Chemical abundances and ionizing clusters of H ii regions in the LINER galaxy NGC 4258     

Angeles I. Díaz  Marcelo Castellanos  Elena Terlevich †  María Luisa García-Vargas 《Monthly notices of the Royal Astronomical Society》2000,318(2):462-474

We present long-slit observations in the optical and near-infrared of eight H  ii regions in the spiral galaxy NGC 4258. Six of the observed regions are located in the south-east inner spiral arms, and the other two are isolated in the northern outer arms. A detailed analysis of the physical conditions of the gas has been performed. For two of the regions, an electron temperature has been derived from the [S  iii ] λ 6312 line. For the rest, an empirical calibration based on the red and near-infrared sulphur lines has been used. The oxygen abundances derived by both methods are found to be significantly lower (by a factor of 2) than previously derived by using empirical calibrations based on the optical oxygen lines.
In the brightest region, 74C, the observation of a prominent feature caused by Wolf–Rayet (WR) stars provides an excellent constraint over some properties of the ionizing clusters. In the light of the current evolutionary synthesis models, no consistent solution is found to explain at the same time both the WR feature characteristics and the emission-line spectrum of this region. In principle, the presence of WR stars could lead to large temperature fluctuations and also to a hardening of the ionizing radiation. None of these effects is found in region 74C, for which the electron temperatures found from the [S  iii ] λ 6312 line and the Paschen discontinuity at 8200 Å are equal within the errors, and the effective temperature of the ionizing radiation is estimated at around 35 300 K.
Both more observations of confirmed high-metallicity regions and a finer metallicity grid for the evolutionary synthesis models are needed in order to understand the ionizing populations of H  ii regions.  相似文献   

The role of hydrological processes in ecosystem conservation: Comprehensive water management for a wetland in an arid climate     

Marcelo A. Lomeli-Banda  Jorge Ramírez-Hernández  Jesús Eliana Rodríguez-Burgueño  Carlos Salazar-Briones 《水文研究》2021,35(2):e14013

Water agreements between Mexico and the United States have been crucial to preserving and restoring the Colorado River Delta's wetlands. Nowadays, increased water demand and climate change in the Colorado River Basin could threaten the conservation of the Ciénega de Santa Clara, a 4709 ha coastal wetland at the Sonoran Desert's edge. The international Ramsar convention recognizes the Ciénega de Santa Clara ecosystem for providing vital ecological services, including habitat for endemic, endangered, and migratory species. The hydrology of this wetland has not been completely understood since the 2010–2011 trial run of the Yuma Desalting Plant. Therefore, this study was conducted to identify and quantify the hydrological elements essential for the conservation of this wetland, under three scenarios: (a) normal inflow conditions of the water source – the Wellton-Mohawk canal; (b) inflow reductions, and; (c) an increase of temperature due to global warming. Water and mass balances estimates were conducted every month during 2014–2015; in situ measurements of inflows were carried out on Southern International Boundary in Wellton-Mohawk canal, the Riíto Drain, groundwater, and precipitation: evapotranspiration outputs were estimated using local weather stations and Penman-Monteith formulations. Temperature increases were based on the Intergovernmental Panel on Climate Change projections for the next 100 years. Results showed disconnection in the surface flow of water from the wetland to the adjacent Gulf of California. This behaviour was observed mainly in the summer months in the three scenarios. The disconnections reduced the wetland area and water storage. The hydrological functionality of the Ciénega de Santa Clara wetland depends on the water supply from the Wellton-Mohawk canal, with a minimum continuous discharge of 5.10 m³ s⁻¹ during the summer months.  相似文献   

Probabilistic modelling of auto-correlation characteristics of heterogeneous slopes     

Thi Minh Hue Le  Marcelo Sánchez  Domenico Gallipoli  Simon Wheeler 《Geomechanics and Geoengineering》2015,10(2):95-108

Spatial variability of soil materials has long been recognised as an important factor influencing the reliability of geo-structures. This study stochastically investigates the influence of spatial variability of shear strength on the stability of heterogeneous slopes, focusing on the auto-correlation function, auto-correlation distance and cross-correlation between soil parameters. The finite element method is merged with the random field theory to probabilistically evaluate factor of safety and probability of failure via Monte-Carlo simulations. The simulation procedure is explained in detail with suggestions on improving efficiency of the Monte-Carlo process. A simple procedure to create cross-correlation between random variables, which allows direct comparison of the influence of each strength variable, is discussed. The results show that the auto-correlation distance and cross-correlation can significantly influence slope stability, while the choice of auto-correlation function only has a minor effect. An equation relating the probability of failure with the auto-correlation distance is suggested in light of the analyses performed in this work and other results from the literature.  相似文献   

Combined effects of elevated [CO2] and high temperature on leaf mineral balance in Coffea spp. plants     

Lima D. Martins  Marcelo A. Tomaz  Fernando C. Lidon  Fábio M. DaMatta  José C. Ramalho 《Climatic change》2014,126(3-4):365-379

Modelling studies predicted that climate change will have strong impacts on the coffee crop, although no information on the effective impact of elevated CO₂ on this plant exists. Here, we aim at providing a first glimpse on the effect of the combined impact of enhanced [CO₂] and high temperature on the leaf mineral content and balance on this important tropical crop. Potted plants from two genotypes of Coffea arabica (cv. Icatu and IPR 108) and one from C. canephora (cv. Conilon Clone 153) were grown under 380 or 700 μL CO₂ L^?1 air, for 1 year, after which were exposed to an stepwise increase in temperature from 25/20 °C (day/night) up to 42/34 °C, over 8 weeks. Leaf macro???(N, P, K, Ca, Mg, S) and micronutrients (B, Cu, Fe, Mn, Zn) concentrations were analyzed at 25/20 °C (control), 31/25 °C, 37/30 °C and 42/34 °C. At the control temperature, the 700 μL L^?1 grown plants showed a moderate dilution effect (between 7 % and 25 %) in CL 153 (for N, Mg, Ca, Fe) and Icatu (for N, K and Fe), but not in IPR 108 (except for Fe) when compared to the 380 μL L^?1 plants. For temperatures higher than control most nutrients tended to increase, frequently presenting maximal contents at 42/34 °C (or 37/30 °C), although the relation between [CO₂] treatments did not appreciably change. Such increases offset the few dilution effects observed under high growth [CO₂] at 25/20 °C. No clear species responses were found considering [CO₂] and temperature impacts, although IPR 108 seemed less sensitive to [CO₂]. Despite the changes promoted by [CO₂] and heat, the large majority of mineral ratios were kept within a range considered adequate, suggesting that this plant can maintain mineral balances in a context of climate changes and global warming.  相似文献   

Spatiotemporal analysis of particulate matter, sulfur dioxide and carbon monoxide concentrations over the city of Rio de Janeiro, Brazil     

Marcelo Zeri  Jos�� Francisco Oliveira-J��nior  Gustavo Bastos Lyra 《Meteorology and Atmospheric Physics》2011,113(3-4):139-152

Time series of pollutants and weather variables measured at four sites in the city of Rio de Janeiro, Brazil, between 2002 and 2004, were used to characterize temporal and spatial relationships of air pollution. Concentrations of particulate matter (PM₁₀), sulfur dioxide (SO₂) and carbon monoxide (CO) were compared to national and international standards. The annual median concentration of PM₁₀ was higher than the standard set by the World Health Organization (WHO) on all sites and the 24?h means exceeded the standards on several occasions on two sites. SO₂ and CO did not exceed the limits, but the daily maximum of CO in one of the stations was 27% higher on weekends compared to weekdays, due to increased activity in a nearby Convention Center. Air temperature and vapor pressure deficit have both presented the highest correlations with pollutant??s concentrations. The concentrations of SO₂ and CO were not correlated between sites, suggesting that local sources are more important to those pollutants compared to PM₁₀. The time series of pollutants and air temperature were decomposed in time and frequency by wavelet analysis. The results revealed that the common variability of air temperature and PM₁₀ is dominated by temporal scales of 1?C8?days, time scales that are associated with the passage of weather events, such as cold fronts.  相似文献   

Late Quaternary paleoenvironments and paleoclimatic conditions in the distal Andean piedmont, southern Mendoza, Argentina     

Alfonsina Tripaldi  Marcelo A. Zárate  George A. Brook  Guo-Qiang Li 《Quaternary Research》2011,76(2):253-263

The Andean piedmont of Mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology. This paper is focused on the San Rafael plain (SRP) environment, situated in the distal Andean piedmont of Mendoza (34° 30′S), and reports the sedimentology and OSL chronology of two representative exposures of late Quaternary deposits, including their paleoenvironmental and paleoclimatic significance. Eleven facies, including channel, floodplain, fluvio–aeolian interaction, and reworked pyroclastic and aeolian deposits, were described and grouped into two facies associations (FA1 and FA2). FA1 was formed by unconfined sheet flows, minor channelized streams and fluvial–aeolian interaction processes. FA2 was interpreted as aeolian dune and sand-sheet deposits. OSL chronology from the SRP sedimentary record indicates that between ca. 58–39 ka and ca. 36–24 ka (MIS 3), aggradation was governed by ephemeral fluvial processes (FA1) under generally semiarid conditions. During MIS 2, the last glacial maximum (ca. 24–12 ka), a major climatic shift to more arid conditions is documented by significant aeolian activity (FA2) that became the dominant sedimentation process north of the Diamante–Atuel fluvial system. The inferred paleoenvironmental conditions from the SRP sections are in broad agreement with regional evidence.  相似文献   

Triterpenols in mangrove sediments as a proxy for organic matter derived from the red mangrove (Rhizophora mangle)     

Boris P. Koch  Pedro W.M. Souza FilhoHermann Behling  Marcelo C.L. CohenGerhard Kattner  Jürgen RullkötterBarbara Scholz-Böttcher  Rubén J. Lara 《Organic Geochemistry》2011,42(1):62-73

Mangroves are the dominant type of vegetation along many tropical coasts. Organic matter (OM) derived from mangrove leaf litter and root material is stored in sediments and is a major contributor to the amount and chemical composition of sedimentary OM. A set of organic biomarkers in sediments was applied as a palaeo-indicator for the Holocene dynamics of a mangrove Estuary (Rio Caeté, Pará, Brazil). Six sediment cores were collected perpendicular to the present coast line and analysed for triterpenols and sitosterol. The influence of microbial biomarker degradation was implemented from a previous study. Biomarker profiles were validated with pollen data and multivariate statistics to test whether these compounds were suitable indicators for the palaeo-vegetation. Sediments deposited up to 2 Ma BP showed biomarker assemblages similar to those of recent surface sediment. In two cores, the biomarker composition revealed a transition from marsh to mangrove vegetation. Taraxerol, germanicol and β-amyrin provided the most significant chemotaxonomical information and, especially in combination, served as reliable proxies for OM from Rhizophora mangle in northern Brazil. The maximum age of the mangrove system ranged between 1000 and 5100 yr depending on the topographic elevation of the drilling location.  相似文献   

New chelid turtles of the lower section of the Cerro Barcino formation (Aptian-Albian?), Patagonia, Argentina     

Marcelo S. de la Fuente  Aldo M. Umazano  Juliana Sterli  José L. Carballido 《Cretaceous Research》2011,32(4):527-537

A new chelid species (Prochelidella cerrobarcinae nov. sp.) are described from the Aptian-Albian? Puesto La Paloma Member, Cerro Barcino Formation, northern of Chubut Province, Argentina. The basal section of this member, which bears the turtle remains, is composed of tuffaceous mudstones with plane parallel lamination, asymmetrical ripples and a chert intercalation suggesting sub-aqueous deposition in a relatively shallow lacustrine environment. Pr. cerrobarcinae nov. sp. is represented by post-cranial remains of several specimens that not only represents the oldest pleurodiran chelid record in the world but, together with the chelid remains of Albian Lightning Ridge, New South Wales, Australia, indicates that chelid diversification began well before the final fragmentation of southern Gondwana.  相似文献   

Distribution of whitemouth croaker (Micropogonias furnieri, Desmarest 1823) larvae in the Río de la Plata estuarine front     

Mara S. Braverman  E. Marcelo Acha  Domingo A. Gagliardini  Martín Rivarossa   《Estuarine, Coastal and Shelf Science》2009,82(4):557-565

Whitemouth croaker (Micropogonias furnieri) larvae obtained and hydrographic data collected in the Rio de la Plata estuary (35°S–56°W) between 1987 and 2000 were used to explore the early life stages spatial and temporal distribution patterns and their relation to oceanographic features. The spatial distribution, restricted to a band in the inner part of the estuary, coincided with the bottom salinity front and the maximum turbidity zone (MTZ, turbidity front). Larvae were present during the warmest months (October through May) within a range of 14–24.5 °C temperature and 0.9–33 salinity. A vertically stratified sampling performed in the region where the largest abundance was found (December 2005 and March 2006) was used to test the hypothesis that larvae retention occurs in the bottom salinity front.The vertically stratified sampling showed larvae throughout the water column with high predominance in the river–estuary transition zone. A positive correlation between abundance and the bottom salinity horizontal gradient was found. The size analysis showed that the largest individuals (>10 mm SL), probably undergoing the settlement process, inhabited near the bottom and that the smallest (<10 mm SL) were present in the whole water column. Length distribution along the front showed no trend.Results support the estuarine retention hypothesis of previous studies on whitemouth croaker gravid females, eggs distribution and outcomes from a numerical simulation model. Retention in the salinity front/MTZ would allow larvae to benefit from food accumulation in the region, the high turbidity level provide shelter against predators and retention in the estuary secure closeness to the main nursery ground.  相似文献   

Ca ii K interstellar observations towards early-type disc and halo stars     

J. V. Smoker  W. R. J. Rolleston  H. R. M. Kay  D. Kilkenny  R. Morras  M. Arnal  F. P. Keenan  C. J. Mooney  P. L. Dufton  R. S. I. Ryans  N. C. Hambly  D. O'Donoghue  H. McGillivray 《Monthly notices of the Royal Astronomical Society》2003,346(1):119-134

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