1,721,023 research outputs found
Recent Developments in Gravity Gradiometry from the Space Shuttle-Borne Tethered Satellite System
No full textAbstract - This paper describes the current development of a noncryogenic gravity gradiometer for future use on board the tethered satellite system (TSS). The paper also proposes a way of testing a single‐axis prototype of such an instrument that makes use of the free‐fall technique in vacuum. This gravity gradiometer has a design sensitivity of the order of 10^-2 EU (1 EU =Eötvös Unit=10^-9 ms-2/m) in 10‐s integration time. Because of the small size and light weight, a noncryogenic gravity gradiometer is a valid candidate to fit the limited accommodation capability of the TSS deployed from the shuttle and maintained, for several days, at an altitude of 120–130 km. This unique capability improves the resolution and accuracy achievable in reconstructing the earth gravity field, in particular at short wavelengths. A preliminary analysis of the dynamics of the TSS satellite indicates the potential of such satellite as a low‐altitude research platform for gravity gradiometry
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
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
Balloon-Released Experiments in Gravitational Physics
No full textAbstract - A 3-m-long, non-propelled cryostat released from a 40-km-high balloon is used to shield a detector free falling inside for 30 s. This facility provides opportunities for accurate experiments in gravitational physics. Among others, two experiments of particular interest are: (a) a free-fall test of the Equivalence Principle; and (b) the local mapping of the gravity field along vertical lines by means of as gravity gradiometer. In experiment (a), the differential accelerations between two test masses of different materials (e.g. aluminum and gold) is measured during free fall. The estimated accuracy in testing the Equivalence Principle in a 30-s free fall is 4 parts in 10^14 with 95% confidence level. In experiment (b), the knowledge of surface gravity anomalies can be improved with a 0.01-E gradiometer and the upward continuation gravity models validated. Copyright © 1993 Published by Elsevier Ltd
THE PICO GRAVITY BOX - AN EFFICIENT PASSIVE NOISE ATTENUATOR IN SPACE
No full textThe effectiveness and simplicity of passive mechanical attenuators of residual spacecraft disturbances has recently been highlighted through the proposal of a Pico Gravity Box (PGB)1 for small-force space experiments. Either alone or in combination with active systems, passive attenuators appear to be essential in providing a quiet environment for space experiments, particularly in the Space Station era. In this paper, the limitations of ideal mechanical suspensions are discussed and the effects of internal damping are investigated. It is concluded that internal damping allows one to eliminate the singularities at response frequencies which are typical of ideal oscillators, as well as providing very effective noise reduction. The problem of reducing noise along the rotational as well as translational degrees of freedom is also addressed
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