324,999 research outputs found
Mission analysis and design of FAR FLYERS (Fractionated-aperture radar based on formation flying for parasitic earth remote sensing)
No full textThis paper presents a preliminary study on the feasibility of a passive distributed radar, realized through a formation of compact satellite receivers flying in Low Earth Orbit (LEO). The cluster is conceived to capture the backscattered echoes of existing space-borne SAR satellites operating in C and X bands. Moreover, it is designed to be rapidly re-configurable. This feature allows the component antennas to change their arrangement in order to perform different multi-static applications, thus overcoming the intrinsic limitations of conventional InSAR techniques, such as along-track interferometry for MTI and cross-track interferometry for DEM generation. The paper focuses on the analysis of the relative dynamics of the space systems involved. The formation is supposed to work with different transmitters, thus very low altitude orbits (order of 300-350 km) are selected to enhance the number of "conjunctions" with active satellites and to achieve a limited lifetime. Flying the receivers at a completely different altitude from the transmitters (generally orbiting around 500-800 km) makes multi-static acquisitions achievable only at given times, when the along-track separation is below a threshold. Moreover, the difference in altitude implies different perturbing effects on the satellite trajectories, with the cluster being affected by the aerodynamic drag to a greater extent. Firstly the relative motion between the illuminator(s) and the cluster imagined as a single satellite is considered. Two different solutions are investigated, with the receiver "co-rotating" or "counter-rotating" with the transmitter(s). Then the problem of the formation design is addressed, with emphasis on relative trajectories that both satisfy multi-static observation requirements and minimize control efforts. The design approach exploits all the degrees of freedom offered by natural dynamics, on the basis of two main concepts: (a) choosing nominal dynamics that is highly stable in presence of orbit perturbations such as Earth oblateness effect, and (b) designing trajectories that minimize the collision risk using "passively safe" configurations. Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved
Lavori di Pubblica Utilità e Reddito Minimo d’Inserimento in Italia: un’analisi della popolazione beneficiaria
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Present and novel biologic drugs in primary Sjogren's syndrome
No full textPrimary Sjogren's syndrome (pSS) is a systemic autoimmune disease characterised by xerostomia and xerophthalmia. In at least one-third of patients, the disease may be complicated by extraglandular involvement. Due to the lack of evidence-based recommendations, current therapeutic options for pSS are mainly empirical, often reflecting their use in other autoimmune diseases. Nevertheless, recent advances in the understanding of pathogenic pathways in pSS encourage the belief that blocking them may be of value in the treatment of the disease. Despite failing to demonstrate efficacy in clinical trials, because of the well-established role of B-lymphocytes in the pathogenesis of pSS, rituximab has been the most frequently used to date, but with much less success than in the treatment of patients with rheumatoid arthritis, vasculitis and lupus. However, in the last few years a number of other biologics have been developed and are under investigation. The aim of this article is to review the use of biologic therapies in pSS
Urban reuse as a chance for an inclusive growth in the European context. The case of coworking and fablabs in Italy
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