排序方式： 共有31条查询结果，搜索用时 31 毫秒
21.
Luca Cenci Leonardo Disperati Maria Giuseppina Persichillo Eduardo R Oliveira Fátima L Alves Michael Phillips 《地理信息系统科学与遥感》2018,55(3):355-375
The precise delineation of coastal areas subject to past, present, and future erosive processes plays a fundamental role in coastal risk management. Within this framework, satellite data represent a valuable synoptic and multi-temporal information source. Therefore, this research integrated remote sensing and GIS techniques for mapping and modeling shoreline evolution through time. Long-term shoreline’s proxy rates of advance and retreat were determined using Landsat data from the mid-1980s to 2011 and subsequently, a short-term scenario (3 years) was predicted and validated. Two different coastal environments, Oceanic and Mediterranean, were investigated. In the first, different proxies were analyzed, thereby enabling a multi-proxy analysis. Findings showed that the method provided more accurate results in higher energy environments (Oceanic) and where the coastline is not urbanized. Results also highlighted the importance of performing multi-proxy analyses in given study areas, to more reliably define shoreline modeling. Importantly, during the analyses, particular attention was given to assessing uncertainty, which is crucial when outcomes of scientific research are considered for management. 相似文献
22.
23.
24.
Giuseppina Micela 《Experimental Astronomy》2015,40(2-3):723-732
Stellar activity is the major astrophysical limiting factor for the study of planetary atmospheres. Its variability and spectral characteristics may affect the extraction of the planetary signal even for moderately active stars. A technique based on spectral change in the visible band was developed to estimate the effects in the infrared due to star activity. This method has been purposely developed for the EChO mission which had the crucial characteristics of monitoring simultaneously a broadband from visible to infrared. Thanks to this capability the optical spectrum, whose variations are mainly due to stellar activity, has been used as in an instantaneous calibrator to correct the infrared spectrum. The technique is based on principal component analysis which significantly reduces the dimensionality of the spectra. The method was tested on a set of simulations with realistic photon noise. It can be generalized to any chromatic variability effects provided that optical and infrared variations are correlated. 相似文献
25.
Maria Boni Rosario Terracciano Giuseppina Balassone Sarah A. Gleeson Alexander Matthews 《Mineralium Deposita》2011,46(7):707-729
Zambian willemite (Zn2SiO4) deposits occur in the metasedimentary carbonate rocks of the Proterozoic Katangan Supergroup. The most important orebodies
are located around Kabwe and contain both sulphides and willemite in dolomites of low metamorphic grade. The Star Zinc and
Excelsior prospects (Lusaka area), discovered in the early 1920s, occur in the metamorphic lithotypes of the late Proterozoic
Zambezi Supracrustal sequence, which were deposited in a transtensional basin formed during the oblique collision of the Kalahari
and Congo cratons. The deposits are hosted by the limestone and dolomitic marbles of the Cheta and Lusaka Formations. Structural
analysis indicates that several fracture sets host the deposits, which may be genetically related to the Pan-African Mwembeshi
dislocation zone (a major geotectonic boundary between the Lufilian Arc and the Zambezi Belt). In both prospects, willemite
replaces the marbles and is found along joints and fissures with open-space filling textures and locally may develop colloform
and vuggy fabrics as well. Silver as well as traces of germanium and cadmium have been detected within the willemite ore,
and lead or zinc sulphides are scarce or absent. Calcite locally replaces willemite. Willemite is associated with specular
hematite and franklinite and post-dates the Zn-spinel gahnite in the paragenesis. Genthelvite [Zn4Be3(SiO4)3S] occurs as a minor phase in irregular aggregates. The willemites from the Lusaka area, though Mn-poor, show green cathodoluminescence
colours and bright green fluorescence in short-wave UV (as the high-temperature willemites in USA). Thermometric analyses
of primary fluid inclusions in willemite yield homogenization temperatures that range from 160°C to 240°C and salinities of
8–16 wt.% equiv. NaCl. The homogenization temperatures suggest a hypogene–hydrothermal origin for the willemite concentrations.
The geochemistry of fluid inclusion leachates suggests that the hydrothermal fluids were brines derived from highly evaporated
seawater. Precise age constraints are currently lacking for the Lusaka area deposits, though the deposits are not deformed,
indicating that they post-date the Lufilian orogeny (~520 Ma). The possibility of precursor ores exists; the gahnite–franklinite–willemite
deposits could have been derived from a metamorphosed primary sulphide (or even nonsulphide) concentration that has subsequently
been completely destroyed. However, there is no real evidence of such a primary source for the willemite mineral association.
The Lusaka zinc ores may have been produced by an extensive hydrothermal system, with fluids discharging along basinal fracture
zones controlled by the pre-Pan-African rifting stage. A paragenesis similar to that of the Lusaka prospects has been proposed
to be a vector towards massive sulphide ores in several parts of the world; therefore, it is possible that these small willemite
showings in Zambia may be part of a much bigger, and still unexplored, zinc province. 相似文献
26.
It is shown that Kantowski–Sachs cosmological models do not exist in Rosen's (1973) bimetric theory of gravitation when the
source of gravitation is either perfect fluid or cosmic string. Hence, the vacuum model is constructed. 相似文献
27.
28.
29.
H. Albert Gilg Maria Boni Giuseppina Balassone Cameron R. Allen David Banks Farid Moore 《Mineralium Deposita》2006,41(1):1-16
The Angouran Zn-(Pb–Ag) deposit, Zanjan Province, NW Iran, is located within the central Sanandaj-Sirjan Zone of the Zagros orogenic belt. The deposit has proven and estimated resources of 4.7 Mt of sulfide ore at 27.7% Zn, 2.4% Pb, and 110 g/t Ag, and 14.6 Mt of oxidized carbonate ores at 22% Zn and 4.6% Pb. It is hosted by a metamorphic core complex that is unconformably overlain by a Neogene volcanic and evaporite-bearing marine to continental sedimentary sequence. The sulfide orebody, precursor to the significant nonsulfide ores, is located at the crest of an open anticline at the contact between Neoproterozoic to Cambrian footwall micaschists and hanging wall marbles. 40Ar–39Ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid Mid-Miocene exhumation of the metamorphic basement (∼20 Ma) and yield an upper age constraint for mineralization. The fine-grained sulfide ore is massive, replacive, often brecciated, clearly postmetamorphic and dominated by Fe-poor sphalerite, with minor galena, pyrite, anhydrite, quartz, muscovite, dolomite, and rare calcite. Sphalerite contains Na–Ca–Cl brine inclusions (23–25 mass% total dissolved solids) with homogenization temperatures of 180–70°C. Fluid inclusion chemistry (Na–K–Li–Ca–Mg–Cl–Br), ore geochemistry, S, and Pb isotope data suggest that the Angouran sulfide ore formed by the interaction of modified, strongly evaporated Miocene seawater and the lithotypes of an exhumed metamorphic core complex. Minor contributions of metals from Miocene igneous rocks cannot be excluded. Mineralization occurred in a collisional intra-arc setting with high heat flow, probably during the transition from an extensional to a compressional regime. The Angouran deposit may represent a new type of low-temperature carbonate-hosted Zn–Pb ore that is distinct from Mississippi Valley type and sedimentary-exhalative deposits.Editorial handling: B. Lehmann 相似文献
30.
Giuseppina Nigro 《地球物理与天体物理流体动力学》2013,107(1-2):101-113
This article addresses the interesting and important problem of large-scale magnetic field generation in turbulent flows, using a self-consistent dynamo model recently developed. The main idea of this model is to consider the induction equation for the large-scale magnetic field, integrated consistently with the turbulent dynamics at smaller scales described by a magnetohydrodynamic shell model. The questions of dynamo action threshold, magnetic field saturation, magnetic field reversals, nature of the dynamo transition and the changes of small-scale turbulence as a consequence of the dynamo onset are discussed. In particular, the stability curve obtained by the model integration is shown in a very wide range of values of the magnetic Prandtl number not yet accessible by direct numerical simulation but more realistic for natural dynamos. Moreover, from our analysis it is shown that the large-scale dynamo transition displays a hysteretic behaviour and therefore a subcritical nature. The model successfully reproduces magnetic polarity reversals, showing the capability to generate persistence times which are increasing for decreasing magnetic diffusivity. Moreover, when the system reaches a statistically stationary dynamo state, where the large-scale magnetic field can abruptly reverse its polarity (magnetic reversal state) or not, keeping the same polarity (steady state), it shows an unmistakable tendency towards the energy equipartition for the turbulence at small scale. 相似文献