1,720,962 research outputs found
The inhibitory effect of difluoromethane on CH4 oxidation in reconstructed peat columns and side-effects on CO2 and N2O emissions at two water levels
No full textMethane emissions from soils are the net result of two processes: methane (CH4) production and CH4 oxidation. In order to understand how both processes respond to environmental changes, it is necessary to distinguish between CH4 production and oxidation. In bacterial cultures and small soil samples, difluoromethane (CH2F2) was found to inhibit CH4 oxidation reversibly, without affecting CH4 production. Hence, CH2F2 allows the study of CH4 production directly and of CH4 oxidation indirectly. To our knowledge, however, the inhibitory effect of CH2F2 within soil columns has not yet been evaluated. We therefore tested which CH2F2 concentration is needed for complete inhibition of CH4 oxidation in reconstructed 28 cm high peat soil columns under different water levels (WL). We found that soil columns require considerably higher headspace CH2F2 concentrations for complete inhibition of CH4 oxidation than small soil samples. Inhibition remained complete until ca. 24 h after CH2F2 exposure. Then, the inhibitory effect diminished. The time needed for the inhibitory effect to disappear depended on WL: at a low WL of -15 cm, the inhibitory effect declined slowly and oxidation rates recovered by 90% only after 12 days. At WL = -5 cm, CH4 oxidation recovered much faster (90% recovery after ca. 3 days). Last, CH2F2 addition significantly decreased the N2O emissions, whereas CO2 emissions remained unaltered. (C) 2009 Elsevier Ltd. All rights reserved
Aeration effects on CO2, N2O, and CH4 emission and leachate composition of a forest soil
No full textThe availability of 02 is one of the most important factors controlling the chemical and biological reactions in soils. In this study, the effects of different aeration conditions on the dynamics of the emission of trace gases (CO2, N2O, CH4) and the leachate composition (NO3-, DOC, Mn, Fe) were determined. The experiment was conducted with naturally structured soil columns (silty clay, Vertisol) from a well aerated forest site. The soil monoliths were incubated in a microcosm system at different 02 concentrations (0, 0.001, 0.005, 0.01, 0.05, and 0.205 m(3) m(-3) in the air flow through the headspace of the microcosms) for 85 days. Reduced O-2 availability resulted in a decreased CO2 release but in increased N2O emission rates. The greatest cumulative N2O emissions (= 1.6 g N2O-N m(-2)) were observed at intermediate O-2 concentrations (0.005 and 0.01 m(3) m(-3)) when both nitrification and denitrification occurred simultaneously in the soil. Cumulative N2O emissions were smallest (= 0.05 g N2O-N m(-2)) for the aeration with ambient air (O-2 concentration: 0.205 m(3) m(-3)), although nitrate availability was greatest in this treatment. The emission of CH4 and leaching of Mn and Fe were restricted to the soil columns incubated under completely anoxic conditions. The sequence of the reduction processes under completely anoxic conditions complied with the thermodynamic theory: soil nitrate was reduced first, followed by the reduction of Mn(IV) and Fe(III) and finally CO2 was reduced to CH4. The re-aeration of the soil columns after 85 days of anoxic incubation terminated the production of CH4 and dissolved Fe and Mn in the soil but strongly increased the emission rates of CO2 and N2O and the leaching of NO3- probably because of the accumulation of DOC and NH4+ during the previous anoxic period
Greenhouse estimates of CO2 and N2O emissions following surface application of grass mulch: importance of indigenous microflora of mulch
No full textThe effects of surface-applied, fresh grass mulch on CO2 and N2O emissions were determined for 7 weeks in a greenhouse microcosm study under aerated conditions with daily irrigation (1.8 mm day(-1)). Dynamics Of CO2 and N2O emissions were determined by automated, continuous flux measurements. Grass mulch was added (C input: 100 g C m(-2), N input: 9.2 g N m(-2)) to Soil columns (Ap horizon of a cambisol) and quartz sand columns to assess the importance of indigenous microflora of grass residues for mulch decomposition and N2O production. About 76% of the grass mulch carbon was respired within 50 days, regardless of whether the grass mulch was added to soil or quartz sand. Total N2O-N emissions caused by the surface application of grass mulch was equivalent to 0.3% (application on soil) and 0.2% (application on quartz sand) of the N applied in the grass mulch. As much as 89% of the diurnal variability in NO emission and 80% of the diurnal variability in CO2 release from the decomposing grass mulch could be explained by changes in the temperature. The results show that indigenous microflora present on the plant residues determine both the decomposition rate of the surface-applied grass mulch and N-mineralisation and denitrification of mulch N. (C) 2002 Elsevier Science Ltd. All rights reserved
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
The determination of delta C-13 in soil microbial biomass using fumigation-extraction
No full textThe determination of the isotopic composition of the microbial biomass C in soil is an important tool to study soil microbial ecology and the decomposition and microbial immobilization of soil organic C. We discuss advantages and disadvantages of different methods to determine C-13/C-12 in soil microbial biomass and propose a new procedure that is based on the UV-catalyzed liquid oxidation of fumigated and non-fumigated soil extracts combined with trapping of the released CO2 in liquid nitrogen and subsequent determination of delta(13)CO(2)-C by a gas chromatograph connected with an isotope ratio mass spectrometer (IRMS). This method was evaluated using test solutions with known isotopic composition and soil extracts. Additionally, the method was compared with an off-line sample preparation technique combined with isotope analysis by a dual-inlet IRMS and an on-line analysis using an elemental analyser connected with an IRMS. All methods applied obtained comparable results and there were no significant differences between the delta(13)C values measured. The off-line preparation procedure had the highest precision but it was also the most labour-intensive. The choice of the most suitable method depends mainly on the number of samples that have to be analysed, the salt concentration of the extracts and the differences of delta(13)C that have to be detected. The application of this method with liquid oxidation and subsequent GC-IRMS analysis showed that microbial biomass C of a grassland soil was C-13-enriched by 2parts per thousand delta(13)C(PDB) compared with the total soil organic C. The addition of maize straw resulted in a rapid immobilization of maize C in the microbial biomass. (C) 2003 Elsevier Science Ltd. All fights reserved
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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