Application of ‘CLEAN’ in the power spectral analysis of non-uniformly sampled pulsar timing data     

A. A. Deshpande  F. D’Alessandro  P. M. McCulloch 《Journal of Astrophysics and Astronomy》1996,17(1-2):7-16

Spectral analysis of the residual pulsearrival times of pulsars is a useful tool in understanding the nature of the underlying processes that may be responsible for the timing noise observed from pulsars. Power spectra of pulsar timing residuals may be described by one or a combination of powerlaws. As these spectra are expected to be very steep, it is important to ensure a high dynamic range in the estimation of the spectrum. This is difficult in practice since one is, in general, dealing with timing measurements made at unevenly placed epochs. In this paper, we present a technique based on, ‘CLEAN’ to obtain high dynamic range spectra from unevenly sampled data. We compare the performance of this technique with other techniques including some that were used earlier for estimation of power spectra of pulsar timing residuals.  相似文献   

Construction of a Nekhoroshev like result for the asteroid belt dynamical system     

Massimilliano Guzzo  Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》1996,66(3):255-292

We investigate the possibility of obtaining a Nekhoroshev like result for the dynamical system describing the motion of an asteroid in the main belt, From the mathematical point of view this is a new result since the problem is degenerate and we want to control also the motion of degenerate actions, We find that there are regions, such as the resonances of low order among the fast angles (mean motion resonances), where a Nekhoroshev like result cannot be proved a priori, Conversely, we are able to confine the motions in the mean motion resonances of logarithmically large order in the perturbation parameters, as well as in the non-resonant region, We discuss also the connection with the existence of invariant tori.  相似文献   

The Kozai resonance in the outer solar system and the dynamics of long-period comets     

Fabrice Thomas  Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》1996,64(3):209-229

We consider the secular evolution of the orbits of bodies in the Outer Solar System under the perturbations of the jovian planets assumed on coplanar and circular orbits. Through the approach used for asteroidal belt by Yoshihide Kozai in 1962, we obtain that the Kozai resonance do not affect the behavior of bodies belonging to the Kuiper belt but concerns the long-timescale evolution of long-period comets. In particular this resonance appears as a process contributing to produce Sun-grazer comets.  相似文献   

Luni-solar effects of geosynchronous orbits at the critical inclination     

Fabienne Delhaise  Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》1993,57(1-2):155-173

The luni-solar effects of a geosynchronous artificial satellite orbiting near the critical inclination is investigated. To tackle this four-degrees-of-freedom problem, a preliminary exploration separately analyzing each harmonic formed by a combination of the satellite longitude of the node and the Moon longitude of the node is opportune. This study demonstrates that the dynamics induced by these harmonics does not show resonance phenomena. In a second approach, the number of degrees of freedom is halved by averaging the total Hamiltonian over the two non-resonant angular variables. A semi-numerical method can now be applied as was done when considering solely the inhomogeneity of the geopotential (see Delhaise et Henrard, 1992). Approximate surfaces of section are constructed in the plane of the inclination and argument of perigee. The main effects of the Sun and Moon attractions compared to the terrestrial attraction alone are a strong increase in the amplitude of libration in inclination (from 0.6° to 3.2°) and a decrease of the corresponding libration period (from the order of 200 years to the order of 20 years).Research Assistant for the Belgian National Fund for Scientific Research  相似文献   

Fluids in early stage hydrothermal alteration of high-sulfidation epithermal systems: A view from the Vulcano active hydrothermal system (Aeolian Island,Italy)     

Adrian J. Boyce  Paolo Fulignati  Alessandro Sbrana  Anthony E. Fallick 《Journal of Volcanology and Geothermal Research》2007

High-sulfidation (HS) epithermal systems have elements in common with passively degassing volcanoes associated with high T, acid fumarole fields or acid crater lakes. They are considered to form in two stages, the first of which involves advanced argillic alteration resulting from intense, strongly acidic fluid–rock interaction. The La Fossa hydrothermal system (Vulcano Island) represents a classic example of such an active HS system and can be considered as a modern analogue of this early stage of alteration, resulting in a core of intense silicic (90–95% pure SiO₂) alteration surrounded by alunitic alteration zones.  相似文献   

A robust empirical model to estimate earthquake-induced excess pore water pressure in saturated and non-saturated soils     

Mele  Lucia  Chiaradonna  Anna  Lirer  Stefania  Flora  Alessandro 《Bulletin of Earthquake Engineering》2021,19(10):3865-3893

In engineering practice, the liquefaction potential of a sandy soil is usually evaluated with a semi-empirical, stress-based approach computing a factor of safety in free field conditions, defined as the ratio between the liquefaction resistance (capacity) and the seismic demand. By so doing, an estimate of liquefaction potential is obtained, but nothing is known on the pore pressure increments (often expressed in the form of normalized pore pressure ratio r_u) generated by the seismic action when the safety factor is higher than 1. Even though r_u can be estimated using complex numerical analyses, it would be extremely useful to have a simplified procedure to estimate them consistent with the stress-based approach adopted to check the safety conditions. This paper proposes such a procedure with reference to both saturated and unsaturated soils, considering the latter as soils for which partial saturation has been artificially generated with some ground improvement technology to increase cyclic strength and thus tackle liquefaction risk. A simple relationship between the liquefaction free field safety factor FS, and r_u(S_r) is introduced, that generalizes a previous expression proposed by Chiaradonna and Flora (Geotech Lett, 2020. https://doi.org/10.1680/jgele.19.00032) for saturated soils. The new procedure has been successfully verified against some experimental data, coming from laboratory constant amplitude cyclic tests and from centrifuge tests with irregular acceleration time histories for soils having different gradings and densities.

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Dynamical downscaling of CMIP5 global circulation models over CORDEX-Africa with COSMO-CLM: evaluation over the present climate and analysis of the added value   总被引：2，自引：1，他引：1  

Alessandro Dosio  Hans-Jürgen Panitz  Martina Schubert-Frisius  Daniel Lüthi 《Climate Dynamics》2015,44(9-10):2637-2661

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Affluence drives the global displacement of land use   总被引：2，自引：0，他引：2  

Jan Weinzettel  Edgar G. Hertwich  Glen P. Peters  Kjartan Steen-Olsen  Alessandro Galli 《Global Environmental Change》2013,23(2):433-438

Increasing affluence is often postulated as a main driver for the human footprint on biologically productive areas, identified among the main causes of biodiversity loss, but causal relationships are obscured by international trade. Here, we trace the use of land and ocean area through international supply chains to final consumption, modeling agricultural, food, and forestry products on a high level of resolution while also including the land requirements of manufactured goods and services. In 2004, high-income countries required more biologically productive land per capita than low-income countries, but this connection could only be identified when land used to produce internationally traded products was taken into account, because higher-income countries tend to displace a larger fraction of land use. The equivalent land and ocean area footprint of nations increased by a third for each doubling of income, with all variables analyzed on a per capita basis. This increase came largely from imports, which increased proportionally to income. Export depended mostly on the capacity of countries to produce useful biomass, the biocapacity. Our analysis clearly shows that countries with a high biocapacity per capita tend to spare more land for nature. Biocapacity per capita can be increased through more intensive production or by reducing population density. The net displacement of land use from high-income to low-income countries amounted to 6% of the global land demand, even though high-income countries had more land available per capita than low-income countries. In particular, Europe and Japan placed high pressure on ecosystems in lower-income countries.  相似文献   

Role of vegetation in shaping Early Pennsylvanian braided rivers: Architecture of the Boss Point Formation,Atlantic Canada     

Alessandro Ielpi  Martin R. Gibling  Arden R. Bashforth  Corinne Lally  Michael C. Rygel  Saif Al‐Silwadi 《Sedimentology》2014,61(6):1659-1700

Vegetation is a major driver of fluvial dynamics in modern rivers, but few facies models incorporate its influence. This article partially fills that gap by documenting the stratigraphy, architecture and palaeobotany of the Lower Pennsylvanian Boss Point Formation of Atlantic Canada, which contains some of the Earth's earliest accumulations of large woody debris. Braided‐fluvial systems occupied channel belts of varied scale within valleys several tens of metres deep and more than 12 km wide, and their deposits predominantly consist of sandy and gravelly bedforms with subordinate accretionary macroforms, high flow‐strength sand sheets and rippled abandonment facies. Discrete accumulations of clastic detritus and woody debris are up to 6 m thick and constitute at least 18% of the in‐channel deposits; they represent lags at the base of large and small channels, fills of minor channels and sandy macroforms that developed in central positions in the upper parts of channel fills. Sandstones with roots and other remnants of in situ vegetation demonstrate that vegetated islands were present, and the abundance of discrete channel fills suggests that the formation represents an anabranching, island‐braided sandbed river, the earliest example documented to date. Although some sphenopsid and lycopsid remains are present, most woody fragments are derived from cordaitalean trees, and the evolution of this group late in the Mississippian is inferred to have exerted a significant influence on fluvial morphodynamic patterns. The formation records a landscape in which active channel belts alternated with well‐drained floodplains colonized by dense, mature forests and local patches of pioneering, disturbance‐tolerant vegetation. Lakes and poorly drained floodplains dominated by carbonate and organic deposition, respectively, were also present. A large supply of woody debris triggered channel blockage and avulsion, and active channel margins and islands within the channel belts were initially colonized by pioneer vegetation and subsequently stabilized by large trees. A similar alternation of stable and unstable conditions is observed in modern braided rivers actively influenced by vegetation.  相似文献   

Excavation of the Aica-Mules pilot tunnel for the Brenner base tunnel: information gained on water inflows in tunnels in granitic massifs   总被引：1，自引：1，他引：0  

Paolo Perello  Alessandro Baietto  Ulrich Burger  Stefan Skuk 《Rock Mechanics and Rock Engineering》2014,47(3):1049-1071

The construction of the Aica-Mules tunnel, completed in 2010, provides a relevant case history for improving the knowledge of hydrogeological issues related to the excavation of deep tunnels in granitic massifs. The Aica-Mules tunnel is a 10 km-long structure, forming part of the high-speed railway connection between Austria and Italy across the Alpine chain, located at an average depth of 500–1,000 m below the surface. Prior to and during the construction, intense hydrogeological monitoring was set up, allowing the collection of abundant data concerning: (1) the evolution of water inflows into the tunnel; (2) the chemistry and temperature of drained groundwater; and (3) the influence of tunnel drainage on springs. Based on detailed analysis of geological/hydrogeological data, this article provides an insight into the permeability distribution in granitic rocks affected by relevant brittle tectonic deformation, and the consequences of water inflow during excavation. The available time series from the principal water discharges in the tunnel have been used in order to test the reliability of some of the most commonly applied analytical methods for the forecast of water inflows into tunnels.  相似文献