Logarithmic spiral trajectories generated by Solar sails     

Marco Bassetto  Lorenzo Niccolai  Alessandro A. Quarta  Giovanni Mengali 《Celestial Mechanics and Dynamical Astronomy》2018,130(2):18

Analytic solutions to continuous thrust-propelled trajectories are available in a few cases only. An interesting case is offered by the logarithmic spiral, that is, a trajectory characterized by a constant flight path angle and a fixed thrust vector direction in an orbital reference frame. The logarithmic spiral is important from a practical point of view, because it may be passively maintained by a Solar sail-based spacecraft. The aim of this paper is to provide a systematic study concerning the possibility of inserting a Solar sail-based spacecraft into a heliocentric logarithmic spiral trajectory without using any impulsive maneuver. The required conditions to be met by the sail in terms of attitude angle, propulsive performance, parking orbit characteristics, and initial position are thoroughly investigated. The closed-form variations of the osculating orbital parameters are analyzed, and the obtained analytical results are used for investigating the phasing maneuver of a Solar sail along an elliptic heliocentric orbit. In this mission scenario, the phasing orbit is composed of two symmetric logarithmic spiral trajectories connected with a coasting arc.  相似文献   

Experiments on Surface Waves Interacting with Flexible Aquatic Vegetation     

Luca Cavallaro  Antonino Viviano  Giovanni Paratore  Enrico Foti 《Ocean Science Journal》2018,53(3):461-474

Surface wave interaction with aquatic vegetation appears to play a key role in coastal hydro-morpho-dynamics. As an example, the presence of a dense meadow at intermediate water depth is usually associated with a stable and resilient shore. Wave-meadow interactions are investigated here by means of physical modelling, with a focus on wave height distribution and hydrodynamics. The central part of a wave flume is covered by flexible artificial seagrass, composed of polyethylene leaves. This vegetation is tested in both near emergent and submerged conditions. The wave height reduction is evaluated by means of a drag coefficient defined from linear wave theory, which contains all the unknowns of the adopted methodology. The behaviour of such a coefficient is investigated as a function of a wave related Reynolds number. The influence of the flexibility of the leaves is also considered, together with a wave frequency parameter. The results show a complex behaviour with three different trends for near rigid, intermediate or highly flexible leaves. Amplitudes of the orbital velocities are investigated and show a fairly good match with the linear wave theory. On the contrary, the mean velocity along the water column appears to be modified by the seagrass for submerged leaves.  相似文献   

Natural highways for end-of-life solutions in the LEO region     

Elisa Maria Alessi  Giulia Schettino  Alessandro Rossi  Giovanni B. Valsecchi 《Celestial Mechanics and Dynamical Astronomy》2018,130(5):34

We present the main findings of a dynamical mapping performed in the Low Earth Orbit region. The results were obtained by propagating an extended grid of initial conditions, considering two different epochs and area-to-mass ratios, by means of a singly averaged numerical propagator. It turns out that dynamical resonances associated with high-degree geopotential harmonics, lunisolar perturbations and Solar radiation pressure can open natural deorbiting highways. For area-to-mass ratios typical of the orbiting intact objects, these corridors can be exploited only in combination with the action exerted by the atmospheric drag. For satellites equipped with an area augmentation device, we show the boundary of application of the drag, and where the Solar radiation pressure can be exploited.  相似文献   

Importance of mixotrophic nanoplankton in Aysén Fjord (Southern Chile) during austral winter     

Till Czypionka  Cristian A. Vargas  Nelson Silva  Giovanni Daneri  Humberto E. González  José Luis Iriarte 《Continental Shelf Research》2011,31(3-4):216-224

Mixotrophy, the combination of autotrophic and heterotrophic nutrition in the same organism, is widespread in planktonic algae. Several reports from temperate and high-latitude fjords in Scandinavia suggest the occurrence of a niche in late summer and autumn during post-bloom conditions in which mixotrophic algae can become important grazers in pelagic ecosystems, accessing the nutrients bound in their prey to overcome nutrient limitation. Here, we experimentally determined the trophic modes and bacterivory rates for the nanoplankton community (2–20 μm) in Aysén Fjord located in the Chilean Northern Patagonia during two contrasting seasons: winter and spring. While mixotrophic nanoplankton was virtually absent from the system in spring, in winter at occasions it even constituted the dominant trophic group of the nanoplankton with abundances of >900 cells mL^?1. This indicates a second niche for mixotrophs in winter, when mixotrophy allows overcoming light limitation.  相似文献   

Early‐middle Holocene land snail shell stable isotope record from Grotta di Latronico 3 (southern Italy)     

André C. Colonese  Giovanni Zanchetta  Elisabeth Dotsika  Russell N. Drysdale  Anthony E. Fallick  Renata Grifoni Cremonesi  Giuseppe Manganelli 《第四纪科学杂志》2010,25(8):1347-1359

This paper compares stable isotope (δ¹⁸O and δ¹³C) records of early–middle Holocene land snail shells from the archaeological deposits of Grotta di Latronico 3 (LTR3; southern Italy) with modern shell isotopic data. No substantial interspecific variability was observed in shell δ¹⁸O (δ¹⁸Os) of modern specimens (Pomatias elegans, Cornu aspersum, Eobania vermiculata, Helix ligata and Marmorana fuscolabiata). In contrast, interspecific shell δ¹³C (δ¹³Cs) variability was significant, probably due to different feeding behaviour among species. The δ¹⁸Os values of living land snails suggest that species hibernate for a long period during colder months, so that the signal of ¹⁸O‐depleted winter rainfall in their δ¹⁸Os is lost. This suggests that δ¹⁸Os and δ¹³Cs values of Pomatias elegans from this archaeological succession provide valuable clues for seasonal (spring–autumn) climatic conditions during the early–middle Holocene. The δ¹⁸Os values of fossil specimens are significantly lower than in modern shells and in agreement with other palaeoclimatic records, suggesting a substantial increase of precipitation and/or persistent changes in air mass source trajectories over this region between ca. 8.8 cal ka BP and 6.2–6.7 ka ago. The δ¹³Cs trend suggests a transition from a slightly ¹³C‐enriched to a ¹³C‐depleted diet between early and middle Holocene compared to present conditions. We postulate that this δ¹³Cs trend might reflect changes in the C3 vegetation community, potentially combined with other environmental factors such as regional moisture increase and the progressive decrease of atmospheric CO₂ concentration. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Multispecies dendroclimatic reconstructions of summer temperature in the European Alps enhanced by trees highly sensitive to temperature     

Giovanni Leonelli  Anna Coppola  Carlo Baroni  Maria Cristina Salvatore  Maurizio Maugeri  Michele Brunetti  Manuela Pelfini 《Climatic change》2016,137(1-2):275-291

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Multi-hazard assessment in Europe under climate change   总被引：2，自引：0，他引：2  

Giovanni Forzieri  Luc Feyen  Simone Russo  Michalis Vousdoukas  Lorenzo Alfieri  Stephen Outten  Mirco Migliavacca  Alessandra Bianchi  Rodrigo Rojas  Alba Cid 《Climatic change》2016,137(1-2):105-119

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A new method for specular and diffuse pseudorange multipath error extraction using wavelet analysis     

Giovanni?Pugliano  Umberto?RobustelliEmail authorView author&#;s OrcID profile  Fabio?Rossi  Raffaele?Santamaria 《GPS Solutions》2016,20(3):499-508

Multipath remains one of the major challenges in Global Navigation Satellite System (GNSS) positioning because it is considered the dominant source of ranging errors, which can be classified into specular and diffuse types. We present a new method using wavelets to extract the pseudorange multipath in the time domain and breaking it down into the two components. The main idea is an analysis-reconstruction approach based on application of both continuous wavelet transform (CWT) and discrete wavelet transform (DWT). The proposed procedure involves the use of L1 code-minus-carrier (CMC) observable where higher-frequency terms are isolated as residuals. CMC residuals are analyzed by applying the CWT, and we propose the scalogram as a technique for discerning time–frequency variations of the multipath signal. Unlike Fourier transform, the potential of the CWT scalogram for examining the non-stationary and multifrequency nature of the multipath is confirmed as it simultaneously allows fine detection and time localization of the most representative frequencies of the signal. This interpretation of the CWT scalogram is relevant when choosing the levels of reconstruction with DWT, allowing accurate time domain extraction of both the specular and diffuse multipath. The performance and robustness of the method and its boundary applicability are assessed. The experiment was carried out using a receiver of Campania GNSS Network. The results are given in which specular multipath error is achieved using DWT level 7 approximation component and diffuse multipath error is achieved using DWT level 6 denoised detail component.  相似文献   

Hexavalent chromium and some trace metals in concrete from buildings of different ages in northern Italy     

Eric Costeri  Giovanni Martinelli  Giampaolo Sighinolfi  Lorenzo Tassi  Paolo Zannini 《Environmental Earth Sciences》2016,75(21):1420

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Activity and kinematic behaviour of deep-seated landslides from PS-InSAR displacement rate measurements     

Paolo Frattini  Giovanni B. Crosta  Micol Rossini  Jacopo Allievi 《Landslides》2018,15(6):1053-1070

Large landslides and deep-seated gravitational slope deformations (DSGSD) represent an important geo-hazard in relation to the deformation of large structures and infrastructures and to the associated secondary landslides. DSGSD movements, although slow (from a few millimetres to several centimetres per year), can continue for very long periods, producing large cumulative displacements and undergoing partial or complete reactivation. Therefore, it is important to map the activity of such phenomena at a regional scale. Ground surface displacements at DSGSD typically range close to the detection limit of monitoring equipment but are suitable for synthetic aperture radar (SAR) interferometry. In this paper, permanent scatterers (PSInSAR?) and SqueeSAR? techniques are used to analyse the activity of 133 DSGSD, in the Central Italian Alps. Statistical indicators for assigning a degree of activity to slope movements from displacement rates are discussed together with methods for analysing the movement and activity distribution within each landslide. In order to assess if a landslide is active or not, with a certain degree of reliability, three indicators are considered as optimal: the mean displacement rate, the activity index (ratio of active PS, displacement rate larger than standard deviation, overall PS) and the nearest neighbor ratio, which allows to describe the degree of clustering of the PS data. According to these criteria, 66% of the phenomena are classified as active in the monitored period 1992–2009. Finally, a new methodology for the use of SAR interferometry data to attain a classification of landslide kinematic behaviour is presented. This methodology is based on the interpretation of longitudinal ground surface displacement rate profiles in the light of numerical simulations of simplified failure geometries. The most common kinematic behaviour is rotational, amounting to 41 DSGSDs, corresponding to the 62.1% of the active phenomena.  相似文献