1,721,509 research outputs found
Contribution of nitrification and denitrification sources for seasonal N2O emissions in an acid German forest soil
No full textA N-15 tracer field experiment was carried out in an acid soil of a beech forest gap at the Solling area in Germany to determine the different formation processes of N2O. This site has been classified as a seasonal N2O emission type forest. Small amounts of highly enriched N-15 tracer were supplied separately as labelled NH4+ and NO3- seven times from May to October 1998. The N-15 compounds were injected with syringes into the upper 10 cm of the soil. The N2O emission showed a seasonal pattern with low emission in spring, high emission in summer, and low emission in autumn and followed the soil temperature. N2O was evolved only from the N-15-labelled NO3- pool in summer under field moist conditions, indicating that its formation was due to denitrification. In spring, early summer and autumn trapped NO or heterotrophic nitrification may also have been involved in N2O emission. (C) 2002 Elsevier Science Ltd. All rights reserved
Dinitrogen and nitrous oxide formation in beech forest floor and mineral soils
No full textA (15)N tracer study was conducted to determine N(2) and N(2)O fluxes and the processes responsible for the formation of N(2)O in two beech (Fagus silvatica L.) forest soils: an acid mineral soil (AM) (pH=3.8) and the overlying acid forest floor (AFF) (pH=3.8) from the Soiling and a less acid mineral soil (LAM) (pH=5.2) from the Gottinger Wald. Ammonium and nitrate of undisturbed soil cores were labeled by injecting (15)N. The evolved gases, N(2)O and N(2), and the ammonium and nitrate concentrations in the soils were measured together with the (15)N abundances over a period of 8 d. Nitrous Oxide was produced in all soils by denitrification. Nitrate was reduced to N(2) at higher soil pH (LAM) and in the AFF. The end product of denitrification at the lower soil pH (AM) was N(2)O The N(2)O and N(2) emission calculated on an areal basis decreased from LAM, AFF, to AM. The N(2)O/(N(2)O+N(2)) ratios decreased from AM (1.0), AFF (0.97), to LAM (0.80) during the initial period indicating that the main product of denitrification was N(2)O. On prolonged incubation the N(2)O/(N(2)O+N(2)) ratios decreased for AFF and LAM to 0.78 and 0.32, respectively, and was attributed to a gradual decrease in nitrate concentration. We estimate the in situ N(2) emissions to he 0.71 and 0.51 kg N ha(-1) yr(-1) for the Gottinger Wald and the Solling, using published annual in situ N(2)O emissions and our N(2)/N(2)O ratios. The in situ N(2)O emissions of the Gottinger Wald and Solling are 0.17 and 3 kg ha(-1) yr(-1) and the N(2) emissions increased the annual denitrification losses to about 0.88 and 3.51 kg ha(-1) yr(-1). The approach for estimating in situ N(2) emissions has to be improved in future studies
Different pathways of formation of N2O, N-2 and NO in black earth soil
No full textThe use of N-15 tracer provides a suitable technique to investigate the processes of N transformation in soils and the origin of the environmentally relevant gaseous N compounds N2O and NO from nitrification and denitrification. incubation experiments with black earth soil under two different water contents are presented here. Nitrification and denitrification proceeded simultaneously, but the importance of these two microbial processes shifted depending on the water content of the soil. Under water-unsaturated conditions the microbial oxidation of NH4+ to NO3- predominated, but a reduction of NO3- also occurred. The emission of NO exceeded the emission of N2O by a factor of up to 20 at the beginning of the experiments. Under water-saturated conditions denitrification was the dominant process of N transformation in the soil. However, nitrification also occurred to a considerable extent. The emission of N2O was greater than under unsaturated conditions. The formation of NO could hardly be observed. N loss by molecular nitrogen from denitrification could be detected under saturated conditions. The N loss amounted to 60% of NO3- and thereby the cumulative N ratio of N-2 to N2O was 3. Under either unsaturated or saturated conditions NO arose from NO2- or during the microbial oxidation of NH4+ to NO2-. However, N2O mainly formed from denitrification under both conditions. Furthermore, NO could not be observed as a precursor of N2O and the free NO2- could not be detected as a common N pool for the formation of N2O and NO. High emissions of NO could be a problem for the black earth soil in the semi-arid climate in central Germany, if there are large amounts of NH4+ in the soil after fertilisation. (C) 2000 Elsevier Science Ltd. All rights reserved
Dinitrogen and nitrous oxide formation in beech forest floor and mineral soils
No full textA (15)N tracer study was conducted to determine N(2) and N(2)O fluxes and the processes responsible for the formation of N(2)O in two beech (Fagus silvatica L.) forest soils: an acid mineral soil (AM) (pH=3.8) and the overlying acid forest floor (AFF) (pH=3.8) from the Soiling and a less acid mineral soil (LAM) (pH=5.2) from the Gottinger Wald. Ammonium and nitrate of undisturbed soil cores were labeled by injecting (15)N. The evolved gases, N(2)O and N(2), and the ammonium and nitrate concentrations in the soils were measured together with the (15)N abundances over a period of 8 d. Nitrous Oxide was produced in all soils by denitrification. Nitrate was reduced to N(2) at higher soil pH (LAM) and in the AFF. The end product of denitrification at the lower soil pH (AM) was N(2)O The N(2)O and N(2) emission calculated on an areal basis decreased from LAM, AFF, to AM. The N(2)O/(N(2)O+N(2)) ratios decreased from AM (1.0), AFF (0.97), to LAM (0.80) during the initial period indicating that the main product of denitrification was N(2)O. On prolonged incubation the N(2)O/(N(2)O+N(2)) ratios decreased for AFF and LAM to 0.78 and 0.32, respectively, and was attributed to a gradual decrease in nitrate concentration. We estimate the in situ N(2) emissions to he 0.71 and 0.51 kg N ha(-1) yr(-1) for the Gottinger Wald and the Solling, using published annual in situ N(2)O emissions and our N(2)/N(2)O ratios. The in situ N(2)O emissions of the Gottinger Wald and Solling are 0.17 and 3 kg ha(-1) yr(-1) and the N(2) emissions increased the annual denitrification losses to about 0.88 and 3.51 kg ha(-1) yr(-1). The approach for estimating in situ N(2) emissions has to be improved in future studies
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
Wolf, I.J. -- 1967 -- Correspondence, Individual -- letter, 1967-09-15
No full textLetter from Wolf, I. J. to Sabin, Albert B. dated 1967-09-15.Sabin Collection Fair Use Policy</a
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
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