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Emiliano?Ortore Marco?Cinelli Christian?CirciEmail author 《Celestial Mechanics and Dynamical Astronomy》2016,124(2):163-175
The determination of analytical expressions which, including the main perturbative effects, allow the retrieval of the orbit elements of a probe represents an important requirement in designing science trajectories. One of these perturbations is given by the third body attraction. The case in which the perturbing body moves on a plane coincident with the equatorial plane of the primary body has been investigated in previous studies and equations able to provide the temporal evolution of the orbit elements have been determined and applied to the main moons of the Solar System. In this paper an extension of this topic has been carried out and equations which allow the determination of the orbit evolution have been analytically retrieved in the general case in which one or more perturbing bodies describe elliptical and inclined orbits with respect to the equatorial plane of the primary. Then, introducing these equations into the periodicity condition for the probe ground track, and considering the \(J_{2}\) and \(J_{4}\) effects coming from the primary body, an equation able to provide repeating ground track orbits has been determined. 相似文献
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Giuseppina Pardi Luigi Piazzi David Balata Ilaria Papi Francesco Cinelli & Lisandro Benedetti-Cecchi 《Marine Ecology》2006,27(4):397-403
This paper investigates patterns of variability in epiphytes of Posidonia oceanica leaves at various spatial scales around Sicily, including geographical differences among the Mediterranean basins, differences between the small islands and mainland, and the variability among and within replicated meadows in each of the previous conditions. Data on percentage cover of the most common epiphytic organisms were analysed by univariate techniques. Encrusting red algae, encrusting brown algae, filamentous algae, encrusting bryozoans, erect bryozoans, hydroids and Foraminifera were the most abundant taxa. Significant differences in the abundance of taxa were detected among geographical regions, while no significant differences were found between the islands and mainland. At smaller scales, variability was concentrated mostly among leaves 100s of centimetres apart and among meadows a few kilometres apart. These results suggest that both geographical and local processes are important in structuring the epiphytes of P. oceanica leaves in this area of the Mediterranean. 相似文献
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Abstract. Posidonia oceanica prairies have been studied and mapped around the Island of Ischia and in adjacent waters. Prairies were found to cover an area of 15.7 km2 and to be distributed between 0.5 and 39 m depth. The observed distribution is comparable to those reported by previous authors indicating that prairies have not undergone remarkable regressions in the last 50 years. Patterns recorded within the beds and at their lower limits, as indicated also by their sediments characteristics, are correlated to hydrodynamic energy. Two main types of water motion are responsible for the different types of erosive features: a) steady currents flowing parallel to the coast; b) rip-, wave induced currents flowing normal to the coast. 相似文献
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Emiliano Ortore Christian Circi Carlo Ulivieri Marco Cinelli 《Earth, Moon, and Planets》2014,111(3-4):157-172
Performances of a planetary observation system are strongly related to the choice of the orbit used. Trajectories with characteristics of periodicity are very useful for the assessment of time-varying phenomena and thus Periodic SunSynchronous and Periodic Multi-SunSynchronous Orbits are particularly suitable to this end. In this paper, the research into these kinds of orbits, previously proposed for the Earth and Mars, has been extended to planets of the Solar System and to their principal moons. In general, these trajectories are typically obtained under the hypothesis that the J2 harmonic is predominant with respect to the other orbital perturbations, since this allows an analytical solution. However, the hypothesis of J2 predominant is not always verified in the Solar System and so analytical techniques must be replaced by numerical simulations. Interesting results have been obtained for the planets Mars and Jupiter and for the moons Europa, Callisto and Titan, where periodic trajectories with reduced revisit times and low altitudes have been found. These solutions allow the observation of time-varying phenomena with high spatial and temporal resolution. 相似文献
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This study tested whether the development of coralligenous assemblages on horizontal and vertical surfaces differed between localities of high and low sediment deposition. The development and structure of these assemblages varied in predictable ways according to the level of sediment deposition. These differences were largely independent of the orientation of substratum. Turfs were more extensive in areas of high sediment deposition while erect and encrusting algae were most extensive in areas of low sediment deposition. Encrusting invertebrates characterised vertical surfaces and were most extensive in areas of high sediment deposition. These results are consistent with studies from other temperate regions of the globe, suggesting that effects of sedimentation on temperate coasts are substantial and widespread. 相似文献
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David Balata Stefano Acunto Francesco Cinelli 《Estuarine, Coastal and Shelf Science》2006,67(4):553-561
Natural assemblages show large variability at multiple scales in space and time as a consequence of several abiotic and biological factors. This study was conducted in conditions of high turbidity of the water and examined the spatio-temporal variability and the vertical distribution at two different depths of a low rocky subtidal assemblage. Algal and invertebrate organisms were sampled at a range of spatial scales extending from meters to a few kilometers, over a period of 21 months. Results indicated that patterns of distribution and abundance of organisms differed between the two depths and at the smallest spatial scales examined. These differences were due to differences in relative abundance rather than differences in composition of taxa. Results showed that assemblages varied largely among dates of sampling, suggesting that temporal variability of these organisms may be more important than previously stated. The patchy distribution and the peculiar life traits of most taxa of these assemblages allowed the concept of metapopulation and metacommunity to be applied to this system. This might have implications for predictions of the responses of subtidal assemblages to environmental changes due to anthropogenic activities. 相似文献
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Abstract. P. oceanica forms broad prairies which completely surround the island of Ischia. This is a histochemical and ultrastructural study of the photosynthetic apparatus of the Posidonia plant. In the leaf, epidermal cells have a porous region underneath the cuticle and contain most of the chloroplasts. Fiber bundles run hypodermally and phenol storing cells are present in the mesophyll. Chloroplast ontogenesis is characterized by juvenile stages with provesicular bodies. Sea depth apparently affects some morphological features of the photosynthetic apparatus, like leaf blade thickness, phenolic cell and hypodermal fiber frequency. 相似文献
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A Comparison Among Assemblages in Areas Invaded by Caulerpa taxifolia and C. racemosa on a Subtidal Mediterranean Rocky Bottom 总被引：1，自引：0，他引：1
Abstract. This study compares the structure of Mediterranean macroalgal assemblages invaded by Caulerpa taxifolia and C. racemosa . Assemblages in areas colonized by the two algae and in reference areas were sampled and analyzed for 2 years. Significant differences were recorded both between reference and invaded areas and between areas invaded by different Caulerpa species. Macroalgal assemblages colonized by C. racemosa were more separated from references than those colonized by C. taxifolia . Differences between assemblages colonized by C. racemosa and the others decreased during the alga's period of vegetative rest and increased at the last sampling date. While erect and turf species showed similar patterns in invaded areas, covers of encrusting algae were lower in C. racemosa areas than in C. taxifolia areas. 相似文献
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A radon risk map for the Walloon region of Belgium, based on the two databases available, has been calculated and is presented
in this work. The data are organized into geological units. For each unit, an average logarithmic standard deviation is calculated,
after correcting the higher variability of short term data. The region is divided with an 1-km grid. For each node, the local
geological unit is determined, as well as the corresponding logarithmic standard deviation. The logarithmic mean is evaluated
by smoothing the data belonging to the same geological unit as the node. Assuming a log-normal distribution, a map that shows
for each node the predicted percentage of buildings with an indoor radon concentration above the Action level (400 Bq/m3) is constructed. This is the first radon risk map for this region that fully takes into account the geological information. 相似文献