1,721,062 research outputs found
Influence of ion mass and ion energy on microstructure of ion assisted deposited zinc selenide thin films
No full textZinc selenide thin films have been deposited by an ion beam assisted evaporation system in order to investigate the influence of some deposition parameters, with particular interest on incident ions energy, on film microstructure by means of x-ray diffraction in conventional Bragg-Brentano reflection geometry. Two different ion kinds (Ar and Xe) have been employed during the deposition process in order to analyze the effect of the ion mass on the microstructure of the growing thin film. The correlation of the microstructure and some mechanical properties of films deposited with different parameters has been analyzed. Moreover, thin films composition has been analyzed by Rutherford backscattering technique and the correlation with the energy ions is reported. © 1994, American Vacuum Society. All rights reserved
Effects of proton irradiation on thin-film materials for optical filters
No full textThe behaviour of interference optical filters for space applications has been investigated under low energy proton irradiation. In order to understand the behaviour of the interference coating subjected to proton irradiation, the interaction of protons with coating and substrate was simulated by the SRIM code. A beam of protons of 60 KeV with an integrated fluence of 1013 p+/cm2 was used. The spectral transmittances of fused silica, TiO2 and HfO2 single layers and interference coatings were measured before and after irradiation and, according to simulations, no significant effects were detected in the visible-near infrared spectrum, while some variations appeared at shorter wavelengths. © 2012 ESA and CNES
Photon momentum change of quasi-smooth solar sails
No full textThe solar photon sail (SPS) allows space missions without propellant that would otherwise not be feasible. Thrust models frequently used in the literature for the calculation of trajectories often underestimate the effect that the surface roughness has on SPS dynamics. A small variation of the thrust vector can induce a large modification of sail flight. In this work, the variation of the photon momentum vector (PMV) is computed as resulting from the incident Sun radiation, taking into account the absorbed and reflected photons. The momentum resulting from diffuse light has been modeled by using vectorial scattering theories in the limit of a quasi-smooth sail where the first-order of Rayleigh–Rice can be applied. In particular, the momentum change resulting from diffuse radiation causes a PMV reduction as well as a deviation of its direction from what is foreseen in the case of an ideally smooth sail. © 2018 Optical Society of America
Erosione sociolinguistica nell'italiano di emigrati. Il caso della lunghezza consonantica
No full textEffects of ultraviolet solar photons on thin-film optical filters for space applications
No full textUltraviolet solar photons could induce some variation in the performance of optical coatings exposed to solar irradiation. Consequently optical components and instruments containing such coatings can suffer performance degradation in the space environment. The effects of ultraviolet solar photons on the transmittance of single layer coatings and optical filters, has been investigated. The beamline of a synchrotron light source was used for the irradiation test, being the irradiance in the ultraviolet region comparable to the solar spectrum. Some changes induced by such irradiation are detected in silicon dioxide, which shows an increased absorption below 350 nm. On the contrary, hafnium oxide characteristics seem unaffected. Narrow-band filters containing both these materials show a reduction of transmission in the passband
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
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