A class of periodic solutions of the N-body problem

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.     

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

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.

     

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

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.     

Growth and evolution of an emergent tuff cone: Considerations from structural geology, geomorphology and facies analysis of São Roque volcano, São Miguel (Azores)

The syn-eruptive and post-eruptive history of São Roque tuff cone, its geological setting and volcanological features were studied in detail to understand the role played by the different factors that contributed to the morphological evolution of this relatively simple and small volcanic edifice.In addition, attention was also focused on the series of natural changes that affected the tuff cone during the course of the years and that finally led to its structural disassembly. A novel model is proposed to explain this process.The São Roque volcanic centre, located on the island of São Miguel (Azores), consists of two well-consolidated bodies and numerous small islets that formed more than 4700 years ago during the hydromagmatic activity that took place along an intruding dyke, whose NNW–SSE trend is in agreement with the regional tectonic pattern. The eruptive vents probably migrated progressively from SSE to NNW, forming small edifices through the rapid accumulation of sediments during alternating phases of “dry” and “wet” magmatic emissions. Syn-eruptive partial collapses greatly modified the original morphological structure of these edifices, probably allowing sea water to continuously flow into the vents. The complex interaction of these factors controlled the depth of magma fragmentation, producing different types of deposits, in which the ash-lapilli ratio varies considerably. The high-water saturation degree of these deposits caused syn-eruptive and post-eruptive remobilization which resulted in collapses and some small-scale landslides.Post-eruptive, WNW–ESE trending transtensional and extensional tectonic activities operated during the initial dissection of the cone, generating instability. Furthermore, the rapid accumulation of “wet” tephra, and its following consolidation, caused selective collapses that favoured the fragmentation of the deposit and caused the formation of numerous islets separated by radially-arranged channels. Collapses also involved the lava units emplaced in more recent times around the tuff cone, which show that brittle deformation has been significant in the area for a prolonged period.     

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

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.     

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

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.     

Lava balloons—peculiar products of basaltic submarine eruptions

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.     

Thermal state and concentration of gas hydrate and free gas of Coyhaique,Chilean Margin (44°30′ S)

In the last decades gas hydrate occurrence along the Chilean continental margin has been well documented. In order to better define the seismic character of the hydrate-bearing sediments, we performed a detailed velocity analysis by using the pre-stack depth migration on part of multichannel reflection seismic line RC2901-734 located offshore Coyhaique.     

A geometrical method for quantifying endmembers' fractions in three-component groundwater mixing

We present a new geometrical method capable of quantifying and illustrating the outcomes of a three-component mixing dynamics. In a three-component mixing scenario, classical algebraic equations and endmember mixing analysis (EMMA) can be used to quantify the contributions from each fraction. Three-component mixing of natural waters, either in an element–element plot or by using the EMMA mixing subspace is described by a triangular shaped distribution of sample points where each endmember is placed on an apex, while each side corresponds to the mixing function of the two endmembers placed at the apex, considering the third endmembers' contribution equal to zero. Along each side, the theoretical mixing fractions can be computed using mass balance equations. Samples with contributions from three endmembers will plot inside the triangle, while the homogeneous barycentric coordinate projections can be projected onto the three sides. The geochemistry observed in the mineralized Ferrarelle aquifer system (southern Italy) results from three-component mixing of groundwater, each with diagnostic geochemical compositions. The defined boundary conditions allow us to parameterize and validate the procedures for modelling mixing, including selection of suitable geochemical tracers.