Post-seismic relaxation and earthquake triggering in the southern Adriatic region   总被引：1，自引：0，他引：1  

Marcello Viti  Francesca D'Onza  Enzo Mantovani  Dario Albarello  Nicola Cenni 《Geophysical Journal International》2003,153(3):645-657

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Fluid Households,Complex Families: The Impacts of Children's Migration as a Response to HIV/AIDS in Southern Africa*     

Lorraine Young  Nicola Ansell 《The Professional geographer》2003,55(4):464-476

The fluidity of southern African families is related to a long history of internal and external migration. Currently, HIV/AIDS is having a dramatic impact on extended family structures, with the migration of individual members employed as a coping strategy. Children's migration is one aspect of this that is often distinct from that undertaken by other household members. This article is based on qualitative research conducted in Lesotho and Malawi with young migrants and the households that receive them. It examines the processes of fragmentation and re‐formation of households through the movements of children that are taking place in response to HIV/AIDS, and explores the impacts these processes have on young migrants and the households they join.  相似文献   

Multiwavelength Study of two Unidentified γ-ray Sources     

Nicola La Palombara  Patrizia Caraveo  Roberto Mignani  Evanthia Hatziminaoglou  Giovanni F. Bignami  Mischa Schirmer 《Astrophysics and Space Science》2005,297(1-4):335-344

Most counterparts of the identified low-latitude γ-ray sources are isolated neutron stars (INSs). Since INSs are characterized by an extremely high value of f _X/f _opt, a systematic X-ray/optical coverage of the fields of unidentified low-latitude γ-ray sources is the best way to unveil INS counterparts of unidentified sources. Since the low-latitude sources are heavily affected by the interstellar absorption in both the X-ray and optical bands, we decided to apply the above strategy to two middle-latitude EGRET sources, which could belong to a local galactic population: 3EG J0616-3310 and 3EG J1249-8330. Here we report on the global X-ray characterization of about 300 objects, on their candidate optical counterparts and on the preliminary results of their identification.  相似文献   

The Chandra view of galaxy mergers     

Nicola J. Brassington  Trevor J. Ponman  rew M. Read 《Monthly notices of the Royal Astronomical Society》2007,377(4):1439-1456

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On the clustering phase transition in self-gravitating N-body systems     

Monica Cerruti-Sola  Piero Cipriani  Marco Pettini 《Monthly notices of the Royal Astronomical Society》2001,328(1):339-352

The thermodynamic behaviour of self-gravitating N -body systems has been worked out by borrowing a standard method from molecular dynamics. The link between dynamics and thermodynamics is made in the microcanonical ensemble of statistical mechanics. Through the computation of basic thermodynamic observables and of the equation of state in the     plane, the clustering phase transition appears to be of the second-order type. The dynamical–microcanonical averages are compared with their corresponding canonical ensemble averages, obtained through standard Monte Carlo computations. The latter seem to have completely lost any information about the phase transition. Finally, our results – obtained in a 'microscopic' framework – are compared with some existing theoretical predictions – obtained in a 'macroscopic' (thermodynamic) framework: qualitative and quantitative agreement is found, with an interesting exception.  相似文献   

Semi-analytical solution for viscous Stokes flow in two eccentrically nested spheres     

Nicola Tosi  Zden&#;k Martinec 《Geophysical Journal International》2007,170(3):1015-1030

Applying the infinite Prandtl number approximation, a semi-analytical solution for computing 2-D axisymmetric viscous Stokes flow in a model consisting of two eccentrically nested spheres of different viscosities is derived. Since numerical codes based on spectral or finite techniques for modelling mantle flow in a spherical geometry in the presence of lateral viscosity variation are becoming more and more popular, reliable examples for testing and validating such codes are extremely useful. The eccentrically nested sphere solution was used to test a numerical algorithm based on a mixed spherical-harmonic finite-element formulation of the Stokes problem, and good agreement was obtained.  相似文献   

Palaeoenvironmental records from fossil corals: The effects of submarine diagenesis on temperature and climate estimates     

Nicola Allison  Adrian A. Finch  David A. Clague 《Geochimica et cosmochimica acta》2007,71(19):4693-4703

The geochemistry of coral skeletons may reflect seawater conditions at the time of deposition and the analysis of fossil skeletons offers a method to reconstruct past climate. However the precipitation of cements in the primary coral skeleton during diagenesis may significantly affect bulk skeletal geochemistry. We used secondary ion mass spectrometry (SIMS) to measure Sr, Mg, B, U and Ba concentrations in primary coral aragonite and aragonite and calcite cements in fossil Porites corals from submerged reefs around the Hawaiian Islands. Cement and primary coral geochemistry were significantly different in all corals. We estimate the effects of cement inclusion on climate estimates from drilled coral samples, which combine cements and primary coral aragonite. Secondary 1% calcite or ∼2% aragonite cement contamination significantly affects Sr/Ca SST estimates by +1 °C and −0.4 to −0.9 °C, respectively. Cement inclusion also significantly affects Mg/Ca, B/Ca and U/Ca SST estimates in some corals. X-ray diffraction (XRD) will not detect secondary aragonite cements and significant calcite contamination may be below the limit of detection (∼1%) of the technique. Thorough petrographic examination of fossils is therefore essential to confirm that they are pristine before bulk drilled samples are analysed. To confirm that the geochemistry of the original coral structures is not affected by the precipitation of cements in adjacent pore spaces we analysed the primary coral aragonite in cemented and uncemented areas of the skeleton. Sr/Ca, B/Ca and U/Ca of primary coral aragonite is not affected by the presence of cements in adjacent interskeletal pore spaces i.e. the coral structures maintain their original composition and selective SIMS analysis of these structures offers a route to the reconstruction of accurate SSTs from altered coral skeletons. However, Mg/Ca and Ba/Ca of primary coral aragonite are significantly higher in parts of skeletons infilled with high Mg calcite cement. We hypothesise this reflects cement infilling of intraskeletal pore spaces in the primary coral structure.  相似文献   

Role of Humification Processes in Recycling Organic Wastes of Various Nature and Sources as Soil Amendments     

Nicola Senesi  César Plaza 《洁净——土壤、空气、水》2007,35(1):26-41

Recycling the large amounts of organic wastes produced by agriculture, forestry, urban and industrial activities as soil, organic amendments are the most popular and efficient option for avoiding their dispersion in the environment and restoring, maintaining, and/or improving the content of soil organic matter. Chemical stability and biological maturity are two important factors for the successful use of organic wastes in agriculture with limited risk for the surrounding environment. Stabilization and maturation of raw organic wastes inherently imply the achievement of an extensive humification, that is, a wide conversion of easily degradable organic matter to refractory organic compounds that resemble native soil humic substances (HS). Soil HS are the most important components of soil organic matter responsible of several soil functions and processes. As a consequence, the amount and quality of HS‐like fractions in any organic amendment are believed to be of primary importance for its agronomic efficacy, environmental safety and economic value. The first part of this review focuses on the chemical and physico‐chemical changes occurring in the humic substances (HS) ‐like fractions of organic wastes of various nature and sources subjected to common treatment processes aimed at producing environmentally‐safe soil amendments with beneficial agronomic properties. The second part discusses the composition, structure, and chemical reactivity of the HS‐like components in organic amendments of various origins and nature, and their effects on native soil HS. The review concludes by highlighting the need for innovative research targeted mainly to achieve a better fundamental understanding of the molecular structure and reactivity of soil HS and HS‐like fractions in organic amendments, the mechanisms of HS formation and transformations in the natural environment and during the treatment processes of raw organic wastes, the interactions with metals and organic xenobiotics, and the direct physiological effects that HS may exert on plants.  相似文献   

Flood hydrograph attenuation induced by a reservoir system: analysis with a distributed rainfall‐runoff model     

Nicola Montaldo  Marco Mancini  Renzo Rosso 《水文研究》2004,18(3):545-563

Spatially distributed hydrologic models can be effectively utilized for flood event simulation over basins where a complex system of reservoirs affecting the natural flow regime is present. Flood peak attenuation through mountain reservoirs can, in fact, mitigate the impact of major floods in flood‐prone areas of the lower river valley. Assessment of this effect for a complex reservoir system is performed with a spatially distributed hydrologic model where the surface runoff formation and the hydraulic routing through each reservoir and the river system are performed at a fine spatial and time resolution. The Toce River basin is presented as a case study, because of the presence of 14 active hydroelectric dams that affect the natural flow regime. A recent extreme flood event is simulated using a multi‐realization kriging method for modelling the spatial distribution of rainfall. A sensitivity analysis of the key elements of the distributed hydrologic model is also performed. The flood hydrograph attenuation is assessed. Several possible reservoir storage conditions are used to characterize the initial condition of each reservoir. The results demonstrate how a distributed hydrologic model can contribute to defining strategies for reservoir management in flood mitigation. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

A 2‐D constitutive model for cyclic interface behaviour     

Giuseppe Mortara  Marc Boulon  Vito Nicola Ghionna 《国际地质力学数值与分析法杂志》2002,26(11):1071-1096

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