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排序方式: 共有285条查询结果,搜索用时 15 毫秒
111.
José Franco Stan E. Kurtz José A. GarcÍa-Barreto Guillermo GarcÍa-Segura Eduardo de la Fuente Peter Hofner Alejandro Esquivel 《Astrophysics and Space Science》2001,277(1):71-74
Here we discuss the effects of large ambient pressures and decreasing density gradients on the observed properties of dusty UC hii regions. Dust absorption can effectively reduce the size of the photo ionized region, and density gradients can modify the spectral index of the emission. The effects of the density gradients seem to be present in both galactic and extragalactic HII regions. 相似文献
112.
Geophysical interpretation of a high-resolution seismic refraction profile in the Northern Apennines
Giancarlo Biella Roberto De Franco Martina Demartin Riccardo Barzaghi Fernando Sanso Domenico Sguerso 《地学学报》1994,6(1):45-53
A combined seismic and gravimetric interpretation in the Northern Apennines area (Italy) is presented. To the knowledge of the authors, this is one of the few attempts to apply tomographic methodology to a seismic refraction profile. This procedure, together with the classical interpretation for defining lower reflectors, led to the formulation of quite an accurate model of the upper crust. A gravity analysis was performed concurrently taking into account the seismic results at different depths which correspond to different frequency domains in the gravity signal. While the medium- and high-frequency patterns have been solved by trial-and-error, the regional trend has been modelled applying the collocation procedure to the gravity data. 相似文献
113.
Photoelectric observations of several minor planets were made from 1975 to 1977 at the Astronomical Observatory of Torino. Lightcurves and period information are given for 7 objects: 37 Fides, 80 Sappho, 97 Klotho, 216 Kleopatra, 270 Anahita, 313 Chaldaea, and 471 Papagena. 相似文献
114.
The angular diameter of minor planets compared with best observation conditions of about one arcsec (seeing) at ground-based observatories, though situated at high sea levels with best climate conditions, usually is too small to be resolved for surface studies or diameter determinations with direct photographic or similar imaging methods.Nevertheless the rough geometry and/or small scale structures on the asteroid's surface can be studied with light-curve observations using high precision photoelectric photometry and the fact that the rotation of an asteroid during a spin period is now determined for slightly more than 200 minor planets.On only a few selected asteroids (63 Ausonia, 88 Thisbe, 92 Undina, 110 Lydia, 118 Peitho, 128 Nemesis, 139 Juewa, 337 Devosa and 599 Luisa) do we show, from details detected in the light-curves, how observations of this type were carried out successfully. From the small scale features we get the rough linear extensions on the asteroid surface from differences in magnitude and time. Such observations will be more useful and important in future with respect to an optimum selection of objects for a possible direct asteroid spacecraft mission.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.Visiting Astronomer, Kitt Peak National Observatory, USA, Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation. A part of the observations was carried out at the Observatoire de Haute Provence (OHP), France. 相似文献
115.
Annalisa?Bracco Fred?KucharskiEmail author Rameshan?Kallummal Franco?Molteni 《Climate Dynamics》2004,23(6):659-678
An atmospheric general circulation model of intermediate complexity is used to investigate the origin and structure of the climate change in the second half of the twentieth century. The variability of the atmospheric flow is considered as a superposition of an internal part, due to intrinsic dynamical variability, and an external part, due to the variations of the sea surface temperature (SST) forcing. The two components are identified by performing a 50-member ensemble of atmospheric simulations with prescribed, observed SSTs in the period 1949–2002. The large number of realizations allows the estimation of statistics of the atmospheric variability with a high confidence level. The analysis performed focuses on interdecadal and interannual variability of 500 hPa geopotential height in the Northern Hemisphere (NH) during winter. The model reproduces well the structure of the observed trend (defined as the difference in the two 25-year intervals 1977–2001 and 1952–1976), particularly in the Pacific region, and about half of the amplitude of the signal. The trend in 500 hPa height projects mainly onto the second empirical orthogonal function (EOF), both in the observations and in the model ensemble. However, differences between the modelled and the observed variability are found in the pattern of the second EOF in the Atlantic sector. SST changes associated with the El Niño southern oscillation (ENSO) are responsible for about 50% of the signal of the 500 hPa height trend in the Pacific. A second 50-member ensemble is used to evaluate the sensitivity of interdecadal variability to an increase in CO2 optical depth compatible with observed concentration changes. In this second experiment, the simulated trend includes a statistically significant contribution from the positive phase of the Arctic oscillation (AO). Such a contribution is also found in observations. Furthermore, the additional CO2 forcing accounts for part of the NH trend in near-surface temperature, and brings the zonal-mean temperature changes in the stratosphere and upper-troposphere closer to observations.
相似文献
Fred KucharskiEmail: |
116.
Franco Mattioli 《Applied Ocean Research》1981,3(1):37-42
An integral method is described which is capable of computing the diffraction field produced by waves incident on a breakwater connected to or placed near a straight coastline. Some simple configurations are studied: a straight breakwater protruding normally from the coast, a straight breakwater parallel to the coast, an ‘elbow-shaped’ breakwater with one end connected to the coast, a pair of straight breakwaters protruding normally from the coast and a series of three equal straight breakwaters parallel to the coast. In all cases the water depth is assumed to be constant, while both the breakwater and the coastline walls are supposed to be perfectly reflective. Within the limits of these hypotheses the method is rather general, because breakwaters of arbitrary shape can be considered. 相似文献
117.
Riccardo Briganti Giorgio Bellotti Leopoldo Franco Julien De Rouck Jimmy Geeraerts 《Coastal Engineering》2005,52(12):351-1174
This paper describes a new station for full-scale measurement of wave overtopping at the Rome yacht harbour rubble mound breakwater in Ostia (Italy) and the results of the successful first measurement campaign carried out during the winter season 2003–2004. The equipment and the research activities were supported by the EU project CLASH, focusing on scale effects for wave overtopping at coastal structures. The site is characterized by a very small tidal range, a long shallow foreshore and depth-limited breaking waves which interact with a shallow sloping porous rock structure. Overtopping water is collected by a steel tank installed on the crown slab behind the parapet wall. The measurement of water level variation inside the tank by means of two pressure transducers allows the calculation of individual overtopping volumes. Incident waves, sea levels and wind are also measured. During seven independent storms, more than 400 individual overtopping events were recorded and about 86 h of valid data are available. This extensive dataset is presented, discussed and then used for comparison with two commonly used overtopping prediction formulae based on small-scale model tests showing their tendency to underestimate the prototype results. A strong correlation between the hourly mean overtopping discharge and corresponding maximum volume is also presented. The paper generally confirms the validity of the approach used in Troch et al. (2004) [Troch, P., Geeraets, J., Van de Walle, B., De Rouck, J., Van Damme, L., Allsop, W., Franco, L., 2004. Full-scale wave overtopping measurements on the Zeebrugge rubble mound breakwater. Coastal Engineering 51, 609–628] for field measurement of wave overtopping. 相似文献
118.
119.
Franco Gianotti Maria Gabriella Forno Susan Ivy-Ochs Peter W. Kubik 《Quaternary International》2008,190(1):123
The Ivrea amphitheatre (IA) in NW Italy has been studied since 1850, on pedostratigraphic and morphological bases. Three stratigraphic groups of glacial sediments were distinguished. Newly recognized stratigraphic boundaries are based on interstadial/interglacial units, palaeosols and lacustrine organic layers interbedded with glacigenic deposits, and on pedostratigraphy. Mapping of morphological features and associated marginal and sub-glacial deposit facies was used to characterize and reconstruct glacial margin fluctuations. Based on the field evidence, the stratigraphical limits recognized at single sites can be interpolated over the whole amphitheatre. Ten stratigraphic units (referred to as alloformations: Afs) were distinguished and mapped. They are related to at least as many glacial episodes ranging in age from the end of the Early Pleistocene to the Late Pleistocene. The youngest three glacial units (Serra Af, Piverone Af and Ivrea Af) and one interstadial level (Alice Superiore Unit between Serra and Piverone Afs) are discussed in detail. Based on biostratigraphical and pedological, as well as sedimentological and morphological data, the Serra Af can be attributed to MIS 6 and Piverone Af to MIS 4. The 10Be surface exposure ages from two boulders (27.9±3.1, 32.4±4.0 kyr) on the Serra d’Ivrea moraine provide only a minimum age for moraine construction. The alignment of typical ice marginal landforms (moraines and kame terraces) for the more recent unit (Ivrea Af) has allowed recognition of 12 principal stadials during the LGM and Lateglacial; 6 stadials in the amphitheatre and 6 stadials in Dora Baltea Valley, and reconstruction of the nature of the last glacial retreat from the amphitheatre to the cirques. 10Be exposure ages from three boulders related to Ivrea Af are 13.1±1.0, 17.4±2.6 and 20.8±1.5 ka. The latter two ages indicate that the Dora Baltea Glacier deposited the Ivrea Af in the IA during MIS 2. The 10Be exposure ages of 14.6±1.2 and 14.0±0.9 ka from a polished bedrock surface some 15 km upstream from the amphitheatre provide a minimum age for ice decay. 相似文献
120.