Constraints on primordial non-Gaussianity from a needlet analysis of the WMAP-5 data     

Davide Pietrobon  Paolo Cabella  Amedeo Balbi  Giancarlo de Gasperis  Nicola Vittorio 《Monthly notices of the Royal Astronomical Society》2009,396(3):1682-1688

We look for a non-Gaussian signal in the Wilkinson Microwave Anisotropy Probe ( WMAP ) 5-year temperature anisotropy maps by performing a needlet-based data analysis. We use the foreground-reduced maps obtained by the WMAP team through the optimal combination of the W, V and Q channels, and perform realistic non-Gaussian simulations in order to constrain the non-linear coupling parameter f _NL. We apply a third-order estimator of the needlet coefficients skewness and compute the  χ²  statistics of its distribution. We obtain  −80 < f _NL < 120  at 95 per cent confidence level, which is consistent with a Gaussian distribution and comparable to previous constraints on the non-linear coupling. We then develop an estimator of f _NL based on the same simulations and we find consistent constraints on primordial non-Gaussianity. We finally compute the three-point correlation function in needlet space: the constraints on f _NL improve to  −50 < f _NL < 110  at 95 per cent confidence level.  相似文献   

Evidence for Mg-rich carbonates on Mars from a 3.9 μm absorption feature     

Ernesto Palomba  Angelo Zinzi  Edward A. Cloutis  Davide Grassi 《Icarus》2009,203(1):58-6003

The origin and nature of the early atmosphere of Mars is still debated. The discovery of sulfate deposits on the surface, coupled with the evidence that there are not large abundances of carbonates detectable on Mars in the optically accessible part of the regolith, leaves open different paleoclimatic evolutionary pathways. Even if carbonates are responsible for the feature observed by TES and Mini-TES at 6.76 μm, alternative hypotheses suggest that it could be due to the presence of Hydrated Iron Sulfates (HIS). Carbonates can be discerned from HIS by investigating the spectral region in which a strong overtone carbonate band is present. The Planetary Fourier Spectrometer on board the Mars Express spacecraft has acquired several thousand martian spectra in the range 1.2-45 μm since January 2004, most of which show a weak absorption feature between 3.8 and 4 μm. A similar feature was observed previously from the Earth, but its origin could not be straightforwardly ascribed to surface materials, and specifically to carbonates. Here we show the surficial nature of this band that can be ascribed to carbonate mixed with the martian soil materials. The materials that best reproduce the detected feature are Mg-rich carbonates (huntite [CaMg₃(CO₃)₄] and/or magnesite [MgCO₃]). The presence of carbonates is demonstrated in both bright and dark martian regions. An evaluation of the likeliest abundance gives an upper limit of ∼10 wt%. The widespread distribution of carbonates supports scenarios that suggest carbonate formation occurred not by precipitation in a water-rich environment but by weathering processes.  相似文献   

Application of the MoniFLaIR early warning system for rainfall-induced landslides in Piedmont region (Italy)   总被引：2，自引：2，他引：0  

Giovanna Capparelli  Davide Tiranti 《Landslides》2010,7(4):401-410

Landslides triggered by rainfall can be foreseen by modeling the relationship between the time occurrence of landslides and rainfall. This paper deals with the argument by adopting a hydrological model called Forecasting of Landslides Induced by Rainfall (FLaIR). The model is applicable for forecasting recurrent landslides and it is based on the identification of a mobility function Y(.) that links the occurrence of a slope movement to the antecedent rainfall. Once the mobility function is defined, it is possible to define its critical values, the exceeding of which indicates that new mobilizations could occur. The FLaIR model has been used to study some phenomena that happened in Lanzo Valleys, a Western Alps sector of the Piedmont region (Northern Italy) where slope debris flows are the predominant landslide type. The study has led to the development of an early warning system, called MoniFLaIR, for real-time monitoring and forecasting of slope hazard. This article describes some details of the system and its performance.  相似文献   

The Influence of Hilly Terrain on Canopy-Atmosphere Carbon Dioxide Exchange   总被引：1，自引：1，他引：1  

G. G. Katul  J. J. Finnigan  D. Poggi  R. Leuning  S. E. Belcher 《Boundary-Layer Meteorology》2006,118(1):189-216

Topography influences many aspects of forest-atmosphere carbon exchange; yet only a small number of studies have considered the role of topography on the structure of turbulence within and above vegetation and its effect on canopy photosynthesis and the measurement of net ecosystem exchange of CO₂ (N_ee) using flux towers. Here, we focus on the interplay between radiative transfer, flow dynamics for neutral stratification, and ecophysiological controls on CO₂ sources and sinks within a canopy on a gentle cosine hill. We examine how topography alters the forest-atmosphere CO₂ exchange rate when compared to uniform flat terrain using a newly developed first-order closure model that explicitly accounts for the flow dynamics, radiative transfer, and nonlinear eco physiological processes within a plant canopy. We show that variation in radiation and airflow due to topography causes only a minor departure in horizontally averaged and vertically integrated photosynthesis from their flat terrain values. However, topography perturbs the airflow and concentration fields in and above plant canopies, leading to significant horizontal and vertical advection of CO₂. Advection terms in the conservation equation may be neglected in flow over homogeneous, flat terrain, and then N_ee = F_c, the vertical turbulent flux of CO₂. Model results suggest that vertical and horizontal advection terms are generally of opposite sign and of the same order as the biological sources and sinks. We show that, close to the hilltop, F_c departs by a factor of three compared to its flat terrain counterpart and that the horizontally averaged F_c-at canopy top differs by more than 20% compared to the flat-terrain case.  相似文献   

Elastic velocity models for gas-hydrate-bearing sediments—a comparison     

Shyam Chand  Tim A. Minshull  Davide Gei  José M. Carcione 《Geophysical Journal International》2004,159(2):573-590

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Marine geology of the Medriff Corridor, Mediterranean Ridge   总被引：1，自引：0，他引：1  

Nicoetta  Fusi  Giovanni Aloisi  de Larderel Ada  Borelu  Ottavio  Amelio  Davide  Castradori  Alessandra  Negri    Bianca  Rimoldi  Rossella  Sanvoisin  Paola  Tarbini  Maria B.  Cita 《Island Arc》1996,5(4):420-439

Abstract Thirty-one piston and/or gravity cores not exceeding 10 m in length were raised in selected areas of a 300 km-long transect (Medriff Corridor) crossing the Mediterranean Ridge, an accretionary complex subject to continent/continent collision, containing an important evaporitic body (Messinian evaporites), in order to ground-truth the geological make-up. Core location, very accurate with reference to a complex bottom configuration, was preceded by swathe mapping, seismic profiling and side-scan sonar investigations. Most sediment cores have a pelagic facies, with biogenic marls as dominant lithology, and sapropels and tephras as minor, isochronous lithologies. A combination of isochronous lithologies and calcareous plankton biochronology permits high resolution stratigraphic correlations. Pelagic facies sediments are Middle Pleistocene to Holocene in age. Two cores associated with mounds located along thrusts contain a matrix-supported mud breccia of deep provenance, Burdigalian-Langhian in age, similar to that characteristic of the Mediterranean Ridge diapiric belt (Cita et al. 1995 ). Three new brine-filled anoxic basins (Urania, l'Atalante and Discovery) were discovered. The brines originated from submarine dissolution of Messinian evaporites and are different in the various basins. The sedimentary record strongly differs from basin to basin. These brine lakes are very young (35 000 years or less). A drastic change in sedimentation rate recorded in the Discovery Basin suggests that basin collapse was sudden and followed by progressive development of basin anoxia. Some cores were analyzed with a prototype multisensor for P-wave velocity, magnetic susceptibility and density. Sapropels show up as abrupt decreases in P-wave velocity and density, and tephra as sudden increases in magnetic susceptibility. Mud breccia displays P-wave velocities greater than pelagic marls, with peaks related to lithic clasts. Anoxic sediments have high P-wave velocities; peaks are associated with gypsum crystals.  相似文献   

Enargite oxidation: A review     

Pierfranco Lattanzi  Stefania Da Pelo  Elodia Musu  Davide Atzei  Bernhard Elsener  Marzia Fantauzzi  Antonella Rossi 《Earth》2008,86(1-4):62-88

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The switching between zonal and blocked mid-latitude atmospheric circulation: a dynamical system perspective     

Davide Faranda  Giacomo Masato  Nicholas Moloney  Yuzuru Sato  Francois Daviaud  Bérengère Dubrulle  Pascal Yiou 《Climate Dynamics》2016,47(5-6):1587-1599

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Acoustic properties of sediments saturated with gas hydrate, free gas and water   总被引：2，自引：0，他引：2  

Davide Gei  José M. Carcione 《Geophysical Prospecting》2003,51(2):141-158

We obtain the wave velocities and quality factors of gas‐hydrate‐bearing sediments as a function of pore pressure, temperature, frequency and partial saturation. The model is based on a Biot‐type three‐phase theory that considers the existence of two solids (grains and gas hydrate) and a fluid mixture. Attenuation is described with the constant‐Q model and viscodynamic functions to model the high‐frequency behaviour. We apply a uniform gas/water mixing law that satisfies Wood's and Voigt's averages at low and high frequencies, respectively. The acoustic model is calibrated to agree with the patchy‐saturation theory at high frequencies (White's model). Pressure effects are accounted by using an effective stress law for the dry‐rock moduli and permeabilities. The dry‐rock moduli of the sediment are calibrated with data from the Cascadia margin. Moreover, we calculate the depth of the bottom simulating reflector (BSR) below the sea floor as a function of sea‐floor depth, geothermal gradient below the sea floor, and temperature at the sea floor.  相似文献   

A Note On The Contribution Of Dispersive Fluxes To Momentum Transfer Within Canopies   总被引：5，自引：12，他引：5  

D. Poggi  G. G. Katul  J. D. Albertson 《Boundary-Layer Meteorology》2004,111(3):615-621

Dispersive flux terms are formed when the time-averaged meanmomentum equation is spatially averaged within the canopy volume.These fluxes represent a contribution to momentum transfer arisingfrom spatial correlations of the time-averaged velocity componentswithin a horizontal plane embedded in the canopy sublayer (CSL).Their relative importance to CSL momentum transfer is commonlyneglected in model calculations and in nearly all fieldmeasurement interpretations. Recent wind-tunnel studies suggestthat these fluxes may be important in the lower layers of thecanopy; however, no one study considered their importance acrossall regions of the canopy and for a wide range of canopy roughnessdensities. Using detailed laser Doppler anemometry measurementsconducted in a model canopy composed of cylinders within a largeflume, we demonstrate that the dispersive fluxes are onlysignificant (i.e., >10%) for sparse canopies. These fluxes arein the same direction as the turbulent flux in the lower layers ofthe canopy but in the opposite direction near the canopy top. Fordense canopies, we show that the dispersive fluxes are <5% atall heights. These results appear to be insensitive to theReynolds number (at high Reynolds numbers).  相似文献