Downstream migration of juvenile European sturgeonAcipenser sturio L. in the Gironde estuary

The European sturgeon (Acipenser sturio) is an endangered diadromous fish species that spawns in the rivers in late spring and early summer. The juveniles spend their first years in the brackish waters (5‰ to 25‰) of the estuary zone before moving out to sea. This study describes the downstream migration pattern of juvenile sturgeon, belonging to the 1994 cohort, the only one born naturally in the Gironde basin, France since the end of the 1980s. During October 1994 to December 1996 the inland section of the Gironde estuary was sampled monthly by trawl (n=818 tows) and all European sturgeon caught (n=381) were marked and released. The first sturgeon of the 1994 cohort (TL=27 cm) were caught in early March 1995 in the zones furthest upstream. During their second fall of life, juveniles gradually acclimatized, and spread over a wide range of salinity conditions. A first incursion into marine water was also observed (at least for a few fish) by the end of the second winter. During this second period, sturgeon showed preference for two particular zones situated at 18 and 38 km, respectively, from the mouth of the estuary. These zones, belonging to two different salinity sectors of the estuary, did not appear to be any different to their neighbors with regards to depth and type of substrate. There were no significant size differences among estuarine zones. Seasonal movements of sturgeon seem to be motivated by a search for warmer temperatures. After a period of early acclimatization of 15 months, juvenile European sturgeon appear to be highly tolerant of salinity variations.     

A regional approach to cultural preservation: A central american example

The transition to democratic governments in Central America over the past decade, and the subsequent emergence of institutional mechanisms for regional cooperation have greatly increased the frequency and productivity of efforts for preservation of cultural patrimony. Both the archaeological and colonial data bases overlap modern political boundaries and regional collaboration in training, pubic education, curation and research is essential. Natural forces continually impact, and human economic forces (especially international tourism) increasingly impact cultural resources. Regional cooperation in the utilization of human resources is necessary to confront the management and salvage demands of major economic development projects, and rescue efforts following natural disasters. The development of policies and programs will be effective only if matched by the growth of cultural preservation professionals in each of the Central American republics. Finally, other art consuming nations in addition to the United States must begin to respect the cultural heritage of the Central American countries and develop policies to deter abuses by diplomatic staff and employees of NGO’s (nongovernment organizations)     

A study of wave impact of horizontal slabs

With the potential danger posed by freak waves, impact loads due to wave slamming on horizontal slabs has become crucial in the context of design of offshore platform decks. A laboratory model study has been carried out to investigate the slamming effect on horizontal slabs using regular waves at different frequencies with the measurement of vertical forces. A modified slamming coefficient independent of frequency has been suggested to be used conveniently for design purposes. A new technique for the generation of freak waves in the laboratory has been successfully achieved without close loop iterations. Finally the impact phenomenon due to freak waves on slabs has been discussed, which includes the study of both vertical and horizontal forces.     

On-line identification and convergence analysis of excitation-force and drag-force models for moored floating structures

This work presents an approach to identify hydrodynamic models for incident, diffraction and viscous forces acting on a moored floating structure. An important aspect treated here is the analysis of the unknown initial condition of the hydrodynamic state for the potential-radiation force. There is established its influence on the parameter convergence and the long-term effects. Afterwards the persistency of excitation of the regressor is analyzed in the case of both poor and rich excitation conditions. Theoretical results show that asymptotic convergence of the estimates takes place under arbitrary conditions of the wave excitation. A case study consisting in the identification of a moored semisubmersible is carried out to exemplify the application of the approach.     

Computational improvement of gravitational mode calculation of basins discretised by orthogonal curvilinear grids

The present note illustrates a criterion to improve the computational capability of the approaches proposed by Beltrami et al. [Beltrami, G.M., Bargagli, A., Briganti, R., 2003. Gravitational mode calculation of basins discretised by orthogonal curvilinear grids. Ocean Engineering 30, 833–853] for the direct numerical solution of the eigenvalue problem associated to the linear shallow-water equations when adiabatic boundary conditions apply. It is shown that—given the nature of its spatial differential operator—the problem can be solved by the singular value decomposition (SVD) of the real bidiagonal matrix resulting from a previous ad hoc Householder reduction of the operator matrix image. This procedure actually requires 1/8 of the random-access memory (RAM) needed by a standard library routine to compute all the eigenvalues and eigenvectors of the matrix image of the above-mentioned differential operator. Given the intrinsic limitation of a computing-machine RAM, this procedure dramatically improves the computational capability of both the proposed approaches.     

Sull'idrologia del Foehn

Riassunto Per alcuni casi diFöhn delle Alpi Italiane, interessanti il Piemonte e la Lombardia, sono state esaminate le variazioni dei deflussi nei giorni in cui soffiava tale vento nonchè in quelli adiacenti, trovando che di regola, quando non intervengono precipitazioni od altri fattori, ilFöhn provoca una diminuzione netta delle portate, che può raggiungere e superare il 10% e che si esplica con relativa prontezza. Si spiega tale riduzione con la forte evaporazione causata dalFöhn.

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Summary Researches have been undertaken on the influence of the Föhn in the italian Alps, regarding the runoff-variations. The Föhn causes as a rule a decrease of the runoff, which, in absence of precipitation, can reach or exceed 10%. It can be explained by the strong evaporation during the Föhn.

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Zusammenfassung Anhand einiger Föhnfälle in den italienischen Alpen wurde der Einfluss des Föhns auf die Aenderungen der Abflussmenge untersucht. Wenn empfindliche Niederschläge oder andere Faktoren nicht vorkommen, verursacht in der Regel der Föhn eine Abnahme der Abflussmenge, die 10% erreichen oder sogar überschreiten kann. Die Erklärung ist in der starken Verdunstung während des Föhns zu suchen.

     

Le barovariographe comme appareil de sondage aérologique

Summary First, the theory of the barovariograph, the deductions from which have also been confirmed by experiments, is presented with some improvements. Then there follows a concise illustration of the various possibilities of applying the instrument for the disclosure of aerological phenomena existing over a given locality.

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Zusammenfassung Zunächst wird, mit einigen Erweiterungen, die Theorie des Barovariographen dargelegt, deren Ableitungen auch experimentell bestätigt wurden. Dann folgt eine kurze Erläuterung der verschiedenen Anwendungsmöglichkeiten des Instrumentes für die Registrierung gewisser aerologischer Erscheinungen über einem Ort.

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Riasunto Dapprima viene esposta con alcuni perfezionamenti la teoria del barovariografo, le cui deduzioni sono state confermate anche sperimentalmente. Segue una illustrazione succinta delle varie possibilità applicative dello strumento per la rilevazione dei fenomeni aerologici sovrastanti una località determinata.

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Communication présentée à l'Association Internationale de Météorologie, IXe Assemblée Générale de l'UGGI, Bruxelles, Séance du 24 Août 1951.     

Nuovo metodo di registrazione dello stato del mare e primi risultati ottenuti a Genova

Riassunto Viene descritto ed illustrato un nuovo procedimento di registrazione del moto ondoso marino, il quale consiste sostanzialmente nel trasformare l'escursione verticale che subisce la superficie del mare nella compressione o dilatazione di una massa d'aria sovrastante racchiusa in un tubo verticale munito superiormente di opportuna membrana sensibile. Un tale apparecchio, installato a Prà (Genova) dal-l'Istituto Geofisico dell'Università di Genova, funziona con successo da alcuni mesi. Segue un esame dei primi risultati ivi conseguiti, dal quale appare l'importanza del passaggio dei fronti freddi sul moto ondoso del mare.

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Summary A new method for the recording of sea-wave motion is described and explained. It consists in having the vertical movement of the sea surface transformed into compression or expansion of a volume of air enclosed in a tube which is carrying on its upper part a sensitive membrane. This self-recording instrument, set up at Prà (Genoa) by the Istituto Geofisico dell'Università di Genova is functioning since several months already without giving rise to objections. Some first results obtained up now are also examided, from which it appears the importance of the passage of cold fronts.

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Zusammenfassung Es wird ein neues Verfahren für die Registrierung der Meereswellenbewegung beschrieben und erläutert. Es besteht darin, dass der vertikale Gang der Meeresoberfläche umgewandelt wird in Kompression oder Expansion einer in einem Rohre befindlichen Luftmasse, welche am oberen Teil von einer empfindlichen Membran geschlossen ist. Dieser Gerät, vom Istituto Geofisico dell'Università di Genova in Prà (Genua) aufgestellt, arbeitet bereits seit einigen Monaten einwandfrei. Einige vorläufige Ergebnisse werden dann erläutert, wofür auf die Bedeutung des Durchganges von Kaltfronten hingewiesen wird.

     

La brezza di mare a Genova ed in altre località costiere italiane

Riassunto Vengono illustrate le principali caratteristiche della brezza marina a Genova, a Savona ed a Belvedere Marittimo. L'esame relativo alle prime due località dimostra fra l'altro l'intervento di unacorrente costiera, diretta in senso ciclonico lungo la Liguria, la cui azione è importante per l'origine della brezza marina e per determinarne il suo comportamento. In base alle registrazioni della radiazione globale eseguite a Genova si trova altresì che la durata minima della brezza di mare dipende dall'intensità della medesima radiazione globale.

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Summary In the present treatise the chief characteristics of the sea breeze of Genoa, Savona and Belvedere Marittimo are being elucidated. Investigations carried out at the first two mentioned places showed a temporary coastal current which is pointing cyclonically along the coast of Liguria. Its activity has an important bearing upon the origin and behaviour of the breeze. The registrations of the total radiation from sun and sky at Genoa furthermore show that the minimum duration of sea breeze depends on the intensity of that radiation.

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Zusammenfassung In der vorliegenden Arbeit werden die wichtigsten Charakteristiken der Seebrise von Genua, Savona und Belvedere Marittimo erläutert. Die Untersuchung an den zwei ersten Orten ergab eine zeitweilige Küstenströmung, die längs der Liguria zyklonal gerichtet ist. Ihre Aktivität ist für den Ursprung und das verhalten der Brise wichtig. Die Registrierungen der Globalstrahlung in Genua zeigen überdies, dass die Minimaldauer der Seebrise von der Intensität der Globalstrahlung abhängt.