Current problems on horizontal branch stars     

Filippina Caputo  Vittorio Castellani 《Astrophysics and Space Science》1975,38(1):39-66

Expected characteristics of RR Lyrae stars as a function of the evolutive parameters are reported. Results from both evolutionary and pulsational investigations are collected in a suitable form, to show the general constraints to any interpretative analysis of the observations. It is shown that the spread in luminosity among the RR Lyrae stars results a function of the original chemical composition. On this basis a set of independent indications is found, suggesting that the globular cluster ω Cen is more He-rich than M 3; agreement with the whole observational frame is attained ifY _ωCen～0.35,Z _ωCen～5×10^?4 andY _M3～0.25,Z _M3～10^?3. No mass loss is needed to account for the RR Lyrae stars observed in ω Cen. The results are discussed, and it is shown that M 13-type clusters can be just characterized by a larger value ofZ in comparison with ω Cen. It is suggested that variations in the original helium content of the order of ΔY～0.1 and a correlationZ=Z(t) can account for some well-observed galactic globular clusters, without allowing for mass loss in the redder HB stars belonging to each cluster.  相似文献   

Primordial non-Gaussianity: local curvature method and statistical significance of constraints on f_NL from WMAP data     

P. Cabella  M. Liguori  F. K. Hansen  D. Marinucci  S. Matarrese  L. Moscardini  N. Vittorio 《Monthly notices of the Royal Astronomical Society》2005,358(2):684-692

We test the consistency of estimates of the non-linear coupling constant f _NL using non-Gaussian cosmic microwave background (CMB) maps generated by the method described in the work of Liguori, Matarrese & Moscardini. This procedure to obtain non-Gaussian maps differs significantly from the method used in previous works on the estimation of f _NL. Nevertheless, using spherical wavelets, we find results in very good agreement with Mukherjee & Wang, showing that the two ways of generating primordial non-Gaussian maps give equivalent results. Moreover, we introduce a new method for estimating the non-linear coupling constant from CMB observations by using the local curvature of the temperature fluctuation field. We present both Bayesian credible regions (assuming a flat prior) and proper (frequentist) confidence intervals on f _NL, and discuss the relation between the two approaches. The Bayesian approach tends to yield lower error bars than the frequentist approach, suggesting that a careful analysis of the different interpretations is needed. Using this method, we estimate   f _NL=−10⁺²⁷⁰₋₂₆₀  at the 2σ level (Bayesian) and   f _NL=−10⁺³¹⁰₋₂₇₀  (frequentist). Moreover, we find that the wavelet and the local curvature approaches, which provide similar error bars, yield approximately uncorrelated estimates of f _NL and therefore, as advocated in the work of Cabella et al., the estimates may be combined to reduce the error bars. In this way, we obtain   f _NL=−5 ± 85  and   f _NL=−5 ± 175  at the 1σ and 2σ level respectively using the frequentist approach.  相似文献   

Evaluation of local amplification in the seismic microzonation: comparison between punctual multidisciplinary integrated studies and macroseismic methods in Fivizzano's area (Toscana, Italy)     

Patrizio Signanini  Vittorio D'Intinosante  Maurizio Ferrini  Mario L. Rainone 《Geotechnical and Geological Engineering》2004,22(2):227-244

In the seismic microzonation the evaluation of the local amplification issue may be solved using different methodological approaches. Taking the hint from the studies made within VEL project framework, sponsored by Tuscany Region on Fivizzano's area we are herewith comparing the results of geotechnical and geophysical integrated multidisciplinary studies with the existing data available from previous studies, mainly using a macroseismic approach, on the same area. This qualitative method does not seem to be able to make any forecasting on the scale whereas generally microzoning is performed. On the contrary, the knowledge of the geological-technical model of the investigated area, obtained by punctual multidisciplinary integrated studies, allows a direct collection of the data to insert in input step of numerical modelling, aimed to local effects evaluation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

An analytical study of the inclinations of the planetary axes of rotation     

Vittorio Banfi 《Earth, Moon, and Planets》1986,36(1):1-10

A theoretical model, based on simple and fundamental concepts of classical mechanics, is presented. It describes the possible historical evolution of the inclination angles of the planetary axes of rotation, with respect to the normal to orbital planes. Owing to the model structure, reasonable agreement with observational facts is expected, especially for the outer and giant planets.  相似文献   

A class of periodic solutions of the N-body problem     

Vittorio Coti Zelati 《Celestial Mechanics and Dynamical Astronomy》1989,46(2):177-186

We prove existence and multiplicity of T-periodic solutions (for any given T) for the N-body problem in ^m (any m 2) where one of the bodies has mass equal to 1 and the others have masses ₂,..., _N , small. We find solutions such that the body of mass 1 moves close to x = 0 while the body of mass _i moves close to one of the circular solutions of the two body problem of period T/k _i, where ki is any odd number. No relation has to be satisfied by k ₂,...,k _N.  相似文献   

L'anticlinale gravimetrica di Fontevivo: Un confronto fra i risultati di due diversi metodi di gravimetria     

Vittorio Scheffer 《Pure and Applied Geophysics》1941,3(1):12-13

Riassunto Sono posti a confronto i risultati del rilevamento gravimetrico della zona di Fontevivo (Parma) eseguiti prima con bilancia di torsione e successivamente con gravimetro (tipc Humble-Truman); ottenendosi un buon accordo fra i due metodi.

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Zusammenfassung Vergleich der Ergebnisse der gravimetrischen Aufnahme von der Umgebung von Fontevivo (Parma), zuerst mit der Drehwaage durchgeführt, nachher mit einem Gravimeter nach Humble-Truman; die Übereinstimmung der Ergebnisse ist befriedigend.

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Résumé Comparaison des résultats du levé gravimétrique de la zone de Fontevivo (Parme) effectué d'abord avec la balance de torsion, ensuite avec un gravimètre type Humble-Truman; bonne concordance entre les deux méthodes.

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The Hyblean xenolith suite (Sicily): an unexpected legacy of the Ionian–Tethys realm     

Fabio Carmelo Manuella  Vittorio Scribano  Serafina Carbone  Alfonso Brancato 《International Journal of Earth Sciences》2015,104(5):1317-1336

The extensive study of a great number of deep-seated xenoliths from Tortonian tuff-breccia pipes in the Hyblean area (Sicily) revealed the following fundamental evidence: (1) typical continental crust rocks are completely absent in the entire xenolith suite; (2) mantle ultramafics are more abundant than gabbroids; (3) sheared oxide–gabbros, closely resembling those from oceanic fracture zones, are relatively common; (4) secondary mineral assemblages, compatible with alteration processes in serpentinite-hosted hydrothermal systems, occur both in peridotites and gabbros. Among the products of this hydrothermal activity, organic compounds, having abiotic origin via Fischer–Tropsch synthesis, occur in some hydrothermally altered gabbro and ultramafic xenoliths, as well as in hydrothermal clays. Moreover, the U–Pb dating of hydrothermal zircon grains, hosted in a xenolith of metasomatized tectonic breccia, indicated an Early–Middle Triassic age of the fossil hydrothermal system. Another line of evidence for the oceanic nature of the Hyblean–Pelagian basement is the complete absence of continental crust lithologies (granites, felsic metaigneous, and metasedimentary rocks) in outcrops and in boreholes, and the oceanic affinity of the Tertiary volcanic rocks from the Hyblean Plateau and the Sicily Channel (Pantelleria and Linosa Islands), which lack of any geochemical signature for continental crust contamination. A reappraisal of existing geophysical data pointed out that serpentinites form the dominant lithologies in the lithospheric basement of the Hyblean–Pelagian area down to a mean depth of 19 km, which represents the regional Moho considered as the serpentinization front, marking the transition from serpentinites to unaltered peridotites. On these grounds, we confirm that Hyblean xenoliths contain mineralogical, compositional, and textural evidence for tectonic, magmatic, and hydrothermal processes indicating the existence of fossil oceanic core complexes, in the geotectonic framework of the Paleo–Mesozoic, ultra-slow spreading, Ionian–Tethys Ocean forming the present Ionian–Hyblean–Pelagian domain.  相似文献   

Lava balloons—peculiar products of basaltic submarine eruptions   总被引：1，自引：1，他引：0  

Ulrich Kueppers  Alexander R. L. Nichols  Vittorio Zanon  Marcel Potuzak  Jose M. R. Pacheco 《Bulletin of Volcanology》2012,74(6):1379-1393

Between December 1998 and April 2001, a submarine basaltic eruption occurred west of Terceira Island, Azores (Portugal) in water depths between 300 and 1,000?m. Physical evidence for the eruption was provided by the periodic occurrence of hot lava “balloons” floating on the sea surface. The balloons consisted of a large gas-filled cavity surrounded by a thin shell (a few centimetres thick). The shells of the collected balloons are composed of two layers, termed the outer layer and the inner layer, defined by different bubble number density, bubble sizes and crystal content. The inner layer is further divided into three sublayers defined by more subtle differences in vesicularity. The outer layer is glassy, golden-coloured and highly porous. It shows signs of fluidal deformation and late-stage extension cracks. Interstitial glass contains 0.29?wt% H₂O and CO₂ is below detection. Melt inclusions contain up to 1.18?wt% H₂O and 1,500?ppm CO₂ (from different inclusions). Cooling rates of the outermost glass of the outer layer are found to be as high as 1,259?K/s. During ascent of low viscosity magma to the ocean floor, volatiles, dominated by CO₂, exsolved from the magma (melt + crystals). The buoyancy of the vapour phase that accumulated below a thin crust on lava ponded at the vent caused bulging and ultimately cracking of the crust. This allowed large bubbles (central cavity) surrounded by a film of vesicular magma (balloon shell) to leak into the water column. On contact with the seawater, the outermost part of the outer layer of the shell hyperquenched. If an entirely closed shell was produced during detachment, the trapped gas inside allowed buoyant rise. Only balloons with the right balance of physical properties (e.g. size and bulk density) rose all the way to the sea surface.  相似文献   

Autochthonous and allochthonous plant contributions to coastal benthic detritus deposits: a dual-stable isotope study in a volcanic lake     

Loreto Rossi  M. Letizia Costantini  Pasquale Carlino  Antonella di Lascio  David Rossi 《Aquatic Sciences - Research Across Boundaries》2010,72(2):227-236

The high numbers of primary producers represent multiple sources of organic matter accumulating onto lake bottoms. The difficulty of distinguishing the relative contribution to the mixture presents considerable challenges to the analysis of these organic deposits. In this study, dual-stable isotope analysis and IsoSource model were used to identify allochthonous and autochthonous components of detritus deposits (Particulate Organic Matter: POM) at two different bottom slope sites of a volcanic lake (lake Bracciano). Experiments were carried out to calibrate IsoSource on constructed plant mixtures and assess changes in isotope ratios during plant decomposition. IsoSource satisfactorily discriminated the constructed mixture sources with a few exceptions. Changes in isotopic enrichment during decomposition were low, and thus did not represent a confounding variable in the isotopic analysis. By contrast, chemical and geological differences of the study sites were associated with differences in plant δ¹³C and δ¹⁵N values (more than 2‰ within single plant species). At both sites, the isotopic signals of POM fell between polygons delineated by source end members with an evident shift of δ¹³C toward allochthonous sources. POM amount and diversity were greater at the flatter bottom site, where allochthonous contributions were larger than at the other site. In particular, IsoSource ranked species contributions as follows: A. glutinosa > P. australis > A. donax > S. alba > P. nigra > the benthic macroalga Chara sp. at the first site, and A. glutinosa > P. nigra > the aquatic macrophyte C. demersum at the latter. The composition of littoral POM was determined by allochthonous sources in proportion to their relative abundances (as percent land cover) with differences between sites due to bottom slope.  相似文献   

Palaeoenvironmental control on sediment composition and provenance in the late Quaternary deltaic successions: a case study from the Po delta area (Northern Italy)     

Pietro Vittorio Curzi  Enrico Dinelli  Marianna Ricci Lucchi  Stefano Claudio Vaiani 《Geological Journal》2006,41(5):591-612

Accumulation of continental, deltaic and shallow‐marine sediments in the Po River coastal plain preserves a record of the Late Quaternary sea‐level changes and shoreline migrations. The palaeoenvironmental evolution of this area and the changes in composition and provenance of sediments have been investigated through integrated sedimentological, micropalaeontological (mainly foraminifers) and geochemical analyses of core S1, from the southern part of the Po River delta, within a chronological framework supported by radiocarbon dating and correlations with adjacent core sequences. Eleven lithofacies, grouped into five facies associations, and four palaeontological assemblages provide the basis to define the palaeoenvironmental reconstruction of this succession consisting, from the base to the top, of: (i) continental sediments accumulated during the Late Pleistocene; (ii) back‐barrier sediments marking the onset of Holocene sea‐level rise; (iii) transgressive sands deposited during the rapid landward migration of a barrier‐lagoon system; (iv) shallow‐marine and prodelta sediments with faunal associations indicating a gradual approach to the Po River mouth; and (v) sub‐recent delta front sands that form a considerable portion of the present coastal plain. Bulk chemical composition of sediments shows remarkable relationships with palaeoenvironments and locally improves facies characterizations. For example, they reveal carbonate leaching that emphasizes the occurrence of palaeosols in continental deposits or record enrichments in loss on ignition, S and Br, diagnostic of organic‐rich layers in back‐shore sediments. Selected geochemical elements (e.g. Mg and Ni) are particularly effective for the recognition of sediment provenances from the three main source areas observed in the subsurface deposits of the Po River coastal plain (e.g. Apenninic rivers, North Adriatic rivers and Po River). An Apenninic provenance is observed in continental and back‐barrier sediments. A North Adriatic provenance characterizes the transgressive sands and the shallow‐marine deposits; a significant Po River provenance is recorded in sediments related to the onset of the prodelta environment, confirmed by foraminiferal assemblages indicating remarkable increase in fluvial influxes. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献