A unified model for AGN feedback in cosmological simulations of structure formation     

Debora Sijacki  Volker Springel  Tiziana Di Matteo  Lars Hernquist 《Monthly notices of the Royal Astronomical Society》2007,380(3):877-900

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Vertical structure of hyper-accreting disks and consequences for gamma-ray burst outflows     

Elena M. Rossi  Philip J. Armitage  Tiziana Di Matteo 《Astrophysics and Space Science》2007,311(1-3):185-190

We discuss the physics of the power source for gamma-ray bursts (GRBs). There is a great variety of stellar systems proposed as progenitors of long and short GRBs, but any current model for the engine ultimately involves the formation of a hyper-accreting disk around a newly-formed black hole of a few solar masses. The study of such disks can shed light onto the burst composition and energy content. We present preliminary results from disk vertical structure calculations. These include neutrino transport, a height-dependent determination of the nuclear composition, and a simplified treatment of turbulent mixing. We find that vertical mixing is rapid enough to largely erase compositional gradients, and as a consequence the upper layers of the disk reflect the neutron-rich composition of the midplane close to the black hole. We review the implications of this for the nuclear composition of outflows in GRBs. Our models suggest an increasing role for pairs in the upper regions of the disk, and we speculate that a pair-driven wind could be a significant source of cooling. Elena M. Rossi is a Chandra Fellow  相似文献   

Size and shape characteristics of drumlins,derived from a large sample,and associated scaling laws     

Chris D. Clark  Anna L.C. Hughes  Sarah L. Greenwood  Matteo Spagnolo  Felix S.L. Ng 《Quaternary Science Reviews》2009,28(7-8):677-692

Ice sheets flowing across a sedimentary bed usually produce a landscape of blister-like landforms streamlined in the direction of the ice flow and with each bump of the order of 10² to 10³ m in length and 10¹ m in relief. Such landforms, known as drumlins, have mystified investigators for over a hundred years. A satisfactory explanation for their formation, and thus an appreciation of their glaciological significance, has remained elusive. A recent advance has been in numerical modelling of the land-forming process. In anticipation of future modelling endeavours, this paper is motivated by the requirement for robust data on drumlin size and shape for model testing.From a systematic programme of drumlin mapping from digital elevation models and satellite images of Britain and Ireland, we used a geographic information system to compile a range of statistics on length L, width W, and elongation ratio E (where E = L/W) for a large sample. Mean L, is found to be 629 m (n = 58,983), mean W is 209 m and mean E is 2.9 (n = 37,043). Most drumlins are between 250 and 1000 metres in length; between 120 and 300 metres in width; and between 1.7 and 4.1 times as long as they are wide. Analysis of such data and plots of drumlin width against length reveals some new insights. All frequency distributions are unimodal from which we infer that the geomorphological label of ‘drumlin’ is fair in that this is a true single population of landforms, rather than an amalgam of different landform types. Drumlin size shows a clear minimum bound of around 100 m (horizontal). Maybe drumlins are generated at many scales and this is the minimum, or this value may be an indication of the fundamental scale of bump generation (‘proto-drumlins’) prior to them growing and elongating. A relationship between drumlin width and length is found (with r² = 0.48) and that is approximately W = 7 L ^1/2 when measured in metres. A surprising and sharply-defined line bounds the data cloud plotted in E–W–L space, and records a scale-dependent maximum elongation limit (approximated by E_max = L^1/3, when L measured in metres). For a given length, for some reason as yet unknown, drumlins do not exceed the elongation ratio defined by this scaling law. We also report and compare our statistics to an amalgamated sample (25,907 drumlins) of measures derived from around 50 published investigations. Any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling.  相似文献   

Clumpy Substructures in Globular Cluster Tidal Tails     

P. Di Matteo  R. Capuzzo Dolcetta  P. Miocchi 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):59-73

In this paper, we present some preliminary results of numerical simulations of a globular cluster orbiting in the inner region of a triaxial galaxy. The formation and evolution of tidal tails around the cluster is discussed, together with their morphology, which shows clumpy substructures as observed, for example, in the galactic globular cluster Palomar 5.  相似文献   

The influence of coastal dynamics on the upper limit of the Posidonia oceanica meadow     

Matteo Vacchi  Monica Montefalcone  Carlo Nike Bianchi  Carla Morri  Marco Ferrari 《Marine Ecology》2010,31(4):546-554

The recognized ecological importance of Posidonia oceanica, the most important seagrass of the Mediterranean Sea, makes it crucial to assess the state of health of its meadows, discriminating natural from anthropogenic impacts. In this paper, the hydrodynamic conditions at the upper limit of P. oceanica meadows along the Ligurian coast (NW Mediterranean Sea) were investigated. A relationship between the distance of the upper limit of the meadow from the shoreline and the morphodynamic domain of the beach (i.e. distinctive types of beach produced by the topography, wave climate and sediment composition) was found. A zonation of the state of the shallow portions of the meadows down the submerged beach profile was identified. Zone a, from the shoreline to the breaking limit, is naturally critical for the development of the meadow. Zone b, from the breaking limit to the closure depth, is subjected to natural and human impacts. Zone c, below the closure depth, is little influenced by coastal dynamics. This study quantifies for the first time how much the status of the shallow portions of P. oceanica meadows is dependent on coastal dynamics, which is important for their proper management.  相似文献   

Flounder growth and production as indicators of the nursery value of marsh habitats in a Mediterranean lagoon     

Anita Franco  Riccardo Fiorin  Matteo Zucchetta  Patrizia Torricelli  Piero Franzoi 《Journal of Sea Research》2010,64(4):457-464

Estuarine marshes are known as suitable nursery areas for many marine migrant fishes, such as flounder. The potential nursery value of such habitats was investigated in the Venice lagoon, by using growth and production of 0-group flounder as indicators. Size–frequency distribution analysis was performed on fish samples collected fortnightly, from March 2004 to June 2005, in two marsh sites, Dese and Tessera, differing in their origin and environmental conditions. Samples were mostly composed of juvenile individuals, belonging to 0- and 1-group cohorts (the latter being present in Tessera only). A higher total production, either annual or monthly, and faster growth of 0-group flounder was observed in Dese, associated to a higher ecological performance of 0-group individuals in this site, as indicated by the higher P:B ratio values. Dese is a site located in a marsh complex characterized by the relevant influence of a nearby river, and the observed higher potential nursery value of this marsh area with respect to the other is discussed in the light of the higher trophic status and other environmental conditions in this site. The production results were also compared to those from other estuarine environments commonly acknowledged as important nurseries for European flounder.  相似文献   

Maximum run-up,breaking conditions and dynamical forces in the swash zone: a boundary value approach     

Antuono Matteo  Maurizio Brocchini 《Coastal Engineering》2008

On the basis of the approximate analytical solution for the nonlinear shallow water equations of Antuono and Brocchini [M. Antuono & M. Brocchini, The boundary value problem for the nonlinear shallow water equation, Stud. Appl. Maths, 119, 71–91 (2007).], we propose useful regression curves for the prediction of maximum run-up and dynamical forces in the swash zone on a frictionless, uniformly sloping beach. For the first time the dependence of the results on both the wave height and the wave steepness is analyzed in detail providing formulae able to describe a wide class of wave inputs. Finally, the regression formulae are validated through comparison with maximum run-up laws and breaking conditions already available in the literature, the present model results appearing to better account for nonlinear effects.  相似文献   

Quantitative methods for estimating flood fatalities: towards the introduction of loss-of-life estimation in the assessment of flood risk   总被引：1，自引：0，他引：1  

Manuela Di Mauro  Karin M. De Bruijn  Matteo Meloni 《Natural Hazards》2012,63(2):1083-1113

Risk, including flood risk, can be defined as ??the combination of the probability of an event and its consequences??. Assessing and managing the risk from flooding should explicitly include the estimation of impacts to people. Extensive research is currently ongoing looking at both quantitative and qualitative approaches for assessing flood impacts on people. Although there is some literature available on such approaches, examples of methodological and routinely applications of these methodologies as part of flood risk assessments are rare. This paper focuses on quantitative approaches for estimating impacts of flooding to people, notably on methods for assessing fatality numbers associated with flooding. Three methods for assessing losses of life are discussed in detail. The methods discussed here constitute the forefront of research in Canada, UK and The Netherlands. These methods provide an assessment of the physical consequences of flooding on people and can be used to introduce the impacts to people as quantitative metric for the assessment of flood risk. In this paper, the three methodologies are discussed and applied in a UK case study reproducing the 1953 East Coast flood event. This study aims to provide a comprehensive comparison on both the reliability and the applicability of the methods. We analyse possible added values on using of these methods in systematic analyses, aiming to provide guidelines for applying these methods for flood fatality risk assessment.  相似文献   

Cooperative evolutionary algorithm for space trajectory optimization     

Matteo Rosa Sentinella  Lorenzo Casalino 《Celestial Mechanics and Dynamical Astronomy》2009,105(1-3):211-227

A hybrid evolutionary algorithm which synergistically exploits differential evolution, genetic algorithms and particle swarm optimization, has been developed and applied to spacecraft trajectory optimization. The cooperative procedure runs the three basic algorithms in parallel, while letting the best individuals migrate to the other populations at prescribed intervals. Rendezvous problems and round-trip Earth–Mars missions have been considered. The results show that the hybrid algorithm has better performance compared to the basic algorithms that are employed. In particular, for the rendezvous problem, a 100% efficiency can be obtained both by differential evolution and the genetic algorithm only when particular strategies and parameter settings are adopted. On the other hand, the hybrid algorithm always attains the global optimum, even though nonoptimal strategies and parameter settings are adopted. Also the number of function evaluations, which must be performed to attain the optimum, is reduced when the hybrid algorithm is used. In the case of Earth–Mars missions, the hybrid algorithm is successfully employed to determine mission opportunities in a large search space.  相似文献   

Camouflaged Galactic cosmic microwave background polarization foregrounds: total and polarized contributions of the kinetic Sunyaev–Zeldovich effect     

André Waelkens  Matteo Maturi  Torsten Enßlin 《Monthly notices of the Royal Astronomical Society》2008,383(4):1425-1430

We consider the role of the Galactic kinetic Sunyaev–Zeldovich (SZ) effect as a cosmic microwave background (CMB) polarization foreground. While the Galactic thermal SZ effect has previously been studied and discarded as a potential CMB foreground, we find that the kinetic SZ effect is dominant in the Galactic case. We analyse the detectability of the kinetic SZ effect by means of an optimally matched filter technique applied to a simulation of an ideal observation. We obtain no detection, getting a signal-to-noise ratio of 0.1, thereby demonstrating that the kinetic SZ effect can also safely be ignored as a CMB foreground. However, we provide maps of the expected signal for inclusion in future high-precision data processing. Furthermore, we rule out the significant contamination of the polarized CMB signal by second scattering of Galactic kinetic SZ photons, since we show that the scattering of the CMB quadrupole photons by Galactic electrons is a stronger effect than the SZ second scattering, and has already been shown to produce no significant polarized contamination.  相似文献