1,721,036 research outputs found
Environmental Evolution of the Archean-early Proterozoic Earth
No full textAlthough, with regard to most parameters, the
rock record shows little evidence of an environment
on the early Earth vastly different from that of
today, there are several biologically important aspects
of the environment that are likely to have
changed. These include:
(1) The length of the day. Throughout the Phanerozoic,
day-length is known to have gradually
increased as a result of dissipation of tidal energy;
in the Precambrian the length of the day was probably
quite different from that of the present.
(2) The average surface temperature of the planet
and the precipitation and weather that it controls.
These are likely to have changed as a result of
changing solar luminosity and atmospheric composition.
(3) The partial pressure of carbon dioxide in the
atmosphere. As a result of man's activities, this
parameter is changing today; it seems quite likely
to have changed in the past in response to biological
and geological evolution.
(4) The partial pressure of oxygen in the atmosphere.
At present, the level of atmospheric oxygen
is sustained by oxygen-producing photosynthetic
organisms; prior to their origin, the oxygen content
of the atmosphere should have been much lower.
(5) The availability to organisms of important
nutrient elements, including biologically useable
nitrogen and dissolved sulfur species. The solubility
of many such nutrients depends on their oxidation
state; their availability may thus have varied with
the partial pressure of atmospheric oxygen. Nitrogen
in a biologically useable form is chiefly produced
today either via lightning-mediated oxidation
reactions in the atmosphere or by nitrogen-fixing
microorganisms; it thus may have been in short
supply prior to the origin of nitrogen-fixing forms
of life.
This chapter discusses the changes that may have
occurred in these biologically important aspects of
the environment. To the extent possible the discussion
is based on geological evidence, but because
this evidence is commonly indirect and incomplete,
it must be interpreted and extrapolated with the
help of theory. Much of the theory that we shall
invoke is either a gross simplification of the real
world, or extremely speculative, or both. It is not
yet possible to reach many firm conclusions concerning
the environmental evolution of the
Archean-Early Proterozoic Earth. Our tentative
conclusions should, therefore, be accepted with
caution (and with regard to the history of some
biologically important environmental parameters,
not even tentative conclusions have yet been
reached)
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
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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