Broad-band and Hα surface photometry of the central regions of nearby active galaxies – I. Observations     

Miguel Sánchez-Portal  Ángeles I. Díaz  Roberto Terlevich  †  Elena Terlevich  ‡  Mar Álvarez Álvarez  Itziar Aretxaga 《Monthly notices of the Royal Astronomical Society》2000,312(1):2-32

Broad-band V , R and I and narrow-band H α CCD surface photometry of a sample of 24 active and three normal nearby galaxies is presented, in order to study their morphological and structural properties. This first paper presents the observations, data reduction and processing techniques used; the main characteristics of the central regions of the sample galaxies are derived from broad-band and H α images; broad-band surface brightness and colour profiles are presented; based on the inspection of individual images and the examination of the radial variation of ellipticity and polar angle, the morphological class of the sample objects is revised: several objects previously classified as non-barred or unclassified are found to be barred galaxies. A high fraction (∼71 per cent) of the objects that present any kind of nuclear activity are barred. This proportion is even higher (∼87 per cent) if only Seyfert galaxies are considered. This result can reinforce the clues about the connection between bars and nuclear activity as a fuelling mechanism that can trigger and sustain nuclear activity.  相似文献   

Zero-metallicity stellar sources and the reionization epoch     

Paolo Cojazzi  Alessandro Bressan  Francesco Lucchin  Ornella Pantano  Miguel Chavez 《Monthly notices of the Royal Astronomical Society》2000,315(4):L51-L55

We reconsider the problem of the cosmological reionization owing to stellar sources. Using a method similar to that developed by Haiman & Loeb, we investigate the effect of changing the stellar models and the stellar spectra adopted for deriving the ionizing photon production rate. In particular, we study the consequences of adopting zero-metallicity stars, which is the natural choice for the first stellar populations. We construct young isochrones representative of Population III stars from existing sets of evolutionary models (by Forieri and Cassisi & Castellani) and calculate a suitable library of zero-metallicity model atmospheres. The number of ionizing photons emitted by such a zero-metal population is about 40 per cent higher than that produced by standard metal-poor isochrones. We find that adopting suitable zero-metallicity models modifies the reionization epoch. However the latter is still largely affected by current uncertainties in other important physical processes such as the efficiency of the star formation and the fraction of escaping UV photons.  相似文献   

Fish under influence: A macroecological analysis of relations between fish species richness and environmental gradients among European tidal estuaries   总被引：1，自引：0，他引：1  

Delphine Nicolas  Jérémy Lobry  Mario Lepage  Benoît Sautour  Olivier Le Pape  Henrique Cabral  Ainhize Uriarte  Philippe Boët 《Estuarine, Coastal and Shelf Science》2010

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Spatial variability of seabird distribution associated with environmental factors: a case study of marine Important Bird Areas in the Azores     

Amorim  Patricia; Figueiredo  Miguel; Machete  Miguel; Morato  Telmo; Martins  Ana; Serrao Santos  Ricardo 《ICES Journal of Marine Science》2009,66(1):29-40

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An elastic–viscous–plastic sea ice model formulated on Arakawa B and C grids     

Sylvain Bouillon  Miguel ngel Morales Maqueda  Vincent Legat  Thierry Fichefet 《Ocean Modelling》2009,27(3-4):174-184

The elastic–viscous–plastic (EVP) sea ice rheology has been introduced in the large-scale Louvain-la-Neuve sea-Ice Model, version 2 (LIM2), and its performance has been evaluated. Centred difference versions of the rheology have been implemented on both an Arakawa B grid and a C grid, and their performance have been intercompared in coupled simulations with the Nucleus for European Modelling of the Ocean (NEMO) model. Integrations with both implementations lead to fairly similar results which compare well with observations and with previous LIM simulations. The C grid version, however, offers a number of advantages: (a) easier ice coupling with NEMO, which is itself defined on a C grid; (b) possibility of representing ice transport across one-cell-wide straits and passages; (c) better representation of inertial-plastic compressive waves. For these reasons, we recommend the use of the C grid EVP formulation of the ice dynamics in future LIM applications.  相似文献   

Productivity and nutrient cycling in salt marshes: Contribution to ecosystem health     

Ana I. Sousa  Ana I. Lillebø  Miguel A. Pardal  Isabel Caçador 《Estuarine, Coastal and Shelf Science》2010

This study aimed to assess the contribution of different salt marsh halophytes (Spartina maritima, Scirpus maritimus, Halimione portulacoides, Sarcocornia fruticosa, and Sarcocornia perennis) to nutrient cycling and sequestration in warm-temperate salt marshes. Carbon, nitrogen and phosphorus concentration in plant organs and rhizosediment, as well as plant biomass were monitored every two months during one year. Results show that the C retained in the rhizosediment does not seem to be species or site specific. However, some halophytes seem to have a higher contribution to retain C from external sources, namely S. perennis and S. maritima. Regarding N, halophytes colonizing the upper and middle marsh areas had the highest NBPP (net belowground primary production) as well as the retention of N in the rhizosediment. Yet, excluding S. maritimus, all halophytes seem to contribute to the retention of N from external sources. The P retained in the rhizosediment does not seem to be species or site specific. Still, only S. maritima colonizing the lower marsh areas, which also had comparatively lower NBPP, seem to have a higher contribution to retain P from external sources. Additionally, it seems that there is no relation between plants sequestration capacity for nutrients and plant photosynthetic pathway. This work shows that nutrient cycling and accumulation processes by salt marsh halophytes contribute to reduce eutrophication (N and P retention) and also to reduce atmospheric CO₂ (C retention), highlighting salt marsh ecosystems services and the crucial role of halophytes in maintaining ecosystem functions and health.  相似文献   

An ANN algorithm for automatic, real-time tsunami detection in deep-sea level measurements     

Gian Mario Beltrami   《Ocean Engineering》2008,35(5-6):572-587

The present paper looks at algorithms to be implemented in the software of bottom pressure recorders (BPRs) for the automatic, real-time detection of a tsunami within recorded signals. The structure of an algorithm based on the use of an artificial neural network (ANN) is presented and compared to the one developed under the Deep-ocean Assessment and Reporting of Tsunamis (DART) program run by the U.S. National Oceanic and Atmospheric Administration (NOAA). The performance and efficiency of the two algorithms are compared using both synthetic and actually measured time series. Results show that an improvement in detection performance can be obtained by using the ANN algorithm.  相似文献   

Fish assemblages and rapid colonization after enlargement of an artificial reef off the Algarve coast (Southern Portugal)     

Francisco Leitão  Miguel N. Santos  Karim Erzini  Carlos C. Monteiro 《Marine Ecology》2008,29(4):435-448

Artificial reefs (ARs) have been deployed in Algarve (Southern Portugal) coastal waters to contribute to the sustainability of local nearshore fisheries. Herein, we describe the colonization process of the recently deployed Faro/Ancão AR, and assess the time until the fish assemblage reaches stability and their seasonal patterns. In addition, we compare the results from the present study with those previously reported for an older AR. The fish assemblages were monitored monthly over a 2‐year period by means of visual census. A rapid increase in fish colonization occurred within the first 4 months. After this initial period the assemblage structure showed high similarity (> 73%). The high rate of colonization of the AR was related to the maturity already achieved by the nearby 14‐year‐old AR and to the fish migration from the Ria Formosa lagoon, a nearby nursery habitat. The reef fish assemblage structure showed a seasonal pattern, mainly associated with recruitment episodes of occasional demersal species (Boops boops, Trachurus trachurus and Pagellus spp.) in spring and summer. A total of 66% of the species found in AR are of commercial and recreational importance. The overall mean density and biomass were 2.8 ind·m^?3 and 207 g·m^?3. The occasional demersal species accounted for 42% of the fish density. The most important species in terms of biomass belong to the Sparidae family along with Dicentrarchus labrax. The fish assemblage of the new ARs showed higher mean number of species, diversity, density and biomass values than those reported for the older AR. This result was associated with enlargement of the AR area and with the fishing exploitation of the isolated, small and patchy old AR. Moreover, the high biomass values recorded in the new ARs were mainly due to the increased density of D. labrax after AR enlargement. The results of the present study are used to define guidelines for suitable management strategies for the AR areas that are exploited by the local commercial and recreational fisheries.  相似文献   

Sources, pathways and sinks of particulate organic matter in Hudson Bay: Evidence from lignin distributions   总被引：1，自引：0，他引：1  

Zou Zou A. Kuzyk  Miguel A. Goi  Gary A. Stern  Robie W. Macdonald 《Marine Chemistry》2008,112(3-4):215-229

Hudson Bay is a large, estuarine, shelf-like sea at the southern margin of the Arctic, where changes in seasonal ice cover and river discharge appear already to be underway. Here we present lignin data for dated sediments from eleven box cores and evaluate sources of terrigenous carbon, transport pathways, and whether terrigenous organic matter has been influenced by recent environmental change. Lignin yields (0.04 to 1.46 mg/100 mg organic carbon) decreased from the margin to the interior and from south to north, broadly reflecting the distribution of river inputs. Lignin compositional patterns indicated distinct regional sources with boreal forest (woody gymnosperm) vegetation an important source in the south, vs. tundra (non-woody angiosperm) in the north. Lignin patterns suggest redistribution of a fine-grained, mineral-associated fraction of the southern-derived terrigenous carbon to the northeast part of the Bay and ultimately into west Hudson Strait with the Bay's cyclonic coastal circulation. A small component of the carbon makes it to the central basins of Hudson Bay but most of the terrigenous organic material in that area appears to derive from resuspension of older, isostatically-rebounding coastal and inner shelf deposits. Most modern plant debris appears to be retained near river mouths due to hydrodynamic sorting, with the exception of the southwest inner shelf, where these materials extend > 30 km from shore. Temporal changes in the composition of terrigenous organic carbon recorded in most of the southern Hudson Bay cores perhaps reflect increases in erosion and cross-shelf transport from coastal deposits, possibly mediated by change in ice climate. In contrast, temporal changes in the northwest may relate to changes in the supply of modern plant debris under recent warmer conditions. On the western shelf, changes may relate to ice climate and the distribution of northern coastal water and/or changes in the delivery of materials by the Churchill River due to water diversion. Although the cores show evidence of change related to the ice climate, there is little evidence that ice itself transports terrigenous organic carbon within the system.  相似文献   

Cenozoic diatreme field in Chubut （Argentina） as evidence of phreatomagmatic volcanism accompanied with extensive Patagonian plateau basalt volcanism？     

Karoly Nemeth Ulrike Martin Miguel J. Haller Viviana I. Alric 《《幕》》2007,30(3):217-223

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