排序方式： 共有14条查询结果，搜索用时 437 毫秒
1.
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
2.
G.A. Milani Gy.M. Szabó G. Sostero R. Trabatti R. Ligustri M. Nicolini M. Facchini D. Tirelli D. Carosati C. Vinante D. Higgins 《Icarus》2007,187(1):276-284
The results of the 9P/Tempel 1 CARA (Cometary Archive for Amateur Astronomers) observing campaign is presented. The main goal was to perform an extended survey of the comet as a support to the Deep Impact (DI) Mission. CCD R, I and narrowband aperture photometries were used to monitor the Afρ quantity. The observed behavior showed a peak of 310 cm 83 days before perihelion, but we argue that it can be distorted by the phase effect, too. The phase effect is roughly estimated around 0.0275 mag/degree, but we had no chance for direct determination because of the very similar geometry of the observed apparitions. The log-slope of Afρ was around −0.5 between about 180-100 days before the impact but evolved near the steady-state like 0 value by the impact time. The DI module impact caused about a 60% increase in the value of Afρ and a cloud feature in the coma profile which was observed just after the event. The expansion of the ejecta cloud was consistent with a fountain model with initial projected velocity of 0.2 km/s and β=0.73. Referring to a 25,000 km radius area centered on the nucleus, the total cross section of the ejected dust was 0.06 days after the impact, and 1.93 days after the impact (A is the dust albedo). Five days after the event no signs of the impact were detected, nor deviations from the expected activity referring both to the average pre-impact behavior and to the previous apparitions. 相似文献
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4.
Gabriel García-Medina H. Tuba Özkan-Haller Peter Ruggiero Rob A. Holman Troy Nicolini 《Natural Hazards》2018,94(2):583-603
Sneaker waves are responsible for many casualties and beach rescues in the Pacific Northwest (PNW) region of the USA. In this paper, a catalogue of these events from 2005 to mid-2017 in Oregon and Northern California is presented. The events are grouped depending on the local characteristics into those involving structures, semi-enclosed beaches, and open-coast beaches. It was found that sneaker waves occurred between the months of October and April, which is also the time of the year of most storm activity in the PNW. The majority of the events are associated with long-period swell approaching the coast. Beach slope and significant wave height were not found to correlate with sneaker wave incidents. However, total water level analysis reveals that the run-up level was expected to reach the beachgoers for the majority of the investigated cases indicating that a forecasting system to warn beachgoers is possible. 相似文献
5.
Modelling the response of fresh groundwater to climate and vegetation changes in coral islands 总被引：2，自引：1，他引：1
Jean-Christophe Comte Jean-Lambert Join Olivier Banton Eric Nicolini 《Hydrogeology Journal》2014,22(8):1905-1920
In coral islands, groundwater is a crucial freshwater resource for terrestrial life, including human water supply. Response of the freshwater lens to expected climate changes and subsequent vegetation alterations is quantified for Grande Glorieuse, a low-lying coral island in the Western Indian Ocean. Distributed models of recharge, evapotranspiration and saltwater phytotoxicity are integrated into a variable-density groundwater model to simulate the evolution of groundwater salinity. Model results are assessed against field observations including groundwater and geophysical measurements. Simulations show the major control currently exerted by the vegetation with regards to the lens morphology and the high sensitivity of the lens to climate alterations, impacting both quantity and salinity. Long-term changes in mean sea level and climatic conditions (rainfall and evapotranspiration) are predicted to be responsible for an average increase in salinity approaching 140 % (+8 kg m?3) when combined. In low-lying areas with high vegetation density, these changes top +300 % (+10 kg m?3). However, due to salinity increase and its phytotoxicity, it is shown that a corollary drop in vegetation activity can buffer the alteration of fresh groundwater. This illustrates the importance of accounting for vegetation dynamics to study groundwater in coral islands. 相似文献
6.
Keller P. Nicolini Katia C. Lombardi Wido H. Schreiner Irineu Mazzaro Fernando Wypych Antonio S. Mangrich 《Mineralogy and Petrology》2009,97(1-2):139-144
We report on a paramagnetic anisotropy study of three layered phyllosilicates. The mineral samples were characterized through X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Based on EPR measurements of samples oriented parallel or perpendicular to the magnetic field lines, we show how the substitutional iron is transformed from Fe(II) (biotite) into Fe(III) (muscovite and kaolinite) species and from axial Fe(III) coordination sites (muscovite) to rhombic (kaolinite) sites in response to weathering. 相似文献
7.
Wim J. Kimmerer Nissa Ferm Mary Helen Nicolini Carolina Peñalva 《Estuaries and Coasts》2005,28(4):541-550
Egg production of planktonic copepods, is commonly measured as a proxy for secondary production in population dynamics studies
and for quantifying food limitation. Although limitation of copepod egg production by food quantity or quality is common in
natural waters, it appears less common or severe in estuaries where food concentrations are often high. San Francisco Estuary,
California, has unusually low concentrations of chlorophyll compared to other estuaries. We measured egg production rates
of three species ofAcartia, with dominate the zooplankton biomass at salinity above 15 psu, on 36 occasions during 1999–2002. Egg production was determined
by incubating up to 40 freshly collected individual copepods for 24 h in 140 ml of ambient water. Egg production was less
than 10 eggs female−1 d−1 most of the year, but as high as 52 eggs female−1 d−1 during month-long spring phytoplankton blooms. Egg production was a saturating function of total chlorophyll concentration
with a mean of 30 eggs female−1 d−1 above a chlorophyll concentration of 12±6 mg chl m−3. We take chlorophyll to be a proxy for total food ofAcartia, known to feed on microzooplankton as well as phytoplankton. These findings, together with long-term records of chlorophyll,
concentration and earlier studies of abundance of nauplius larvae in the estuary, imply chronic food limitation ofAcartia species, with sufficient food for maximum egg production <10% of the time over the last 25 yr. These results may show the
most extreme example of food limitation of copepod reproduction in any temperate estuary. They further support the idea that
estuaries may provide suitable habitat forAcartia species by virtue of other factors than high food concentration. 相似文献
8.
Summary Chaco jet events (CJEs) are a subset of South American low-level jet events to the east of the Andes, characterized by enhanced
poleward penetration and by a strong impact on precipitation over southeastern South America. The present study uses the Eta
model short range weather forecasts produced operationally in the Brazilian Center for Weather Forecasts and Climate Studies
(Centro de Previs?o de Tempo e Estudos Climáticos, CPTEC) to characterize the CJEs and the related precipitation during the
1997–1998 warm season.
An enhanced diurnal cycle in precipitation with respect to that found during the warm season mean can be recognized during
CJEs in Eta/CPTEC model output, with preference for a nocturnal maximum over southern Brazil, Uruguay, and the central part
of northern Argentina, and a daytime maximum near high topography (northwestern Argentina, the Brazilian Planalto). The analysis
of thermodynamic and dynamic forcing appearing during CJEs, helps to explain the modeled precipitation cycle: the nocturnal
maximum is mostly explained by enhanced low-level convergence at night, while the diurnal one is mainly a response to radiative
warming. Boundary-layer convergence, and convective instability, present within the CJEs environment, work together to provide
both dynamic forcing and potential for convection. The simulated precipitation cycle is complemented with surface observations
of “current weather” that corroborate the main oscillations found in simulated precipitation. 相似文献
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P. Persi M. Ferrari-Toniolo A. R. Marenzi M. Busso L. Corcione G. Nicolini K. Shivanandan 《Experimental Astronomy》1994,3(1-4):171-172
We present the main characteristics of a new mid-IR camera, TIRCAM, operating at the 1.5 m Italian Infrared Telescope. 相似文献