High-redshift galaxies in the Hubble Deep Field— II. Colours and number counts     

Lucia Pozzetti  Piero Madau  Gianni Zamorani  Henry C. Ferguson  & Gustavo Bruzual A. 《Monthly notices of the Royal Astronomical Society》1998,298(4):1133-1144

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Human alteration of groundwater–surface water interactions (Sagittario River,Central Italy): implication for flow regime,contaminant fate and invertebrate response     

Mariachiara Caschetto  Maurizio Barbieri  Diana M. P. Galassi  Lucia Mastrorillo  Sergio Rusi  Fabio Stoch  Alessia Di Cioccio  Marco Petitta 《Environmental Earth Sciences》2014,71(4):1791-1807

Many rivers worldwide are undergoing severe man-induced alterations which are reflected also in changes of the degree of connectivity between surface waters and groundwater. Pollution, irrigation withdrawal, alteration of freshwater flows, road construction, surface water diversion, soil erosion in agriculture, deforestation and dam building have led to some irreversible species losses and severe changes in community composition of freshwater ecosystems. Taking into account the impact of damming and flow diversion on natural river discharge, the present study is aimed at (i) evaluating the effects of anthropogenic changes on groundwater/surface water interactions; (ii) analyzing the fate of nitrogenous pollutants at the floodplain scale; and (iii) describing the overall response of invertebrate assemblages to such changes. Hydrogeological, geochemical and isotopic data revealed short- and long-term changes in hydrology, allowing the assessment of the hydrogeological setting and the evaluation of potential contamination by nitrogen compounds. Water isotopes allowed distinguishing a shallow aquifer locally fed by zenithal recharge and river losses, and a deeper aquifer/aquitard system fed by surrounding carbonate aquifers. This system was found to retain ammonium and, through the shallow aquifer, release it in surface running waters via the hyporheic zone of the riverbed. All these factors influence river ecosystem health. As many environmental drivers entered in action offering a multiple-component artificial environment, a clear relationship between river flow alteration and benthic and hyporheic invertebrate diversity was not found, being species response driven by the combination of three main stressors: ammonium pollution, man-induced changes in river morphology and altered discharge regime.  相似文献   

Long-term summer temperature reconstruction inferred from tree-ring records from the Eastern Carpathians     

Ionel Popa  Zoltán Kern 《Climate Dynamics》2009,32(7-8):1107-1117

The first 1,000 year long Carpathian tree-ring width chronology was established based on living and subfossil stone pine (Pinus cembra L.) samples from an upper timberline forest located in Calimani Mts. (Romania). Tree-ring data were standardized using the regional curve standardization method in order to preserve the low and medium frequency climate signals. The de-trended index strongly correlates with summer mean temperature both at annual and decadal scales. The Calimani summer mean temperature anomalies were reconstructed for the period ad 1163-2005 applying the rescaling method. This new climate proxy from the Carpathians shows similar fluctuations to other North Hemispheric temperature reconstructions, but with periods of distinct differences. The fingerprint of Little Ice Age in the Calimani area is visible between ad 1370 and 1630 followed by lagged cold decades in ad 1820 and 1840. The recent warming is evident only after the 1980s in our reconstruction.  相似文献   

Rainfall trends in the Brazilian Amazon Basin in the past eight decades     

Prakki Satyamurty  Aline Anderson de Castro  Julio Tota  Lucia Eliane da Silva Gularte  Antonio Ocimar Manzi 《Theoretical and Applied Climatology》2010,99(1-2):139-148

Rainfall series at 18 stations along the major rivers of the Brazilian Amazon Basin, having data since 1920s or 1930s, are analyzed to verify if there are appreciable long-term trends. Annual, rainy-season, and dry-season rainfalls are individually analyzed for each station and for the region as a whole. Some stations showed positive trends and some negative trends. The trends in the annual rainfall are significant at only six stations, five of which reporting increasing trends (Barcelos, Belem, Manaus, Rio Branco, and Soure stations) and just one (Itaituba station) reporting decreasing trend. The climatological values of rainfall before and after 1970 show significant differences at six stations (Barcelos, Belem, Benjamin Constant, Iaurete, Itaituba, and Soure). The region as a whole shows an insignificant and weak downward trend; therefore, we cannot affirm that the rainfall in the Brazilian Amazon basin is experiencing a significant change, except at a few individual stations. Subregions with upward and downward trends are interspersed in space from the far eastern Amazon to western Amazon. Most of the seasonal trends follow the annual trends, thus, indicating a certain consistency in the datasets and analysis.  相似文献   

Two-component galaxies with flat rotation curve     

Luca Ciotti  Lucia Morganti †  P. T. de Zeeuw 《Monthly notices of the Royal Astronomical Society》2009,393(2):491-500

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Simulating the formation of a protocluster at z∼ 2     

A. Saro  S. Borgani  L. Tornatore  G. De Lucia  K. Dolag  G. Murante 《Monthly notices of the Royal Astronomical Society》2009,392(2):795-800

We present results from two high-resolution hydrodynamical simulations of protocluster regions at   z ≃ 2.1  . The simulations have been compared to observational results for the so-called Spiderweb galaxy system, the core of a putative protocluster region at   z = 2.16  , found around a radio galaxy. The simulated regions have been chosen so as to form a poor cluster with   M ₂₀₀≃ 10¹⁴  h ⁻¹ M_⊙  (C1) and a rich cluster with   M ₂₀₀≃ 2 × 10¹⁵  h ⁻¹ M_⊙  (C2) at   z = 0  . The simulated protoclusters show evidence of ongoing assembly of a dominating central galaxy. The stellar mass of the brightest cluster galaxy of the C2 system is in excess with respect to observational estimates for the Spiderweb galaxy, with a total star formation rate which is also larger than indicated by observations. We find that the projected velocities of galaxies in the C2 cluster are consistent with observations, while those measured for the poorer cluster C1 are too low compared with the observed velocities. We argue that the Spiderweb complex resembles the high-redshift progenitor of a rich galaxy cluster. Our results indicate that the included supernovae feedback is not enough to suppress star formation in these systems, supporting the need of introducing active galactic nuclei feedback. According to our simulations, a diffuse atmosphere of hot gas in hydrostatic equilibrium should already be present at this redshift, and enriched at a level comparable to that of nearby galaxy clusters. The presence of this gas should be detectable with future deep X-ray observations.  相似文献   

A site evaluation campaign for a ground based atmospheric Cherenkov telescope in Romania     

Aurelian Andrei Radu  Tatiana Angelescu  Valentin Curtef  Florin Delia  Daniel Felea  Ioana Goia  Dumitru Ha?egan  Bogdan Lucaschi  Ancuta Manea  Vlad Popa  Ioan Rali??  Radu V?c?reanu 《Experimental Astronomy》2012,34(1):31-42

Around the world, several scientific projects share the interest of a global network of small Cherenkov telescopes for monitoring observations of the brightest blazars??the DWARF network. A small, ground based, imaging atmospheric Cherenkov telescope of last generation is intended to be installed and operated in Romania as a component of the DWARF network. To prepare the construction of the observatory, two support projects have been initiated. Within the framework of these projects, we have assessed a number of possible sites where to settle the observatory. In this paper we submit a brief report on the general characteristics of the best four sites selected after the local infrastructure, the nearby facilities and the social impact criteria have been applied.  相似文献   

Effect of the wind acceleration magnitude during the first stages of the wind-wave generation process     

Robles-Diaz  Lucia  Ocampo-Torres  Francisco J.  Branger  Hubert  Garcia-Nava  Hector  Osuna  Pedro  Rascle  Nicolas 《Ocean Dynamics》2021,71(10):981-992

Ocean Dynamics - A comprehensive analysis of the wavefield evolution under accelerated wind conditions provides an essential contribution to understanding the wind-wave generation process. A set of...  相似文献   

Ram-pressure histories of cluster galaxies     

M. Brüggen  G. De Lucia 《Monthly notices of the Royal Astronomical Society》2008,383(4):1336-1342

Ram-pressure stripping can remove significant amounts of gas from galaxies that orbit in clusters and massive groups, and thus has a large impact on the evolution of cluster galaxies. In this paper, we reconstruct the present-day distribution of ram pressure and the ram-pressure histories of cluster galaxies. To this aim, we combine the Millennium Simulation and an associated semi-analytic model of galaxy evolution with analytic models for the gas distribution in clusters. We find that about one quarter of galaxies in massive clusters are subject to strong ram pressures that are likely to cause an expedient loss of all gas. Strong ram pressures occur predominantly in the inner core of the cluster, where both the gas density and the galaxy velocity are higher. Since their accretion on to a massive system, more than 64 per cent of galaxies that reside in a cluster today have experienced strong ram pressures of  >10⁻¹¹ dyn cm⁻²  which most likely led to a substantial loss of the gas.  相似文献   

The dependence of galaxy formation on cosmological parameters: can we distinguish between the WMAP1 and WMAP3 parameter sets?     

Jie Wang  Gabriella De Lucia  Manfred G. Kitzbichler  Simon D. M. White 《Monthly notices of the Royal Astronomical Society》2008,384(4):1301-1315

We combine N -body simulations of structure growth with physical modelling of galaxy evolution to investigate whether the shift in cosmological parameters between the first- and third-year results from the Wilkinson Microwave Anisotropy Probe ( WMAP ) affects predictions for the galaxy population. Structure formation is significantly delayed in the WMAP3 cosmology, because the initial matter fluctuation amplitude is lower on the relevant scales. The decrease in dark matter clustering strength is, however, almost entirely offset by an increase in halo bias, so predictions for galaxy clustering are barely altered. In both cosmologies, several combinations of physical parameters can reproduce observed, low-redshift galaxy properties; the star formation, supernova feedback and active galactic nucleus feedback efficiencies can be played off against each other to give similar results. Models which fit observed luminosity functions predict projected two-point correlation functions which scatter by about 10–20 per cent on large scale and by larger factors on small scale, depending both on cosmology and on details of galaxy formation. Measurements of the pairwise velocity distribution prefer the WMAP1 cosmology, but careful treatment of the systematics is needed. Given present modelling uncertainties, it is not easy to distinguish between the WMAP1 and WMAP3 cosmologies on the basis of low-redshift galaxy properties. Model predictions diverge more dramatically at high redshift. Better observational data at   z > 2  will better constrain galaxy formation and perhaps also cosmological parameters.  相似文献