A field experiment on the small-scale model of a gravity offshore platform     

Paolo Boccotti   《Ocean Engineering》1995,22(6)

The 1:50 scale model of a big offshore gravity platform was placed off the beach at Reggio-Calabria, where the wind waves typically have significant height ranging from 0.20 to 0.40 m and peak period from 1.8 to 2.6 sec. A first set of pressure transducers was assembled at the boundary of the platform and a second set, with the same configuration as the first one, was assembled in the undisturbed wave field, in order to compare the force amplitude on the platform to the force amplitude on an ideal equivalent mass of water (Froude-Krylov force amplitude). Along with the pressure transducers, a few wave gauges were functioning in the undisturbed wave field. It was found that the time histories of the pressure induced by the highest waves, at the columns and at the platform base, were very similar to the measured covariances of the pressure fluctuations. The statistical distribution of the forces on the platform proved to be coincident with the statistical distribution of the Froude-Krylov forces. The spectrum of the force process proved always to be narrow even in the case of the broad wave spectrum. The diffraction coefficient (ratio of the actual force amplitude to the Froude-Krylov force amplitude) was found to depend essentially on a marked reduction of the propagation speed of the pressure head waves, both at the columns and at the platform base.  相似文献   

Temporal Dynamics and Biomass Partitioning in Three Adriatic Seagrass Species: Posidonia oceanica,Cymodocea nodosa,Zostera marina     

Paolo Guidetti  Maurizio Lorenti  Maria&#x;Cristina Buia  Lucia Mazzella 《Marine Ecology》2002,23(1):51-67

Abstract. The temporal dynamics of three seagrasses, Posidonia oceanica, Cymodocea nodosa and Zostera marina, was studied in different areas of the Adriatic Sea by analysing phenological parameters and biomass trends in different compartments of seagrass systems. For this purpose, samplings were conducted in 1997 once per season at each station, Otranto (southern Adriatic Sea) and Grado (northern Adriatic Sea). Structural parameters and biomass of plant compartments differed among seagrasses both in absolute values and in seasonal variability. P. oceanica was the largest plant, showing the highest number of leaves per shoot, highest leaf surface, Leaf Area Index and shoot weight. Z. marina was intermediate in size and had the longest leaves, whereas C. nodosa was the smallest seagrass. P. oceanica accounted for the highest total biomass (mean ± SE: 1895.9 ± 180.2 g DW · m^–2; CV = coefficient of variation: 19.0 %), considerably more than C. nodosa (mean ± SE: 410.4 ± 88.4 g DW·m^–2; CV: 43.1 %) and Z. marina (mean ± SE: 312.1 ± 75.1 g DW · m^–2; CV: 48.1 %), although the two latter species displayed a higher seasonal variability. Similarly, other features, such as shoot density, leaf surface, LAI, shoot weight and relative contributions of above‐ and below‐ground compartments, were less variable across seasons in P. oceanica than in the two other seagrasses, while leaf length showed the highest seasonal fluctuation in P. oceanica. As for biomass partitioning, C. nodosa showed a higher proportion of the below‐ground relative to above‐ground biomass (up to 90 %), with a distinct seasonality, whereas in P. oceanica the proportion of below‐ground biomass (around 80 %) was fairly constant during the year. We infer that in P. oceanica the seasonal forcing is probably buffered by the availability of internal resources stored permanently during the year in the below‐ground. In C. nodosa and Z. marina, instead, growth processes seem to be amplified by a greater influence of environmental factors.  相似文献   

Far-infrared emission from an intergalactic dust cloud?     

Bogdan Wszolek  Konrad Rudnicki  Silvia Masi  Paolo De Bernardis  Antonio Salvi 《Astrophysics and Space Science》1989,152(1):29-34

We used theIRAS All Sky Maps in order to search for infrared emission in the direction of the Okroy Cloud (R.A.=12^h50^m, =22°). An enhancement of 100 m diffuse emission is evident in such a region, with an anomalous value of the ratioI _v (100 m)/A _v ; hydrogen 21 cm emission is also present with low radial speed, thus suggesting that the cloud could be a satellite of our Galaxy.  相似文献   

High‐resolution mapping of Manawatu palaeochannels          下载免费PDF全文

Giulia Lo Re  Ian C. Fuller  Giulia Sofia  Paolo Tarolli 《New Zealand geographer》2018,74(2):77-91

New remote sensing techniques, such as airborne laser scanning (LiDAR), have led to a dramatic increase in terrain information, providing new opportunities for landform analysis. A major advance in using LiDAR‐derived high‐resolution topography (HRT) is the capability to provide an accurate and detailed terrain morphology. This study aims to use LiDAR HRT to identify palaeochannels of the Manawatu River (New Zealand) using an automated procedure based on the statistical analysis of landform curvature. The approach can provide rapid assessment and classification of floodplain topography. The proposed analysis is crucial, especially for intensively used floodplains requiring effective flood management and mitigation.  相似文献   

Dynamics of snow ablation in a small Alpine catchment observed by repeated terrestrial laser scans     

Luca Egli  Tobias Jonas  Thomas Grünewald  Michael Schirmer  Paolo Burlando 《水文研究》2012,26(10):1574-1585

The spatio‐temporal distribution of snow in a catchment during ablation reflects changes in the total amount of snow water equivalent and is thus a key parameter for the estimation of melt water run‐off. This study explores possible rules behind the spatial variability of snow depth during the ablation season in a small Alpine catchment with complex topography. The snow depth observations are based on more than 160 000 terrestrial laser scanner data points with a spatial resolution of 1 m, which were obtained from 11 scanning campaigns of two consecutive ablation seasons. The analysis suggests that for estimating cumulative snow melt dynamics from the catchment investigated, assessing the initial snow distribution prior to the melt season is more important than addressing spatial differences in the melt behaviour. Snow volume and snow‐covered area could be predicted well using a conceptual melt model assuming spatially uniform melt rates. However, accurate results were only obtained if the model was initialized with a pre‐melt snow distribution that reflected measured mean and standard deviation. Using stratified melt rates on the other hand did not improve the model results. At least for sites with similar meteorological and topographical conditions, the model approach presented here comprises an efficient way to estimate snow depletion dynamics, especially if persistent snow accumulation pattern between years facilitate the characterization of the initial snow distribution prior to the melt. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Possible impact of climate change on the occurrence and the epidemic development of cercospora leaf spot disease (Cercospora beticola sacc.) in sugar beets for Rhineland-Palatinate and the southern part of Hesse     

Pascal Kremer  Jan Schlüter  Paolo Racca  Hans-Joachim Fuchs  Christian Lang 《Climatic change》2016,135(3-4):481-491

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Raman spectroscopy of CaCoSi2O6–Co2Si2O6 clinopyroxenes     

Luciana Mantovani  Mario Tribaudino  Irene Aliatis  Erica Lambruschi  Pier Paolo Lottici  Danilo Bersani 《Physics and Chemistry of Minerals》2015,42(3):179-189

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Prelude     

Yongkang Xue  Paolo M. Ruti 《Climate Dynamics》2010,35(1):1-2

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Coexistence of fault‐propagation and fault‐bend folding in curve‐shaped foreland fold‐and‐thrust belts: examples from the Northern Apennines (Italy)     

Fernando Calamita  Paolo Pace  Sara Satolli 《地学学报》2012,24(5):396-406

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Detection of Miocene saucer‐shaped sills (offshore Senegal) via integrated interpretation of seismic,magnetic and gravity data     

Sergio Rocchi  Alfredo Mazzotti  Michele Marroni  Luca Pandolfi  Paolo Costantini  Bertozzi Giuseppe  Davide di Biase  Francesco Federici  Papa Goumbo L 《地学学报》2007,19(4):232-239

The Atlantic margin offshore Senegal has been explored by seismic reflection and GRAV‐MAG surveys. High‐amplitude, laterally transgressive seismic reflectors are found to coincide with gravimetric and magnetic highs. Once seismic data are integrated with potential fields modelling, these reflectors can be safely interpreted as saucer‐shaped igneous sills, up to some hundreds of metres thick, some km wide. The occurrence of hydrothermal vent complexes and forced folds in the stratigraphic sequence above the sills constrain the intrusion age to the Miocene. Field observations and in‐situ magnetic susceptibility measurements of Oligocene–Miocene and Quaternary igneous rocks emplaced in coastal Senegal support this interpretation.  相似文献