La conducibilità termica di alcune rocce italiane

Riassunto Il lavoro riguarda una serie di misure su campioni di 5 tipi diversi di rocce italiane aventi lo scopo di determinare la rispettiva conducibilità termica. Dopo la descrizione dell'apparecchiatura usata, vengono esposti i risultati ottenuti, analizzando in dettaglio l'influenza della scistosità. In base alle misure fatte su campioni di ardesia questa influenza può esprimersi con la formola:k =k ₉₀+m cos , dove è l'angolo fra la direzione del flusso termico ed il piano di stratificazione, mentrem è una costante caratteristica della scistosità.

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Summary Experiments made for obtain the thermal conductivity of different kinds of italian rocks are described and discussed. The effect of schistosity was derived for slate rocks and it can be represented with the formula:k =k ₉₀+m cos , where is the angle between the direction of thermal flux and the plain of stratification, whereasm is a constant characterizing the schistosity.

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Lavoro eseguito con un contributo del Consiglio Nazionale delle Ricerche (Comitato per la Geologia).     

Magma-induced strain localization in centrifuge models of transfer zones

Scaled centrifuge experiments have been used to investigate the dynamic relations between deformation and magma distribution in rift-related transfer zones. The physical models were built using suitable analogue materials, such as sand to represent the brittle upper crust, various kinds of silicone mixtures to simulate the lower crust and upper mantle and glycerol to reproduce magma. Models simulated the development of transfer zones across pre-existing glycerol reservoirs placed at the base of the analogue continental crust. In plan view, different geometries, dimensions and positions of subcrustal reservoirs were reproduced in three different sets of experiments; to compare results, models were also performed without magma-simulating glycerol.Set 1 experiments, incorporating a narrow rectangular glycerol reservoir, show that the low-viscosity material is able to localise deformation into the overlying crust, giving rise to discrete transfer zones. This concentrated surface deformation corresponds at depth to major magma accumulation. Set 2 experiments, with an initial wide squared glycerol reservoir, show instead that deformation is distributed across the whole model surface, corresponding at depth to relatively minor magma accumulation. Set 3 experiments explored various positions of a small squared reservoir that invariably localised faulting in the overlying analogue brittle crust at the onset of model deformation.The overall model behaviour suggests that magma distribution at depth can effectively control the strain distribution in the overlying crust and the deformative pattern of transfer zones. Strain distribution, in turn, may control magma emplacement as localized deformation would favour major accumulation of magma at transfer zones. Coupled to a strong thermal weakening of the country rocks, this process may ultimately lead to a positive feedback interaction between magma and deformation.     

Duration of strong ground motion during Mexican earthquakes in terms of magnitude,distance to the rupture area and dominant site period

A study of the duration of strong ground motion using accelerometric data of subduction and normal‐faulting Mexican earthquakes is presented. Duration is obtained based on the time between 2.5 and 97.5 per cent of the Arias intensity. An expression to predict this duration in terms of the magnitude, distance to the rupture area and site period is proposed and compared with predictions available in the literature. The effect of large duration for very distant sites and the contribution of soft soils to the duration of strong ground motion are widely discussed. We have found that large magnitude not only yields long duration at the source, but also proportionally longer duration with distance and with dominant site period compared to small magnitude. The duration obtained from the regression is used as a parameter to obtain input and hysteretic energy and on the use of damage models available in the literature. Finally, duration is used together with the random vibration theory to predict response spectra. Copyright © 2001 John Wiley & Sons, Ltd.     

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.