1,721,042 research outputs found
The overall configuration of the interplanetary magnetic field upstream of Saturn as revealed by Cassini observations
No full textThe Cassini spacecraft approached Saturn during the declining phase of the solar cycle, at a time when the heliosphere was highly structured by compressions and rarefactions associated with corotating interaction regions (CIRs). We examine in detail the hourly averaged interplanetary magnetic field (IMF) data prior to Saturn Orbit Insertion and during one subsequent orbit of Cassini closer to solar minimum, where the spacecraft spent several months in me solar wind. We observe the effects of CIRs on IMF structure and show examples of where this structure is disturbed by the passage of strong coronal mass ejections and by solar cycle effects. We examine the field directions and find that in general, they correspond well to the predictions of the Parker model, but with several notable deviations, which we discuss.</p
Titan's influence on Saturnian substorm occurrence
No full textSubstorms play an important role in the energization and transport of plasmas in planetary magnetospheres, including the shedding of the mass added by moons in the case of Jupiter and Saturn. Mass shedding occurs through rapid reconnection in the near tail resulting in dipolarization on the magnetospheric side of the reconnection point and plasmoid formation down tail. Observations of these sudden reconnection events in Saturn's near-tail region provide additional insight into this process. Saturnian substorms, at least on occasion, have a plasmoid formation phase leading to a traveling compression region. Changes in the field strength across reconnection events suggest that open flux has been removed fromthe tail. The timing of tail reconnection events appears to be controlled by both the orbital phase of Titan, and the variable stretching of the near-tail field as Saturn rotates.</p
Cassini observations of the Interplanetary Medium Upstream of Saturn and their relation to the Hubble Space Telescope aurora data
No full textWe present Cassini magnetometer and plasma data for the January 2004 'solar wind campaign' in which the particles and fields instruments monitored the solar wind and interplanetary magnetic field, while the Hubble Space Telescope (HST) simultaneously observed the UV aurora in Saturn's southern ionosphere. Clear structuring is evident in the data which is associated with the highly developed nature of corotating interaction regions (CIRs) at this distance. The interplanetary medium during January consisted of four distinct types of behaviour. We see a 'major' compression region at the start of the interval followed by a rarefaction region, a 'minor' compression region, an 'intermediate' rarefaction region, and another major compression region at the end of the month. The highly dynamic nature of Saturn's aurora revealed by the HST observations appears to relate directly to the concurrent solar wind activity measured by Cassini. Collectively these data provide a unique insight into the solar wind driving of Saturn's magnetosphere and consequent auroral response.</p
Interplanetary magnetic field at ∼9 AU during the declining phase of the solar cycle and its implications for Saturn's magnetospheric dynamics
No full textWe study the interplanetary magnetic field (IMF) data obtained by the Cassini spacecraft during a ∼6.5-month interval when the spacecraft was approaching Saturn at heliocentric distances between ∼8.5 and ∼8.9 AU. It is shown that the structure of the IMF is consistent with that expected to be formed by corotating interaction regions (CIRs) during the declining phase of the solar cycle, with two sectors during each solar rotation, and crossings of the heliospheric current sheet generally embedded within few-day higher-field compression regions, separated by several-day lower-field rarefaction regions. This pattern was disrupted in November 2003, however, by an interval of high activity on the Sun. These data have then been employed to estimate the voltage associated with open flux production at Saturn's magnetopause using an empirical formula adapted from Earth. The results show that the CIR-relaved structuring of the IMF leads to corresponding structuring of the interplanetary interaction with Saturn's magnetosphere and hence also to intervals of very different dynamical behavior. During few-day compression regions where the IMF strength is ∼0.5-2 nT, the average Dungey cycle voltage is estimated to be ∼100 kV, such that the open flux produced over such intervals is ∼30-40 GWb, similar to the typical total amount present in Saturn's magnetosphere. The magnetosphere is thus significantly driven by the solar wind interaction during such intervals. During some rarefaction intervals, on the other hand, the field strength remains ∼0.1 nT or less over several days, implying reconnection voltages of ∼10 kV or less, with negligible production of open flux. The magnetosphere is then expected to enter a quiescent state, dominated by internal processes. Overall, ∼100 GWb of open flux is estimated to be produced during each ∼25-day solar rotation, about 3 times the typical flux contained in the tail, and sufficient to drive three to five substorms. We point out, however, that CIR-related variations in solar wind dynamic pressure will also occur in synchronism with the field variations, which may also play a role in modulating the open flux in the system, thus reinforcing the synchronization of the pattern of growth and decay of open flux to the CIR pattern. Estimates of open flux production associated with the period of strong solar activity indicate that major magnetospheric dynamics were excited by reconnection- mediated solar wind interaction during this interval.</p
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
Strong rapid dipolarizations in Saturn's magnetotail: In situ evidence of reconnection
Full text linkThe oppositely directed magnetic field in the kronian magnetic tail is expected eventually to reconnect across the current sheet, allowing plasma to escape in an anti-solar direction down the tail. This reconnection process accelerates ions and electrons both toward and away from the planet, allowing the magnetotail to relax to a more dipolar configuration. Previous missions to Saturn shed no light on the possible presence of this critical process in the kronian magnetosphere. Recent Cassini measurements of the magnetic field in the magnetotail, reported herein, reveal strong, rapid dipolarizations between 40 and 50 Saturn radii (R-S) downtail, signalling the episodic release of energy to the magnetosphere and ions to the solar wind
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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