排序方式： 共有41条查询结果，搜索用时 31 毫秒
21.
R. Ragazzoni M. Tordi E. Diolaiti D. Kirkman 《Monthly notices of the Royal Astronomical Society》2001,327(3):949-954
An innovative concept of wavefront sensing for Rayleigh beacons is introduced along with an example of a possible wavefront sensor. This new approach does not require the gating technique to limit the useful range of the laser source and therefore looks simpler to implement than previous Rayleigh concepts, and may additionally allow more efficient use of the photons emitted by the Rayleigh beacon. Our technique is based upon an optical element in the focal plane area whose section does not change for the conjugation of different ranges from the telescope aperture, hence the name z -invariant. The wavefront sensor shown here is an example of this new class. It is a compact pupil-plane wavefront sensor and as such allows for a layer-oriented configuration. It is shown that its sensitivity, while higher than usual gating approaches, is far from the possible limits leading us to speculate that other z -invariant wavefront sensors can reach much larger efficiencies. 相似文献
22.
The Cengio sandstone member of the Tertiary Piedmont Basin in northwestern Italy has a conservatively estimated volume of
2.5 to 3 km3 (length: 6.4 km; width: 4.8 km; thickness: 170 m). It is interpreted as a sandstone-rich submarine fan deposit. The Cengio
member consists of eight tabular depositional sandstone lobes that are 5- to 25-m thick. These lobes filled a submarine structural
depression and onlap and/or pinch-out against bounding slope mudstones. The stacking of the lobe units was related to synsedimentary
tectonism.
Margin setting represents fan and/or source area 相似文献
23.
Cristiana Guerranti Stefania Ancora Nicola Bianchi Guido Perra Emiliano Leonida Fanello Simonetta Corsolini Maria Cristina Fossi Silvano Ettore Focardi 《Marine pollution bulletin》2013
Perfluorinated compounds (PFCs), widely used for their hydro-oil repellent properties, are almost non-degradable in the environment; there is scientific evidence that indicate bioaccumulation. They represent a threat to many organisms, because they are toxic and are endocrine disruptors. Scientific studies have demonstrated the presence of PFCs in blood and liver samples of fish, turtles, birds and mammals of marine ecosystems in different geographical areas. The aim of this study was to determine the distribution of PFOS and PFOA in blood samples of the marine turtle Caretta caretta, using a minimally invasive sampling procedure. 49 blood samples of marine turtle, taken from several Italian marine turtle rescue centers, were analyzed. While PFOA was never detected, measurable concentrations of PFOS were found in 15 blood samples; the values show a range from 1.14 ng/g to 28.51 ng/g (wet wt.). No differences between groups of samples taken from different areas were found. 相似文献
24.
Ubiquity of Endocrine Disruptors Nonylphenol and Its Mono‐ and Di‐Ethoxylates in Freshwater,Sediments, and Biosolids Associated with High and Low Density Populations of Buenos Aires,Argentina 
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下载免费PDF全文 25.
Dale P. Cruikshank Joshua P. Emery Katherine A. Kornei Emiliano d’Aversa 《Icarus》2010,205(2):516-527
We obtained time-resolved, near-infrared spectra of Io during the 60-90 min following its reappearance from eclipse by Jupiter on five occasions in 2004. The purpose was to search for spectral changes, particularly in the well-known SO2 frost absorption bands, that would indicate surface-atmosphere exchange of gaseous SO2 induced by temperature changes during eclipse. These observations were a follow-on to eclipse spectroscopy observations in which Bellucci et al. [Bellucci et al., 2004. Icarus 172, 141-148] reported significant changes in the strengths of two strong SO2 bands in data acquired with the VIMS instrument aboard the Cassini spacecraft. One of the bands (4.07 μm [ν1 + ν3]) observed by Bellucci et al. is visible from ground-based observatories and is included in our data. We detected no changes in Io’s spectrum at any of the five observed events during the approximately 60-90 min during which spectra were obtained following Io’s emergence from Jupiter’s shadow. The areas of the three strongest SO2 bands in the region 3.5-4.15 μm were measured for each spectrum; the variation of the band areas with time does not exceed that which can be explained by the Io’s few degrees of axial rotation during the intervals of observation, and in no case does the change in band strength approach that seen in the Cassini VIMS data. Our data are of sufficient quality and resolution to show the weak 2.198 μm (4549.6 cm−1) 4ν1 band of SO2 frost on Io for what we believe is the first time. At one of the events (June 22, 2004), we began the acquisition of spectra ∼6 min before Io reappeared from Jupiter’s shadow, during which time it was detected through its own thermal emission. No SO2 bands were superimposed on the purely thermal spectrum on this occasion, suggesting that the upper limit to condensed SO2 in the vertical column above Io’s surface was ∼4 × 10−5 g cm−2. 相似文献
26.
A. Maria del Rosario Prieto B. Ricardo García-Herrera Emiliano Hernández Martin 《Climatic change》2004,66(1-2):29-48
The use of documentary sources has proven useful to identify extremeclimatic events and their variability during the pre-instrumental period. Theaim of this paper is to describe iceberg sightings in the Western SouthAtlantic during the second half of the 18th century, as recorded from Spanishlogbooks. A total of five sightings have been found, two corresponding toisolated bergs and three to outbreaks. The relevance of these results istwofold: they are the first documented iceberg sightings to date and, aboveall, they correspond to very unusual episodes, characterized by a high numberof high-sized bergs and by the relatively low latitude of their location. Itis suggested that they could be associated to cold episodes in Antarctica. 相似文献
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28.
Federica Donda Edy Forlin Emiliano Gordini Giuliana Panieri Stefan Buenz Valentina Volpi Dario Civile Laura De Santis 《Basin Research》2015,27(4):531-545
In the Northern Adriatic Sea, the occurrence of gas seepage and of unique rock outcrops has been widely documented. The genesis of these deposits has recently been ascribed to gas venting, leading to their classification as methane‐derived carbonates. However, the origin of seeping gas was not clearly constrained. Geophysical data collected in 2009 reveal that the gas‐enriched fluid vents are deeply rooted. In fact, the entire Plio‐Quaternary succession is characterized by widespread seismic anomalies represented by wipe‐out zones, and interpreted as gas chimneys. They commonly root at the base of the Pliocene sequence but also within the Palaeogene succession, where they appear to be associated to deep‐seated faults. We suggest that there is a structural control on chimney distribution. Chimneys originate and terminate at different stratigraphic levels; commonly they reach the seafloor, where authigenic carbonate deposits form locally. Gas analyses of some gas bubble streams just above the rock outcrops reveal that gas is composed mainly of methane. Geochemical analyses performed at four selected outcrop sites show that these deposits formed as a consequence of active gas venting. In particular, geochemical analyses indicate carbonate precipitation from microbial oxidation of methane‐rich fluids, although a straightforward correlation with the source depth of gas feeding the authigenic carbonates cannot yet be clearly defined. 相似文献
29.
Miriam Baglioni Emiliano Giovannetti Maria Vittoria Masserotti Chiara Renso Laura Spinsanti 《Transactions in GIS》2008,12(Z1):31-44
Querying geographical information systems has been recognized as a difficult task for non‐expert users. Furthermore, user queries are often characterized by semantic aspects not directly managed by traditional spatial databases or GIS. Examples of such semantic geospatial queries are the use of implicit spatial relations between objects, or the reference of domain concepts not explicitly represented in data. To handle such queries, we envisage a system that translates natural language queries into spatial SQL statements on a database, thus improving standard GIS with new semantic capabilities. Within this general objective, the contribution of this article is to introduce a methodology to handle semantic geospatial queries issued over a spatial database. This approach captures semantics from an ontology built upon the spatial database and enriched by domain concepts and properties specifically defined to represent the localization of objects. Some examples of the use of the methodology in the urban domain are presented. 相似文献
30.
Amplitude dependence of equivalent modal parameters in monitored buildings during earthquake swarms 下载免费PDF全文
下载免费PDF全文 Rosario Ceravolo Emiliano Matta Antonino Quattrone Luca Zanotti Fragonara 《地震工程与结构动力学》2017,46(14):2399-2417
This paper investigates the dynamic response of three sample buildings belonging to the Seismic Observatory for Structures, the Italian network for the permanent seismic monitoring of strategic structures, managed by the Italian Department of Civil Protection. The case studies cover different building types that could loosely represent the Italian building stock, with a special emphasis on cultural heritage and masonry structures. Observed under a low‐intensity seismic swarm comprising about 30 aftershocks after a main event, the three buildings are analysed through an input–output, model‐driven linear dynamic identification procedure, depicting the relation between the shaking level at the site and the variation of the equivalent structural modal parameters, while keeping into account the effects of soil–structure interaction. Finite element models will be used to investigate one of the case studies and to compare the law of variation of the structural modal parameters with respect to simplified models proposed by technical standards. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献