Nebular emission from star-forming galaxies   总被引：1，自引：0，他引：1  

Stéphane Charlot †  Marcella Longhetti‡ 《Monthly notices of the Royal Astronomical Society》2001,323(4):887-903

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Parametric Study of Urban-Like Topographic Statistical Moments Relevant to a Priori Modelling of Bulk Aerodynamic Parameters   总被引：1，自引：1，他引：0  

Xiaowei Zhu  G. Valerio Iungo  Stefano Leonardi  William Anderson 《Boundary-Layer Meteorology》2017,162(2):231-253

For a horizontally homogeneous, neutrally stratified atmospheric boundary layer (ABL), aerodynamic roughness length, \(z_0\), is the effective elevation at which the streamwise component of mean velocity is zero. A priori prediction of \(z_0\) based on topographic attributes remains an open line of inquiry in planetary boundary-layer research. Urban topographies – the topic of this study – exhibit spatial heterogeneities associated with variability of building height, width, and proximity with adjacent buildings; such variability renders a priori, prognostic \(z_0\) models appealing. Here, large-eddy simulation (LES) has been used in an extensive parametric study to characterize the ABL response (and \(z_0\)) to a range of synthetic, urban-like topographies wherein statistical moments of the topography have been systematically varied. Using LES results, we determined the hierarchical influence of topographic moments relevant to setting \(z_0\). We demonstrate that standard deviation and skewness are important, while kurtosis is negligible. This finding is reconciled with a model recently proposed by Flack and Schultz (J Fluids Eng 132:041203-1–041203-10, 2010), who demonstrate that \(z_0\) can be modelled with standard deviation and skewness, and two empirical coefficients (one for each moment). We find that the empirical coefficient related to skewness is not constant, but exhibits a dependence on standard deviation over certain ranges. For idealized, quasi-uniform cubic topographies and for complex, fully random urban-like topographies, we demonstrate strong performance of the generalized Flack and Schultz model against contemporary roughness correlations.  相似文献   

Supernova remnants, planetary nebulae and the distance to NGC 4214     

Michael A. Dopita  Daniela Calzetti  Jesús Maíz Apellániz  William P. Blair  Knox S. Long  Max Mutchler  Bradley C. Whitmore  Howard E. Bond  John MacKenty  Bruce Balick  Marcella Carollo  Michael Disney  Jay A. Frogel  Robert O’Connell  Donald Hall  Jon A. Holtzman  Randy A. Kimble  Patrick McCarthy  Francesco Paresce  Abhijit Saha  Alistair R. Walker  Joe Silk  Marco Sirianni  John Trauger  Rogier Windhorst  Erick Young 《Astrophysics and Space Science》2010,330(1):123-131

We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.  相似文献   

The Australia telescope 20 GHz survey: hardware, observing strategy, and scanning survey catalog     

Paul Jacob Hancock  Paul Roberts  Michael J. Kesteven  Ronald D. Ekers  Elaine M. Sadler  Tara Murphy  Marcella Massardi  Roberto Ricci  Mark Calabretta  Gianfranco de Zotti  Philip G. Edwards  Jennifer A. Ekers  Carole A. Jackson  Mark Leach  Chris Phillips  Robert J. Sault  Lister Staveley-Smith  Ravi Subrahmanyan  Mark A. Walker  Warwick E. Wilson 《Experimental Astronomy》2011,32(2):147-177

The Australia Telescope 20 GHz (AT20G) survey is a large area (2?? sr), sensitive (40 mJy), high frequency (20 GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. (MNRAS 402:2403, 2010). In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog.  相似文献   

The symbiotic system AG Draconis: Soft X-ray bremsstrahlung from the nebulae     

Marcella Contini  Rodolfo Angeloni 《New Astronomy》2011,16(3):199-208

The modeling of UV and optical spectra emitted from the symbiotic system AG Dra, adopting collision of the winds, predicts soft X-ray bremsstrahlung from nebulae downstream of the reverse shock with velocities > 150 km s^?1 and intensities comparable to those of the WD black body flux. At outbursts, the envelop of debris, which corresponds to the nebula downstream of the high velocity shocks (700–1000 km s^?1) accompanying the blast wave, absorbs the black body soft X-ray flux from the WD, explains the broad component of the H and He lines, and leads to low optical-UV–X-ray continuum fluxes. The high optical-UV flux observed at the outbursts is explained by bremsstrahlung downstream of the reverse shock between the stars. The depletion of C, N, O, and Mg relative to H indicates that they are trapped into dust grains and/or into diatomic molecules, suggesting that the collision of the wind from the WD with the dusty shells, ejected from the RG with a ～1 year periodicity, leads to the U-band fluctuations during the major bursts.  相似文献   

Ecological implications of biomass and morphotype variations of bacterioplankton: an example in a coastal zone of the Northern Adriatic Sea (Mediterranean)   总被引：1，自引：0，他引：1  

Rosabruna La Ferla  & Marcella Leonardi 《Marine Ecology》2005,26(2):82-88

This study had the objective of quantifying the variability in abundance, cell volume, morphology and C content of a natural bacterioplankton community in a coastal zone of the North Adriatic Sea during two periods (February and June) of two consequent years (1996 and 1997). We used epifluorescence microscopy with Acridine Orange staining procedures and a microphotographic technique. Low variability in bacterial abundance (range 0.3–3.1 × 10⁵ cells ml^?1) occurred between summer and winter periods. Conversely, the cell volume and the calculated carbon content changed greatly with warm and cold periods (ranges: 0.015–0.303 μm³ and 5.83–42.17 fg C cell^?1, respectively). Elongated bacteria were dominant while coccoid cells prevailed only in February 1997. Biomass showed high variability (range 0.12–10.21 μg C l^?1) whilst the abundance did not show noticeable differences among the sampling periods. As a consequence, quantification of bacterial biomass based solely on cell abundance must be considered with caution because the true biomass could depend on variability in cell volumes and morphotypes.  相似文献   

Analysis of dust through extinction     

Marcella Contini 《Astrophysics and Space Science》1992,198(1):29-51

Extinction is treated through the optical thickness . Some important characters of dust, such as the composition and the size of grains, are reviewed in the light of observational evidence. Extinction is investigated through three kind of parameters: (1) those affecting it directly such as the geometrical cross sections of the grains (through the radius) and the wavelength of radiation interacting with them; (2) those connected witht the solid state constitution of grains, such as the dielectric constant and the conductivity; and (3) those connected with the distribution of dust in the intergalactic medium (IGM), such as the dust density and the geometrical thickness of dust slabs. The results are discussed and compared with observations.  相似文献   

Multi-step SETARMA predictors in the analysis of hydrological time series   总被引：1，自引：0，他引：1  

Alessandra Amendola  Marcella Niglio 《Physics and Chemistry of the Earth》2006,31(18):1118-1126

The performance of the self-exciting threshold autoregressive moving average model in forecasting river flow data is investigated. Multi-step forecasts of two daily time series are generated through three different nonlinear predictors. The model adequacy to capture the main features of the data under study and its forecasting performance are analysed and discussed.  相似文献   

The role of chemical composition in RR Lyrae pulsationalproperties – I. Periods     

Filippina Caputo  Marcella Marconi  & Patrizia Santolamazza 《Monthly notices of the Royal Astronomical Society》1998,293(4):364-368

We analyse the periods of theoretical radial pulsators, covering the range of total masses, luminosities, effective temperatures and chemical compositions expected for RR Lyrae variables in both galactic fields and globular clusters.
We show that for fixed values of the structural parameters (mass, luminosity and effective temperature), the period of fundamental and first-overtone pulsators is independent of the helium content ( Y ), whereas it slightly increases as the amount of metals ( Z ) increases. Furthermore, we find that the period along the blue edge for first-overtone pulsation is a function of mass, luminosity and helium content, with a marginal dependence on Z .
On these grounds, new linear relations connecting the periods to stellar parameters are derived. Such new relations should allow a more accurate interpretation of the RR Lyrae observed periods and, in particular, they should help in ascertaining the calibration of the mean absolute magnitude of RR Lyrae stars in terms of metal content.  相似文献   

Neighbourhoods and the implementation of city plans     

Raffaella Y. Nanetti  Robert Leonardi 《Geoforum》1979,10(4):363-388

This article addresses the alternatives posed by urban decentralization as a new institutional framework within which change in city planning goals and administrative practices can take place. Considering that, traditionally, the professions of city planning and public administration have been haunted by a low level of implementation of plans and a high level of dissatisfaction with public-service delivery, the attempt is made to identify the root causes of the two shortcomings. In the process, the thesis is sustained that neighbourhoods endowed with formal decision-making powers have the potential to increase the degree of implementation of plans and to ensure greater efficiency in, and satisfaction with, the delivery of public services. A case study provides a data base to illustrate a number of working hypotheses.  相似文献