Apparent diameters of 172 B5V-A5V stars of the Catalogue of Geneva Observatory

The spectrophotometric method for computing the apparent stellar diameters, proposed by Chalonge and Divan (1950) and modified by Fracassini and Pasinetti (1967) has been applied to 172 B5V-A5V stars (single and belonging to galactic clusters) of the Catalogue of Geneva Observatory (Rufener, 1971). In the straight line diagrams log vsm, drawn for the stars of the same spectral type, it is possible to identify some peculiar stars (with peculiarities in the diameter or monochromatic brightness). The agreement with the values of the apparent diameters of Leo, Ori, Lyr and CMa, obtained by Hanbury Brownet al. (1967), is very good. The comparison with the diagramss _v vs (B-V)₀,R vs (B-V)₀ deduced by Wesselink (1969), seems satisfactory. The comparison with the results obtained by other authors and the great number of stars which will be observed in the photometric system in seven colors of Geneva, demonstrate the wide possibilities of this spectrophotometric method for determining the apparent stellar diameters.

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Sommario Il metodo spettrofotometrico di Chalonge e Divan (1950) per il calcolo dei diametri stellari apparenti, modificato da Fracassini e Pasinetti (1967), è stato applicato a 172 stelle B5V-A5V (isolate e in ammassi galattici) del Catalogo dell'Osservatorio di Ginevra (Rufener, 1971). Costruiti i diagrammi lineari log -m _v per i vari gruppi di stelle dello stesso tipo spettrale, è possibile identificare alcune stelle peculiari con diametri e brillanze monochromatiche anomale. Il confronto con i diametti apparenti di Leo, Ori, Lyr e CMa determinati da Hanbury Brownet al. (1967) mostra un accordo molto buono. Il confronto con le relazionis _v -(B-V)₀eR-(B-V) ₀ ottenute da Wesselink (1969) appare soddisfacente. Il confronto con i risultati ottenuti da altri autori e il grande numero di stelle che saranno osservate nel sistema fotometrico in sette colori di Ginevra, dimostrano le ampie possibilità di questo metodo spettrofotometrico per la determinazione dei diametri stellari apparenti.

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Thesis for the degree on Applied Physics.     

Field measurements of intertidal bar evolution on a high‐energy beach system

Nearshore bars play a pivotal role in coastal behaviour, helping to protect and restore beach systems particularly in post‐storm conditions. Examination of bar behaviour under various forcing conditions is important to help understand the short‐ to medium‐term evolution of sandy beach systems. This study carried out over a nine‐week period examines, the behaviour of three intertidal bars along a high energy sandy beach system in northwest Ireland using high‐frequency topographic surveys and detailed nearshore hydrodynamic modelling. Results show that, in general, there was onshore migration for all the bars during the study period, despite the variability observed between bars, which was driven mostly by wave dominated processes. Under the prevailing conditions migration rates of up to 1.83 m day^?1 and as low as 0.07 m day^?1 were observed. During higher wave energy events the migration rates of the bars decelerated in their onshore route, however, under lower wave energy conditions, they quickly accelerated maintaining their shoreward migration direction. Tidal influence appears to be subordinate in these conditions, being restricted to moderating the localized wave energy at low tides and in maintaining runnel configurations providing accommodation space for advancing slip faces. The study highlights the intricate behavioural patterns of intertidal bar behaviour along a high energy sandy coastline and provides new insights into the relative importance of wave and tidal forcing on bar behaviour over a relatively short time period. Copyright © 2016 John Wiley & Sons, Ltd.     

Frequency‐dependent multi‐offset phase analysis of surface waves: an example of high‐resolution characterization of a riparian aquifer

Multi‐offset phase analysis of seismic surface waves is an established technique for the extraction of dispersion curves with high spatial resolution and, consequently, for the investigation of the subsurface in terms of shear wave velocity distribution. However, field applications are rarely documented in the published literature. In this paper, we discuss an implementation of the multi‐offset phase analysis consisting of the estimation of the Rayleigh wave velocity by means of a moving window with a frequency‐dependent length. This allows maximizing the lateral resolution at high frequencies while warranting stability at the lower frequencies. In this way, we can retrieve the shallow lateral variability with high accuracy and, at the same time, obtain a robust surface‐wave velocity measurement at depth. In this paper, we apply this methodology to a dataset collected for hydrogeophysical purposes and compare the inversion results with those obtained by using refraction seismics and electrical resistivity tomography. The surface‐wave results are in good agreement with those provided by the other methods and demonstrate a superior capability in retrieving both lateral and vertical velocity variations, including inversions. Our results are further corroborated by the lithological information from a borehole drilled on the acquisition line. The availability of multi‐offset phase analysis data also allows disentangling a fairly complex interpretation of the other geophysical results.     

Quelques appareils pour l'étude de la structure physique des brouillards et des nuages

Résumé L'auteur décrit un appareil permettant de déterminer le contenu en eau liquide des brouillards et des nuages, dont il discute le principe thermodynamique. En plus, on décrit un tunnel placé au Monte Cimone (2164 m) qui, par sa tourelle tournante, permet d'observer et de mesurer la structure physique des nuages sous les conditions de la circulation naturelle. Enfin, on montre la construction d'une chambre à expansion qui permet d'étudier en laboratoire les différentes phases de développement des gouttelettes sous les conditions d'une expansion qui se produit d'une manière aussi lente qu'elle est observée dans la nature.

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Summary The author describes an apparatus for the determination of the content of liquid water in fogs and clouds and discusses its thermodynamic principle. Further, a wind channel placed on Mount Cimone (2164 m) is described which, owing to a revolving turret, allows to observe and measure the physical structure of the clouds under the natural conditions of the circulation. Finally, the construction of an expansion chamber is shown, which can be used for investigating in the laboratory the different phases in the formation of droplets, this under conditions happening as slowly as in nature.

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Zusammenfassung Es wird eine Apparatur zur Bestimmung des Gehaltes von Nebeln und Wolken an flüssigem Wasser beschrieben und ihr thermodynamisches Prinzip erläutert. Sodann wird ein Windkanal beschrieben, der auf dem Monte Cimone (2164 m) aufgestellt ist und dank seinem Drehturm gestattet, die physikalische Struktur der Wolken unter den Bedingungen der natürlichen Strömung zu beobachten und zu messen. Schließlich wird die Konstruktion einer Expansionskammer entwickelt, mit der die verschiedenen Phasen der Tröpfchenentwicklung im Laboratorium untersucht werden können, und zwar unter den Bedingungen einer Expansion, die so langsam verläuft wie in der Natur.

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Avec 5 figures.     

Hydrozoa (Cnidaria) symbiotic with Porifera: a review

Many hydroids are symbiotic with other organisms. Sponges, because of their complex canal system and their filter‐feeding activity inducing a continuous water flow, are used by numerous species as either exclusive or facultative substrata. The associated hydroid fauna thriving on or inside sponges shows a wide range of relationships with their hosts. Hydroids may be simply epibiotic on sponges, their stolons running on the host surface. Alternatively, the stolons may grow inside the sponge body, the polyps emerging from the sponge surface, having also the possibility of retraction inside the sponge tissue. Finally, stolons and branches may develop deeply inside the sponge body, producing a skeletal network for sponge growth. This paper reviews the described relationships of hydrozoans symbiotic with sponges and reports new observations.     

Parallel solution to ill‐conditioned FE geomechanical problems

Parallel computers are potentially very attractive for the implementation of large size geomechanical models. One of the main difficulties of parallelization, however, relies on the efficient solution of the frequently ill‐conditioned algebraic system arising from the linearization of the discretized equilibrium equations. While very efficient preconditioners have been developed for sequential computers, not much work has been devoted to parallel solution algorithms in geomechanics. The present study investigates the state‐of‐the‐art performance of the factorized sparse approximate inverse (FSAI) as a preconditioner for the iterative solution of ill‐conditioned geomechanical problems. Pre‐and post‐filtration strategies are experimented with to increase the FSAI efficiency. Numerical results show that FSAI exhibits a promising potential for parallel geomechanical models mainly because of its almost ideal scalability. With the present formulation, however, at least 4 or 8 processors are required in the selected test cases to outperform one of the most efficient sequential algorithms available for FE geomechanics, i.e. the multilevel incomplete factorization (MIF). Further research is needed to improve the FSAI efficiency with a more effective selection of the preconditioner non‐zero pattern. Copyright © 2011 John Wiley & Sons, Ltd.     

Resistive instabilities in coronal conditions

Resistive instabilities in a context referring to the solar corona are rigorously investigated. Various equilibrium configurations are considered, differing, among other things, by their behaviour with respect to fast, ideal instabilities. The computations presented cover in a unified scheme all known regimes of resistive modes and allow one to determine the fastest timescale over which resistivity can play a role. Comparisons with previous work as well as possible extensions are presented.     

Association between Messinian drainage network formation and major tectonic activity in the Marche Apennines (Italy)

The Marche Apennines (Italy) offer an excellent opportunity to constrain the temporal and spatial relationships between drainage network formation and tectonic activity. Using a combination of field data, seismic lines and boreholes we show that the main deformation phase took place during the Messinian when the area, affected by the Messinian sea level drop, emerged and evolved from marine to continental conditions. The results highlight that during the Messinian emersion a drainage network developed contemporaneously with an increase in tectonic activity that could be related to sea level fall and river erosion. The present‐day river system, which is dominated by transverse rivers that cut straight across the tectonic grain, is located in older Messinian palaeovalleys, even though the region was subsequently covered by water until the late Pliocene–early Pleistocene.