Stellar populations in the Canis Major overdensity     

Giovanni Carraro †  ré Moitinho †  Ruben A. Vázquez † 《Monthly notices of the Royal Astronomical Society》2008,385(3):1597-1604

We performed a photometric multicolour survey of the core of the Canis Major overdensity at     , reaching   V ∼ 22  and covering  0.3 × 1.0  arcmin². The main aim is to unravel the complex mixture of stellar populations toward this Galactic direction, where in the recent past important signatures of an accretion event have been claimed to be detected. While our previous investigations were based on disjointed pointings aimed at revealing the large-scale structure of the third Galactic Quadrant, we now focus on a complete coverage of a smaller field centred on the Canis Major overdensity. A large wavelength baseline, in the UBVRI bands, allows us to build up a suite of colour–colour and colour–magnitude diagrams, providing a much better diagnostic tool to disentangle the stellar populations of the region. In fact, the simple use of one colour–magnitude diagram, widely employed in all the previous studies defending the existence of the Canis Major galaxy, does not allow one to separate the effects of the different parameters (reddening, age, metallicity and distance) involved in the interpretation of data, forcing to rely on heavy modelling. In agreement with our previous studies, in the same general region of the Milky Way, we recognize a young stellar population compatible with the expected structure and extension of the Local (Orion) and Outer (Norma–Cygnus) spiral arms in the Third Galactic Quadrant. Moreover, we interpret the conspicuous intermediate-age metal-poor population as belonging to the Galactic thick disc, distorted by the effect of strong disc warping at this latitude, and to the Galactic halo.  相似文献   

Summer rainstorm associated with a debris flow in the Amarilla gully affecting the international Agua Negra Pass (30°20′S), Argentina     

Carolina Lauro  Stella M. Moreiras  Sebastian Junquera  Ivan Vergara  Rafael Toural  Johannes Wolf  Ruben Tutzer 《Environmental Earth Sciences》2017,76(5):213

The Central-West region of Argentina was seriously affected by a series of convective summer storms on January–February of 2013 generating many debris flows and rockfall in the Central Andes mountain regions. In particular, the unreported 8th February event caused the sad death of a 10-year-old child being completely ignored by society and local authorities. Despite this, meteorological conditions associated with this event and further episodes were rarely measured and determined mainly due to scarce meteorological stations in Andean mountain areas. In this paper, meteorological data from CMORPH algorithm and measurements of surrounding gauges were analyzed for estimating the triggering precipitation value of this event. As well, the particular debris flow channeled into the main branch of the Amarilla gully in the Agua Negra valley was geomorphologically described. The amount of precipitation associated with this debris flow was 5.5 and 13.2 mm accumulated previous to the event. This violent debris flow was generated in a talus zone in a periglacial environment located just below a covered rock glacier. However, the influence of the permafrost thawing in this process is not feasible. The altitude of the 0 °C isotherm was lower during the previous days of the event, and no monitoring on permafrost is available for this area. The volume of removed mass was estimated in 5 × 10⁴ m³, and the mean velocity was 35 km/h. Boulders of 4 m diameter were found in the source area, while the deposit is up to 75% sandy with clasts that hardly exceed 10 cm in the alluvial fan distal part. Herein the main objective is to advice about the probable catastrophic impact of similar events in the future. These findings could be useful for hazard remediation, mitigation, and prevention plans for the Agua Negra international pass under construction.  相似文献   

A model of producer incentives for livestock disease management     

Ram Ranjan  Ruben N. Lubowski 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(5):315-325

We examine the management of livestock diseases from the producers‘ perspective, incorporating information and incentive asymmetries between producers and regulators. Using a stochastic dynamic model, we examine responses to different policy options including indemnity payments, subsidies to report at-risk animals, monitoring, and regulatory approaches to decreasing infection risks when perverse incentives and multiple policies interact. This conceptual analysis illustrates the importance of designing efficient combinations of regulatory and incentive-based policies.

Ram RanjanEmail:

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Biomass estimation from surveys with likelihood-based geostatistics   总被引：1，自引：0，他引：1  

Roa-Ureta  Ruben; Niklitschek  Edwin 《ICES Journal of Marine Science》2007,64(9):1723-1734

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Synthetic coprecipitates of exopolysaccharides and ferrihydrite. Part II: Siderophore-promoted dissolution     

Christian Mikutta  Ruben Kretzschmar 《Geochimica et cosmochimica acta》2008,72(4):1128-1142

Ferrihydrite (Fh) coprecipitated with exopolymers of plants and microbes may differ in its geochemical reactivity from its abiotic counterpart. We synthesized Fh in the presence and absence of acid polysaccharides (polygalacturonic acid (PGA), alginate, xanthan) and characterized the physical and structural properties of the precipitates formed [Mikutta C., Mikutta R., Bonneville S., Wagner F., Voegelin A., Christl I. and Kretzschmar R. (2008) Synthetic coprecipitates of exopolysaccharides and ferrihydrite. Part I: Characterization. Geochim. Cosmochim. Acta]. In this paper, we focus on the reactivity of PGA and alginate coprecipitates and pure Fh, and studied their interaction with the microbial siderophore desferrioxamine B (DFOB) in the presence and absence of low molecular weight organic (LMWO) acid anions (malate, citrate). Batch adsorption and dissolution experiments were performed in the dark at pH 7 in 10 mM NaClO₄ background electrolyte. In the dissolution experiments, different modes of ligand addition were applied (single, simultaneous, stepwise). With an estimated Langmuir sorption maximum of 15 mmol/mol Fe, a PGA coprecipitate with 11% C_org sorbed about four times as much DFOB as pure Fh, and the amount of DFOB sorbed was ∼4-fold larger than estimated from the sum of DFOB sorption to pure Fh and PGA alone. The apparent initial dissolution rates, R_app-initial, and pseudo-first order rate coefficients, k, of the coprecipitates exceeded those of pure Fh by up to two orders of magnitude. Citrate and malate exerted a strong synergistic effect on the DFOB-promoted dissolution of pure Fh, whereas synergistic effects of both anions were absent or negligible for the coprecipitates. R_app-initial of the citrate and DFOB-promoted dissolution of PGA coprecipitates increased with increasing molar C/Fe ratio of the coprecipitates, independent of the charge of the LMWO ligand. Our results indicate that polyuronates stabilize Fh particles sterically and /or electrostatically, thus increasing the mineral surface area accessible to LMWO ligands. In contrast, pure Fh was coagulated at pH 7 (pH_iep of Fh = 7.1), and hence only a small fraction of the Fh surface underwent dissolution. The increase in ligand-accessible surface area of Fh upon coprecipitation with acid polysaccharides seems to primarily control the kinetics of the ligand-promoted dissolution at neutral pH. In pH environments where the solubility of Fe(III) is very low, dissolution rates of Fe(III) (hydr)oxides in such coprecipitates may therefore exceed those of pure minerals by several orders of magnitude, despite a similar crystallinity of the minerals.  相似文献   

Spatial and Temporal Ion Dynamics on a Complex Hydrological System: The Lower Luján River (Buenos Aires,Argentina)     

Ruben J. Lombardo  Inés O’Farrell  María dos Santos Afonso 《Aquatic Geochemistry》2010,16(2):293-309

The interplay of the geochemistry of the lower stretch of the Luján River is analyzed with its natural geomorphology (basin features), local hydrometeorology (tidal regime and “sudestada” events) and the impact of polluted tributaries. Major ions, dissolved heavy metals and limnological variables were analyzed using multivariate techniques. The water quality of the mainstream of the Luján River, flowing through urbanized and industrialized areas is strongly and positively influenced by the input of the Paraná River through deltaic watercourses and is negatively impacted after receiving the discharge from polluted watercourses. The longitudinal spatial variations evidenced major discontinuities in the Lower Luján Basin, showing clearly the riverine and the deltaic water influenced zones. Seasonal variations were also marked and were either temperature driven or associated with the estuarine cycle and the “sudestada”.  相似文献   

Constraints on the accretion history of massive black holes from faint X-ray counts     

Marta Volonteri  Ruben Salvaterra  Francesco Haardt 《Monthly notices of the Royal Astronomical Society》2006,373(1):121-127

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Calcium isotopes in a proglacial weathering environment: Damma glacier, Switzerland     

Ruth S. Hindshaw  Ben C. Reynolds  Ruben Kretzschmar 《Geochimica et cosmochimica acta》2011,75(1):106-7046

The biogeochemical cycling and isotopic fractionation of calcium during the initial stages of weathering were investigated in an alpine soil chronosequence (Damma glacier, Switzerland). This site has a homogeneous silicate lithology and minimal biological impacts due to sparse vegetation cover. Calcium isotopic compositions, obtained by TIMS using a ⁴³Ca-⁴⁶Ca double spike, were measured in the main Ca pools. During this very early stage of weathering, the young soils which have formed (δ^44/42Ca=+0.44‰) were indistinguishable to the rocks from which they were derived (δ^44/42Ca=+0.44‰) and stream water (δ^44/42Ca=+0.48‰) was also within error of the average rock. This lack of variation indicates that the dissolution of the bulk silicate rock does not strongly fractionate Ca isotopes. The only Ca pool which was strongly fractionated from bulk rock was vegetation, which exhibited an enrichment of light Ca isotopes. Significant Ca isotope fractionation between bulk rock and the dissolved flux of Ca is likely to only occur where the Ca biogeochemical cycle is dominated by secondary processes such as biological cycling, adsorption and secondary mineral precipitation.  相似文献   

Stability of pyrochlores in alkaline matrices: Solubility of calcium antimonate   总被引：1，自引：0，他引：1  

Geert Cornelis  Tom Van Gerven  Ruben Snellings  Bram Verbinnen  Jan Elsen  Carlo Vandecasteele 《Applied Geochemistry》2011,26(5):809-817

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Chloride and Boron behavior in fluids of Los Humeros geothermal field (Mexico): A model based on the existence of deep acid brine     

Ruben Bernard  Yuri Taran  Maddalena Pennisi  Enrique Tello  Alejandro Ramirez 《Applied Geochemistry》2011,26(12):2064-2073

Geothermal field Los Humeros, Mexico, is characterized by a high steam fraction in the well fluids, by extremely high B concentrations in separated water (grams per liter, with a magmatic B signature, δ¹¹B ± 2σ = −0.8 ± 1.6‰), by the absence of correlation between B and Cl concentrations and by positive correlation between B content in separated water and fluid enthalpy. Such behavior is consistent with the existence of moderately acid brine (pH 3–5) at depth with a high B concentration (500–600 mg/kg). In this case a 3-level model can be suggested for Los Humeros: (1) immature, moderately acid brine at depth which is boiling at a temperature ∼350 °C producing the HCl-bearing vapor with a high B content; (2) partial condensation of this vapor at the upper level accompanying water–rock interaction and neutralization; (3) formation of a shallow water-dominated aquifer above a lithologic low-permeability boundary as has been proposed by other authors. A thermochemical computer code has been used to model boiling of an aqueous fluid at 350 °C with 0.1 M of NaCl, 0.05 M of H₃BO₃ and variable amount of HCl (0.001–0.1 M), then a partial condensation of the produced vapor at 250 °C and then separation of the steam–water mixture at 150 °C. Results of simulation are in a qualitative agreement with the observed data.  相似文献