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1.
Nikos Prantzos 《Astrophysics and Space Science》2003,284(2):675-684
We develop a detailed model of the Milky Way (a `prototypical' disk galaxy) and extend it to other disks with the help of
some simple scaling relations, obtained in the framework of Cold Dark Matter models. This phenomenological (`hybrid') approach
to the study of disk galaxy evolution allows us to reproduce successfully a large number of observed properties of disk galaxies
in the local Universe and up to redshift z ∼ 1. The important conclusion is that, on average, massive disks have formed the bulk of their stars earlier than their lower
mass counterparts: the `star formation hierarchy' has been apparently opposite to the `dark matter assembly' hierarchy. It
is not yet clear whether `feedback' (as used in semi-analytical models of galaxy evolution) can explain that discrepancy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
S. Boissier A. Boselli N. Prantzos G. Gavazzi 《Monthly notices of the Royal Astronomical Society》2001,321(4):733-742
We study the star formation history of normal spirals by using a large and homogeneous data sample of local galaxies. For our analysis we utilize detailed models of chemical and spectrophotometric galactic evolution, calibrated on the Milky Way disc. We find that star formation efficiency is independent of galactic mass, while massive discs have, on average, lower gas fractions and are redder than their low-mass counterparts; put together, these findings convincingly suggest that massive spirals are older than low-mass ones. We evaluate the effective ages of the galaxies of our sample and we find that massive spirals must be several Gyr older than low-mass ones. We also show that these galaxies (having rotational velocities in the 80–400 km s−1 range) cannot have suffered extensive mass losses, i.e. they cannot have lost during their lifetime an amount of mass much larger than their current content of gas+stars. 相似文献
3.
Modelling surface runoff to evaluate the effects of wildfires in multiple semi‐arid,shrubland‐dominated catchments 下载免费PDF全文
Wildfires change the infiltration properties of soil, reduce the amount of interception and result in increased runoff. A wildfire at Northeast Attica, Central Greece, in August 2009, destroyed approximately one third of a study area consisting of a mixture of shrublands, pastures and pines. The present study simultaneously models multiple semi‐arid, shrubland‐dominated Mediterranean catchments and assesses the hydrological response (mean annual and monthly runoff and runoff coefficients) during the first few years following wildfires. A physically based, hydrological model (MIKE SHE) was chosen. Calibration and validation results of mean monthly discharge presented very good agreement with the observed data for the pre‐wildfire and post‐wildfire period for two subcatchments (Nash–Sutcliffe Efficiency coefficient of 79.7%). The model was then used to assess the pre‐wildfire and post‐wildfire runoff responses for each of seven catchments in the study area. Mean annual surface runoff increased for the first year and after the second year following the wildfires increased by 112% and 166%, respectively. These values are within the range observed in similar cases of monitored sites. This modelling approach may provide a way of prioritizing catchment selection with respect to post‐fire remediation activities. Additionally, this modelling assessment methodology would be valuable to other semi‐arid areas because it provides an important means for comprehensively assessing post‐wildfire response over large regions and therefore attempts to address some of the scaled issues in the specific literature field of research. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
4.
Pantelis Soupios Nikos Papadopoulos Ilias Papadopoulos Maria Kouli Filippos Vallianatos Apostolos Sarris Thrassyvoulos Manios 《Environmental Geology》2007,53(3):661-675
An integrated suite of environmental methods was used to characterize the hydrogeological, geological and tectonic regime
of the largest waste disposal landfill of Crete Island, the Fodele municipal solid waste site (MSW), to determine the geometry
of the landfill (depth and spatial extent of electrically conductive anomalies), to define the anisotropy caused by bedrock
fabric fractures and to locate potential zones of electrically conductive contamination. A combination of geophysical methods
and chemical analysis was implemented for the characterization and management of the landfill. Five different types of geophysical
surveys were performed: (1) 2D electrical resistance tomography (ERT), (2) electromagnetic measurements using very low frequencies
(VLF), (3) electromagnetic conductivity (EM31), (4) seismic refraction measurements (SR), and (5) ambient noise measurements
(HVSR). The above geophysical methods were used with the aim of studying the subsurface properties of the landfill and to
define the exact geometrical characteristics of the site under investigation. 相似文献
5.
Nikos D. Lagaros 《Bulletin of Earthquake Engineering》2007,5(3):425-442
The objective of this study is to perform life-cycle cost analysis on three design practices namely weak ground storey, short
and floating columns and their combinations. Life-cycle cost analysis is recognized as the only suitable tool for assessing
the structural performance when the structure is expected to be functional for a long period of time. Life-cycle cost analysis
is considered in this study assessing the behaviour of the three design practices against earthquake hazard. Although, a number
of checks are performed in order to reduce the influence of these design practices on the seismic behaviour of reinforced
concrete (RC) framed structures, it was found that the total life-cycle cost of partially infilled RC designs is significantly
increased compared to that of the fully infilled one. Through the test example examined in the framework of this study general
conclusions are obtained regarding the behaviour of the three design practices. 相似文献
6.
The static, cyclic, and dynamic response of a massive caisson foundation embedded in nonlinear layered or inhomogeneous soil and loaded at its top is investigated. The caisson is supported against horizontal displacement and rotation by four types of inelastic springs and dashpots, described with the BWGG model that was developed in the preceding companion paper [Gerolymos N, Gazetas G. Development of winkler model for static and dynamic response of caisson foundations with soil and interface nonlinearities. Soil Dyn Earthq Eng, submitted companion paper]. The prediction of the model is satisfactorily compared with results from 3D-finite element analysis. Some experimental corroboration of the method is provided with the help of a 1/3-scale lateral load test that had been conducted in the field by EPRI. An illustrative example of a caisson embedded in linearly-inhomogeneous clay and subjected to static and dynamic loading is analysed. Characteristic results are presented highlighting the role of soil inelasticity and its interplay with the two dominant interface nonlinearities: separation (gapping) of the caisson shaft from the surrounding soil, and uplifting of the base from the underlying soil. 相似文献
7.
Spyros Basilakos Nikos Voglis 《Monthly notices of the Royal Astronomical Society》2007,374(1):269-275
We study the virialization of the cosmic structures in the framework of flat cosmological models where the dark energy component plays an important role in the global dynamics of the Universe. In particular, our analysis focuses on the study of the spherical matter perturbations, as the latter decouple from the background expansion, start to 'turn around' and finally collapse. We generalize this procedure, taking into account models with an equation of state which vary with time, and provide a complete formulation of the cluster virialization attempting to address the non-linear regime of structure formation. In particular, assuming that clusters have collapsed prior to the epoch of z f ≃ 1.4, in which the most distant cluster has been found, we show that the behaviour of the spherical collapse model depends on the functional form of the equation of state. 相似文献
8.
High connectivity and directional gene flow in European Atlantic and Mediterranean populations of Ciona intestinalis sp. A 下载免费PDF全文
Ornella Affinito Nikos Andreakis Luigi Caputi Rita Marino Raimondo Pannone Paolo Sordino Gabriele Procaccini 《Marine Ecology》2015,36(4):1230-1243
Understanding the factors that cause population divergence has long been of interest to marine biologists in their attempts to interpret the effect of human‐mediated vectors. Broadcast‐spawning species with limited dispersal capability are excellent candidates to measure the present‐day patterns of genetic diversity. The tunicate Ciona intestinalis (Ascidiacea) is comprised of a complex of morphologically cryptic species that form vigorous aggregates in eutrophic habitats (harbors, gulfs and lagoons) where they can compete with the epibenthic community and cause biofouling problems. This study investigated biogeographic variability and migration patterns of C. intestinalis sp. A along Northeast Atlantic and Mediterranean coasts using microsatellite markers. Data presented here on 371 specimens collected from 17 populations reveal high genetic polymorphism, but with a deficit of heterozygote deficiency. Absence of evidence for isolation by distance suggests that the genetic patterns do not reflect the geographic distribution of sampled populations. Substantial gene flow and artificial potential for dispersal boost high levels of within‐population genetic variability and prevent genetic differentiation within and between seas. A predominant eastward migration pattern was revealed by the data set, with very limited opportunity for C. intestinalis sp. A to travel westward. This directional movement indicates that other properties (e.g. habitat quality, genetic traits, mating system, life cycle) may cause adaptive divergence at a large biogeographic scale. 相似文献
9.
Hamdan Hamdan Nikos Andronikidis George Kritikakis Nikos Economou Zacharias Agioutantis Paul Schilizzi Chrysanthos Steiakakis Christodoulos Papageorgiou Panagiotis Tsourlos George Vargemezis Antonis Vafidis 《Environmental Earth Sciences》2014,72(5):1589-1598
In this paper, the application of 2D and 3D electrical resistivity methods in geotechnical investigations is explored through a case study in Northern Greece. These two methods were employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonate formations near the southern limits of the pit, as well as to estimate the thickness of the carbonate rocks on top of the Schist formations to evaluate the stability of the southern slopes. Synthetic data were initially generated to help plan an efficient electrical tomography survey, in a region with complex geology and irregular terrain. Three configurations (Wenner–Schlumberger and dipole–dipole or pole–dipole) proved essential in such conditions and helped improving the resolution of the resistivity section. The sections were then calibrated by boreholes. Finally, the geophysical survey provided invaluable data regarding the geometry of the bedrock and possible faults, which was essential for the slope stability calculations. 相似文献
10.
N. Prantzos 《Astrophysics and Space Science》1999,265(1-4):411-415
A brief review is presented of our current understanding of the chemical evolution of the Milky Way and, in particular, of
the solar neighbourhood and the disc of our Galaxy, in the light of recent theoretical and observational results. We explore
the implications of this understanding for studies of `cosmic chemical evolution'.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献