1,721,102 research outputs found
A global colour mosaic of Mars from high altitude observations
No full textColour images of Mars are strongly affected by the planet’s varying atmospheric scattering
such that colour shifts between images may be comparable in magnitude to the actual surface
colour variation within an image. The processing of this product addresses this problem by
making use only of relative colour information within single images, used iteratively to derive
a global colour model, offering absolute colour brightness estimates at all locations (Michael
et al, in review).
The current processing iteration uses around 90 images with pixel scales greater than 200 m,
selected for minimal influence of atmospheric dust while clipping out any significant areas of
cloud, and processed to 2 km/pixel. There remain a small number of coverage gaps which we
hope to fill during the 2023-2026 mission extension.A high-altitude observation campaign with the Mars Express High Resolution Stereo Camera
was used to construct five global mosaics of Mars from images captured through each of its
five different spectral filters: panchromatic, red, green, blue and infra-red.
The substantial overlaps of high-altitude images enable the calculation of a global colour
model yielding mosaics which both retain long range colour information and maintain high
relative colour accuracy. The mosaics are currently processed at 2 km/pixel
Topographical Analysis of Libya Linea on Europa: Geologic Evolution and Identification of a New Putative Cryovolcanic or Diapir Field
No full textOn Jupiter's icy moon Europa, bands played a crucial role in its geological evolution. Large-scale bands such as Libya Linea (LL), which has previously not been studied with an applied method as other prominent Europan bands, offer insights into the icy moon's regional geologic history. To unravel the evolution of LL, our study employed a detailed topographic analysis, complementing a previous tectonic reconstruction (Collins et al., 2022, https://doi.org/10.1029/2022JE007492). While said reconstruction provided a comprehensive view of western LL's tectonic evolution, our study introduces a critical topographic dimension, revealing nuanced differences and emphasizing the importance of an investigation that included LL's eastern portions. We identified distinctive topographic signatures indicative of different deformation stages. The analysis of eastern LL, previously not studied in detail, allowed us to define and characterize the topographic signatures of younger and older parts of LL. In western LL, the topographic characteristics of some branches of LL aligned with those of young branches in its eastern parts, while the topographic signatures in other LL branches supported their previous interpretation as formed during early and intermediate deformation stages. Furthermore, the identification of transpressive features in western LL partially challenged the previous reconstruction, suggesting reworking processes at late evolutionary stages. Overall, our integrated topographic and morpho-stratigraphic analysis broadens the understanding of LL's evolution and bands on Europa in general. Additionally, the identification of a small area of putative cryovolcanic or diapiric activity adds intriguing elements for future exploration of this region with the Europa Clipper and JUICE spacecraft
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
Araneiformes Gelände auf dem Mars — Räumliche Konfiguration und Bildungsmechanismen
No full textThe focus of this thesis is the investigation of the spatial configuration and formation mechanisms of a type of terrain known as araneiform terrain or "spiders" found in the south polar regions of Mars. Seasonal sublimation and condensation of CO2 at the poles are an essential part of cycles of global volatiles (CO2 and H2O) and dust, e.g., up to 25% of the Martian atmosphere's CO2 interacts annually with the polar surfaces. The seasonal CO2 ice condenses on the poles of Mars each autumn/winter; it can form translucent slab ice which is transparent in the visible light and opaque in the infrared. This physical property allows basal sublimation of the seasonal CO2 ice under insolation in spring. The resulting CO2 accumulation and jetting leads to transitional features such as dark spots/fans and radial or dendritic troughs known as araneiform terrain (“spiders”). Thus, spider formation is linked to the global CO2 cycle and the seasonal evolution of the Martian poles which are sensitive to the Mars climate. It is one of the most active current erosive processes on Mars which involves mobilization of material jetted from the substrate relocating a greater mass of dust than either dust storms or the cumulative effect of dust devils.
Observations at seven study regions in this work reveal diverse morphologies of spider forms, which suggest variability of araneiform formation processes. Based on my observations, a spider formation model is developed to explain the formation of spiders and their growth processes. I consider the migration of pressurized CO2 through the porous substrate towards cracks in the overlying CO2 ice layer, and the effect of the substrate's cohesive strength on the development of spider troughs. Thus, substrate properties (permeability, porosity, and cohesion) are significant parameters controlling the mechanism of spider growth. The major advantage of this model is that it explains the mechanism of the growth of central pits and radiating troughs, and parameters (e.g., trough length) of their morphologies, which have not been considered before. This model suggests that spider troughs are created from the developments of random protrusions of initial degradational forms. My trough orientation mappings and constructed rose diagrams are consistent with this theory showing that spider troughs do not have preferred orientations and appear randomly distributed. Due to rate differences between local pressure accumulation and lateral gas migration, the model reveals an inhibited zone existing around a newly formed spider that diminishes pressure accumulation preventing another CO2 jet. This suggests the spatial distributions of spiders to be non–random. Spatial randomness analysis of the seven spider populations confirms this non–randomness and indicates a strong regional variation of spider average spacings. Regional differences in substrate properties (permeability, porosity, and cohesion) are the likely causes of the regional variation. Other parameters, such as seasonal CO2 ice thickness and grain size, local climate, obliquity, and latitude, also influence spider formation and spatial configurations.
This research improves the understanding of how CO2 jetting and subsequent spider formation shaped and modified the south polar surface of Mars which may actively occur at the present time, and how volatiles (CO2 and water) and dust play their roles in the polar processes and Mars global circulation. Furthermore, it provides insight into the recent climate conditions of Mars.Der Schwerpunkt dieser Arbeit liegt auf der Untersuchung der räumlichen Konfiguration und des Bildungsmechanismus eines polaren Geländetyps, der als araneiformes Gelände oder "Spinnen" am Südpol des Mars bekannt ist. Saisonale Sublimation und Kondensation von CO2 an den Polen sind ein wesentlicher Bestandteil der globalen Zyklen von Volatilen (CO2 und H2O) und Staub, z. B. interagieren bis zu 25% des CO2 der Marsatmosphäre jährlich mit den polaren Oberflächen des Mars. Das saisonale CO2-Eis kondensiert jeden Herbst/Winter an den Polen des Mars. Es kann in Form von durchscheinendem Eisplatten vorliegen, die im sichtbaren Licht transparent und im Infrarot undurchsichtig sind. Diese physikalische Eigenschaft ermöglicht eine Sublimation des saisonalen CO2-Eises an der Basis unter Sonneneinstrahlung in Quellen. Das dadurch verursachte Herausschießen von CO2 führt zur Bildung vergänglicher Geländemerkmale wie dunklen Flecken / Fächern und radialen oder dendritischen Tälern, die als araneiformes Gelände (“Spinnen“) bekannt sind. Somit ist die Spinnenbildung mit dem globalen CO2-Kreislauf und der saisonalen Entwicklung der Mars-Pole gekoppelt. Beide Prozesssysteme sind für das Mars-Klima empfindlich. Die Bildung von araineiformen Gelände ist einer der derzeit aktivsten erosiven Prozesse auf dem Mars, bei dem Material mobilisiert wird, welches aus dem Substrat ausgestoßen wird und so eine größere Staubmasse als Staubstürme oder die kumulative Wirkung von Staubteufeln verlagert.
In dieser Arbeit zeigen Beobachtungen in sieben Untersuchungsregionen verschiedene Morphologien von Araneiformen, die auf die Variabilität der Bildungsprozesse hindeuten. Basierend auf meinen Beobachtungen wird ein Modell zur Bildung von Spinnen entwickelt, um die Spinnenbildung und ihre Wachstumsprozesse zu erklären. Ich betrachte die Migration von unter Druck stehendem CO2 durch das poröse Substrat zu Rissen in der darüber liegenden CO2-Eisschicht und den Einfluss der Kohäsion des Substrats auf die Entwicklung von Spinnen-Hohlformen. Dabei sind Substrateigenschaften (Permeabilität, Porosität und Kohäsion) wichtige Parameter, die den Mechanismus des Spinnenwachstums steuern. Der Hauptvorteil dieses Modells besteht darin, dass es sowohl den Mechanismus des Wachstums von zentralen Trögen und davon radialen Rinnen als auch Parameter (z. B. Troglänge) ihrer Morphologie erklärt, die zuvor nicht berücksichtigt wurden. Dieses Modell legt nahe, dass sich die radialen Spinnentröge aus zufälligen Vorsprüngen anfänglicher Erosionsformen entwickeln. Meine Kartierung der Orientierung der einzelnen Rinnen und die konstruierten Rosendiagramme stimmen mit dieser Theorie überein und zeigen, dass Spinnentröge keine bevorzugten Orientierungen haben und zufällig verteilt erscheinen. Aufgrund von Geschwindigkeitsunterschieden zwischen lokaler Druckakkumulation und lateraler Gasmigration zeigt das Modell eine verbotene Zone um eine neu gebildete Spinne, die die Druckakkumulation verringert und die Ausbildung eines weiteren CO2-Strahls verhindert. Dies legt nahe, dass die räumlichen Verteilungen von Spinnen nicht zufällig sind. Die räumliche Zufallsanalyse der sieben Spinnenpopulationen bestätigt diese Nicht-Zufälligkeit und zeigt eine starke regionale Variation der durchschnittlichen Abstände der Araneiformen. Regionale Unterschiede in den Substrateigenschaften (Permeabilität, Porosität und Kohäsion) sind die wahrscheinlichen Ursachen für diese regionale Variation. Andere Parameter wie die Dicke des saisonalen CO2-Eises und seine Korngröße, das lokale Klima, die Neigung und der Breitengrad beeinflussen ebenfalls die Bildung von Spinnen und die ihre räumlichen Konfigurationen.
Diese Forschung verbessert das Verständnis dafür, wie CO2-Jets sowie die durch sie verursachte Spinnenbildung als derzeit aktiv auftretende Prozesse die Marsoberfläche im Bereich des Südpols geformt und modifiziert haben, und wie flüchtige Stoffe (CO2 und Wasser) und Staub ihre Rolle bei den polaren Prozessen spielen und Mars globale Verbreitung. Darüber hinaus ermöglicht sie Einblicke in die rezenten Klimabedingungen des Mars
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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