1,721,087 research outputs found
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
Measurement of properties of the lunar surface using the Diviner Lunar Radiometer experiment on the NASA Lunar Reconnaissance Orbiter
Get PDFThe Diviner Lunar Radiometer is a nine-channel radiometer on board the Lunar Reconnaissance Orbiter, launched in June 2009 and currently orbiting the Moon. Diviner is the first orbiting multi-spectral instrument to observe the lunar surface in the mid- and far- infrared, therefore this thesis details the first steps towards utilising observations in this new spectral region.The author, as part of the Diviner instrument team, contributed to the pre-launch testing and calibration of Diviner. Specifically, the transmission profiles of the B2 and B3 filters, which could not be measured after integration into the instrument due to their long wavelength passbands, were determined. Further investigations of the far-infrared mesh filters were also conducted, as the spectral responses of similar mesh filters were found to have broadened after integration into the Mars Climate Sounder instrument, the pre-cursor instrument to Diviner. To test if this would occur in Diviner also, a new setup was made to approximately re-create the instruments' optical layout. No such spectral broadening was measured in the B1, B2 or B3 filters. The linearities of Diviner's detectors were also confirmed through analysis of the pre-flight calibration data.Laboratory emission spectra taken under ambient conditions differ from those taken in a lunar environment, which induces a temperature gradient in soil and mineral samples. Due to a lack of spectra measured under such conditions, which are directly comparable to Diviner‟s measurements, a new chamber for performing high-resolution emission measurements in a simulated lunar environment was built and calibrated. This setup induces a temperature gradient in each sample by heating it from below while it is surrounded by a cooled radiation shield, all enclosed in a very low pressure vacuum chamber. Lunar analogue minerals have been measured, first in reflectance, and then in simulated lunar conditions, forming the basis of a new lunar spectral library.The uses of the mid- and far-infrared have been described herein, utilising calibrated Diviner observations to: [1] map the temperatures of the lunar poles; [2] investigate regions containing higher than average abundances of rocks; and [3] determine the composition of regions of the lunar surface by combining observations with the new spectral library made during this project
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
Chang'E lunar microwave radiometer data analysis and lunar subsurface temperature profile modelling
Get PDFThe subsurface temperature distribution of airless bodies across the Solar System can provide important clues to their formation and evolution. This thesis investigates the lunar soil temperature profile using data from the recent Chinese lunar orbiting spacecrafts ChangâE 1 and 2 to explore variations in the subsurface temperature of the Moon. These variations include heat flow information of the subsurface and the interior of the Moon. Before the launch of Chang'E-1 (CE-1), the temperatures of the deep layers of the Moon have only been measured at the landing sites of Apollo 15 and 17 by in situ temperature probes. The CE-1/2 lunar orbiters were both equipped with a 4-frequency microwave radiometer (MRM) to detect the lunar surface brightness temperature (TB) and to retrieve data on lunar regolith thickness, temperature, dielectric constant, and other related properties. The MRM can penetrate to a nominal depth of 5 metres in the subsurface with the 3 GHz channel. This research aims to develop a radiative transfer forward model for an airless body and then utilize MRM data to study an observed anomaly of elevated 2 m deep TBs measurements in the Oceanus Procellarum region on the lunar subsurface.
After initial validation of the MRM data and modelling of the lunar regolith parameters, a multi-layer radiative transfer forward model has been derived using the fluctuation dissipation theorem. The forward model calculates the radiometric contribution from several depths on the TB that would be observed by the MRM instrument around the Moon (at different frequencies), as a basis for an inverse method. Sensitivity analysis indicates that, as expected, mineralogy and density information are very important to the inverse calculation. Therefore new FeO/TiO2 distributions derived from the Moon Mineralogy Mapper (M3) were incorporated into the calculation. The derived FeO/TiO2 distributions were also used to derive the bulk density of the lunar surface which was also incorporated into the calculation.
The forward model was then used to invert the MRM measured TB data to generate 2 m depth subsurface temperature profiles. The provisional results show that, as expected, the 2 m subsurface temperature is potentially correlated to the distribution of radioactive elements such as uranium and thorium in the lunar crust. The 2 m subsurface temperature map was then converted to a lunar heat flow map, which was validated by the Apollo 15 and 17 measurements. Inspecting this heat flow map, abnormal high heat flow in the Oceanus Procellarum KREEP Terrain (PKT) region was noticed. The PKT is enriched with a high abundance of radioactive elements such as uranium and thorium. Hence a heat flow model based on radioactive elements as well as internal cooling was built up to investigate such a finding.
In this thesis, a radiative transfer model for the analysis of MRM was developed and proven to be a useful tool for studying the lunar heat flow, as well as subsurface temperature. Rough surface scattering effects on the MRM measured TB values were also analyzed for future calibration. Possible improvements to the MRM instrument design are discussed in the future work as well as the possible application of the MRM instrument on the Martian surface.</p
Exploring the moon in the thermal infrared: the space environment goniometer
Get PDFMeasurements of the light scattering behaviour of the regolith of airless bodies in the Solar System, across wavelengths from the visible to the far infrared are essential to understanding their physical properties. This thesis describes the design, build and calibration of a novel instrument to measure the angular directionality of thermal infrared emission from surfaces (direction emissivity, DE). This work was originally motivated by the need for new DE measurements to support analysis of data collected by the thermal and far infrared Diviner Lunar Radiometer instrument (8 â 400 μm) currently in orbit around the Moon.
To fully interpret the brightness temperatures measured by the Diviner instrument a three dimensional thermal physical model is required. These models typically assume that infrared radiation is scattered isotropically from the lunar surface. Although generally the models are in very good agreement with Diviners measured brightness temperatures, there are some discrepancies particularly in permanently shadowed regions near the lunar poles. One possible reason for these discrepancies is that the thermal infrared DE of the lunar surface is not isotropic as is typically assumed by many of these models. The "Oxford Space Environment Goniometer" (OSEG) was developed to measure the DE of surface across wavelengths from the visible to the thermal and far infrared.
Analysis and modelling of initial DE measurements made with the OSEG show that the DE is dependent on the optical properties and roughness of the surface. DE measurements of the lunar regolith analogue material JSC-1AF have been incorporated into a three dimensional thermal physical model to show that the predicted surface temperatures of a polar lunar-like permanently shadowed region can differ by 10 K compared to assuming an isotropic DE.</p
Shape of (101955) Bennu indicative of a rubble pile with internal stiffness
Get PDFThe shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, Earth-based radar imaging gave an overview of (101955) Bennu’s shape. Here we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennu’s top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. High-standing, north–south ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. Today, Bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting
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