Testing the consistency of the Starburst scenario for active galactic nuclei     

María Luisa García Vargas  Angeles Díaz  Roberto Terlevich  Elena Terlevich 《Astrophysics and Space Science》1993,205(1):77-84

In the frame of the Starburst Model, we show that the evolution of a massive stellar cluster in a high metallicity environment can reproduce the observed emission-line spectrum and the UV-optical Spectral Energy Distribution of the Seyfert 2 galaxies and LINERs. We apply the results of our models to three objects: NGC 5506, NGC 5643 and Mk 348.  相似文献   

The luminosity oscillation of X-ray bursters and recurrent novae     

Roberto Aquilano  Mario Castagnino  Luis Lara 《Astrophysics and Space Science》1987,138(1):41-48

Thermo-mechanical oscillations of a radiating spherically-symmetric shell containing a fermion gas (i.e., oscillation where only mechanical, thermodynamical, and eventually radiation phenomena are taken into account) are studied. With a reasonable choice of the three relevant parameters all other observational data are similar to the ones of X-ray bursters and recurrent novae.Therefore, thermo-mechanical oscillations could play an important role in the oscillation spectrum of these astronomical objects.  相似文献   

Response of antioxidant systems to copper in the gills of the clam Ruditapes decussatus     

Florence Geret  Angela Serafim  Luisa Barreira  Maria Joo Bebianno 《Marine environmental research》2002,54(3-5)

Copper (Cu) is an essential element for biological systems, however, when present in excess, is toxic. Metallothioneins can play an important role in Cu homeostasis and detoxification. Moreover, Cu can catalyse the production of toxic hydroxyl radicals that cause lipid peroxidation but defence systems in the cells can limit the oxidative damage. The present study was performed to investigate the effect of three Cu concentrations (0.5, 2.5 and 25 μg l⁻¹) on the response of antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathion peroxidase and total glutathion peroxidase), total proteins, metallothioneins (MT), malondialdehyde (MDA) concentrations in the gills of the clam, Ruditapes decussatus. The activity of antioxidant enzymes and total proteins, MT and MDA concentrations were measured in the gills of the clams after 1, 3, 7, 14, 21 and 28 days of Cu exposure. Results indicate that Cu only induces an imbalance in the oxygen metabolism during the first week of Cu exposure due to a decrease in mitochondrial SOD and CAT, selenium-dependent and total glutathion peroxidase activities. Cu also causes lipid peroxidation, measured by the MDA formation, that was Cu dependent. In the gills of clams exposed to 25 μg Cu/l, the excess of Cu triggers the induction of MT synthesis after 3 days of exposure.  相似文献   

Seasonal variations of water system distribution and flow patterns in the southern sea area of Hokkaido,Japan     

Ana Luisa Rosa  Yutaka Isoda  Kazuyuki Uehara  Tomokazu Aiki 《Journal of Oceanography》2007,63(4):573-588

Hydrographic data and composite current velocity data (ADCP and GEK) were used to examine the seasonal variations of upper-ocean flow in the southern sea area of Hokkaido, which includes the “off-Doto” and “Hidaka Bay” areas separated by Cape Erimo. During the heating season (April–September), the outflow of the Tsugaru Warm Current (TWC) from the Tsugaru Strait first extends north-eastward, and then one branch of TWC turns to the west along the shelf slope after it approaches the Hidaka Shelf. The main flow of TWC evolves continuously, extending eastward as far as the area off Cape Erimo. In the late cooling season (January–March), part of the Oyashio enters Hidaka Bay along the shallower part of the shelf slope through the area off Cape Erimo, replacing almost all of the TWC water, and hence the TWC devolves. It is suggested that the bottom-controlled barotropic flow of the Oyashio, which may be caused by the small density difference between the Oyashio and the TWC waters and the southward migration of main front of TWC, permits the Oyashio water to intrude along the Hidaka shelf slope.  相似文献   

Study of an unexpected convective storm     

Maria E. Saluzzi  Laura Levi  Luisa Lubart  Gustavo Carri 《Atmospheric Research》1997,44(3-4)

The occurrence of a severe storm in the Argentine littoral has been analyzed. Although general atmospheric conditions were not favorable to the development of deep convection, this storm produced strong winds and hail of considerable intensity. Its occurrence was associated with the entrance of a pulse of humid air at low levels and could be related to the development of two vorticity centers in the region. Atmospheric conditions existing above a low-level inversion are used to simulate two possible clouds, with base altitudes at 2200 and 3000 m and updraft speeds reaching maximum values of 27 and 29 m s⁻¹ respectively. It is noted that the base temperature of about 13°C, found for the first cloud, can be correlated with the prevalence of frozen drop embryos, observed in an analyzed hailstone sample. Hailstone vertical trajectories are simulated in both modeled clouds, assuming spheroidal and spherical particles and assigning different values to the drag coefficient C_d.  相似文献   

Spatiotemporal estimation of snow depth using point data from snow stakes,digital terrain models,and satellite data          下载免费PDF全文

Antonio‐Juan Collados‐Lara  Eulogio Pardo‐Igúzquiza  David Pulido‐Velazquez 《水文研究》2017,31(10):1966-1982

Snow availability in Alpine catchments plays an important role in water resources management. In this paper, we propose a method for an optimal estimation of snow depth (areal extension and thickness) in Alpine systems from point data and satellite observations by using significant explanatory variables deduced from a digital terrain model. It is intended to be a parsimonious approach that may complement physical‐based methodologies. Different techniques (multiple regression, multicriteria analysis, and kriging) are integrated to address the following issues: We identify the explanatory variables that could be helpful on the basis of a critical review of the scientific literature. We study the relationship between ground observations and explanatory variables using a systematic procedure for a complete multiple regression analysis. Multiple regression models are calibrated combining all suggested model structures and explanatory variables. We also propose an evaluation of the models (using indices to analyze the goodness of fit) and select the best approaches (models and variables) on the basis of multicriteria analysis. Estimation of the snow depth is performed with the selected regression models. The residual estimation is improved by applying kriging in cases with spatial correlation. The final estimate is obtained by combining regression and kriging results, and constraining the snow domain in accordance with satellite data. The method is illustrated using the case study of the Sierra Nevada mountain range (Southern Spain). A cross‐validation experiment has confirmed the efficiency of the proposed procedure. Finally, although it is not the scope of this work, the snow depth is used to asses a first estimation of snow water equivalent resources.  相似文献   

Implications of measurement metrics on soil freezing curves: A simulation of freeze–thaw hysteresis     

Renato Pardo Lara  Aaron A. Berg  Jon Warland  Gary Parkin 《水文研究》2021,35(7):e14269

Soil freeze–thaw events have important implications for water resources, flood risk, land productivity, and climate change. A property of these phenomena is the relationship between unfrozen water content and sub-freezing temperature, known as the soil freezing characteristic curve (SFC). It is documented that this relationship exhibits hysteretic behaviour when frozen soil thaws, leading to the definition of the soil thawing characteristic curve (STC). Although explanations have been given for SFC/STC hysteresis, the effect that ‘scale’ – particularly ‘measurement scale’ – may have on these curves has received little attention. The most commonly used measurement scale metric is the ‘support’, which is the spatial (or temporal) unit within which the measured variable is integrated or soil volume sampled. We show (a) measurement support can influence the range and shape of the SFC and (b) hysteresis can be attributed, in part, to the support and location of the measurements comprising the SFC/STC. We simulated lab measured temperature, volumetric water content (VWC), and permittivity from soil samples undergoing freeze–thaw transitions using Hydrus-1D and a modified Dobson permittivity model. To assess the effect of measurement support and location on SFC/STC, we masked the simulated temperature and VWC/permittivity extent to match the instrument's support and location. By creating a detailed simulation of the intra- and inter-support variability associated with the penetration of a freezing front, we demonstrate how measurement support and location can influence the temperature range over which water freezing events are captured. We show it is possible to simulate hysteresis in homogenous media with purely geometric considerations, suggesting that SFC/STC hysteresis may be more of an apparent phenomenon than mechanistically real. Lastly, we develop an understanding of how the location and support of soil temperature and VWC/permittivity measurements influence the temperature range over which water freezing events are captured.  相似文献   

Assessment of the acid drainage neutralization capacity and the toxic metals lixiviation of tailing from Guanajuato mining district,Mexico   总被引：1，自引：0，他引：1  

María Elena García-Arreola  Luisa María Flores-Vélez  Marcos Loredo-Tovías  Alfredo Aguillón-Robles  Rubén Alfonso López-Doncel  Irene Cano-Rodríguez  Sonia Hortensia Soriano-Pérez 《Environmental Earth Sciences》2018,77(9):355

In Mexico, many environmental problems are generated by large mining activities taking place in several mining districts. These mining activities produce great quantities of residues; large majorities of these have high sulfur content, which could generate acid drainage due to their interaction with the oxygen in the environment. The study area was located in the Mining District of Guanajuato, Mexico with abandoned tailings generated mainly by the gold and silver production. Two areas, called as Monte de San Nicolás (SN) and Peregrina (P) were selected for this study. The results study shows that there was no risk of production of acid drainage, since these tailings contained high amount of carbonates, which neutralized the generation of acidity and consequently decreased the possibility of leaching of some elements. However, not all elements leach in acid pH, as arsenic bound to oxyhydroxides, which is in a basic environment and its increased release by increasing the pH.  相似文献   

Characterization of fluid inclusions from mineralized pegmatites of the Damara Belt,Namibia: insight into late-stage fluid evolution and implications for mineralization     

Ashworth  Luisa  Kinnaird  Judith Ann  Nex  Paul Andrew Martin  Erasmus  Rudolph Marthinus  Przybyłowicz  Wojciech Józef 《Mineralogy and Petrology》2018,112(6):753-765

Mineralogy and Petrology - Mineralized NYF and LCT pegmatites occur throughout the northeast-trending Neoproterozoic Damara Belt, Namibia. Mineralization in the pegmatites varies geographically,...  相似文献   

Development,urban planning and political decisions. A triad that built territories at risk     

Lara  Alejandro  Bucci  Felipe  Palma  Cristobal  Munizaga  Juan  Montre-Águila  Victor 《Natural Hazards》2021,109(2):1935-1957

Natural Hazards - Chilean geography exposes the country to high-level risks such as earthquakes and tsunamis. The disasters of 1930, 1960, 2010, and 2014 testify to the continuous link between...  相似文献