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171.
172.
Andrea Cortis Carlos E. Puente Huai-Hsien Huang Mahesh L. Maskey Bellie Sivakumar Nelson Obregón 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(6):1421-1429
In this study, we attempt to offer a solid physical basis for the deterministic fractal–multifractal (FM) approach in geophysics (Puente, Phys Let A 161:441–447, 1992; J Hydrol 187:65–80, 1996). We show how the geometric construction of derived measures, as Platonic projections of fractal interpolating functions transforming multinomial multifractal measures, naturally defines a non-trivial cascade process that may be interpreted as a particular realization of a random multiplicative cascade. In such a light, we argue that the FM approach is as “physical” as any other phenomenological approach based on Richardson’s eddies splitting, which indeed lead to well-accepted models of the intermittencies of nature, as it happens, for instance, when rainfall is interpreted as a quasi-passive tracer in a turbulent flow. Although neither a fractal interpolating function nor the specific multipliers of a random multiplicative cascade can be measured physically, we show how a fractal transformation “cuts through” plausible scenarios to produce a suitable realization that reflects specific arrangements of energies (masses) as seen in nature. This explains why the FM approach properly captures the spectrum of singularities and other statistical features of given data sets. As the FM approach faithfully encodes data sets with compression ratios typically exceeding 100:1, such a property further enhances its “physical simplicity.” We also provide a connection between the FM approach and advection–diffusion processes. 相似文献
173.
Andrea Penna Paolo Morandi Maria Rota Carlo Filippo Manzini Francesca da Porto Guido Magenes 《Bulletin of Earthquake Engineering》2014,12(5):2255-2273
The earthquake sequence started on May \(20\) th 2012 in Emilia (Italy) affected a region where masonry constructions represent a large part of the existing building stock and the construction of new modern masonry buildings is a common practice. The paper is focused on the performance of common architectural configurations, typical for residential or business use. The large majority of old masonry buildings is made of fired clay bricks. The seismic performance of these buildings is particularly interesting since major past earthquakes in Italy affected areas with mainly stone masonry structures. Apart from examples showing systematic or peculiar structural deficiencies governing the vulnerability of several buildings, the overall seismic performance of these structures to repeated shaking, with PGA as large as 0.25–0.3 g was rather good, despite the major part of them were only conceived for carrying vertical loads. In fact, seismic design is mandatory in the area only since 2003. Modern low-rise masonry buildings erected after this date and incorporating seismic design and proper detailing resulted in most cases practically undamaged. The examples reported in the paper allow an evaluation of the superior performance of seismically designed modern masonry buildings in comparison to older ones. 相似文献
174.
Gaetano Manfredi Andrea Prota Gerardo Mario Verderame Flavia De Luca Paolo Ricci 《Bulletin of Earthquake Engineering》2014,12(5):2275-2298
Data of the Italian National Institute of Statistics are collected aimed at characterizing Reinforced Concrete (RC) building stock of the area struck by the 2012 Emilia earthquake (number of storeys, age of construction, structural typology). Damage observations, collected right after the event in reconnaissance reports, are shown and analyzed emphasizing typical weaknesses of RC buildings in the area. The evolution of seismic classification for Emilia region and RC buildings’ main characteristics represent the input data for the assessment of non-structural damage of infilled RC buildings, through a simplified approach (FAST method), based on EMS-98 damage scale. Peak Ground Acceleration (PGA) capacities for the first three damage states of EMS-98 are compared with registered PGA in the epicentral area. Observed damage and damage states evaluated for the PGA of the event, in the epicentral area, are finally compared. The comparison led to a fair agreement between observed and numerical data. 相似文献
175.
In the western part of the city of Zagreb, Croatia, hydrogeochemical and isotopic investigations of the Samobor aquifer were
carried out with the aim of determining the differences in hydrogeochemical characteristics at increasing aquifer depths.
The aquifer comprises 40-m thick gravelly–sandy deposits, with lenses and interlayers of silt and clay. The analyses have
proven that with increasing aquifer depth, there are decreases in groundwater temperature and the values of electrical conductivity
and increases in the sodium, iron and manganese concentrations. The δ13C distribution shows an evident increase in biogenic carbon concentrations with increasing aquifer depth. The measured specific
14C activities showed that the deeper part of the aquifer is characterized by slow water exchange, while the shallower part
is influenced by current recharge, although the pumping wells located on the well-field downstream penetrate the aquifer fully.
A direct exchange of water from the Sava River and groundwater occurs in the near vicinity of the river. This exchange weakens
further away, while the difference in hydrogeochemical characteristics between the Sava River water and groundwater increases. 相似文献
176.
The St. Louis site, located in the Plains–Parkland transition zone along the South Saskatchewan River, in Saskatchewan, Canada, is a multiple‐component site consisting of stratified floodplain alluvium with multiple, weakly developed soils. Human occupation at the site spans the Late Paleoindian to Middle Precontact periods (10,000–5,000 14C yr B.P.), a time poorly represented archaeologically on the Northern Plains. The dearth of early–middle Holocene‐age archaeological sites is often attributed to reduced inhabitability of the Northern Plains during the Hypsithermal, a period of maximum aridity and limited water availability. Stable isotope and phytolith data from the site indicate increased temperatures during the Hypsithermal and an expansion of Northern Plains grasslands into north‐central Saskatchewan. Although characterized by increased xeric conditions, human occupation at the St. Louis site, as well as the predominance of C3 grasses, attests to the habitability of Northern Plains river systems during this time period. © 2011 Wiley Periodicals, Inc. 相似文献
177.
Sandra Hochscheid Andrea Travaglini Fulvio Maffucci Graeme C. Hays Flegra Bentivegna 《Marine Ecology》2013,34(3):321-333
Understanding the role that consumers play in an ecosystem requires knowledge about food selection and intake rates. However, such basic data are often difficult to obtain, particularly for marine animals that are not easy to observe. To overcome this problem, a beak movement sensor was employed on a free‐ranging loggerhead turtle in a neritic foraging habitat at the Domitian littoral (SW Italy). In combination with gastrointestinal content analysis from six turtles found dead in the same area we sought to identify which beak movement patterns were associated with which prey type, and to quantify the ingestion of the various prey types. Brachyuran crabs (100% occurrence), in particular Liocarcinus vernalis, and small molluscs (66% occurrence) were found most frequently in the stomach and intestine of the turtles. Beak movements revealed average ingestion rates of (mean ± SE) 0.27 ± 0.13 food items per minute and that feeding occurred predominantly during dives >4 m and during early morning and evening. Interestingly, the time spent feeding amounted to only 2.2% of the total observation time, whereas feeding‐associated dives added up to just above 10% of the total time. We thus established that loggerhead turtles in this area are specialised on brachyuran crabs, on which they prey with high success during the short time dedicated to foraging. This information strengthens our knowledge about turtle–prey and turtle–habitat interactions, which are essential data to delineate the role that turtles play in this and similar marine ecosystems. Moreover, since the same area is also intensively used by the regional bottom trawl fishery, our results have important conservation implications, because they clearly show the time of day and water depths for which fishing activity should be regulated to reduce the number of turtles that are currently being incidentally caught in this area. 相似文献
178.
This paper addresses oil spill detection from remotely sensed optical images. In particular, it focuses on the automatic classification
of regions of interest (ROIs) in two classes, namely oil spills or look-alikes. Candidate regions and the corresponding boundaries
have been manually identified from full resolution Moderate Resolution Imaging Spectroradiometer images, related to the Mediterranean
Sea over the years 2008 and 2009. Then, a set of features has been extracted from each ROI, allowing to formulate the oil
spill detection problem as a two-class classification task on the provided regions (i.e. using a supervised learning strategy).
Since ROI classification is challenging, some desired characteristics for the classification algorithm are first identified,
such as accuracy, robustness, etc. Then, a solution (called SVME) is provided: it is based on an ensemble of incremental/decremental
cost-oriented Support Vector Machines, aggregated with the Receiving Operating Characteristic (ROC) convex hull method in
the ROC space. Such a solution addresses all the desired characteristics. Finally, the results obtained on the collected dataset
are shown. The importance of this study is the devising of a powerful classification technique that may have an impact on
optical oil spill detection from space, especially if fused with satellite synthetic aperture radar data. Moreover, it is
shown how the proposed system can be used as a decision support tool, to help a junior operator in making more reliable detections. 相似文献
179.
180.
A model problem of the flow under an air-cushion vessel is studied. Two different numerical techniques are used to determine the solution of the free-surface elevation and the wave resistance for a range of Froude number, Reynolds number, value of the pressure applied in the cushion, and depth of the water. The first numerical technique uses a velocity potential that satisfies linearized free-surface boundary conditions, whereas the second employs a finite-volume method to find a solution that satisfies the fully nonlinear free-surface boundary conditions. The results clearly show that for high Froude number and practical values of the cushion pressure, the linear-theory solution is in excellent agreement with the more exact nonlinear prediction. For lower Froude number the solution becomes unsteady, and the disagreement between the two methods is larger. 相似文献