Application of a Bivariate Gamma Distribution for a Chemically Reacting Plume in the Atmosphere     

Enrico Ferrero  Luca Mortarini  Stefano Alessandrini  Carlo Lacagnina 《Boundary-Layer Meteorology》2013,147(1):123-137

The joint concentration probability density function of two reactive chemical species is modelled using a bivariate Gamma distribution coupled with a three-dimensional fluctuating plume model able to simulate the diffusion and mixing of turbulent plumes. A wind-tunnel experiment (Brown and Bilger, J Fluid Mech 312:373–407, 1996), carried out in homogeneous unbounded turbulence, in which nitrogen oxide is released from a point source in an ozone doped background and the chemical reactions take place in non-equilibrium conditions, is considered as a test case. The model is based on a stochastic Langevin equation reproducing the barycentre position distribution through a proper low-pass filter for the turbulence length scales. While the meandering large-scale motion of the plume is directly simulated, the internal mixing relative to the centroid is reproduced using a bivariate Gamma density function. The effect of turbulence on the chemical reaction (segregation), which in this case has not yet attained equilibrium, is directly evaluated through the covariance of the tracer concentration fields. The computed mean concentrations and the O₃–NO concentration covariance are also compared with those obtained by the Alessandrini and Ferrero Lagrangian single particle model (Alessandrini and Ferrero, Physica A 388:1375–1387, 2009) that entails an ad hoc parametrization for the segregation coefficient.  相似文献   

A multiwavelength map of the nuclear region of NGC 7582     

Stefano Bianchi  Marco Chiaberge  Enrico Piconcelli  Matteo Guainazzi 《Monthly notices of the Royal Astronomical Society》2007,374(2):697-702

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A simple test of the external shock model for the prompt emission in gamma-ray bursts     

Enrico Ramirez-Ruiz  Jonathan Granot   《New Astronomy》2007,12(8):630-634

It is demonstrated here that if the prompt GRB emission is produced by the simplest version of the external shock model, a specific relation should prevail between the observed duration, isotropic equivalent energy, and photon peak energy. In essence, this relation arises because both the burst duration and the typical energy of the emitted synchrotron photons depend on the same combination of the, usually poorly constrained, external density at the deceleration radius, n_dec, and initial bulk Lorentz factor, Γ₀. This has the fortunate consequence of making the relation independent of both Γ₀ and n_dec. Unless the efficiency of electron acceleration is very low, synchrotron gamma-rays from the external shock would fail to meet the current observational constraints for the vast majority of GRBs, including those with a smooth, single peak temporal profile. This argues either against an external shock origin for the prompt emission in GRBs or for changes in our understanding of the microphysical and radiation processes occurring within the shocked region.  相似文献   

Flaring up: radio diagnostics of the kinematic, hydrodynamic and environmental properties of gamma-ray bursts     

Alicia M. Soderberg †  Enrico Ramirez-Ruiz 《Monthly notices of the Royal Astronomical Society》2003,345(3):854-864

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Completely dark galaxies: their existence, properties and strategies for finding them     

Neil Trentham  Ole Möller  Enrico Ramirez-Ruiz 《Monthly notices of the Royal Astronomical Society》2001,322(3):658-668

There are a number of theoretical and observational hints that large numbers of low-mass galaxies composed entirely of dark matter exist in the field. The theoretical considerations follow from the prediction of cold dark matter theory that there exist many low-mass galaxies for every massive one. The observational considerations follow from the observed paucity of these low-mass galaxies in the field but not in dense clusters of galaxies; this suggests that the lack of small galaxies in the field is due to the inhibition of star formation in the galaxies as opposed to the fact that their small dark matter haloes do not exist. In this work we outline the likely properties of low-mass dark galaxies, and describe observational strategies for finding them, and where in the sky to search. The results are presented as a function of the global properties of dark matter, in particular the presence or absence of a substantial baryonic dark matter component. If the dark matter is purely cold and has a Navarro, Frenk & White density profile, directly detecting dark galaxies will only be feasible with present technology if the galaxy has a maximum velocity dispersion in excess of 70 km s⁻¹, in which case the dark galaxies could strongly lens background objects. This is much higher than the maximum velocity dispersions in most dwarf galaxies. If the dark matter in galaxy haloes has a baryonic component close to the cosmic ratio, the possibility of directly detecting dark galaxies is much more realistic; the optimal method of detection will depend on the nature of the dark matter. A number of more indirect methods are also discussed.  相似文献   

Measurement of fast bars in a sample of early-type barred galaxies     

J. A. L. Aguerri  Victor P. Debattista  Enrico Maria Corsini 《Monthly notices of the Royal Astronomical Society》2003,338(2):465-480

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Flow directions of stream-groundwater exchange in a headwater catchment during the hydrologic year     

Enrico Bonanno  Günter Blöschl  Julian Klaus 《水文研究》2021,35(8):e14310

Understanding near-stream groundwater dynamics and flow directions is important for predicting hillslope-stream connectivity, streamflow generation, and hydrologic controls of streamwater quality. To determine the drivers of groundwater flow in the stream corridor (i.e., the stream channel and the adjacent groundwater in footslopes and riparian areas), we observed the water levels of 36 wells and 7 piezometers along a headwater stream section over a period of 18 months. Groundwater dynamics during events were controlled by the initial position of the groundwater table relative to the subsurface structure. The near-stream groundwater table displayed a fast and pronounced response to precipitation events when lying in fractured bedrock with low storage capacity, and responded less frequently and in a less pronounced way when lying in upper layers with high storage capacity. Precipitation depth, intensity, regolith thickness above the fractured bedrock, and proximity to and elevation above the stream channel also had an effect on the groundwater dynamics, which varied with hydrologic conditions. Our high-frequency and spatially dense measurements highlight the competing influence of groundwater inflow from upslope locations, streamwater level and bedrock properties on the spatiotemporal dynamics of flowpaths in the stream corridor. Near-stream groundwater pointed uniformly towards the stream channel when the stream corridor was hydrologically connected to upslope groundwater. However, local interruptions of the water inflow from upslope locations caused flow reversals towards the footslopes. The direction of near-stream groundwater followed the local fractured bedrock topography during dry hydrologic conditions on a few occasions after events. The outcomes of this research contribute to a better understanding of the drivers controlling spatiotemporal changes in near-stream groundwater dynamics and flow directions in multiple wetness states of the stream corridor.  相似文献   

Forest fire effects on groundwater in a coastal aquifer (Ravenna,Italy)          下载免费PDF全文

Beatrice M. S. Giambastiani  Nicolas Greggio  Giovanni Nobili  Enrico Dinelli  Marco Antonellini 《水文研究》2018,32(15):2377-2389

We examined the fire‐induced changes in groundwater recharge rate. This aspect is particularly important in the case of large forested areas growing over a coastal aquifer affected by saltwater intrusion. In the Ravenna coastal area (Italy), pine forests grow on coastal dune belts, overlying a sandy unconfined aquifer, which is strongly affected by marine ingression. Three groundwater profiles across the forest and perpendicular to the coastline were monitored for groundwater level, physical, and chemical parameters. The aims were to define groundwater quality, recharge rate, freshwater volume, and highlight change, which occurred after a forest fire with reference to pre‐fire conditions. Analytical solutions based on Darcy Law and the Dupuit Equation were applied to calculate unconfined flow and compare recharge rates among the profiles. The estimated recharge rates increased in the partially and completely burnt areas (219 and 511 mm year^?1, respectively) compared with the pristine pine forest area (73 mm year^?1). Although pre‐fire conditions were similar in all monitored profiles, a post‐fire decrease in salinity was observed across the burnt forest, along with an increase in infiltration and freshwater lens thickness. This was attributed to decrease canopy interception and evapotranspiration caused by vegetation absence after the fire. This research provided an example of positive forest fire feedback on the quantity and quality of fresh groundwater resources in a lowland coastal aquifer affected by saltwater intrusion, with limited availability of freshwater resources. The fire provided an opportunity to evaluate a new forest management approach and consider the restoration and promotion of native dune herbaceous vegetation.  相似文献   

Crossed molecular beam study of gas phase reactions relevant to the chemistry of planetary atmospheres: The case of C₂+C₂H₂     

Francesca Leonori  Enrico Segoloni  Sébastien D. Le Picard 《Planetary and Space Science》2008,56(12):1658-1673

The reaction between dicarbon (C₂) and acetylene was recently suggested as a possible competitive reaction in the atmospheres of Titan, Saturn and Uranus by rate constant measurements at very low temperatures [see Canosa, A., Páramo, A., Le Picard, S.D., Sims, I.R., 2007. An experimental study of the reaction kinetics of C₂(X¹Σ_g⁺) with hydrocarbons (CH₄, C₂H₂, C₂H₄, C₂H₆ and C₃H₈) over the temperature range 24-300 K: implications for the atmospheres of Titan and the Giant Planets. Icarus 187, 558-568]. We have investigated the reaction of the two low lying electron states of C₂ and acetylene by the crossed molecular beam (CMB) technique with mass spectrometric detection. C₄H, already identified as a primary product in previous CMB experiments, is confirmed as such, even though the mechanism of formation is inferred to be partly different with respect to the previous study. An experimental setup has been devised to characterize the internal population of C₂ and refine the interpretation of the scattering results. The implications for the modelling of the atmospheres of Giant Planets and Titan, as well as cometary comae and the interstellar medium, are discussed.  相似文献   

Non‐impact origin of the crater‐like structures in the Gilf Kebir area (Egypt): Implications for the geology of eastern Sahara     

Letizia ORTI  Mario DI MARTINO  Marco MORELLI  Corrado CIGOLINI  Enrico PANDELI  Alessandra BUZZIGOLI 《Meteoritics & planetary science》2008,43(10):1629-1639

Abstract— Several small crater‐like structures occur in Gilf Kebir region (SW Egypt). It has been previously suggested that they could be the result of meteoritic impacts. Here we outline the results of our geological and geophysical survey in the area. The proposed impact origin for these structures is not supported by our observations and analyses, and we suggest an alternative interpretation. The crater‐like structures in Gilf Kebir area are likely related to endogenic processes typical of hydrothermal vent complexes in volcanic areas which may reflect the emplacement of subvolcanic intrusives.  相似文献