The clustering of barred galaxies in the local Universe     

Cheng Li  Dimitri A. Gadotti  Shude Mao  Guinevere Kauffmann 《Monthly notices of the Royal Astronomical Society》2009,397(2):726-732

We study the clustering properties of barred galaxies using data from the Sloan Digital Sky Survey. We compute projected redshift-space two-point cross-correlation functions   w _p( r _p)  for a sample of nearly 1000 galaxies for which we have performed detailed structural decompositions using the methods described in Gadotti. The sample includes 286 barred galaxies. The clustering of barred and unbarred galaxies of similar stellar mass is indistinguishable over all the scales probed (∼20 kpc–30 Mpc). This result also holds even if the sample is restricted to bars with bluer   g − i   colours (and hence younger ages). Our result also does not change if we split our sample of barred galaxies according to bar-to-total luminosity ratio, bar boxyness, effective surface brightness, length or the shape of the surface density profile within the bar. There is a hint that red, elliptical bars are more strongly clustered than red and less elliptical bars, on scales  ≳1 Mpc  , although the statistical significance is not high. We conclude that there is no significant evidence that bars are a product of mergers or interactions. We tentatively interpret the stronger clustering of the more elliptical bars as evidence that they are located in older galaxies, which reside in more massive haloes.  相似文献   

Seismic behavior of composite steel/concrete MRFs: deformation assessment and behavior factors     

Konstantinos A. Skalomenos  George D. Hatzigeorgiou  Dimitri E. Beskos 《Bulletin of Earthquake Engineering》2015,13(12):3871-3896

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Speciation and natural attenuation of arsenic and iron in a tidally influenced shallow aquifer   总被引：2，自引：0，他引：2  

Robert A. Root  Dimitri Vlassopoulos  Nelson A. Rivera  Michael T. Rafferty  Charles Andrews  Peggy A. O&#x;Day 《Geochimica et cosmochimica acta》2009,73(19):5528-5553

The mobility of subsurface arsenic is controlled by sorption, precipitation, and dissolution processes that are tied directly to coupled redox reactions with more abundant, but spatially and temporally variable, iron and sulfur species. Adjacent to the site of a former pesticide manufacturing facility near San Francisco Bay (California, USA), soil and groundwater arsenic concentrations are elevated in sediments near the prior source, but decrease to background levels downgradient where shallow groundwater mixes with infiltrating tidal waters at the plume periphery, which has not migrated appreciably in over two decades of monitoring. We used synchrotron X-ray absorption spectroscopy, together with supporting characterizations and sequential chemical extractions, to directly determine the oxidation state of arsenic and iron as a function of depth in sediments from cores recovered from the unsaturated and saturated zones of a shallow aquifer (to 3.5 m below the surface). Arsenic oxidation state and local bonding in sediments, as As-sulfide, As(III)-oxide, or As(V)-oxide, were related to lithologic redox horizons and depth to groundwater. Based on arsenic and iron speciation, three subsurface zones were identified: (i) a shallow reduced zone in which sulfide phases were found in either the arsenic spectra (realgar-like or orpiment-like local structure), the iron spectra (presence of pyrite), or both, with and without As(III) or As(V) coordinated by oxygen; (ii) a middle transitional zone with mixed arsenic oxidation states (As(III)–O and As(V)–O) but no evidence for sulfide phases in either the arsenic or iron spectra; and (iii) a lower oxidized zone in the saturated freshwater aquifer in which sediments contained only oxidized As(V) and Fe(III) in labile (non-detrital) phases. The zone of transition between the presence and absence of sulfide phases corresponded to the approximate seasonal fluctuation in water level associated with shallow groundwater in the sand-dominated, lower oxic zone. Total sediment arsenic concentrations showed a minimum in the transition zone and an increase in the oxic zone, particularly in core samples nearest the former source. Equilibrium and reaction progress modeling of aqueous-sediment reactions in response to decreasing oxidation potential were used to illustrate the dynamics of arsenic uptake and release in the shallow subsurface. Arsenic attenuation was controlled by two mechanisms, precipitation as sulfide phases under sulfate-reducing conditions in the unsaturated zone, and adsorption of oxidized arsenic to iron hydroxide phases under oxidizing conditions in saturated groundwaters. This study demonstrates that both realgar-type and orpiment-type phases can form in sulfate-reducing sediments at ambient temperatures, with realgar predicted as the thermodynamically stable phase in the presence of pyrite and As(III) under more reduced conditions than orpiment. Field and modeling results indicate that the potential for release of arsenite to solution is maximized in the transition between sulfate-reduced and iron-oxidized conditions when concentrations of labile iron are low relative to arsenic, pH-controlled arsenic sorption is the primary attenuation mechanism, and mixed Fe(II,III)-oxide phases do not form and generate new sorption sites.  相似文献   

Distribution, Speciation, and Extractability of Cadmium in the Sedimentary Phosphorite of Hahotoé-Kpogamé (Southern Togo)     

K. Gnandi  M. H. Rezaie Boroon  Deheyn D. Dimitri 《Aquatic Geochemistry》2009,15(4):485-495

The geochemistry and extractability of Cd in the phosphorite deposits of Hahotoé-Kpogamé (southern Togo) have been studied using various methodologies such as Cd distribution in profiles, grain-size dependence analysis of Cd content, Cd localization using scanning electron microscopy (SEM), sequential acid extraction, and a leaching experiment with artificial seawater. Results demonstrate that in the phosphorite deposits of Hahotoe-Kpogame, Cd is enriched by a factor of 157 compared to shale and by a factor of 3 compared to average world phosphorite composition. The main carrier of Cd appears to be apatite. This is evidenced by significant high positive correlations between the Cd content and P₂O₅ (in bulk sedimentr = 0.7 and in the 1–0.2 mm fraction r = 0.9). The grain-size dependence of Cd contents (concentrations decreasing with decreasing grain size) and SEM analysis supports these conclusions. Secondary Cd carriers include calcite, goethite, and various bone fragments. Sequential extraction tests with acetic acid and EDTA show an extraction rate reaching up to 40%. Leaching experiments with artificial seawater show evidence of Cd release in seawater. This leads to the conclusion that the processing of phosphorite by wet sieving using seawater and dumping of phosphorite tailings into the coastal waters of Togo can be a major source of marine pollution with Cd.  相似文献   

Improving flood forecasting using an input correction method in urban models in poorly gauged areas     

Maria Clara Fava  Maurizio Mazzoleni  Narumi Abe  Eduardo Mario Mendiondo  Dimitri P. Solomatine 《水文科学杂志》2020,65(7):1096-1111

ABSTRACT

Poorly monitored catchments could pose a challenge in the provision of accurate flood predictions by hydrological models, especially in urbanized areas subject to heavy rainfall events. Data assimilation techniques have been widely used in hydraulic and hydrological models for model updating (typically updating model states) to provide a more reliable prediction. However, in the case of nonlinear systems, such procedures are quite complex and time-consuming, making them unsuitable for real-time forecasting. In this study, we present a data assimilation procedure, which corrects the uncertain inputs (rainfall), rather than states, of an urban catchment model by assimilating water-level data. Five rainfall correction methods are proposed and their effectiveness is explored under different scenarios for assimilating data from one or multiple sensors. The methodology is adopted in the city of São Carlos, Brazil. The results show a significant improvement in the simulation accuracy.  相似文献   

Prediction of surface charge on oxides in salt solutions: Revisions for 1:1 (ML) electrolytes     

Dimitri A. Sverjensky 《Geochimica et cosmochimica acta》2005,69(2):225-257

Quantitative characterization of the development of proton surface charge on the surfaces of minerals is necessary for a fundamental understanding of reactions between minerals and aqueous electrolyte solutions. Despite many experimental studies of charge development, few attempts have been made to integrate the results of such studies with a theoretical framework that permits prediction. The present study builds on a theoretical framework to analyze a total of 55 sets of proton surface charge data referring to wide ranges of ionic strengths, and types of electrolyte and oxide. The resulting parameters were interpreted with the aid of crystal chemical, electrostatic, and thermodynamic theory, which enable a number of generalizations. Prediction of values of the pHZPC and ΔpKnθ reduces the number of triple-layer parameters to be estimated. New standard states for the equilibrium constants for electrolyte adsorption (KM+θ and KL−θ) permit direct comparison of samples with a range of surface areas or site densities. Predicted cation binding on high dielectric constant solids (e.g., rutile) shows KM+θ, increasing in the sequence Cs+, Rb+, K+, Na+, Li+. In contrast, on low dielectric constant solids (e.g., amorphous silica), the predicted sequence is Li+, Na+, K+, Rb+, Cs+. The opposite sequences are attributable to the large solvation energy contribution opposing adsorption on low-dielectric constant solids. Cation and anion binding constants are in general different, which enables direct prediction of the point-of-zero-salt effect (pHPZSE) relative to the pristine point-of-zero charge. The inner and outer capacitances in the triple-layer model (C1 and C2) are predictable parameters consistent with physically reasonable distances and interfacial dielectric constants for water. In summary, all the parameters in the triple-layer model can be estimated with the revised equations of this study, which enables prediction of proton surface charge for any oxide in 1:1 electrolyte solutions independent of experiments. Such predictions can serve as a complement to the experimental study of new oxide/electrolyte systems, or more complex systems, where additional mechanisms of charge development are likely.  相似文献   

Physical constraints in engineering seismic hazard analysis     

Dimitri Papastamatiou  Sarada K. Sarma 《地震工程与结构动力学》1988,16(7):967-984

In engineering seismic hazard probabilistic analysis, physical constraints are generally overlooked. We formulate such constraints for the general case of a site within an annular seismogenic zone. This configuration provides a first approximation of seismic hazard analysis within a broad zone undergoing crustal deformation; such zones are a common expression of continental tectonics. Applications are restricted to medium size earthquakes (M_s < 7). The formulation is applied to two cases reflecting the mid-plate (case I) and plate boundary (case II) seismotectonic environments. It is found that, for a given strain rate and for an upper bound magnitude of 6 3/4, the extreme hazard in both the environments is the same but of different character. In the plate boundary example, it is associated with widespread ground deformation while in the mid-plate example, it involves more intense ground motion. On the other hand, if the upper bound magnitude is 5 3/4, the extreme hazard is likely to be an order of magnitude less in case I than in case II. Moreover, when the extreme hazard is associated with singular conditions generated by a single fault, the assumption of a Poissonian process may not be safe for earthquake resistant design decisions.  相似文献