1,721,029 research outputs found
Interaction between the ion beam produced by an electric thruster and the surface of the host spacecraft.
No full text“Dielectric Measurements of Saline Ices: Implications for Jovian Satellites Radar Exploration”.
No full textCoaxial-Cage Transmission Line for Electromagnetic Parameters Estimation
No full text"We present the measurements performed with a. custom coaxial-cage line designed to determine the complex. dielectric permittivity of large samples, made of granular and\/or. liquid materials. The open structure of the cage facilitates the. filling of the line, and allows the uniform compactness of the. granular materials having large grain size. The electromagnetic. parameters of the samples are retrieved using the line scattering. coefficients (S-parameters), measured with a vector network analyzer. in the frequency range 1MHz to 3 GHz. The measurements. are carried out on water, ethanol, and glass beads using the. Boughriet method, which, for non magnetic materials, optimizes. the Nicolson–Ross–Weir algorithm. The results confirm that such. a device accurately estimates the material complex permittivity. in a wide frequency band. However, at very low frequencies and. at frequencies multiple of the line half-wavelength resonances,. the accuracy significantly reduces. In particular, the accuracy. gets worse for materials with high permittivity and low losses.. Nevertheless, for natural geo-materials, usually characterized by. appreciable losses, the coaxial-cage line can effectively be used. to accurately estimate the material electromagnetic properties in. a wide frequency band.
Satellite deorbiting by means of electrodynamic tethers: system configuration and performance
No full textThermal and electromagnetic models for radar sounding of the Galilean satellite icy crusts
No full textThe icy crusts of the Galilean satellites of Jupiter are supposed to be one of the potentially habitable zones of the solar system, and subsurface water oceans are believed to lie beneath them.
The ice penetrating radar sounder RIME (Radar for Icy Moon Exploration) housed on board the JUICE (JUpiter ICy moons Explorer) mission is expected to probe the icy crust of Europa, Ganymede and Callisto up to a depth of about 9 km. The main objectives of RIME are: the characterization of the ice shell of Ganymede; the detection of melt materials inside the Europa's ice shell; the determination of the regolith thickness on Callisto.
The penetration of the radar signal is strictly connected to the electromagnetic properties of the ice, that in turn depends on the presence of contaminants and temperature profile inside the satellite's crust.
Laboratory measurements carried out in the temperature range of (100-273)K provided the dielectric properties of pure and doped ice (salts, acids and dusts), whereas temperature profiles are obtained taking into account the heat conduction and diapiric convection models for the Galilean satellites.
The combination of electromagnetic and thermal properties of the icy crust, allowed us to generate simulated radar data at the operation frequency of RIME (9 MHz). Such simulations are important to determine the radar performance in the icy crusts, and in particular to estimate the signal penetration and the capability to resolve buried layers
Electromagnetic propagation of GPR signals in Martian subsurface scenarios including material losses and scattering
No full textA study on the electromagnetic propagation in various models of the Martian subsurface is performed with a relevance to ground penetrating radar (GPR) operating onboard rover missions. Measurements of the electromagnetic properties of Mars soil simulants are obtained; on this basis, the attenuation features of the GPR signals are estimated, including both electric and magnetic losses. The effect on propagation of inhomogeneities inside the soil is also taken into account by means of a specific model with randomly distributed scatterers. The GPR performance in terms of resolution and maximum penetration depth is evaluated in the considered scenarios for different operating frequencies, thus providing a basic information for the design of systems for future subsurface sounding investigations on Mars
Studio delle caratteristiche elettriche di un sistema granulare in grado di simulare un suolo marziano
No full textLo scopo di questo lavoro è quello di studiare i fenomeni di rilassamento generati da sistemi granulari in grado di simulare la parte più superficiale del suolo marziano, nell’ipotesi che contenga una significativa percentuale di acqua. I campioni sono stati analizzati mediante spettroscopia dielettrica, in una banda di frequenze compresa tra 0,1Hz e 10MHz. Lo studio è stato sviluppato nell’ambito del progetto A.CQ.U.A., finanziato dall’ A.S.I. rivolto alla realizzazione di un esperimento per la caratterizzazione del suolo marziano, nel sito di atterraggio di un modulo lander di una prossima missione su Marte
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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