Do high-velocity clouds form by thermal instability?     

James Binney  Carlo Nipoti  Filippo Fraternali 《Monthly notices of the Royal Astronomical Society》2009,397(4):1804-1815

We examine the proposal that the H  i 'high-velocity' clouds (HVCs) surrounding the Milky Way and other disc galaxies form by condensation of the hot galactic corona via thermal instability. Under the assumption that the galactic corona is well represented by a non-rotating, stratified atmosphere, we find that for this formation mechanism to work the corona must have an almost perfectly flat entropy profile. In all other cases, the growth of thermal perturbations is suppressed by a combination of buoyancy and thermal conduction. Even if the entropy profile were nearly flat, cold clouds with sizes smaller than  10 kpc  could form in the corona of the Milky Way only at radii larger than  100 kpc  , in contradiction with the determined distances of the largest HVC complexes. Clouds with sizes of a few kpc can form in the inner halo only in low-mass systems. We conclude that unless even slow rotation qualitatively changes the dynamics of a corona, thermal instability is unlikely to be a viable mechanism for formation of cold clouds around disc galaxies.  相似文献   

On the Transits of Solar System Objects in the Forthcoming Planck Mission: Data Flagging and Coeval Multi-Frequency Observations     

Michele Maris  Carlo Burigana 《Earth, Moon, and Planets》2009,105(2-4):81-88

In the context of current and future microwave surveys mainly dedicated to the accurate mapping of Cosmic Microwave Background (CMB), mm and sub-mm emissions from Solar System will represent a potential source of contamination as well as an opportunity for new Solar System studies. In particular, the forthcoming ESA Planck mission will be able to observe the point-like thermal emission from planets and some large asteroids as well as the diffused Zodiacal Light Emission (ZLE). After a brief introduction to the field, we focus on the identification of Solar System discrete objects in the Planck time ordered data.  相似文献   

Late Holocene glacial and periglacial evolution in the upper Orco Valley, northwestern Italian Alps     

Carlo Giraudi 《Quaternary Research》2009,71(1):1-8

The sediments present in some areas of the Orco Valley provide indications on climatic variations that occurred during the last 6000 years on the southern slopes of the Alps. In particular, distribution and ages of peat layers help define periods and extent of glacial fluctuation in the last 2200 years. Sampling of soils involved in periglacial processes provided a basis for development of a chronological framework of late Holocene environmental change. The data indicate a trend toward cooler climate in the second half of the Holocene. A strong relationship exists between phases of River Po flooding and expansion/retreat phases of the Swiss glaciers: major glacial advances were coeval with periods of intense flooding of the River Po, whereas the phases of glacial retreat coincided with periods of little flooding of the Po. Only in three cases do relationships between glacier activity and floods show weak correlations; two of the cases relate to the warmest periods in approximately the last 2200 years, while the third is the present period. Paleoclimatic evidence from the study region indicates the relatively warm Roman Period between about 2200 and 1900 cal yr BP appears to better represent modern conditions than does the Medieval Warm Period.  相似文献   

Dynamical friction in modified Newtonian dynamics     

Carlo Nipoti  Luca Ciotti  James Binney  Pasquale Londrillo 《Monthly notices of the Royal Astronomical Society》2008,386(4):2194-2198

We have tested a previous analytical estimate of the dynamical friction time-scale in modified Newtonian dynamics (MOND) with fully non-linear N -body simulations. The simulations confirm that the dynamical friction time-scale is significantly shorter in MOND than in equivalent Newtonian systems, i.e. systems with the same phase-space distribution of baryons and additional dark matter. An apparent conflict between this result and the long time-scales determined for bars to slow and mergers to be completed in previous N -body simulations of MOND systems is explained. The confirmation of the short dynamical-friction time-scale in MOND underlines the challenge that the Fornax dwarf spheroidal poses to the viability of MOND.  相似文献   

Robust numerical implementation of a 3D rate-dependent model for reservoir geomechanical simulations     

Giovanni Isotton  Pietro Teatini  Massimiliano Ferronato  Carlo Janna  Nicolò Spiezia  Stefano Mantica  Giorgio Volonte 《国际地质力学数值与分析法杂志》2019,43(18):2752-2771

A 3D elasto-plastic rate-dependent model for rock mechanics is formulated and implemented into a Finite Element (FE) numerical code. The model is based on the approach proposed by Vermeer and Neher (A soft soil model that accounts for creep. In: Proceedings of the International Symposium “Beyond 2000 in Computational Geotechnics,” pages 249-261, 1999). An original strain-driven algorithm with an Inexact Newton iterative scheme is used to compute the state variables for a given strain increment.The model is validated against laboratory measurements, checked on a simplified test case, and used to simulate land subsidence due to groundwater and hydrocarbon production. The numerical results prove computationally effective and robust, thus allowing for the use of the model on real complex geological settings.  相似文献   

Use of a watershed hydrologic model to estimate interbasin groundwater flow in a Costa Rican rainforest          下载免费PDF全文

Carlo Zanon  David P. Genereux  Steven F. Oberbauer 《水文研究》2014,28(10):3670-3680

The watershed hydrologic model TOPMODEL was used to estimate interbasin groundwater flow (IGF) into a small lowland rainforest watershed in Costa Rica. IGF is a common hydrological process but often difficult to quantify. Four‐year simulations (2006–2009) using three different model approaches gave estimates of IGF that were very similar to each other (10.1, 10.2, and 9.8 m/year) and to an earlier estimate (10.0 m/year) based on 1998–2002 data from a budget study that did not use a hydrologic simulation model, providing confidence in the new estimates and suggesting each of the three model approaches is viable. Results show no significant temporal variation in IGF during 2006–2009 (or between this period and the earlier study from 1998–2002). Simulations of the 16 consecutive 3‐month periods in 2006–2009 gave 16 values of IGF rate with a mean (10.1 m/year, standard deviation = 0.6 m/year) very similar to the estimates above from the 4‐year simulations. This suggests the modified version of TOPMODEL can be used to model stream discharge and estimate IGF for sub‐annual time periods during which change in water storage is not necessarily equal to zero. Thus, simple watershed models may be used to estimate IGF based on even relatively short calibration periods, making such models useful tools in the study of this widespread hydrological process that affects water and chemical fluxes and budgets but is often difficult and costly to quantify. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Rappresentazione di curve spaziali materializzate     

Dr. Carlo Bernasconi 《Pure and Applied Geophysics》1951,19(1-2):39-43

Riassunto Per rappresentare una curva spaziale su un piano si può piegare un filo metallico secondo la curva e fotografarlo, operazione che però richiede molto tempo. Nel presente articolo l'A. illustra un dispositivo ottico che, sostituito alla matita della tavola di egresso della macchina diBush, è atto a descrivere su pellicola una curva simile all'immagine fotografica del filo. In questo studio si sono considerati soltanto i casi in cui la sorgente di luce che illumina la è all'infinito o nella origine delle coordinate, mentre il punto di vista à sempre all'infinito.

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Summary One may represent a spatial curve on a plane by bending a metal thread along the curve and then photographing it, but in this way much time is wasted. In the present paper the A. suggests an optical device which, replaced to the pencil of the out-put table ofBush's machine, traces on film a curve that should look like the photographic image of the thread. In this study were taken into account only the cases in which the light source lighting , is at the infinite or in the coordinate origin, while the point of view is always at the infinite.

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La scintillazione delle stelle nella previsione del tempo     

Dott. Carlo Alfredo Murri 《Pure and Applied Geophysics》1944,6(1-2):135-146

Riassunto Richiamate brevemente le conoscenze fondamentali sulla scintillizzazione stellare, si espongono i principi generali di un procedimento inteso a ricavare elementi d'integrazione alle osservazioni sinottiche per la formulazione del presagio meteorico locale, partendo dalla accurata e sistematica misura della scintillazione stessa. Lo studio ha carattere preliminare, contenendo considerazioni generali la cui applicazione dovrà trovare conferma dallo sviluppo delle relative osservazioni.

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Zusammenfassung Nach einem Überblick über die Entwicklung unserer Kenntnissen zur Erklärung des Funkelns der Sterne, gibt der Verf. die allgemeinen Richtlinien einer Methode, welche, stützend auf systematischen Beobachtungen dieser Erscheinung, die synoptischen Verfahren der Wettervorhersage unterstützen und ergänzen kann. Die Schrift gilt als vorläuflge Mitteilung, besonders in Anbetrachtung der Notwendigkeit einer entsprechenden Entwicklung und Verfeinerung der Beobachtungen.

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Misure di magnetismo terrestre in Ungheria     

Prof. Dr. Carlo Kántás 《Pure and Applied Geophysics》1948,13(1-2):11-19

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Reconstruction of a destructive debris‐flow event via numerical modeling: the role of valley geometry on flow dynamics          下载免费PDF全文

Luca Schilirò  Fabio V. De Blasio  Carlo Esposito  Gabriele Scarascia Mugnozza 《地球表面变化过程与地形》2015,40(14):1847-1861

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