Chemical Evolution in the Early Universe: Can Damp Lyα Systems Be Spiral Galaxies?     

Ángeles I. Díaz  Mercedes Mollá  Federico Ferrini 《Astrophysics and Space Science》1998,263(1-4):71-74

The distribution of element abundances with redshift in Damped Lyα (DLA) systems can be adequately reproduced by the same models reproducing the halo and disk components of the Milky Way Galaxy at different galactocentric distances. In this sense, DLA systems are well represented by normal spiral galaxies in their early evolutionary stages. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Dust transport and palaeoclimate during the Oldest Dryas in Central Europe — implications from varves (Lake Constance)     

Frank Niessen  Guy Lister  Federico Giovanoli 《Climate Dynamics》1992,8(2):71-81

This paper evaluates evidence for seasonal loess deposits in peri-Alpine Lake Constance at the end of the last Glacial (Oldest Dryas chronozone). The usefulness of such lacustrine deposits for palaeoclimatic interpretations is discussed. The sedimentology of laminated couplets comprising yellow and grey silts has been investigated to test the hypothesis that the couplets are varves (i.e. annual rhythmites) comprising alternations of loess and glacial silt and clay. The laminae are mostly less than 1 mm thick and include from bottom to top: (1) a matrix of well-sorted, non-graded fine yellow silt with sand-size intraclasts, (2) coarsening-upward grey silt with a cap of fining-upward silt to clay. The latter is typical for varves in modern proglacial lakes and reflects summer and winter deposits (silt and clay, respectively). We propose that the lack of grading and the matrix supported fabric is indicative of aeolian transport and therefore interpret the yellow laminae as loess deposits. Volcanic glass intraclasts in the loess layers are probably derived from volcanic terrain to the west of the lake, indicating an easterly palaeowind direction. Deposition of loess in the lake occurred regularly at the beginning of each annual cycle, suggesting that the palaeowinds were associated with winter and/or spring conditions. Two transport scenarios are suggested to explain the sand grains scattered in this deep-water lacustrine record. 1. The grains may have been transported as bedload over the annual winter ice-cover of the lake under moderate wind strengths, frozen into the ice, and released for deposition during spring melt. 2. The sand grains were blown directly out onto the lake water by very strong winds during spring. The first scenario is contrary to the general view that loess was transported during summer, and that loess deposits thus reflect summer conditions only. Loess input to the lake shows a transitional decrease after ca. 14.3 kyr BP and cessation at ca. 14 kyr BP, probably as a result of a change of wind behaviour, increased humidity and/or vegetational changes during the Oldest Dryas in central Europe.This paper was presented at Clima Locarno 90, the International Conference on Past and Present Climate Dynamics: Reconstruction of Rates of Change, held in Locarno, Switzerland, September 24 to 28, 1991, supported by a grant from the Swiss Academy of Sciences. It was convened jointly by the Swiss National Climate Program - ProClim, the Swiss Committee for the IGBP, the Swiss COL, the Swiss SCOPE Committee, and the Swiss CCA. Guest editor for the papers published following the conference is Dr. K. Kelts (see also Climate Dynamics 6:3/4, Jan. 1992)  相似文献   

The at-rest earth pressure coefficient prediction using simple elasto-plastic constitutive models     

Antonio Federico  Gaetano Elia  Agnese Murianni 《Computers and Geotechnics》2009,36(1-2):187-198

The paper deals with the theoretical prediction of the at-rest earth pressure coefficient for normally consolidated soils (k_0(NC)) using simple elasto-plastic constitutive models. In the first part of the work, the k_0(NC) expressions derived from critical state soil mechanics models are critically discussed. It is shown that, adopting typical values of the models parameters, the experimental k_0(NC) values are usually over-predicted. In the second part, a possible modification of the critical state model formulation, which allows to predict lower k_0(NC) values for a fixed angle of shearing resistance, is considered. Finally, a discussion of the results and some brief conclusions are proposed.  相似文献   

Managing coastal erosion: A management proposal for a littoral cell in Todos Santos Bay,Ensenada, Baja California,Mexico     

Carlos Peynador  Federico Méndez-Sánchez 《Ocean & Coastal Management》2010,53(7):350-357

A diagnostic of coastal erosion and shoreline retreat occurring at a 7-km long sandy beach (Littoral Cell III) located in Todos Santos Bay (Baja California, Mexico) is performed trough the analysis of aerial photographs. Around 82,000 m² of this sandy beach have been lost in a 20 year period (1985–2005), at a beach loss rate of 2,100 m² per year. This indicates that coastal erosion is becoming a hazard to human lives and coastal infrastructure. Due to the latter, the implementation of a Shoreline Erosion Management Plan (SEMP) is proposed as the best management approach to deal with the problem. The Littoral Cell III SEMP considers four core policies, eight management strategies and a group of specific measures.  相似文献   

Field investigation and rockfall hazard zonation at the Shijing Mountains Sutra caves cultural heritage (China)   总被引：2，自引：0，他引：2  

Xueliang Wang  Luqing Zhang  Sijing Wang  Federico Agliardi  Paolo Frattini  Giovanni B. Crosta  Zhifa Yang 《Environmental Earth Sciences》2012,66(7):1897-1908

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Prediction of time to slope failure: a general framework   总被引：4，自引：1，他引：3  

A. Federico  M. Popescu  G. Elia  C. Fidelibus  G. Internò  A. Murianni 《Environmental Earth Sciences》2012,66(1):245-256

The prediction of time to slope failure (TSF) is a goal of major importance for both landslide researchers and practitioners. A reasonably accurate prediction of TSF allows human losses to be avoided, damages to property to be reduced and adequate countermeasures to be designed. A pure “phenomenological” approach based on the observation and interpretation of the monitored data is generally employed in TSF prediction. Such an approach infers TSF mainly from the ground surface displacements using regression techniques based on empirical functions. These functions neglect the rheological soil parameters in order to reduce the prediction uncertainties. This paper presents an overlook of the methods associated with this approach and proposes a unique expression encompassing most of the previously proposed equations for TSF prediction, thus offering a general framework useful for comparisons between different methods. The methods discussed in this paper provide an effective tool, and sometimes the only tool, for TSF prediction. The fundamental problem is always one of data quality. A full confidence in all assumptions and parameters used in the prediction model is rarely, if ever, achieved. Therefore, TSF prediction models should be applied with care and the results interpreted with caution. Documented case studies represent the most useful source of information to calibrate the TSF prediction models.  相似文献   

Numerical modeling and mechanical analysis of an innovative soil anchoring system     

Claudio di Prisco  Federico Pisanò 《Acta Geotechnica》2014,9(6):1013-1028

In this paper, the pull-out performance of an innovative system for soil anchoring is mechanically interpreted on the basis of a preliminary finite element investigation. The system consists of a tie rod equipped with thick steel sockets, extruding into the soil to increase the overall pull-out bearing capacity. The effectiveness of the anchorage is shown to be mainly due to the steel sockets, producing two correlated strength mechanisms: a direct one, associated with the shear/flexural strength of the sockets themselves; and an indirect one, in the form of a remarkable increase in the normal confinement on the tie rod and hence in the mobilizable shear stresses. The numerical results are finally exploited to conceive a simplified mechanical model for the interpretation/prediction of the pull-out anchor performance.  相似文献   

Interaction between ultrapotassic magmas and carbonate rocks: Evidence from geochemical and isotopic (Sr, Nd, O) compositions of granular lithic clasts from the Alban Hills Volcano, Central Italy     

Angelo Peccerillo  Marcella Federico  Mauro Brilli 《Geochimica et cosmochimica acta》2010,74(10):2999-95

Magma-carbonate rock interaction is investigated through a geochemical and Sr-Nd-O isotope study of granular lithic clasts (ejecta) from the Alban Hills ultrapotassic volcano, Central Italy. Some samples (Group-1) basically represent intrusive equivalents of Alban Hills magmas. A few samples (Group-2) are ultramafic, have high MgO (∼30 to 40 wt%) and δ¹⁸O‰, and originated by accumulation of mafic phases that crystallised from ultrapotassic melts during assimilation of dolomitic rocks. Group-3 ejecta consist of dominant K-feldspar, and show major element compositions similar to phonolites, which, however, are absent among the Alban Hills volcanics. Finally, another group (Group-4) contains corroded K-feldspars, surrounded by a microgranular to porphyritic matrix, made of igneous minerals (K-feldspar, foids, clinopyroxene, phlogopite) plus wollastonite, garnet, and some cuspidine. Group-4 ejecta are depleted in SiO₂ and enriched in CaO with respect to Group-3.The analysed ejecta have similar ¹⁴³Nd/¹⁴⁴Nd (0.51204-0.51217) as the Alban Hills lavas, whereas ⁸⁷Sr/⁸⁶Sr (0.70900-0.71067) is similar to lower. Whole rocks δ¹⁸O‰ ranges from +7.0 to +13.2, reaching maximum values in ultramafic samples. A positive correlation with CaO is observed in single rock groups. Large Ion Lithophile Element (LILE) abundances and REE fractionation are generally high, and extreme values of Th, U and LREE are found in some Group-3 and Group-4 rocks.Mineralogical, petrological and geochemical data reveal extensive interaction between magma and carbonate wall rocks, involving both dolostones and limestones. These processes had dramatic effects on magma compositions, especially on phonolites, which were transformed to foidites. Evidence of such a process is found in Group-4 samples, in which K-feldspar is observed to react with a matrix that represents strongly undersaturated melts formed by interaction between silicate magma and carbonates. Trace element data also testify to a very important role for F-CO₂-H₂O-S fluids during magma-wall rock interaction. Fluid transfer was responsible for extreme enrichments in Th, U, and LREE especially observed in Group-3 and Group-4 rocks. Implications of these processes for potassic magma evolution in Central Italy are discussed.  相似文献   

The Prestige oil spill: a scientific response     

Albaigés J  Morales-Nin B  Vilas F 《Marine pollution bulletin》2006,53(5-7):205-207

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Geological characterization of the Prestige sinking area     

Ercilla G  Córdoba D  Gallart J  Gràcia E  Muñoz JA  Somoza L  Vázquez JT  Vilas F;Prestige Group 《Marine pollution bulletin》2006,53(5-7):208-219

The tanker Prestige sank off NW Iberia on the 19th November 2002. The stern and bow of the Prestige wreck are located on the southwestern edge of the Galicia Bank, at 3565 m and 3830 m water depths, respectively. This bank is a structural high controlled by major faults with predominant N-S, NNE-SSW, and NNW-SEE trends. It is characterized by moderate to low seismic activity. The faults have controlled the local depositional architecture, deforming, fracturing, relocating and distributing sediments since the Valangian (early Cretaceous). The Prestige sinking area corresponds to an asymmetric half-graben structure with a N-S trend, which conditions the present-day morphology. The faulted flank outcrops and its activity and erosion have favoured the occurrence of mass-movements (slumps, slump debris, mass-flows and turbidity currents), building valleys and depositional lobes. Nearsurface sediments comprise mostly terrigenous and biogenous turbiditic muds and sands with a minor presence of hemipelagic muds, except on the fault scarp where pelagites predominate. Potential geological hazards resulting from tectonic and sedimentary processes affect almost the entire Prestige sinking area.  相似文献