1,721,046 research outputs found
Stereo Camera for satellite application: A new testing method
No full textThe Stereo Camera (STC) of the SIMBIO-SYS imaging suite of the BepiColombo ESA mission to Mercury is based on an innovative and compact design in which the light, independently collected by two optical channels at ±20° separation with respect to nadir, falls on a common bidimensional detector. STC adopts a novel stereo acquisition mode, based on the push-frame concept, never used before on a space mission
Complex history of the Rembrandt basin and scarp system, Mercury
No full textDuring its second and third flybys, the
MESSENGER spacecraft imaged the wellpreserved
Rembrandt basin in Mercury’s southern
hemisphere. With a diameter of 715 km, Rembrandt
is the second largest impact structure recognized on
Mercury after the 1550-km-diameter Caloris basin.
Rembrandt is also one of the youngest major basins
and formed near the end of the Late Heavy
Bombardment (~3.8 Ga). Much of the basin interior
has been resurfaced by smooth, high-reflectance units
interpreted to be of volcanic origin. These units
host sets of contractional and extensional landforms
generally oriented in directions radial or concentric to
the basin, similar to those observed within the Caloris
basin; these structures are probably products of
multiple episodes of deformation.
Of particular note in the Rembrandt area is a
1,000-km-long reverse fault system that cuts the
basin at its western rim and bends eastward toward
the north, tapering into the impact material. On the
basis of its shape, the structure has previously been
characterized as a lobate scarp. Its formation and
localization have been attributed to the global
contraction of Mercury.
From MESSENGER flyby and orbital images, we
have identified previously unrecognized kinematic
indicators of strike-slip motion along the Rembrandt
scarp, together with evidence of interaction between
the scarp orientation and the concentric basin-related
structural pattern described above. Here we show
through cross-cutting relationships and scarp
morphology that the development of the Rembrandt
scarp was strongly influenced by tectonics related to
basin formation and evolution
MPF model ages of the Rembrandt basin and scarp system, Mercury.
No full textThe 715-km-diameter Rembrandt basin is the largest well-preserved impact feature of the southern hemisphere
of Mercury, and was imaged for the first time during the second flyby of the MErcury Surface, Space
ENvironment, GEochemistry, and Ranging (MESSENGER) mission. Much of the basin interior is covered
by smooth, high-reflectance plains interpreted to be of volcanic origin that host sets of contractional and
extensional tectonic structures. Notably, Rembrandt basin and its smooth plains are cross-cut by a 1,000-km-long
reverse fault system that trends E–W, bending toward the north within the basin. The individual faults of
this system accommodated crustal shortening that resulted from global contraction as Mercury’s interior cooled. The current shape of the reverse fault system may have been influenced by the formation of the Rembrandt
basin.
The emplacement of the interior smooth plains predates both the basin-related tectonism and the final development
of the giant scarp, which is suggestive of either short-lived volcanic activity immediately after basin formation or
a later volcanic phase set against prolonged tectonic activity.
In order to quantify the duration of volcanic and tectonic activity in and around Rembrandt basin, we determined
the crater count-derived ages of the involved terrains by means of the Model Production Function (MPF) chronology
of Mercury, which is rely on the knowledge of the impactors flux on the planet. Crater chronology
allowed us to constrain the Rembrandt basin formation to the early Calorian period and a widespread resurfacing
up to 3.5 Ga ago. The volcanic activity affected both the basin and its surroundings, but ended prior to some
basin-related and regional faulting. Hence, if the giant scarp begun to develop even before the basin formation (as
suggested by its length-displacement profile across the basin itself) the regional tectonic activity along this
structure might have started even before the Late Heavy Bombardment period and lasted for more than 300 Ma,
when the volcanic activity in this part of hermean surface was already accomplished
AGE RELATIONS OF THE REMBRANDT BASIN AND SCARP SYSTEM, MERCURY.
No full textThe 715-km-diameter Rembrandt basin is the largest well-preserved impact feature of the southern hemisphere of Mercury, and was imaged for the first time during the second flyby of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission. Much of the basin interior is covered by smooth, high-reflectance plains interpreted to be of volcanic origin that host sets of contractional and extensional tectonic structures. This pattern resembles the arrangement of structures observed within the Caloris basin, with individual sets of radial and concentric landforms most likely due to multiple episodes of deformation. Notably, Rembrandt basin and its smooth plains are cross-cut by a 1,000-km-long reverse fault system that trends ~E–W, bending toward the north within the basin. The individual faults of this system accommo-dated crustal shortening that resulted from global con-traction as Mercury’s interior cooled. The current shape of the reverse fault system may have been influ-enced by the formation of the Rembrandt basin.
As the Rembrandt basin area was affected by many commonly found processes that modified the surface of Mercury (i.e., basin formation and impact gardening, global and basin-related tectonics, and volcanic resur-facing), it is well suited for understanding the sequence and duration of such processes. The emplacement of the interior smooth plains predates both the basin-related tectonism and the final development of the giant scarp, which is suggestive of either short-lived volcanic activity immediately after basin formation or a later volcanic phase set against prolonged tectonic activity.
In order to quantify the duration of volcanic and tectonic activity in and around Rembrandt basin, we determined the crater count-derived ages of the involved terrains by means of the Model Production Function (MPF) chronology of Mercury, which is rely on the knowledge of the impactors flux on the planet
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
Method for studying the effects of thermal deformations on optical systems for space application
No full textIn this paper, the results of the thermo-elastic analysis performed on the stereo channel of the imaging
system Integrated Observatory System for the BepiColombo European Space Agency mission to Mercury
are presented. The aim of the work is to determine the effects of ambient parameter variations on the
equipment performance; the optical performance is changing during the mission lifetime primarily
because of the optics misalignments and deformations induced by temperature variations. The camera
optics and their mountings are modeled and processed by a thermo-mechanical finite element model
(FEM) program, which reproduces the expected optics and structure thermo-elastic deformations in
the instrument foreseen operative temperature range, i.e., between −20 °C and 30 °C. The FEM outputs
are elaborated using a MATLAB optimization routine: an algorithm based on nonlinear least square data
fitting is adopted to determine the surface equation (plane, spherical, nth polynomial) which best fits the
deformed optical surfaces. The obtained surfaces are then directly imported into a ZEMAX code for
sequential ray-tracing analysis. Variations of the optical spot diagrams, modulation transfer function
curves, and ensquared energy are then computed. The overall analysis shows that the preferred solution
for mounting the optical elements is adopting the kinematic constraints instead of using the classical glue
solution
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
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
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