1,721,372 research outputs found
Detection of Energetic Neutral Particles
No full textThe techniques for the detection of energetic neutral atoms (ENAs) currently in use and those developed for future application in space research are reviewed. Various sources of ENA are currently the target of intense investigations. Typically, ENAs are produced from plasma ions by charge-exchange with a neutral background gas.In addition, the neutral interstellar gas penetrating the heliosphere is also an important source of ENAs. Since ENAs travel virtually unperturbed for very long distances they can be used for remote sensing of space plasma populations, for objects ranging from planetary magnetospheres at all scales to the quite distant heliospheric termination shock. The ENA sources and their respective energy ranges and fluxes are discussed briefly. The energy range of ENAs accessible to direct observation spans from about 10 eV to more than 1 MeV. On the high-energy side, the energy limit for ENAs is given by experimental limitations, but there are also good scientific reasons why ENA fluxes should be negligible at these energies. At the low-energy side, the limit is given by the available instrumentation. Several fundamentally different experimental techniques are necessary to cover such a large energy range. Moreover, not just the mere detection of the ENAs is desired but also the measurement of their arrival direction, possibly in two dimensions, is needed for many applications
Heating and acceleration of coronal ions interacting with plasma waves through cyclotron and Landau resonance.
No full textOn the basis of quasi-linear theory, the parallel and perpendicular wave heating and acceleration rates for gyrotropic particle velocity distribution functions are derived. These rates can be used in anisotropic multicomponent fluid equations, in order to describe the wave-particle interactions of ions with, for examples, kinetic Alfven and electromagnetic or electrostatic ion cyclotron, respectively, magnetosonic waves propagating along or obliquely to the mean magnetic field. The waves of coronal origin propagating away from the Sun into the interplanetary medium can resonantly heat the solar wind ions and accelerate minor ions preferentially with respect to the protons. Such processes are required in order to explain and understand the measured characteristics of ion velocity distributions in the solar wind and to interpret the recent spectroscopic evidence obtained from EUV emission line measurements made by the Solar and Heliospheric Observatory (SOHO) spacecraft, which indicate cyclotron-resonance-related line broadenings and shifts.Astronomy & AstrophysicsSCI(E)58ARTICLEA1227-23810
Non-Gaussian probability distributions of solar wind fluctuations
No full textThe probability distributions of field
differences ∆x(τ)=x(t+τ)-x(t),
where the variable x(t) may denote any solar wind scalar field or
vector field component at time t, have been calculated from time series
of Helios data obtained in 1976 at heliocentric distances near 0.3 AU. It is
found that for comparatively long time lag τ, ranging from a few hours
to 1 day, the differences are normally distributed according to a Gaussian. For
shorter time lags, of less than ten minutes, significant changes in shape are
observed. The distributions are often spikier and narrower than the equivalent
Gaussian distribution with the same standard deviation, and they are enhanced
for large, reduced for intermediate and enhanced for very small values of
∆x. This result is in accordance with fluid observations and
numerical simulations. Hence statistical properties are dominated at small scale
τ by large fluctuation amplitudes that are sparsely distributed, which
is direct evidence for spatial intermittency of the fluctuations. This is in
agreement with results from earlier analyses of the structure functions of
∆x. The non-Gaussian features are differently developed for
the various types of fluctuations. The relevance of these observations to the
interpretation and understanding of the nature of solar wind magnetohydrodynamic
(MHD) turbulence is pointed out, and contact is made with existing theoretical
concepts of intermittency in fluid turbulence
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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