1,721,130 research outputs found
The influence of long-term tillage systems on symbiotic N-2 fixation of pea (Pisum sativum L.) and red clover (Trifolium pratense L.)
No full textPea as a grain legume and red clover as a forage legume in the seeding year were cultivated in two long-term differentiated tillage systems on a loess soil in Germany. A continuous conventional tillage system (plow; CT) and a continuous minimum tillage system (rotary harrow; MT) were established in 1970. With pea and red clover dry matter accumulation and N parameters (N accumulation, Ndfa, N-harvest-index, N balance) were investigated in 1998 and 1999. Differences in the N-2 fixation of pea due to the tillage system could clearly be shown whereas grain yields and total N accumulation were equal in both tillage systems and years. In both years a significantly (P < 0.05) higher Ndfa in the MT system was found at least in the final harvest (maturity of pea): 1998/1999, 0.42/0.54 in CT, 0.62/0.75 in MT. The differences in N-2 fixation of pea may be explained by the delayed soil N supply in MT at the beginning of the vegetative period. Simplified N balances of pea were -18 and -25 kg N ha(-1) in CT and -5 and +1 kg N ha(-1) in MT for 1998 and 1999, respectively. Red clover showed no significant differences in the DM and N accumulation between both tillage systems but a year dependent effect caused by different stubble and root yields between the years was apparent. With red clover slightly, but also significantly (P < 0.05) increased Ndfa values were found in the MT system compared to the CT system with 0.55/0.62 in CT (1998/1999) and 0.64/0.71 in MT. However, the difference in Ndfa between the tillage systems (9 percentage points) was much smaller with red clover than with pea (20 and 21 percentage points in 1998 and 1999, respectively). Soil N uptake of red clover using the longer growing season reflected the more adjusted N supply in both long-term differentiated tillage systems, whereas pea in using only a short-term vegetative period reacted stronger to the lower N mineralization in the MT system in springtime
Pro/con clinical debate: Is high-volume hemofiltration beneficial in the treatment of septic shock?
No full textAlthough there have been exciting advances in the management of sepsis and septic shock, mortality still remains high. Recent data suggest that high-volume hemofiltration (HVHF) may play a role in these patients. In contrast to the usual rate of hemofiltration, HVHF is felt to be better able to remove the inflammatory mediators associated with sepsis and septic shock. Such an approach is currently incapable of selectively removing specific mediators. This may be a problem when one considers that several mediators may in fact be beneficial. When determining whether HVHF should be instituted in a patient with septic shock, one need remember that its role is far from clear and its usefulness remains the subject of much debate. Although early data is encouraging, it is clear that additional data is required before HVHF becomes standard management. The authors of this pro/con debate, which is based on a clinical scenario, first describe their own position and then respond to their opponent's position
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
Estimation of symbiotic N2 fixation by a low-level, large-scale 15N application technique
No full textA modified approach is presented for the N-15 isotope dilution method to estimate the proportion of plant nitrogen derived from the atmosphere (Ndfa). This approach utilizes a low-level, large-scale application of N-15 enriched fertiliser. In a field study, pea (Pisum sativum L.) was cultivated in two long-term (since 1970) tillage systems (conventional: CT, minimum tillage: MT). Nitrogen (26 g NO3-N ha(-1) with 10 at.% N-15) was distributed with a conventional field sprayer to increase the plant available soil N-15 level up to the desired range of delta(15)N > 5parts per thousand. A formula for determining the desired amounts of N-15 application is presented and a model is introduced comparing the apparent Ndfa calculated by field data to the theoretically calculated true values of Ndfa. The model makes it possible to consider three basic factors: (i) the amount of plant available soil nitrogen, (ii) the distribution of N-15 enrichment in different soil layers and (iii) the soil N uptake proportions of the legume and the reference plant when the amount of applied N-15 fertilizer is the dependent variable. Errors in estimating Ndfa by the N-15 dilution method can be quantitatively determined with different soil N uptake patterns of legumes and reference plants at varying N-15 enrichment levels. The model shows that results obtained by using the low-level, large-scale N-15 enrichment technique produced a slightly smaller margin of error than did the addition of larger amounts of N-15 labelled fertilizer when N uptake patterns of the legume and the reference plant differ. The new technique offers distinct advantages, in that it is very practical and makes the enlargement of plots possible at low cost and with marginal effort. The results of the low-level enrichment field study were evaluated using the model as well as the results of an investigation on pea with moderate N-15 enrichment by liquid manure (isotope dilution method). (C) 2002 Elsevier Science Ltd. All rights reserved
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