Three-dimensional nonlinear random wave groups in intermediate water depth

High waves at ocean occur during a complex space–time evolution of wave groups. In this paper the nonlinear structure of three-dimensional sea wave groups at intermediate water depth is investigated. To this purpose, the Boccotti's Quasi-Determinism theory is firstly applied to describe the linear wave groups when a given exceptionally high crest occurs. Then, the second-order correction to the linear solution is derived for the general condition of three-dimensional wave groups, at a finite water depth. Several numerical applications, finally, have been carried out in order to show how both the spectral bandwidth and the directional spreading modify the nonlinear high waves at different water depth.     

Viscosity of a Teide phonolite in the welding interval

The viscosity of a natural phonolitic composition with variable amounts of H₂O has been experimentally determined. The starting materials were crystal-free phonolitic glasses from Montaña Blanca, situated within the Las Cañadas caldera of Teide. Dry phonolitic melt viscosities were determined using concentric cylinder viscometry in the low viscosity range. The glassy quench products of these runs were then hydrated by high pressure synthesis in a piston–cylinder apparatus to generate a suite of samples with water contents ranging from 0.02 to 3.75 wt%. Samples thus hydrated were quenched rapidly and prepared (cut and polished) for the determination of water contents by infrared spectroscopy before and after experimental viscometry. The viscosities of the melts (dry and hydrated) were determined at 1 bar using a micropenetration technique. Samples were stable under the measurement conditions up to 3.75 wt% H₂O. Homogeneity of water content was confirmed by infrared spectroscopy and total water contents were calculated using absorptivity coefficients for compositions extremely close to that investigated here. The variation of viscosity as a function of water content and temperature can be described in the high viscosity interval of relevance to many welding processes by the non-Arrhenian expression:

(1)

log₁₀ η=−5.900−0.286 ln (H₂O)+(10775.4−394.8(H₂O))/(T−148.7+21.65 ln (H₂O))

whereas the high viscosity range alone is adequately described by the Arrhenian expression

(2)

log₁₀ η=−10.622−0.738 ln (H₂O)+(17114.3−590.4(H₂O))×1/T

where η is the viscosity in Pa s, H₂O is the water content in wt% and T is the temperature in K.These results are particularly useful for the scaling of conditions extant during the welding of phonolitic products of Montaña Blanca. The welding of glassy phonolitic rocks is enhanced by the lower viscosity of these melts with respect to calcalkaline rhyolites. The ratio of viscosities of phonolitic to calcalkaline rhyolitic melts is a complex function of temperature and water content and reaches up to 10^4.5 at 0.1 wt% H₂O and 500°C. Abundant evidence of welding and remobilisation of pyroclastic and spatter products of Teide system volcanism are consistent with these experimental observations.     

A statistical analysis of sunspot groups hosting M and X flares

In this paper we present the results obtained from a statistical analysis carried out by correlating sunspot‐group data collected at the INAF‐Catania Astrophysical Observatory and in the NOAA reports with data on Mand X flares obtained by the GOES‐8 satellite in the soft X‐ray range during the period January 1996–June 2003. These results allow us to provide a quantitative estimate of the parameters typical for an active region with very energetic flares. Moreover, the analysis of the flare productivity as a function of the group evolutionary stage indicates that the flaring probability of sunspots slightly increases with the spot age during the first passage across the solar disk, and that flaring groups are characterized by longer lifetimes than non‐flaring ones. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reliability of digit length impression as a character of tetrapod ichnotaxobase: considerations from the Carboniferous–Permian ichnogenus Ichniotherium

Although the relative length of digit impressions is often adopted as a binding character in ichnotaxa discrimination and trackmaker identification, it cannot be considered unequivocally operative. The reliability of this character has been evaluated by means of principal component analysis on several well‐preserved footprints (both manus and pes) referred to as Ichniotherium sphaerodactylum from the Early Permian Tambach Formation (Thuringia, Germany). The analysis reveals a substantial variability of digit impression length (especially in the manus), relativizing the validity of digit IV length as a diagnostic character as practised in different ichnological studies. Regarding the use of such a character, results clearly suggest the need to preliminarily conduct explorative analysis on the whole available ichnological material in order to detect which digit is the most consistent from an ichnotaxonomical standpoint, thus avoiding an arbitrary selection. Such a preliminary analysis should provide a better control on ichnotaxonomical splitting/lumping, particularly in the case of allied footprints, and can also be considered a valuable tool, if associated to functionality analysis, in improving and refining trackmaker identification. Copyright © 2014 John Wiley & Sons, Ltd.     

Magnetic helicity transport in corona and filament eruptions

Using a 28-hour time series of line-of-sight magnetograms taken by the Michelson Doppler Imager (MDI), we determined the magnetic flux variations and the rate of magnetic helicity transport at the footpoints of a filament in active region NOAA 8375. The filament was characterized by a positive helicity change due to shearing motions in both footpoints and showed several partial eruptions during the observing time. In particular, we considered 4 events registered in the Hα daily reports of Solar Geophysical Data. We found a strong temporal correlation between filament eruptions and helicity transport from the photospheric magnetic structures at the filament footpoints into the corona: in at least one footpoint, all of the events were preceded by an evident increase and followed by a small decrease of the emerging magnetic flux and of the magnetic helicity change due to shearing motions. We compared these two mechanisms of helicity transport and found that the predominant role to drive filament instability is played by emergence of new magnetic flux from the convection zone.     

Italian Diluvianism and antidiluvianism within the international arena: the great debate that lasted more than six centuries

As early as the thirteenth century naturalists of the Italian panorama began to look for a possible explanation for fossils found on emerged land. From the beginning, they tended quite naturally to resort to a catastrophic phenomenon, which found a direct ‘confirmation’ in the Holy Scriptures: the Great Flood. As an element found in numerous peoples, from the Babylonians, to ancient Egypt and the Chinese culture, the Flood became for a long time the only process able to explain the presence of marine fossils on the highest mountains, in a period dominated by a static concept of planet Earth. On the Italian scene, the supporters of the Flood were quite numerous, but equally numerous were the authors who brought evidence against the Deluge hypothesis, preferring a long stationing of the sea in places where the fossils are found today. An influential part of the second group is represented by the glorious Tuscan school that, starting from Boccaccio, includes prominent figures as Leonardo da Vinci, Baldassarri, Bastiani, Giovanni Targioni Tozzetti, Caluri, and Matani. In any case, the aspect that characterizes the majority of Italian authors from both the two interpretative factions, is a predilection to the study of deposits and fossils directly in the field, rather than the construction of ‘big systems’ simply based on the authority of sacred texts or other ancient authors.