1,720,977 research outputs found
Spectral studies in view of the Hera mission
No full textDidymos is a binary asteroid system composed of (65803) Didymos and its
small satellite, Dimorphos. The NASA’s DART planetary defense mission
demonstrated the possibility of asteroid deflection by changing the Dimorphos
orbit through an artificial impact. Understanding the physical and compositional
characteristics of the target is crucial for analyzing the outcomes of this
impact experiment.
The Hera mission, developed by the European Space Agency (ESA), was
launched in October 2024, to study the Didymos system and to investigate
the aftermath of the DART impact on Dimorphos, assessing any changes to
its orbit and surface characteristics. The mission will gather critical data
regarding the composition and structure of both Didymos and Dimorphos,
providing invaluable insights into the nature of these small solar system bodies.
By enhancing our knowledge of these asteroids, Hera will play a pivotal role in
refining our planetary defense strategies and improving our understanding of
the building blocks of the solar system.
This dissertation aims to conduct spectroscopic studies in preparation
for the Hera mission, with a particular focus on the ASPECT spectrometer.
It begins with the search for meteorite which best reproduce Didymos; this
selection will be very useful in preparation for Didymos studies, in particular to
assess space weathering effects (i.e., solar wind, micrometeoroid bombardments
and cosmic ray effects) and photometric behaviors (i.e., changes in the spectral
shape due to different phase angles of observation) on spectroscopic data. Additionally,
identifying these analogues may assist in calibrating the instruments
aboard the Hera mission. We utilized two online databases of meteorite spectra
along with recent spectra of Didymos captured both before and after the DART
impact. Our initial selection was carried out by comparing the band center
values of the silicate absorption bands, localized at 1 and 2 μm, between Didymos
and the meteorites. In the second selection a four-dimensional parameter
space was defined, where the dimensions corresponded to the band depth and
the slope of the two absorption bands, each normalized to Didymos values. We
then identified the meteorites closest to Didymos within this space. A final
selection took into account multiple spectra of the same meteorite (especially
those from different databases), the match in the Mid Infrared (MIR), and
the comparison with the literature. One of the results of this work is a list of
six meteorites that are the most analogous to the Didymos system. We also
found out that Didymos is most probably mainly composed of L/LL ordinary
chondrites, with a preference for the LL sub-type. From our list of meteorites,
we were able to estimate the normalized abundance of olivine and pyroxene
of Didymos. Finally, a match between Didymos and OC meteorites was also
found in the Mid-InfraRed (MIR) range.
Another goal of this thesis is the definition of new spectra parameters to
maximize the scientific return from the ASPECT spectrometer on board Hera,
by inferring the Didymos system composition of the olivine and pyroxene
relative abundance (olv/(olv +pyx)). ASPECT data range from the visible up
to shortwave infrared (SWIR) wavelengths (650-2500 nm) using four different
channels. The SWIR channel, being a single-pixel channel, has a much lower
spatial resolution than the other three channels. Consequently, for the highestresolution
mapping of the Didymos surface, we concentrated on the first three
channels (650–1600 nm). So, new spectral parameters should be defined
within this limited spectral range. For this reason, we first analyzed spectral
parameters over a broader range commonly used in the literature to determine
the composition of S-type asteroids. We then developed new methods specific to
the ASPECT instrument’s spectral range to determine the mineral composition
of Didymos and, more broadly, of S-type asteroids or other type of asteroids
with a silicate surface (such as Vesta). These methods were initially established
using binary mineral mixtures, then calibrated and validated with ordinary
chondrite meteorites. To further validate these methods, we applied them to
other asteroids previously visited by spacecraft, Vesta and Itokawa. The result
of this work is a comprehensive analysis procedure, designed for ASPECT data,
that enables a detailed mapping of mineral distributions across the asteroid’s
surface.
Finally, a method to retrieve and study hydroxyl signatures was defined (in
view of the Didymos exploration) and applied to Vesta. We took advantage of
the newly calibrated data of the VIR spectrometer onboard the NASA’s Dawn
mission to characterize spectral features not or weakly detected in previous
studies thanks to the improved signal-to-noise (S/N) ratio for these spectra. The
goals were to confirm, reinforce and characterize the OH distribution on Vesta
by studying the 2.8 μm band and to look for OH combination bands around
2.2–2.4 μm by defining a spectral analysis procedure that could be applied
also to the ASPECT data. The analysis of hydroxyl absorption bands revealed
an anti-correlation between the abundance of hydroxyl-bearing molecules and
surface reflectance, supporting the link between hydroxyl presence and Vesta’s
dark units. This finding reinforces the hypothesis that the dark areas on Vesta
are due to exogenous carbonaceous chondrites, which are often characterized
by hydroxyl-bearing molecules. Otherwise, no 2.2–2.4 μm feature associated
with OH was detected, indicating that it is not related to hydroxyl presence.
Nonetheless, the method developed for investigating this feature will still be
applied to ASPECT data for further analysis of the Didymos asteroid.
In conclusion, this research not only provides critical insights into the
composition and characteristics of Didymos but also establishes methodologies
that can be instrumental in analyzing the data that will be obtained from
the Hera mission. The findings and techniques developed herein serve as a
foundation for enhanced understanding of small solar system bodies and their
roles in planetary science
Antenna arrays diagnosis through inverse-based approaches
No full textTwo effective regularization approaches for detecting faults in antenna arrays are discussed in this paper. The first one exploit the matrix method for fast and low-cost diagnostics. The second technique relies upon an inversion scheme in Lebesgue spaces, allowing an effective regularization of the problem. Preliminary results are discussed, showing the effectiveness of the approaches
Hybrid microwave approach for phaseless imaging of dielectric targets
No full textA hybrid approach for phaseless imaging of dielectric targets is proposed in this letter. A two-probe measurement strategy with the related phase-retrieval method is adopted in conjunction with an inversion procedure based on an inexactNewton method to give an efficient and low-cost imaging setup, avoiding the need of multiple acquisition surfaces. A preliminary experimental validation on real input data is presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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