The evolution of massive black hole seeds     

Marta Volonteri  Giuseppe Lodato  Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2008,383(3):1079-1088

We investigate the evolution of high-redshift seed black hole masses at late times and their observational signatures. The massive black hole seeds studied here form at extremely high redshifts from the direct collapse of pre-galactic gas discs. Populating dark matter haloes with seeds formed in this way, we follow the mass assembly of these black holes to the present time using a Monte Carlo merger tree. Using this machinery, we predict the black hole mass function at high redshifts and at the present time, the integrated mass density of black holes and the luminosity function of accreting black holes as a function of redshift. These predictions are made for a set of three seed models with varying black hole formation efficiency. Given the accuracy of present observational constraints, all three models can be adequately fitted. Discrimination between the models appears predominantly at the low-mass end of the present-day black hole mass function which is not observationally well constrained. However, all our models predict that low surface brightness, bulgeless galaxies with large discs are least likely to be sites for the formation of massive seed black holes at high redshifts. The efficiency of seed formation at high redshifts has a direct influence on the black hole occupation fraction in galaxies at   z = 0  . This effect is more pronounced for low-mass galaxies. This is the key discriminant between the models studied here and the Population III remnant seed model. We find that there exist a population of low-mass galaxies that do not host nuclear black holes. Our prediction of the shape of the M _BH–σ relation at the low-mass end is in agreement with the recent observational determination from the census of low-mass galaxies in the Virgo cluster.  相似文献   

The population of dark matter subhaloes: mass functions and average mass-loss rates     

Carlo Giocoli  Giuseppe Tormen  Frank C. van den Bosch 《Monthly notices of the Royal Astronomical Society》2008,386(4):2135-2144

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A Time-Evolving 3D Method Dedicated to the Reconstruction of Solar Plumes and Results Using Extreme Ultraviolet Data     

Nicolas Barbey  Frédéric Auchère  Thomas Rodet  Jean-Claude Vial 《Solar physics》2008,248(2):409-423

An important issue in the tomographic reconstruction of the solar poles is the relatively rapid evolution of the polar plumes. We demonstrate that it is possible to take into account this temporal evolution in the reconstruction. The difficulty of this problem comes from the fact that we want a four-dimensional reconstruction (three spatial dimensions plus time) whereas we only have three-dimensional data (two-dimensional images plus time). To overcome this difficulty, we introduce a model that describes polar plumes as stationary objects whose intensity varies homogeneously with time. This assumption can be physically justified if one accepts the stability of the magnetic structure. This model leads to a bilinear inverse problem. We describe how to extend linear inversion methods to these kinds of problems. Studies of simulations show the reliability of our method. Results for SOHO/EIT data show that we can estimate the temporal evolution of polar plumes to improve the reconstruction of the solar poles from only one point of view. We expect further improvements from STEREO/EUVI data when the two probes will be separated by about 60°.  相似文献   

Combined hydrogeological and nitrate modelling to manage water resources of the Middle Soummam Aquifer,Northeast of Algeria     

Farès Kessasra  Mohamed Mesbah  Zineb Khemissa  Noussaiba Bouab  Soumia Khaled-Khodja  Hanane Lamari 《Arabian Journal of Geosciences》2017,10(16):368

Water management is one of the most challenges in Algeria, a semi-arid Mediterranean country confronted to a serious water stress. The country will have to endure, beyond 2025, a situation of chronic water penury, adding an excessive pollution of the majority of groundwater reservoirs. The management of water resources by combined approach using hydrogeological model and nitrates evolution model was experimented in the Middle Soummam valley. The alluvial aquifer, offering good hydrodynamic and geometrical characteristics, is over-exploited, providing in drinking water Akbou and Tazmalt cities and irrigation perimeters. If exploitation continues at these steady paces, the depletion of the water resource and the hydrochemical imbalance will be inevitable. On the one hand, the results of hydrodynamic model, based on an increase of the water takings and simulated needs from 24.71 Mm³/year in 2015 into 39.69 Mm³/year in 2030, show a critical withdrawal. The aquifer budget expresses the inversion of flow between the wadi and the aquifer where the wadi feeds the groundwater reservoir. This hydrodynamic inversion was attributed to simulated pumping rates which increased and exceeded 100,000 m³/day, but the aquifer was partially relieved by the weight of the exploitation through Tichy Haf dam. The water management strategy adopted in this study was based on management measures promoting zones, which have been delimited between Tazmalt and Akbou, and containing important water quantities available in the axis of the valley. However, according to the depleted in isotopes of ¹⁸O and ²H, which could be explained by the influence of a paleoclimatic effect and suggested that the aquifer recharge would have largely been made under a colder climate, pumped groundwater could be old, and the implementation of new pumping sites has been studied minutely. On the other hand, the hydrogeochemical modelling allowed following nitrates concentrations in order to project their evolution. Four wells on 25 react in face to the imposed conditions in each scenario simulated until 2030, showing inertia of pollution, and confirmed after three series of tests. This inertia would be related to the hydraulic gradients and hydraulic conductivities, aquifer thickness and recharge. The low hydraulic gradients lead to a rather slow flow velocity and thus to an inertia in the dispersion of nitrates, with a mass transport weakened by the hydrodynamic conditions. It is also related to the aquifer thickness; when the aquifer is powerful (65–85 m), the stock of water would be important and allows a dilution process. The reverse is true for the simulated boreholes where the concentrations remain invariant; the aquifer is less powerful (32–37 m). Finally, the recharge effect through the rain was evoked; the aquifer is unconfined, and the rain water and pollution that reached the piezometric level can remain in position in slow hydrodynamic conditions. The methodology was demonstrated through a combination of monitoring and modelling for both water quantity and quality and the importance to use numerical models to support water resources management strategy in the Mediterranean aquifers.  相似文献   

Experimental and numerical evaluation of single-layer covers placed on acid-generating tailings     

Thomas Pabst  Michel Aubertin  Bruno Bussière  John Molson 《Geotechnical and Geological Engineering》2017,35(4):1421-1438

This study focuses on the reclamation work being performed on two former acid-generating tailings sites, located in Quebec, Canada. At both sites, the tailings were partially oxidized due to extended exposure, and the pore water is acidic. The reclamation solution applied to control acid mine drainage is a monolayer cover, made of non acid-generating tailings in one case and a till in the other. The goal of this project was to assess the response of the tailings-cover systems under various conditions. Tailings samples were collected in situ and characterized in the laboratory. Large column tests were conducted to evaluate the hydrogeological and geochemical behaviour of the covered tailings following wetting and drying cycles. The instrumented columns were designed to reproduce some of the existing site conditions and provide representative results for longer term analyses. Volumetric water content, suction, and oxygen concentrations were also monitored over time. The experimental data were used to validate different numerical models including those constructed with Vadose/W (GeoSlope Int.). Additional simulations were conducted under field conditions to evaluate the effect of various influence factors such as the depth of the water table, climatic conditions and the thickness of the cover. The combination of experimental and numerical results show how the behaviour and efficiency of a monolayer cover placed over reactive tailings depend on these factors, highlighting the importance of hydrogeological properties and water table depth. In many instances, the cover materials were prone to desaturation, especially when the water table was deeper than about 2 m below the tailings-cover interface. These results tend to indicate that relatively thin monolayer covers would not be able to prevent oxygen ingress under some of the conditions observed in the field. Desaturation of the cover and/or reactive tailings is due to a combination of drainage and evaporation. In such cases, increasing the thickness of the monolayer cover only has a limited effect. A discussion follows on the practical implications of these laboratory experiments and the numerical simulations for field design of reclamation measures at these two tailings impoundments.  相似文献   

Monitoring of 45 pesticides in Lebanese surface water using Polar Organic Chemical Integrative Sampler (POCIS)     

Al Ashi Aisha  Wael Hneine  Samia Mokh  Marie-Hélène Devier  Hélèn Budzinski  Farouk Jaber 《Ocean Science Journal》2017,52(3):455-466

The aim of this study is to assess the dissolved concentration of 45 pesticides in the surface waters of the Lebanese Republic using Polar Organic Chemical Integrative Sampler "POCIS". All of the sampling sites are located in the major agricultural land areas in Lebanon. POCIS (n = 3) were deployed at Ibrahim River, Qaraoun Lake and Hasbani River for a duration of 14 days. The total concentration of pesticides ranged from not detected (nd) to 137.66 ng.L^-1. Chlorpyrifos, DDE-pp, diazinon and Fenpropathrin were the most abundant compounds. Qaraoun Lake and Hasbani River were found to be more polluted than Ibrahim River, since they receive large amounts of waste water derived from nearby agricultural lands and they had the lowest dilution factor. The aqueous average concentration of the target compounds were estimated using sampling rates obtained from the literature. Comparison between Time Weighed Average concentrations "TWA" using POCIS and spot sampling is presented. Results showed that POCIS TWA concentrations are in agreement with spot sampling concentrations for Ibrahim and Hasbani Rivers. The toxicity of the major detected pesticides on three representative aquatic species (Daphnia magna, Scenedesmus quadricauda and Oncorhynchus mykiss) is also reported.  相似文献   

Surface exposure dating and geophysical prospecting of the Holocene Lauvitel rock slide (French Alps)     

Romain Delunel  Didier Hantz  Régis Braucher  Didier L. Bourlès  Philippe Schoeneich  Jacques Deparis 《Landslides》2010,7(4):393-400

Large rock falls and rockslides represent a risk for human communities in mountainous areas as they can cause fatalities and destruction of settlements and infrastructures. Assessing the associated hazard requires constraining the time frequency of such events. Since large rockslides are not common, estimating their frequency requires recording them over a long period of time. The Holocene period then appears as pertinent, which implies that rockslide features have to be dated with absolute chronology methods. This paper presents a characterisation and dating of the Lauvitel rockslide, one of the largest Holocene rockslides in the French Alps. Combining field observation with electrical tomography profiles performed on the rockslide deposit that constitutes the Lauvitel Lake dam allows estimating its volume at a minimum of 12?×?10⁶?m³. In addition, cosmic ray exposure dating using in situ-produced ¹⁰Be concentration measurements has been applied to date seven samples collected both on the main sliding surface and on blocks lying on the dam and further downstream. Ages obtained are consistent with a single large rockslide event, which occurred at 4.7?±?0.4 ¹⁰Be-ka and formed two distinct deposits. However, from a mechanical point of view, these clearly separated deposits could hardly result from a single movement. A comparison of their reach angles with those reviewed in the literature highlights that the lower deposit must result from rock avalanches larger than 10⁷?m³, while the upper one (the Lauvitel dam) must result from several events smaller than 10⁶?m³. In the context of hazard assessment for land use planning, these events can, however, be considered as a unique event.  相似文献   

GGR Critical Review of Analytical Developments in 2008–2009: An Introduction     

Janet M. Hergt  Ricardo Arevalo Jr  L. Paul Bèdard  Jeremy Bellucci  Jacinta Enzweiler  Klaus Peter Jochum  Kathryn L. Linge  William F. McDonough  Regina Mertz-Kraus  Michael Wiedenbeck  Xiaohong Wang  Jon D. Woodhead 《Geostandards and Geoanalytical Research》2010,34(4):325-326

This collection of articles represents the fourth in a series of reviews in which authors have aimed at capturing the key advances in a range of analytical fields ( Hergt et al. 2005, 2006, 2008 ). The publication period under review is 2008–2009 and the intention here is to provide readers with a summary of the most influential developments published during this period, across a broad range of topics appropriate to the Earth and environmental sciences. Most authors comment on the ways in which the emphases of research in their specific fields of examination have changed over time. All note an increase in rigour and focus on data quality. Whether advances have taken place in instrumentation, sample manipulation or data deconvolution, there are a large number of dedicated scientists out there contributing to the high quality of geochemical data employed in geological and environmental research.  相似文献   

Chemical transformations of peptide containing fine particles: oxidative processing,accretion reactions and implications to the atmospheric fate of cell-derived materials in organic aerosol     

Scott Geddes  James Zahardis  Giuseppe A. Petrucci 《Journal of Atmospheric Chemistry》2009,63(3):187-202

The atmospheric processing by ozone of peptide-containing mixed particles was investigated as proxies for biogenic and sea spray primary organic aerosol. Reactions were performed in a flow reactor and particle composition was monitored by photoelectron resonance capture ionization aerosol mass spectrometry. Mixed particles containing dipeptides in a saturated organic matrix of stearic and palmitic acids showed no reaction under ozonolysis at exposure levels of 2.5 × 10⁻⁴ atm s O₃. However reactions of mixed particles of a dipeptide (Leu-Leu) in an unsaturated matrix (oleic acid) under the same conditions resulted in a rapid loss of the peptide ion signal, as well as the carrier matrix, and appearance of a number of ion signals corresponding to secondary products. High molecular weight imides and amides have been identified corresponding to possible reactions of ozonolysis products and reactive intermediates (i.e. aldehydes, stabilized Criegee intermediates). Additionally, tautomerisation of the imides to enamines in the particle phase is postulated, with ozonolysis of the enamine followed by regioselective decomposition of the primary ozonide to form an amide whereby the peptide incorporates an aldehydic group at the N-terminus. The same general reactivity pattern was observed for mixed particles of diglycine and oleic acid. This behavior was not observed in solution phase experiments, where the tautomerisation favors the more stable imine form, indicating that particulate phase reactions of this nature may be dependent on the specific particle physical properties. The implications of this chemistry with respect the atmospheric aging of cell-derived organic aerosol are discussed.  相似文献   

The role of strong earthquakes and tsunami in the Late Holocene evolution of the Fortore River coastal plain (Apulia, Italy): A synthesis     

Giuseppe Mastronuzzi  Paolo Sansò 《Geomorphology》2012,138(1):89-99

Morphological analysis of the Fortore River coastal plain and the Lesina Lake coastal barrier integrated with radiocarbon age data indicates that the evolution of the coastal landscape has been strongly affected by a number of strong earthquakes and related tsunamis which occurred during the last 3000 years. The first seismic event struck this coastal area in the V century BC. It produced strong erosion of the Fortore River coastal plain and significant emersion of Punta delle Pietre Nere, as well as the large tsunami responsible for the development of the Sant'Andrea washover fan. The second event occurred in 493 AD; it induced severe erosion of the Fortore River coastal plain and triggered the large tsunami that hit the Lesina Lake coastal barrier, producing the Foce Cauto washover fan. Then later in 1627, an earthquake was responsible for the further coseismic uplift of Punta delle Pietre Nere, the subsidence of Lesina village area and the development of a tsunami which produced two washover fans.Morphological analysis points out that seismic events strong enough to control the morphological evolution of local coastal landscapes show a statistical return period of about 1000 years. These major events produced important coseismic vertical movements and large tsunamis. However, the correct identification of the tectonic structure responsible for the generation of these strong earthquakes is still an unsolved problem.  相似文献