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31.
Elisabetta?Brizi Sabrina?NazzareniEmail author Francesco?Princivalle Pier?Francesco?Zanazzi 《Contributions to Mineralogy and Petrology》2003,145(5):578-584
Optically homogeneous augite xenocrysts, closely associated with spinel–peridotite nodules, occur in alkali basalts from Hannuoba (Hebei province, China). They were studied by electron and X-ray diffraction to define the occurrence and significance of pigeonite exsolution microtextures. Sub-calcic augite (Wo34) exsolved into En62–62Fs25–21Wo13–17 pigeonite and En46–45Fs14–14Wo40–42 augite, as revealed by TEM through diffuse coarser (001) lamellae (100–300 Å) and only incipient (100) thinner ones (<70 Å). C2/c augite and P21/c pigeonite lattices, measured by CCD-XRD, relate through a(Aug)?a(Pgt), b(Aug)?b(Pgt), c(Aug)≠c(Pgt) [5.278(1) vs 5.189(1)Å] and β(Aug)≠β(Pgt) [106.55(1) vs 108.55(2)°]. Cell and site volumes strongly support the hypothesis that the augite xenocrysts crystallised at mantle depth from alkaline melts. After the augite xenocrysts entered the magma, (001) lamellae first formed by spinodal decomposition at a Tmin of about 1,100 °C, and coarsened during very rapid transport to the surface; in a later phase, possibly on cooling, incipient (100) lamellae then formed. 相似文献
32.
Warmuth Alexander Hanslmeier Arnold Messerotti Mauro Cacciani Alessandro Moretti Pier Francesco Otruba Wolfgang 《Solar physics》2000,194(1):103-120
NOAA 8210 has been a region showing a remarkable level of activity well before solar maximum. Dominated by a large, rapidly rotating spot, it produced several intense flares during its disk passage at the end of April–beginning of May 1998. We examine the development of AR 8210 in H and white light (WL) and study the evolution of its complex magnetic topology. While the other principal flares are briefly reviewed, the great X1.1/3B flare of 2 May, which was observed at Kanzelhöhe Solar Observatory during a SOHO/UVCS ground support campaign, is studied in detail. This event has been documented in full-disk H and Na-D intensitygrams, Dopplergrams, and magnetograms, with a time cadence of one minute each. The flare was associated with a CME and produced significant geomagnetic effects. Furthermore, we point out the perspectives for our planned Flare Monitoring and Alerting System, since the two new instruments (Magneto-Optical Filter and Digital H camera), which made their first operational run with the campaign, are crucial components for this program. 相似文献
33.
Ernesto Bonomi Leesa M. Brieger Luca Cazzola Francesco Zanoletti 《Geophysical Prospecting》2006,54(5):505-514
Prestack wave‐equation migration has proved to be a very accurate shot‐by‐shot imaging tool. However, 3D imaging with this technique of a large field acquisition, especially one with hundreds of thousands of shots, is prohibitively costly. Simply adapting the technique to migrate many superposed shot‐gathers simultaneously would render 3D wavefield prestack migration cost‐effective but it introduces uncontrolled non‐physical interference among the shot‐gathers, making the final image useless. However, it has been observed that multishot signal interference can be kept under some control by averaging over many such images, if each multishot migration is modified by a random phase encoding of the frequency spectra of the seismic traces. In this article, we analyse this technique, giving a theoretical basis for its observed behaviour: that the error of the image produced by averaging over M phase encoded migrations decreases as M?1 . Furthermore, we expand the technique and define a general class of Monte‐Carlo encoding methods for which the noise variance of the average imaging condition decreases as M?1 ; these methods thus all converge asymptotically to the correct reflectivity map, without generating prohibitive costs. The theoretical asymptotic behaviour is illustrated for three such methods on a 2D test case. Numerical verification in 3D is then presented for one such method implemented with a 3D PSPI extrapolation kernel for two test cases: the SEG–EAGE salt model and a real test constructed from field data. 相似文献
34.
The present study focused on detecting variations in trophic relationships among blue crab (Callinectes sapidus) consumers according to water quality along two estuaries in North Carolina. Stable isotope (δ15N and δ13C) analyses of particulate organic matter and bivalve(Rangia cuneata andCorbicula fluminea) food sources were examined in combination with an Isosource mixing model. Results suggest that blue crab δ13C values increased significantly with increasing salinity from upper to lower sites along the Neuse River estuary (NRE; R2
= 0.87, p < 0.01) and Alligator River estuary (R2 = 0.92, p < 0.01). There was a positive relationship between blue crab δ15N values and nitrate concentrations for the NRE (R2 = 0.48, p = 0.12). This study found that blue crab δ13C values increased with salinity from upper to lower regions along both estuaries. Results suggest that blue crab production
may have used alternative food sources that were isotopically (δ13C) depleted, especially in the upper NRE, and enriched sources in the mid to lower regions of both estuaries. Consumers sampled
from the upper NRE may be influenced by higher nitrogen input from urban land use and municipal wastewater. 相似文献
35.
Vít Kárník Dana Procházková Zdeňka Schenková Julius Drimmel Dieter Mayer-Rosa Dragutin Cvijanovic Vladimir Kuk Andelka Miloševič Francesco Giorgetti Reviewer J. Janský 《Studia Geophysica et Geodaetica》1978,22(4):411-414
Summary Isoseismal maps of the three strongest Friuli aftershocks of September 1976 were compiled using the contributions from European countries within the shaken area. The characteristic features of the macroseismic fields are discussed. 相似文献
36.
A structural and geophysical approach to the study of fractured aquifers in the Scansano-Magliano in Toscana Ridge, southern Tuscany, Italy 总被引:1,自引:0,他引:1
Roberto Francese Francesco Mazzarini Andrea Bistacchi Gianfranco Morelli Giorgio Pasquarè Nicola Praticelli Henry Robain Nigel Wardell Annalisa Zaja 《Hydrogeology Journal》2009,17(5):1233-1246
Fresh water availability has recently become a serious concern in the Italian Apennines, as various activities rely on a predictable supply. Along the ridge between Scansano and Magliano in Toscana, in southern Tuscany, the situation is further complicated by contamination of the nearby alluvial aquifers. Aquifers locally consist of thin fractured reservoirs, generally within low-permeability formations, and it can be difficult to plan the exploitation of resources based on conventional techniques. An integrated study based on geological data investigated the link between tectonics and groundwater circulation, to better define the hydrological model. After the regional identification of fault and fracture patterns, a major structure was investigated in detail to accurately map its spatial position and to understand the geometry and properties of the associated aquifer and assess its exploitation potential. The subsurface around the fault zone was clearly imaged using ground probing radar, two-dimensional and three-dimensional resistivity tomography, and three-dimensional shallow seismic surveys. The vertical and horizontal contacts between the different geological units of the Ligurian and Tuscan series were resolved with a high degree of spatial accuracy. Three-dimensional high-resolution geophysical imaging proved to be a very effective means of characterising small-scale fractured reservoirs. 相似文献
37.
Valerio Iafolla David M. Lucchesi Sergio Nozzoli Francesco Santoli 《Celestial Mechanics and Dynamical Astronomy》2007,97(3):165-187
We have estimated a preliminary error budget for the Italian Spring Accelerometer (ISA) that will be allocated onboard the
Mercury Planetary Orbiter (MPO) of the European Space Agency (ESA) space mission to Mercury named BepiColombo. The role of
the accelerometer is to remove from the list of unknowns the non-gravitational accelerations that perturb the gravitational
trajectory followed by the MPO in the strong radiation environment that characterises the orbit of Mercury around the Sun.
Such a role is of fundamental importance in the context of the very ambitious goals of the Radio Science Experiments (RSE)
of the BepiColombo mission. We have subdivided the errors on the accelerometer measurements into two main families: (i) the
pseudo-sinusoidal errors and (ii) the random errors. The former are characterised by a periodic behaviour with the frequency
of the satellite mean anomaly and its higher order harmonic components, i.e., they are deterministic errors. The latter are
characterised by an unknown frequency distribution and we assumed for them a noise-like spectrum, i.e., they are stochastic
errors. Among the pseudo-sinusoidal errors, the main contribution is due to the effects of the gravity gradients and the inertial forces, while among the random-like errors the main disturbing effect is due to the MPO centre-of-mass displacements produced by the onboard High Gain Antenna (HGA) movements and by the fuel consumption and sloshing. Very subtle to be considered
are also the random errors produced by the MPO attitude corrections necessary to guarantee the nadir pointing of the spacecraft.
We have therefore formulated the ISA error budget and the requirements for the satellite in order to guarantee an orbit reconstruction
for the MPO spacecraft with an along-track accuracy of about 1 m over the orbital period of the satellite around Mercury in
such a way to satisfy the RSE requirements. 相似文献
38.
Enrico Costa Ronaldo Bellazzini Gianpiero Tagliaferri Giorgio Matt Andrea Argan Primo Attinà Luca Baldini Stefano Basso Alessandro Brez Oberto Citterio Sergio Di Cosimo Vincenzo Cotroneo Sergio Fabiani Marco Feroci Antonella Ferri Luca Latronico Francesco Lazzarotto Massimo Minuti Ennio Morelli Fabio Muleri Lucio Nicolini Giovanni Pareschi Giuseppe Di Persio Michele Pinchera Massimiliano Razzano Luigia Reboa Alda Rubini Antonio Maria Salonico Carmelo Sgro’ Paolo Soffitta Gloria Spandre Daniele Spiga Alessio Trois 《Experimental Astronomy》2010,28(2-3):137-183
Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. Polarization from celestial X-ray sources may derive from emission mechanisms themselves such as cyclotron, synchrotron and non-thermal bremsstrahlung, from scattering in aspheric accreting plasmas, such as disks, blobs and columns and from the presence of extreme magnetic field by means of vacuum polarization and birefringence. Matter in strong gravity fields and Quantum Gravity effects can be studied by X-ray polarimetry, too. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. The heart of the detector is an Application-Specific Integrated Circuit (ASIC) chip with 105,600 pixels each one containing a full complete electronic chain to image the track produced by the photoelectron. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. A filter wheel hosting calibration sources unpolarized and polarized is dedicated to each detector for periodic on-ground and in-flight calibration. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 × 15 arcmin and with an energy resolution of 20% at 6 keV. The Minimum Detectable Polarization is 12% for a source having a flux of 1 mCrab and 105 s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher. The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75% open to the community while 25% + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument. A nice to have idea is to use the same existing mandrels to build two additional telescopes of iridium with carbon coating plus two more detectors. The effective area in this case would be almost doubled. 相似文献
39.
Francesco Di Benedetto Francesco D’Acapito Gabriele Fornaciai Massimo Innocenti Giordano Montegrossi Luca A. Pardi Silvia Tesi Maurizio Romanelli 《Physics and Chemistry of Minerals》2010,37(5):283-289
An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of α-quartz, SiO2) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112 eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe2+ is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell: = 1.78(2) Å, the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe3+ variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4+ or 3+. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe4+ is stabilised by the favourable local structural arrangement. 相似文献
40.
In recent years, debris flows have represented a severe natural hazard in South-Gargano watersheds (Puglia Region, Southern Italy). Hill slopes erosion, caused by the inadequate protection of the degraded forests, produces large amounts of soil and debris that are conveyed downstream during heavy rainstorms. The involved material is characterized by limestone fragments and blocks in a sandy-silt matrix. In this paper, the rheological properties of such debris-flow materials have been investigated. Eight specimens of particulated sediments of particle diameter of d ≤ 4 mm have been analysed using a rheometric tool for large particle suspensions, the ball measuring system (BMS). The influence of sediment concentration on the bulk rheological behaviour has been evaluated at concentrations by volume obtained in fully water-saturated conditions (volumetric sediment concentration C V ~ 0.8) and with fixed water content (C V = 0.42). The rheological data were fitted to the Bingham, Herschel–Bulkley, and O’Brien and Julien models to define viscosity and yield stress dependency on sediment concentration, to provide viscosity information for hazard mitigation as well as for comparison to other debris-flow events. 相似文献