the surface to 2.47 m height in an urban vegetated park and its surroundings in central Stockholm, Sweden. Measurements were conducted during three summer days by mobile traverses. Air temperature differences between the built-up area and the park were in the range of 0.5–0.8 °C during the day and reached a maximum of 2 °C at sunset. The thermal stratification of the air was mainly stable in the park and unstable in the built-up area. Inverse air temperature profiles in the park were less stable in open than in shady areas, and close to neutral at midday. The most unstable air was found in the north–south orientated canyons in the early afternoon. Possible heat advection from the surroundings, and thus uncoupling between the surface and the air, was identified through temperature gradients pointing at different directions within the 2.47 m profile. Examples at midday indicated that warm air advected as far as 150 m into the park.  相似文献   

Dynamics of day and night aurora during substorms     

V.G. Vorobjev  G. Gustafsson  G.V. Starkov  Y.I. Feldstein  N.F. Shevnina 《Planetary and Space Science》1975,23(2):269-278

The motion of auroral forms on the day- and nightside of the Earth has been studied during different substorm phases by means of all-sky camera films. A substorm is characterized by a shift of the luminescence region towards the equator at noon and mainly towards the pole at midnight. However, individual forms drift predominantly toward the pole on the dayside and towards the equator on the nightside. The velocity of the poleward motion at noon is largest during the expansive phase of a substorm and amounts on the average to 330 $\text{m}\text{sec}$ but even during relatively quiet magnetic conditions a poleward motion is observed.  相似文献