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1.
Gianluca Loffredo Filippo Frontera Damiano Pellicciotta Alessandro Pisa Vito Carassiti Stefano Chiozzi Federico Evangelisti Luca Landi Michele Melchiorri Stefano Squerzanti 《Experimental Astronomy》2005,20(1-3):413-420
We will report on the current configuration of the X-ray facility of the University of Ferrara recently used to perform reflectivity tests of mosaic crystals and to calibrate the experiment JEM–X aboard Integral. The facility is now located in the technological campus of the University of Ferrara in a new building (named LARIX laboratory= ̳LARge ̳Italian ̳X-ray facility) that includes a tunnel 100 m long with, on the sides, two large experimental rooms. The facility is being improved for determining the optical axis of mosaic crystals in Laue configuration, for calibrating Laue lenses and hard X-ray mirror prototypes. 相似文献
2.
Ezio Caroli Natalia Auricchio Lorenzo Amati Yuriy Bezsmolnyy Carl Budtz-JøRgensen Rui M. Curado da Silva Filippo Frontera Alessandro Pisa Stefano Del Sordo John B. Stephen Giulio Ventura 《Experimental Astronomy》2005,20(1-3):341-351
The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1mm, an energy resolution of a few keV at 500keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy.
Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies. 相似文献
3.
Roberto F. Viotti Rosario González-Riestra Takashi Iijima Stefano Bernabei Riccardo Claudi Jochen Greiner Michael Friedjung Vito Francesco Polcaro Corinne Rossi 《Astrophysics and Space Science》2005,296(1-4):435-439
We review the main characteristics of the symbiotic system AG Draconis, with special emphasis on its optical and X-ray variations.
We also discuss the X-ray to visual energy distribution during quiescence and outburst and describe our spectroscopic and
X-ray observations during the 2003 outburst.
Based on X-ray observations collected with the XMM–Newton Observatory, on INES data from the IUE satellite, and on optical
spectra collected with the Asiago–Cima Ekar, Bologna–Loiano and La Palma–Galileo Italian telescopes. 相似文献
4.
5.
Fabio Fontanot Pierluigi Monaco Stefano Borgani 《Monthly notices of the Royal Astronomical Society》2003,341(2):692-706
We apply the ztrace algorithm to the optical NOG and infrared PSC z galaxy catalogues to reconstruct the pattern of primordial fluctuations that have generated our local Universe. We check that the density fields traced by the two catalogues are well correlated, and consistent with a linear relation [either in δ or in log (1 +δ) ] with relative bias (of NOG with respect to PSC z ) b rel = 1.1 ± 0.1 . The relative bias relation is used to fill the optical zone of avoidance at | b | < 20° using the PSC z galaxy density field.
We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber klim ≃ 0.4 h Mpc−1 beyond which all information is lost. We find that the improvement arising from the denser sampling of the optical catalogue is compensated by the uncertainties connected to the larger zone of avoidance.
The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSC z ) to be consistent with a Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe. 相似文献
We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber k
The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSC z ) to be consistent with a Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe. 相似文献
6.
7.
Stefano Poli 《Contributions to Mineralogy and Petrology》1991,106(4):399-416
The transition from feldspar amphibolite to eclogite is a very wide P-T field that extends from some-where close to 5 kbar where the garnet-amphibole pair starts to appear, to 10–20 kbar at albite-out reaction, then up to 25–30 kbar where an hydrated phase such as amphibole can be stable with pyroxene and garnet. Thus the assemblage garnet (py)+ amphibole (tr)+epidote (cz)±plagioclase (ab)±clinopyroxene (di)±quartz (qz)±fluid is commonly reported in a large number of metamorphic terrains. These mineral phases are complex solid-solutions which adapt to variations in environmental conditions mainly by means of continuous reactions. The reaction space, introduced by. Thompson in 1982a, provides a very elegant and powerful tool to approach these high-variance assemblages. The reactions:
相似文献
8.
Benthic fluxes of mercury species in a lagoon environment (Grado Lagoon,Northern Adriatic Sea,Italy)
Stefano Covelli Jadran Faganeli Cinzia De Vittor Sergio Predonzani Alessandro Acquavita Milena Horvat 《Applied Geochemistry》2008
The role of the major biogeochemical processes in Hg cycling at the sediment–water interface was investigated in the Grado Lagoon (Northern Adriatic Sea). This wetland system has been extensively contaminated from the Idrija Hg Mine (Slovenia) through the Isonzo River suspended load carried by tidal fluxes. Three approaches were used to study the sediment–water exchange of total Hg (THg), methylmercury (MeHg), reactive Hg (RHg) and dissolved gaseous Hg (DGHg): (1) estimation of diffusive fluxes from porewater and overlying water concentrations, (2) measurements of benthic fluxes using a deployed light benthic chamber in situ and (3) measurements of benthic fluxes during oxic–anoxic transition with a laboratory incubation experiment. The THg solid phase, ranging between 9.5 and 14.4 μg g−1, showed slight variability with depth and time. Conversely, MeHg contents were highest (up to 21.9 ng g−1) at the surface; they tended to decrease to nearly zero concentration with depth, thus suggesting that MeHg production and accumulation occur predominantly just below the sediment–water interface. Porewater MeHg concentrations (0.9–7.9 ng L−1, 0.15–15% of THg) varied seasonally; higher contents were observed in the warmer period. The MeHg diffusive fluxes (up to 17 ng m−2 day−1) were similar to those in the nearby Gulf of Trieste [Covelli, S., Horvat, M., Faganeli, J., Brambati, A., 1999. Porewater distribution and benthic flux of mercury and methylmercury in the Gulf of Trieste (Northern Adriatic Sea). Estuar. Coast. Shelf Sci. 48, 415–428], although the lagoon sediments contained four-fold higher THg concentrations. Conversely, the THg diffusive fluxes in the lagoon (up to 110 ng m−2 day−1) were one- to two-fold higher than those previously estimated for the Gulf of Trieste. The diurnal MeHg benthic fluxes were highest in summer at both sites (41,000 and 33,000 ng m−2 day−1 at the fishfarm and in the open lagoon, respectively), thus indicating the influence of temperature on microbial processes. The diurnal variations of dissolved THg and especially MeHg were positively correlated with O2 and inversely with DIC, suggesting an important influence of benthic photosynthetic activities on lagoon benthic Hg cycling, possibly through the production of organic matter promptly available for methylation. The results from the dark chamber incubated in the laboratory showed that the regeneration of dissolved THg was slightly affected by the oxic–anoxic transition. Conversely, the benthic flux of MeHg was up to 15-fold higher in sediments overlain by O2 depleted waters. In the anoxic phase, the MeHg fluxes proceeded in parallel with Fe fluxes and the methylated form reached approximately 100% of dissolved THg. The MeHg is mostly released into overlying water (mean recycling efficiency of 89%) until the occurrence of sulphide inhibition, due to scavenging of the available Hg substrate for methylation. The results suggest that sediments in the Grado Lagoon, especially during anoxic events, should be considered as a primary source of MeHg for the water column. 相似文献
9.
The Messinian Sicilian stratigraphy revisited: new insights for the Messinian salinity crisis 总被引:1,自引:0,他引:1
Controversies around the Messinian salinity crisis (MSC) are because of the difficulties in establishing genetic and stratigraphic relationships between its deep and shallow‐water record. Actually, the Sicilian foreland basin shows both shallow and deep‐water Messinian records, thus offering the chance to reconstruct comprehensive MSC scenarios. The Lower Gypsum of Sicily comprises primary and resedimented evaporites separated in space and time by the intra‐Messinian unconformity. A composite unit including halite, resedimented gypsum and Calcare di Base accumulated between 5.6 and 5.55 Ma in the main depocentres; it records the acme of the Messinian Salinity Crisis during a tectonic phase coupled with sea‐level falls at glacials TG14‐TG12. These deposits fully post‐date primary gypsum, which precipitated in shallow‐water wedge‐top and foreland ramp basins between 5.96 and 5.6 Ma. This new stratigraphic framework results in a three‐stage MSC scenario characterized by different primary evaporite associations: selenite in the first and third stages, carbonate, halite and potash salt in the second one associated with hybrid resedimented evaporites. 相似文献
10.
An unusual feature has been observed in polychaetes regarding their capacity to accumulate high levels of relatively toxic forms of arsenic in specific tissues. Basal levels of arsenic and distribution of its compounds were investigated in tissues of the Mediterranean polychaete Sabella spallanzanii. Particularly high concentrations were measured in the branchial crown (1036+/-136 microg/g d.w.) and chemical speciation revealed that the predominant form was the relatively toxic dimethylarsinate (DMA). These data suggest a potential role of As as anti-predatory strategy in polychaetes. 相似文献
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