SporadicE-layer ionization and sunspot cycle     

Mario Bossolasco  Antonio Elena 《Pure and Applied Geophysics》1963,56(1):142-149

Summary The correlation between the sunspot cycle and the sporadicE-layer ionization is investigated at middle latitudes. Higher mean values off ₀Es occur generally with higher sunspot numbers. Some evidence for a phase-shift between long term time-variation in sunspot numbers andf ₀Es is obtained. The solar cycle variation ofEs is somewhat larger over the Far East. Regarding the behaviour of the time-development ofEs events in diurnal variation, an interpretation is proposed.  相似文献   

The European Water Framework Directive 2000/60/EC in the evaluation of the ecological status of watercourses. Case study: the river Chienti (central Apennines,Italy)     

Stefania Scuri  Mariacristina Torrisi  Mario Cocchioni  Antonio Dell'Uomo 《洁净——土壤、空气、水》2006,34(5):498-505

The quality of the river Chienti (eastern‐central Apennines, Italy) has been evaluated according to the Water Framework Directive 2000/60/EC, taking into consideration both biotic (animal and vegetable) and chemical parameters. In studying the biotic component, two indices were used: the E.B.I, Extended Biotic Index (version adapted to the Italian rivers), based on macroinvertebrates, and the EPI‐D, the Eutrophication and/or Pollution Index, based on diatoms. For both macroinvertebrates and diatoms, two samplings were conducted, one in June and the other in October 2003. Instead, according to the Italian Law 152/99 the chemical and bacteriological analyses were conducted monthly for the entire year. The results of biomonitoring and chemical‐bacteriological analyses unanimously demonstrated a good ecological situation for the upper section of the Chienti, though the situation tends to worsen as the river continues its descent and undergoes increased anthropogenic pressure. Data obtained were correlated with Spearman's coefficients and principal component analysis. Both statistical calculations showed clear, direct correlation between the two biotic indices and an inverse correlation between these and the chemical and bacteriological parameters. However, a few differences of judgement that emerged among the various indices highlight the importance of using them simultaneously in order to obtain a more accurate diagnosis of the ecological status of the watercourses.  相似文献   

Effects of column axial force – bending moment interaction on inelastic seismic response of steel frames     

Marina Como  Mario De Stefano  Roberto Ramasco 《地震工程与结构动力学》2003,32(12):1833-1852

It is well known that axial force – bending moment interaction (N–M interaction) affects to a large extent the cyclic inelastic behaviour of structural elements, especially columns in framed structures, with reduction in bending capacity and loss of available ductility. A few studies have also shown that significant inelastic axial shortening affects the response of column elements subjected to medium–high levels of axial loads and cyclic bending. This paper is primarily aimed at evaluating the effects of column N–M interaction on the inelastic seismic response of steel frames. By considering the contemporaneous action of vertical loads, due to gravity, and of horizontal seismic excitation, it is shown that the progressive axial shortening of adjacent columns may differ substantially, thus inducing significant relative settlements at the ends of the connecting beams and, then, remarkable amplifications in beam plastic rotations. An evaluation of additional beam plastic rotations induced by column N–M interaction is carried out for real structures by investigating the inelastic response of steel frames designed according to European standards under horizontal and vertical earthquake excitations. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Morphologic changes in the Paraná River channel (Argentina) in the light of the climate variability during the 20th century     

Mario L. Amsler  Carlos G. Ramonell  Horacio A. Toniolo   《Geomorphology》2005,70(3-4):257

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Paleoenvironmental Changes during the Last 4000 yr in the Tigray, Northern Ethiopia     

Maria J. Machado  Alfredo Pérez-González  Gerardo Benito 《Quaternary Research》1998,49(3):312-321

In the Tigray region at the northern Ethiopian Highlands, paleoenvironmental reconstruction based on several infilled valley deposit sequences suggests that the past 4000 yr comprised three major wetter periods (ca. 4000–3500 yr B.P., 2500–1500 yr B.P., and 1000–960 yr B.P.), during which soils were formed, and two degradation episodes (ca. 3500–2500 yr B.P. and 1500–1000 yr B.P.), during which there was an increase of sediment yield from the slopes into the valleys. For the past 1000 yr, and in particular since the early 17th century, stratigraphic records together with historic chronicles suggest increasing aridity. Although difficulties arise in distinguishing between natural and human impacts, particularly in a region with a long established agricultural background, stratigraphical and proxy paleoclimatic data have indicated climate as the main controlling factor responsible for the environmental changes in the Tigray.  相似文献   

Potassium-argon dating of igneous activity in the central Chilean Andes — latitude 33°S     

Robert E. Drake  Garniss Curtis  Mario Vergara   《Journal of Volcanology and Geothermal Research》1976,1(3):285-295

Potassium-argon dating of volcanic and plutonic rocks in the Andean region of central Chile has revealed previously unrecognized episodes of igneous activity during Cretaceous and Cenozoic time. These results indicate the need to re-evaluate the classic stratigraphic subdivisions that have evolved on lithologic rather than time-stratigraphic criteria.Four radiometric age groups have been identified in the coast range volcanic belt:

1. (1) Las Chilcas Formation — Early Cretaceous continental volcanic strata (120-110 m.y.).

2. (2) Lo Valle Formation — Late Cretaceous continental volcanic strata (78-65 m.y.).

3. (3) Late Oligocene extrusive volcanics (31-28 m.y.).

4. (4) Early Miocene intrusive volcanics (20.6–19.5 m.y.).

Two radiometric age groups have also been identified in the adjacent Andean Cordillera:

1. (1) Farellones Formation — continental volcanic strata (18.5–17.3 m.y.).

2. (2) Early Pliocene extrusive volcanics (5-4 m.y.).

An older group of continental volcanic strata in the Andes represented by the Abanico Formation remains undated but is intruded by plutons dated at 19.5 and 24 m.y.Available chronologic evidence indicates that volcanic activity moved eastward from the coast range volcanic belt to the Andean Cordillera between 20 and 18 m.y. ago and remained there to the present time.  相似文献   

Seven landslide dams of old seismic origin in southeastern Sicily (Italy)   总被引：3，自引：0，他引：3  

Pier Giorgio Nicoletti  Mario Parise   《Geomorphology》2002,46(3-4)

This paper focuses on origin, morphology and evolution of seven landslide dams in southeastern Sicily. These landforms are part of a set of 146 landslides recently recognised in this area, which was hitherto considered to have little or no slope instability. Southeastern Sicily consists of a plateau (the Hyblaean Mountains) incised by canyons and surrounded by lower lands. It is underlain mostly by subhorizontal, moderately to well-lithified carbonate rocks. Relief is low.Several lines of evidence justify the assumption of a seismic trigger for the landslides in this area: (1) the geo-climatic environment is not favourable to landsliding, (2) low-angle basal shear surfaces are very frequent, (3) landslide distribution is consistent with the known magnitude–distance relationships for earthquake-induced landslides, (4) historical documents testify to earthquake-triggered slope instability and (5) a specific landslide can be exactly dated.The phenomena illustrated here include six rock slides (one with a debris-flow component) and one rock fall. Slip surfaces are mostly non-circular. Landslide volume ranges from about 50×10³ to 34×10⁶ m³.With reference to the Costa and Schuster [Geol. Soc. Am. Bull. 100 (1988) 1054] classification of landslide dams, five cases belong to type II (spanning the entire valley), and two to type IV (failures from both valley sides, with frontal or side contact between failed masses). With reference to Crozier and Pillans [Catena 18 (1991) 471] classification of landslide lakes, all cases show a main valley lake while tributary valley, back and supra lakes are sporadically present. One damming is attributable to the 1693 earthquake with certainty; another damming, to the same earthquake with high probability. Three dams were reincised, one breached or reincised, one is slightly reincised and two more or less intact; correspondingly, five silting up deposits were reincised, one is being reincised at present and two are still under formation.  相似文献   

Cyclostratigraphy and high-frequency carbon isotope fluctuations in Upper Cretaceous shallow-water carbonates, southern Italy   总被引：2，自引：0，他引：2  

Francesco P. Buonocunto  Mario Sprovieri†  Adriana Bellanca†  Bruno D'Argenio‡  Vittoria Ferreri‡  Rodolfo Neri†  Gaetano Ferruzza† 《Sedimentology》2002,49(6):1321-1337

Abstract A detailed carbon isotope study has been carried out on a Santonian (Upper Cretaceous) carbonate platform succession that crops out at Monte Sant'Erasmo (southern Italy). Previous centimetre‐scale studies on this succession have shown that high‐frequency eustatic changes, resulting from the Earth's orbital fluctuations, controlled the hierarchical organization of the depositional and early diagenetic features in elementary cycles, bundles (groups of three to five elementary cycles) and superbundles (groups of three or four bundles). The elementary cycles, which correspond to single beds, suggest a control caused by Earth's precession; the bundles and superbundles record the short (≈ 100 kyr) and long (≈ 400 kyr) eccentricity periodicity respectively. The δ¹³C signal of the Monte Sant'Erasmo succession is cyclic in nature and may be considered to be a reliable proxy for the sedimentary evolution (and related sea‐level history) of the analysed sequence. The carbon isotope cyclicity is recorded at bundle and superbundle level, but it is not evident at the scale of the elementary cycles, at least with the sampling interval used in this study. Spectral analysis of the δ¹³C record shows two main peaks corresponding to the short‐ and long‐eccentricity periodicity, whereas the precession signal is not evident in the power spectrum. In addition, lithofacies analysis shows that, in each bundle (and superbundle), higher C isotope values occur in sediments characterized by marine cements, whereas lower values are normally found in more restricted deposits overprinted by early meteoric diagenesis. Early diagenesis, driven by periodic sea‐level fluctuations, developed in either shallow‐subtidal (marine diagenesis) or subaerial‐exposed (meteoric overprint) sedimentary environments and directly influenced the carbon isotope signature. As a consequence, the δ¹³C record at Monte Sant'Erasmo reflects high‐frequency climatic oscillations controlling both environmental and early diagenetic changes. The long‐term isotopic record is similar to that of contemporaneous pelagic sections in England and elsewhere in Italy. It is concluded that the δ¹³C signature of shallow‐water carbonates, such as those of Monte Sant'Erasmo, offers great potential for correlation with coeval sections, including those of the pelagic realm.  相似文献   

A non-parametric bivariate entropy estimator for spatial processes     

Mario Rossi  Donato Posa 《Mathematical Geology》1992,24(5):539-553

In this paper, entropy is presented as an alternative measure to characterize the bivariate distribution of a stationary spatial process. This non-parametric estimator attempts to quantify the concept of spatial ordering, and it provides a measure of how Gaussian the experimental bivariate distribution is. The concept of entropy is explained and the classical definition presented, along with some important results. In particular, the reader is reminded that, for a known mean and covariance, the bivariate Gaussian distribution maximizes entropy. A relative entropy estimator is introduced in order to measure departure of an experimental bivariate distribution from the bivariate Gaussian. Two case studies are presented as examples.  相似文献   

The Serchio River catchment,northern Tuscany: Geochemistry of stream waters and sediments,and isotopic composition of dissolved sulfate     

Gianni Cortecci  Enrico Dinelli  Tiziano Boschetti  Paola Arbizzani  Loredana Pompilio  Mario Mussi 《Applied Geochemistry》2008

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