1,720,977 research outputs found
Cloud-Top evaluation of a Saturn's giant vortex by Cassini VIMS-V observations
No full textRecent observations of Saturn performed by the Cassini probe, orbiting the ringed system since July 2004, show that a giant oval structure has formed in the planet's North hemisphere. The structure has been observed in different hyperspectral images retrieved by VIMS-V, on board Cassini, starting from May 2011. VIMS is a multi-channel imaging spectrometer, able to produce 2D images of the observed target that also contain their spectral information. The instrument consists of an infrared channel (VIMS-IR) ranging from 0.85 to 5.1 mum and a visual channel (VIMS-V) operating in the wavelength range 0.35 - 1.05 mum; the visual channel has a nominal spectral resolution of 7.3 nm and a nominal angular resolution of 500 murad; in this study we will work on the data collected by this last one. We evaluate the top level of the clouds located over the oval structure observed on January 2012 by VIMS around 35° North latitude, by examining the bottom of the 0.89-mum methane (CH4) absorption band by means of the VIMS-V hyperspectral images analysis. Methane is indeed the most absorbing gas in Saturn's atmosphere in the wavelength range covered by VIMS-V. Moreover, the 0.89 mum absorption band is the strongest in this wavelength range and it allows us to sound the highest levels of the atmosphere. A radiative transfer model has been developed to simulate the radiance field on the planet. This model uses the discrete ordinate solver for a plane parallel atmosphere and considers different configurations of microphysical, optical and geometrical parameters both for clouds and aerosols. These parameters have been tested to fit to the 0.89 mum CH4 absorption band whose depth depends also on the reflection by the highest clouds and/or haze layers. Finally, aerosol parameters must be carefully tuned to obtain the same shape between the synthetic and VIMS-V measured spectra. Vortices have been observed at Saturn since the Voyager missions, but thanks to Cassini we now have the possibility to study their evolution with a better continuity and with high spatial and spectral resolution. The temporal variability for the retrieved cloud-top level is then checked by analyzing two hyperspectral observations imaging the same vortex, recorded on a time lapse of five months. To this extent we'll take advantage of the results obtained in a parallel study (Moriconi et al., 2012) and presented in a second abstract. References M.L. Moriconi, E. D'Aversa, A. Adriani, G.Filacchione: Cassini VIMS-V observations of a giant dynamical structure in the Saturn's northern hemisphere. Abstract submitted to this meeting, 2012
Haze and clouds properties of Saturn's 2011 giant vortex retrieved from Cassini VIMS-V data
No full textThis work is focused on the retrieval of the microphysical and geometrical properties of the clouds and hazes overlying the giant vortex observed in 2011 at Saturn, by the Visual and Infrared Mapping Spectrometer (VIMS) on board of Cassini. The retrieval algorithm is based on the optimal estimation technique [15] and takes advantage of a forward radiative transfer model developed by adapting the LibRadtran code [13] to the atmosphere of Saturn. For each of the retrieved parameters - that are effective radii, top pressures and total number densities for each considered deck - a 2D spatial map has been produced
Vertical structure mapping of Saturn’s 2011 - 2012 giant vortex by means of Cassini VIMS-V data analysis.
No full textOn December 2010 a giant storm erupted in Saturn's North springtime hemisphere. A giant vortex formed in the storm wake and persisted after the principal outburst exhausted on July 2011. The vortex had been imaged several times by the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini probe, starting from May 2011, and it was still present in the December 2012 observations In this work we have analyzed the data recorded by the visual channel of the spectrometer (VIMS-V). VIMS-V operates in the spectral range 350 - 1050 nm with a nominal spectral resolution of 7.3 nm and a nominal angular resolution of 500 murad. Spectral data have been first analyzed by a forward radiative transfer model based on the LibRadtran code, then an inverse model has used to retrieve microphysical and geometrical properties of the clouds overlying the vortex. The forward model relies on the assumptions of a plane parallel atmosphere, multiple scattering, the Mie theory to compute single scattering properties and the molecular scattering adapted to Saturn's atmosphere. The inverse code is based on the optimal estimation technique, it is robust and capable to handle several free parameters at a time. The best fits to the observed radiance spectra are obtained by means of a least square analysis, in which the cost function is minimized taking advantage of the Gauss-Newton method. Applying this procedure, we produced spatial maps for each of the free parameters, including: effective radii for the particles size distributions of each cloud or aerosol deck; total number densities of the particles; and top pressures of each deck. In this work we focused on the data retrieved by VIMS on August 2011. We plan to extend the analysis on data retrieved months later, to map the evolution the parameters undergo in time. The analysis extension to the range 1.0-5.0 micron, covered by the infrared channel of VIMS (VIMS-IR) is also planned
ASA - exploring Materials and Solutions for Hot Structures to be implemente in Next-generation Re-entry/Hypersonic Vehicles
No full text
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
Are Titan aerosols really tholins ? Analysis of VIMS night-side spectra between 4 and 5 μm
No full textVariations 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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
