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141.
Miriam Garcia 《Astrophysics and Space Science》2011,335(1):131-136
The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through
spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though
relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends
code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association’s color-magnitude diagrams (CMDs) and the automatic determination of evolutionary
masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary
stages (Garcia et al. in Astron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC 1613 as illustration of the potential of the method. 相似文献
142.
Water concentrates from Turia river (1.5 mg L−1 total organic C) obtained by nanofiltration (membrane mass cut-off 90 Da) were fractioned by non-ionic Amberlite resins (DAX8 and XAD4) to afford three samples termed as hydrophobic acid (50%), transphilic acid (24%) and hydrophobic neutral (12%). If a nanofiltration membrane 270 Da mass cut-off is used then about 50% of dissolved organic matter is not retained. These three fractions were characterized by analytical and spectroscopic techniques (1H NMR, MALDI–TOF-MS, ESI–API-MS, ESI–MS/MS). Overall, these data are compatible with the presence of oligosaccharides, oligopeptides and fatty acids as the main components of dissolved organic matter. Particularly revealing was the information from MALDI–TOF-MS and ESI–MS/MS where series of compounds differing in the number of hexose units were identified. The three fractions have many spectroscopic similarities and, particularly the hydrophobic and transphilic ones, are really almost identical. This similarity in the fraction composition shows that the conventional fractionation procedure is inefficient as a standard general method for separation of different compound types. The composition of dissolved organic matter was confirmed, and some individual organic compounds identified, by GC–MS analysis of the silylated derivatives obtained by reacting the fractions with a mixture of N,O-bis(trimethylsilyl)trifluoroacetamide with trimethylchlorosilane (10%). Thus, rather surprisingly, the dissolved organic matter of this natural raw water is predominantly composed of a relatively simple mixture of a few types of compounds with molecular weights well below 1100 Da (about six hexose units). These results, particularly the absence of detectable amounts of high molecular weight humic acids and low molecular weight phenolic compounds indicates that trihalomethanes formed in the water disinfection process by Cl2 really derive from oligosaccharides and oligopeptides. Also, the data suggests alternative strategies to effect a more efficient fractionation of the dissolved organic matter. 相似文献
143.
An integrated methodology for evaluation of overwash vulnerability is developed with respect to the historical washover evolution
of a barrier island system. Three different aspects of overwash are addressed in the vulnerability indices developed: overwashed
shoreline ratio, maximum overwash intrusion recurrence, and complete barrier overwash. The indices were applied to the barriers
in the Ria Formosa system in Southern Portugal using an aerial photography catalogue covering the period 1947–2001. Historical
trends of washover evolution were observed to be different between the barriers analysed, but generally, there was a decrease
in washover number and dimensions throughout the analysed period. The final overwash diagnostic obtained allowed an integrated
overwash vulnerability rating to be defined for each barrier, with vulnerabilities ranging from low to extreme. The methodology
has produced results that may assist coastal managers with information concerning barrier island system overwash hazard, define
the temporal and geographical distributions of overwash, and provide indications as to where overwash is most likely to occur
in the future. 相似文献
144.
L. Borgnino M. G. Garcia M. V. del Hidalgo M. Avena C. P. De Pauli M. A. Blesa P. J. Depetris 《Aquatic Geochemistry》2010,16(2):279-291
We propose a model that explains the acid–base surface properties of clastic sediments from two Argentinean reservoir lakes.
The model uses potentiometric titration data sets and fixed parameters such as the apparent stability constants and reaction
stoichiometries of acid–base equilibriums involving known mineral phases. The model considers that sediments act as a set
of independent sorption surfaces, such as organic matter, clay silicate, and iron (hydr)oxides, thus the acid–base equilibrium
and the correspondent protolytic constants are represented by a humic acid, a Na-illite, and a poor crystalline Fe-hydr(oxide).
In agreement with experimental data, the model predicts that all sediment samples show a similar charging behavior, increasing
the negative charge as the pH increases. The net charge of sediments is controlled by the presence of negatively charged minerals
and/or organic matter coatings. This reveals the great influence of clays and organic matter functional groups on the acid–base
surface properties of sediments, and consequently on the surface reactivity toward contaminant transport. 相似文献
145.
Paulo C. Abreu Marli Bergesch Luis A. Proen?a Carlos A. E. Garcia Clarisse Odebrecht 《Estuaries and Coasts》2010,33(2):554-569
In the shallow microtidal Patos Lagoon estuary, southern Brazil (32° 07′ S–52° 06′ W), chlorophyll a (Chl a) variability was studied at different time scales during the last 25 years (hourly–daily sampling in 1984/1985; weekly sampling
in 1986 and from 1988 to 1990; monthly sampling from 1993 to 2008). Phytoplankton biomass variation seems to be most influenced
by hydrology, which is primarily driven by meteorological factors like wind, rainfall, and evaporation. However, it was observed
that the hydrological driving forces play different roles at different time scales. For instance, short-term Chl a variability is mainly controlled by winds, while long-term changes are related to the freshwater input by rainfall. Significant
correlation was found between the total amount of rain in the year and the mean annual value of Chl a, though this relationship was linear until 1,500 mm of rain per year. After this threshold, mean annual Chl a values dropped significantly, probably due to a washout of the produced biomass from the estuary. Similarly, low rainfall
levels and drought years lead to small phytoplankton biomass due to scarcity of nutrient, mainly silicate, or a possible inhibitory
effect generated by high ammonium concentration. In this sense, large-scale Chl a variability would be related to the El Ni?o-Southern Oscillation climatic anomaly, which influences the rainfall levels in
Southern Brazil, though sampling periodicity has also great influence on this relationship. No Chl a or nutrient enrichment was observed in the estuarine region along the last years, indicating that this estuary is not subject
to an eutrophication process. In contrast, signals of an ongoing oligotrophication are observed, possibly a remote effect
of the eutrophication in the Northern area of the lagoon where the phytoplankton nutrients uptake may act as a biological
filter mechanism. 相似文献
146.
Servando Chinchón-Payá Bravo I. De Blas Roldán M. J. Nueda Andreu F. Garcia 《Environmental Earth Sciences》2010,61(5):1005-1012
A model has been developed to predict the origin of uncontrolled water flows. For this purpose, we analysed a total of 52
elements using ICP techniques on 72 water samples in all: 40 of them from leaks in the drinking water supply network and the
remaining 32 from groundwater outcrops. The study focused on the cases registered within the Alicante town limits (Spain).
The use of multivariate statistical classification tools such as discriminant analysis made it possible not only to reduce
the number of analytes, but also to design a predictive model capable of assigning the group to which a new sample belongs.
The elements that comprise the model are B, Mn, Te, Ce, Re, Sr, Li and Tl. Given the concentration of each element in the
sample, the model can assign its precedence with a total success rate higher than 94%. 相似文献
147.
N. Pesenti C. Dougados S. Cabrit D. O'Brien P.J.V. Garcia 《Astrophysics and Space Science》2004,292(1-4):539-545
We investigate in this contribution emissivity properties of the [Fe ii] near-IR lines and their application to the study of jets in young stars. We report a model-independent method to determine the gas phase abundance in jets. Then, we present synthetic maps deduced from a recent self-consistent MHD cold disk wind model from which the thermal solution has been solved a posteriori. Kinematics is compared with observations in the [Fe ii] near-IR lines of L1551-IRS5. General kinematical behaviour is well reproduced, the existence of two velocity components in particular. However, we note a relative deficit in emission at intermediate velocity as observed in the jets from optically visible T Tauri stars. We examine predicted rotation signatures for various types of MHD disk winds. Compared to observations of DG Tau, warm disk winds reproduce quite well observed velocity shifts, whereas cold solutions predict too high toroidal velocities by a factor 2–3. 相似文献
148.
Darren M. O'Brien Paulo J.V. Garcia Jonathan Ferreira Sylvie Cabrit Luc Binette 《Astrophysics and Space Science》2004,292(1-4):609-617
The effects of phenomenological heating functions on the flow thermodynamics of cold T-Tauri disk winds are examined. Turbulent dissipation (mechanical) heating and a warm disk corona are invoked to heat the wind. The temperature and ionization evolution are solved for along the flow. The results allow the construction of synthetic observations; emission maps, forbidden line ratios, line fluxes and line profiles; and successfully reproduce a number of observed trends. Mechanical heating produces line ratios and fluxes that fit very well with observations. Invoking a warm disk corona successfully reproduces forbidden line profile low velocity components. 相似文献
149.
R. Stein B. Boucsein K. Fahl T. Garcia de Oteyza J. Knies F. Niessen 《Global and Planetary Change》2001,31(1-4)
Data on the amount and composition of organic carbon were determined in sediment cores from the Kara and Laptev Sea continental margin, representing oxygen isotope stages 1–6. The characterization of organic matter is based on hydrogen index (HI) values, n-alkanes and maceral composition, indicating the predominance of terrigenous organic matter through space and time. The variations in the amount and composition of organic carbon are mainly influenced by changes in fluvial sediment supply, Atlantic water inflow, and continental ice sheets. During oxygen isotope stage (OIS) 6, high organic carbon contents in sediments from the Laptev Sea and western East Siberian Sea continental margin were probably caused by the increased glacial erosion and further transport in the eastward-flowing boundary current along the continental margin. During OIS 5 and early OIS 3, some increased amounts of marine organic matter were preserved in sediments east of the Lomonosov Ridge, suggesting an influence of nutrient-rich Pacific waters. During OIS 2, terrigenous organic carbon supply was increased along the Barents and western Kara Sea continental margin caused by extended continental ice sheets in the Barents Sea (Svalbard to Franz Josef Land) area and increased glacial erosion. Along the Laptev Sea continental margin, on the other hand, the supply of terrigenous (organic) matter was significantly reduced due to the lack of major ice sheets and reduced river discharge. Towards the Holocene, the amount of total organic carbon (TOC) increased along the Kara and Laptev Sea continental margin, reaching average values of up to 0.5 g C cm−2 ky−1. Between about 8 and 10 ka (9 and 11 Cal ka), i.e., during times when the inner shallow Kara and Laptev seas became largely flooded for the first time after the Last Glacial Maximum, maximum supply of terrigenous organic carbon occurred, which is related to an increase in coastal erosion and Siberian river discharge. During the last 8000 years, the increased amount of marine organic carbon preserved in the sediments from the Kara and Laptev Sea continental margin is interpreted as a result of the intensification of Atlantic water inflow along the Eurasian continental margin. 相似文献
150.
Peter John Marcotullio Andrea Sarzynski Jochen Albrecht Niels Schulz Jake Garcia 《Climatic change》2013,121(4):621-634
The purpose of this paper is to describe global urban greenhouse gas emissions by region and sector, examine the distribution of emissions through the urban-to-rural gradient, and identify covariates of emission levels for our baseline year, 2000. We use multiple existing spatial databases to identify urban extent, greenhouse gas emissions (CO2, N2O, CH4 and SF6) and covariates of emissions in a “top-down” analysis. The results indicate that urban activities are significant sources of total greenhouse gas emissions (36.8 and 48.6 % of total). The urban energy sector accounts for between 41.5 and 66.3 % of total energy emissions. Significant differences exist in the urban share of greenhouse gas emissions between developed and developing countries as well as among source sectors for geographic regions. The 50 largest urban emitting areas account for 38.8 % of all urban greenhouse gas emissions. We find that greenhouse gas emissions are significantly associated with population size, density, growth rates, and per capita income. Finally, comparison of our results to “bottom-up” estimates suggest that this research’s data and techniques are best used at the regional and global scales. 相似文献