排序方式: 共有30条查询结果,搜索用时 15 毫秒
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.
Ignacio Ferreras Alessandro Melchiorri Domenico Tocchini-Valentini 《Monthly notices of the Royal Astronomical Society》2003,344(1):257-261
The age of the Universe has been increasingly constrained by different techniques, such as the observations of type Ia supernovae (SNIa) at high redshift or dating the stellar populations of globular clusters. In this paper, we present a complementary approach using the colours of the brightest elliptical galaxies in clusters over a wide redshift range ( z ≲ 1) . We put new and independent bounds on the dark energy equation of state parametrized by a constant pressure-to-density ratio w Q and by a parameter (ξ) which determines the scaling between the matter and dark energy densities. We find that accurate estimates of the metallicities of the stellar populations in moderate and high-redshift cluster galaxies can pose stringent constraints on the parameters that describe dark energy. Our results are in good agreement with the analysis of dark energy models using SNIa data as a constraint. Accurate estimates of the metallicities of stellar populations in cluster galaxies at z ≲ 2 will make this approach a powerful complement to studies of cosmological parameters using high-redshift SNIa. 相似文献
3.
A survey is made of the present constraints on cosmological parameters from Cosmic Microwave Background Anisotropies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Melchiorri A Ade PA de Bernardis P Bock JJ Borrill J Boscaleri A Crill BP De Troia G Farese P Ferreira PG Ganga K de Gasperis G Giacometti M Hristov VV Jaffe AH Lange AE Masi S Mauskopf PD Miglio L Netterfield CB Pascale E Piacentini F Romeo G Ruhl JE Vittorio N 《The Astrophysical journal》2000,536(2):L63-L66
We use the angular power spectrum of the cosmic microwave background, measured during the North American test flight of the Boomerang experiment, to constrain the geometry of the universe. Within the class of cold dark matter models, we find that the overall fractional energy density of the universe Omega is constrained to be 0.85=Omega=1.25 at the 68% confidence level. Combined with the COBE measurement, the data on degree scales from the Microwave Anisotropy Telescope in Chile, and the high-redshift supernovae data, we obtain new constraints on the fractional matter density and the cosmological constant. 相似文献
5.
K.N. AbazajianE. Calabrese A. CoorayF. De Bernardis S. Dodelson A. FriedlandG.M. Fuller S. HannestadB.G. Keating E.V. Linder C. LunardiniA. Melchiorri R. Miquel E. PierpaoliJ. Pritchard P. SerraM. Takada Y.Y.Y. Wong 《Astroparticle Physics》2011,35(4):177-184
Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach. 相似文献
6.
Natan Micheletti Loris Foresti Sylvain Robert Michael Leuenberger Andrea Pedrazzini Michel Jaboyedoff Mikhail Kanevski 《Mathematical Geosciences》2014,46(1):33-57
This paper explores the use of adaptive support vector machines, random forests and AdaBoost for landslide susceptibility mapping in three separated regions of Canton Vaud, Switzerland, based on a set of geological, hydrological and morphological features. The feature selection properties of the three algorithms are studied to analyze the relevance of features in controlling the spatial distribution of landslides. The elimination of irrelevant features gives simpler, lower dimensional models while keeping the classification performance high. An object-based sampling procedure is considered to reduce the spatial autocorrelation of data and to estimate more reliably generalization skills when applying the model to predict the occurrence of new unknown landslides. The accuracy of the models, the relevance of features and the quality of landslide susceptibility maps were found to be high in the regions characterized by shallow landslides and low in the ones with deep-seated landslides. Despite providing similar skill, random forests and AdaBoost were found to be more efficient in performing feature selection than adaptive support vector machines. The results of this study reveal the strengths of the classification algorithms, but evidence: (1) the need for relying on more than one method for the identification of relevant variables; (2) the weakness of the adaptive scaling algorithm when used with landslide data; and (3) the lack of additional features which characterize the spatial distribution of deep-seated landslides. 相似文献
7.
8.
Distribution of trace elements in the coastal sea sediments of Maslinica Bay, Croatia 总被引:1,自引:0,他引:1
Nenad Mikulic Visnja Orescanin Loris Elez Ljiljana Pavicic Durdica Pezelj Ivanka Lovrencic Stipe Lulic 《Environmental Geology》2008,53(7):1413-1419
Spatial distributions of trace elements in the coastal sea sediments and water of Maslinica Bay (Southern Adriatic), Croatia
and possible changes in marine flora and foraminifera communities due to pollution were investigated. Macro, micro and trace
elements’ distributions in five granulometric fractions were determined for each sediment sample. Bulk sediment samples were
also subjected to leaching tests. Elemental concentrations in sediments, sediment extracts and seawater were measured by source
excited energy dispersive X-ray fluorescence (EDXRF). Concentrations of the elements Cr, Cu, Zn, and Pb in bulk sediment samples
taken in the Maslinica Bay were from 2.1 to over six times enriched when compared with the background level determined for
coarse grained carbonate sediments. A low degree of trace elements leaching determined for bulk sediments pointed to strong
bonding of trace elements to sediment mineral phases. The analyses of marine flora pointed to higher eutrophication, which
disturbs the balance between communities and natural habitats. 相似文献
9.
Mauskopf PD Ade PA de Bernardis P Bock JJ Borrill J Boscaleri A Crill BP DeGasperis G De Troia G Farese P Ferreira PG Ganga K Giacometti M Hanany S Hristov VV Iacoangeli A Jaffe AH Lange AE Lee AT Masi S Melchiorri A Melchiorri F Miglio L Montroy T Netterfield CB Pascale E Piacentini F Richards PL Romeo G Ruhl JE Scannapieco E Scaramuzzi F Stompor R Vittorio N 《The Astrophysical journal》2000,536(2):L59-L62
We describe a measurement of the angular power spectrum of anisotropies in the cosmic microwave background (CMB) at scales of 0&fdg;3 to 5 degrees from the North American test flight of the Boomerang experiment. Boomerang is a balloon-borne telescope with a bolometric receiver designed to map CMB anisotropies on a long-duration balloon flight. During a 6 hr test flight of a prototype system in 1997, we mapped more than 200 deg(2) at high Galactic latitudes in two bands centered at 90 and 150 GHz with a resolution of 26&arcmin; and 16&farcm;5 FWHM, respectively. Analysis of the maps gives a power spectrum with a peak at angular scales of 1 degrees with an amplitude 70 μK(CMB). 相似文献
10.
G. Loffredo F. Frontera D. Pellicciotta A. Pisa V. Carassiti S. Chiozzi F. Evangelisti L. Landi M. Melchiorri S. Squerzanti 《Experimental Astronomy》2004,18(1-3):1-11
We will report on the equipment and performance of the X-ray facility of the University of Ferrara. Initially developed to
test the PDS (Phoswich Detection System) instrument aboard the BeppoSAX satellite and to perform reflectivity measurements
of mosaic crystal samples of HOPG (Highly Oriented Pyrolytic Graphite), with time the facility has been improved and its applications
extended. Now these applications include test and calibration of hard X-ray (> 10 keV) detectors, reflectivity measurements
of hard X-ray mirrors, reflectivity tests of crystals and X-ray transparency measurements. The facility is being further improved
in order to determine the optical axis mosaic crystals in Laue configuration within a project devoted to develop a hard X-ray
(> 60 keV) focusing optics (Pisa, A. et al.: in press, Feasibility study of a Laue lens for hard X-rays for space astronomy,
SPIE Proc., 5536). 相似文献