1,721,133 research outputs found
Location, movement and reactions of impurities in solid ice
No full textThe aim of drilling ice cores is to obtain paleoatmospheric information of wide significance. However, the concentrations of chemicals found in the- ice are determined both by the atmospheric concentrations, and by depositional and post-depositional processes. Other papers in this volume discuss the depositional processes, ami the processes that subsequently alter the concentrations in near-surface (up to a metre or so depth) snow. However, there arc a number of documented cases where further changes occur below the surf act snow. Additionally, there is the possibility that chemical changes can occur, at least to more complex species, over tlx: long timescales that arc relevant for ice. Diffusion is bound to take place to some extent, affecting the apparent rate of temporal change inferred from ice core profiles. Discussion of all the factors requires an understanding of the way in which impurities are held in the ice This paper discusses all these items, conccntrating on processes in solid ice. and in firm below the top metre or two
The record of aerosol deposited species in ice cores, and problems of interpretation
No full textIce cores have now become established as one of the primary archives of paleoclimatic information, covering timescales from seasonal up to 100,000 years or more. In the polar ice sheets, where there is little or no melting, snow layers build up year by year. Included in them are samples of the atmosphere: trace gases in air bubbles, particles and adsorbed gases, and the water molecules themselves. By drilling into the ice at suitable places, we can collect cores that give profiles of chemical content and physical properties of the ice. These are then used to infer the state of the atmosphere in the past
Gas Diffusion in Firn
No full textDifferent components and properties of the ice deposits on the earth (glaciers, ice sheets) store information on the climate and environment. We can mainly distinguish between three storage types: a) properties and isotopie composition of the ice itself, b) solid (and liquid) trace substances in the ice, and c) gaseous and volatile components. This article reviews some aspects of the transfer of gaseous components from the atmosphere to the ice
The Record of Gases and Reactive Species in Ice Cores, and Problems of Interpretation
No full textSince the start of the ice core drilling some 30 years ago, a whole zoo of species and parameter have been measured and reported in the literature. Those records per se are of minor relevance. Of great interest is the link to the corresponding atmospheric concentrations, which are related to basic parameter of the Earth System
Overview of Recent Field Experiments for the Study of the Air-Snow Transfer of H2O2 and HCHO
No full textThe analysis of hydrogen peroxide and formaldehyde in ice cores offers the potential to reconstruct the oxidation capacity of the atmosphere in the past [Neftel and Fuhrer, 1993], since these species are closely linked to the odd H and the odd O budget of the atmosphere [Thompson, 1992]. These species are so-called reversibly deposited on the snow surface since they show a strong exchange with the gas phase after deposition and their ice concentrations are dominated to a large extent by postdepositional changes in the firn. Therefore, the transfer from the atmosphere into the snow is an important step in the overall transfer function of these species [Neftel, this issue]. To get a better understanding of this step several field experiments were carried out during the 1993 and 1994 summer seasons at Summit in Central Greenland, in the 1993/94 Austral summer in Antarctica along the Swedish traverse (SWEDARP), and at South Pole in November and December, 1994. We will give an overview of the data and point out possible contradictions and knowledge gaps
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
Feedbacks on climate in the Earth system: introduction
Full text linkIn the last century, the Earth has undergone a very fast and unusual change in the radiative forcing of its climate, resulting from human actions. This change in forcing has resulted not only mainly from rising concentrations of greenhouse gases, particularly carbon dioxide (CO2), but also from changes in the nature of the land surface and changes in the concentrations of aerosol particles in the atmosphere and of ozone-destroying chemicals in the stratosphere. If the changes in forcing continue on their current trajectory, then very substantial changes in climate are predicted by the end of the centur
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
- …
