121,860 research outputs found
Multi‐instrument investigation of the location of Saturn's magnetotail x‐line
No full textReconnection is a fundamentally important process in planetary magnetospheres, with both local and global effects. At Saturn, observations of the magnetotail reconnection site (or x‐line) are rare, with only one in‐situ encounter reported to date. In this work, an extensive database of plasmoids and dipolarizations [Smith et al., 2016] was investigated from a multi instrument perspective in order to probe the location and variability of the magnetotail x‐line. Several clear intervals were identified in which the x‐line location could be indirectly inferred to move on relatively short timescales. Two case studies are presented, the first of which concerns short lived flows, suggesting the reconnection sites can be either short lived (∼10 minutes) or extremely azimuthally limited (∼3RS/0.4 hours of local time). The second interval concerns the tailward motion of the reconnection site (or sites), inferred from the increasing electron temperature (and diminishing electron density) associated with the flows. This tailward motion occurs over ∼2.5 hours (approximately a quarter of a planetary rotation). The composition of the suprathermal plasma suggests that this could be an example of the gradual depletion of mass loaded flux tubes (that must occur prior to lobe reconnection). These case studies are consistent with previous statistical work that suggested that the site of reconnection in the Kronian magnetotail can be highly dynamic
Dipolarization fronts with associated energized electrons in Saturn’s magnetotail
No full textWe present a statistical study of dipolarization fronts within Saturn’s magnetotail. Automated methods were used to identify 28 significant southward rotations of the field coupled with enhancements in the electron energy. The observed dipolarizations cover the majority of the magnetotail, though possess a strong dawn-dusk asymmetry (79% occur postmidnight). Almost half (43%) of dipolarizations occur within 3 hr of another event, though these chains are solely observed postmidnight. Most pitch angle distributions of the heated electron populations show increased relative fluxes parallel or perpendicular to the field, likely due to nonlocal heating effects. The electron temperature and density following the passage of a front are anticorrelated; the temperature increases are accompanied by a decrease in their density. The temperature increases by factors of 4–12, while the density drops by factors of 3–10. Premidnight events consistently show the smallest relative heating and density depletion, suggesting they are observed closer to their generation. In contrast, the location of the postmidnight x-line is inferred to be more variable, with a large variety of heating factors observed. Forty percent of the events show a strong reduction in water (W+) group fraction, likely related to either the preferential lossof equatorial heavy ions in departing plasmoids or the closure of open field. Two of these events show significant compositional changes suggesting the addition of plasma of external origin; we suggest that these events involved the closure of open field
Sources of local time asymmetries in magnetodiscs
No full textThe rapidly rotating magnetospheres at Jupiter and Saturn contain a near-equatorial thin current sheet over most local times known as the magnetodisc, resembling a wrapped-up magnetotail. The Pioneer, Voyager, Ulysses, Galileo, Cassini and New Horizons spacecraft at Jupiter and Saturn have provided extensive datasets from which to observationally identify local time asymmetries in these magnetodiscs. Imaging in the infrared and ultraviolet from ground- and space-based instruments have also revealed the presence of local time asymmetries in the aurora which therefore must map to local time asymmetries in the magnetosphere. Asymmetries are found in (i) the configuration of the magnetic field and magnetospheric currents, where a thicker disc is found in the noon and dusk sectors; (ii) plasma flows where the plasma flow has local time-dependent radial components; (iii) a thicker plasma sheet in the dusk sector. Many of these features are also reproduced in global MHD simulations. Several models have been developed to interpret these various observations and typically fall into two groups: ones which invoke coupling with the solar wind (via reconnection or viscous processes) and ones which invoke internal rotational processes operating inside an asymmetrical external boundary. In this paper we review these observational in situ findings, review the models which seek to explain them, and highlight open questions and directions for future work.</p
Survey of magnetosheath plasma properties at Saturn and inference of upstream flow conditions
No full textA new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416 s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties of various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach-number bow shock is ~4% of the dissipated flow energy. The data set is available as supporting information to this paper.</p
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
Dipolarization Fronts With Associated Energized Electrons in Saturn's Magnetotail
No full textWe present a statistical study of dipolarization fronts within Saturn's magnetotail. Automated methods were used to identify 28 significant southward rotations of the field coupled with enhancements in the electron energy. The observed dipolarizations cover the majority of the magnetotail, though possess a strong dawn‐dusk asymmetry (79% occur postmidnight). Almost half (43%) of dipolarizations occur within 3 hr of another event, though these chains are solely observed postmidnight. Most pitch angle distributions of the heated electron populations show increased relative fluxes parallel or perpendicular to the field, likely due to nonlocal heating effects. The electron temperature and density following the passage of a front are anticorrelated; the temperature increases are accompanied by a decrease in their density. The temperature increases by factors of 4–12, while the density drops by factors of 3–10. Premidnight events consistently show the smallest relative heating and density depletion, suggesting they are observed closer to their generation. In contrast, the location of the postmidnight x‐line is inferred to be more variable, with a large variety of heating factors observed. Forty percent of the events show a strong reduction in water (W+) group fraction, likely related to either the preferential loss of equatorial heavy ions in departing plasmoids or the closure of open field. Two of these events show significant compositional changes suggesting the addition of plasma of external origin; we suggest that these events involved the closure of open field
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Spin-Echo aufgelöste Neutronenstreuung von selbstorganisierten Polymergrenzflächen
No full textThis thesis focused on two main objectives: First, the clarification of the prospects of the spin-echo resolved grazing incidence neutron scattering method (SERGIS) for the investigation of buried interfaces. And second, the investigation of the self-organisation (i.e. microphase separation and dewetting) of ultrathin poly(styrene-block-isoprene) diblock copolymer films on silicon substrates by means of SERGIS and complementary techniques.
SERGIS is a novel neutron scattering technique which was implemented and further developed at the new neutron / x-ray reflectometer N-REX+ at the FRM II (Garching, Germany). In contrast to conventional small-angle scattering methods, SERGIS characterises the lateral structure and morphology of interfaces and thin-film systems in real space. The technique uses a polarised primary beam, and the measured quantity is the integral polarisation of the scattered beam. By decoupling the measurement resolution and the beam divergence (in a first approximation), SERGIS aims at a good resolution and a good measurement statistics simultaneously.
As a first systematic application of SERGIS to a real physical problem, the dewetting and internal structure of ultrathin poly(styrene-block-isoprene) diblock copolymer films were studied by means of SERGIS and complementary surface sensitive techniques, namely neutron and x ray reflectivity and atomic force microscopy (AFM).Diese Dissertation widmet sich zwei Forschungsschwerpunkten: Erstens, den Möglichkeiten und Grenzen der Spin-Echo aufgelösten Neutronen Streuung (SERGIS) zur Untersuchung von verborgenen Grenzflächen. Und zweitens, der Untersuchung von Selbstorganisation (Mikrophasenseparation und Entnetzen) sehr dünner poly(styrol-block-isopren) Diblock Copolymer Filme auf Siliziumsubstrat mittels SERGIS und komplementärer Methoden.
SERGIS ist eine neue Neutronenstreumethode, die am neuen Neutronen- / Röntgen-Reflektometer N REX+ am FRM II (Garching, Deutschland) implementiert und weiterentwickelt wurde. Im Gegensatz zu konventionellen Neutronen Kleinwinkelstreumethoden, wird mittels SERGIS die laterale Struktur und Morphologie an Grenzflächen und Dünnfilmsystemen im Realraum charakterisiert. Die Messgröße ist die Depolarisierung eines zu Beginn vollständig polarisierten Neutronenstrahls. In dem die Auflösung und die Strahldivergenz in erster Ordnung entkoppelt sind, soll sowohl eine gute Auflösung als auch eine gute Statistik erreicht werden.
Als erste systematische Anwendung von SERGIS an einem physikalischen Problem wurde das Entnetzen und die interne Struktur von sehr dünnen Poly(Styrol-block-Isopren) Diblock Copolymer Filmen mittels SERGIS und komplementären oberflächensensitiven Methoden, wie Neutronen- und Röntgen-Reflektivität als auch Raster-Kraft-Mikroskopie (AFM) untersucht
The vanishing author in computer-generated works: a critical analysis of recent Australian case law
No full textAbstract
The use of software is ubiquitous in the creation of many copyright works, yet the requirement in copyright law that every work have a human author who engages in independent intellectual effort means that its use may prevent copyright subsistence. Several recent Australian cases have refocused attention on authorship as an essential criterion of copyright subsistence, and these cases suggest that much computer-produced output may be authorless and thus lack copyright protection. This article, the first in a two-part series, analyses how each case deals with the question of authorship of computer-produced works and why the use of software diminishes copyright protection for a significant number of computer-generated works. The article critiques the application of conventional notions of human authorship developed in the pre-computer age to modern productions and suggests alternative approaches to authorship that satisfy both the major objectives of copyright policy and the need to adapt to the computer age. The article argues that, without a broader judicial approach to authorship of computer-generated works, Parliament must remedy the lacuna in protection for these ‘authorless’ works. Possible solutions for reform are suggested. In a forthcoming article, the author comprehensively examines those reform proposals
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
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