1,721,006 research outputs found
Hydrogen production dynamic during cheese whey Dark Fermentation: New insights from modelization
No full textThe modelization of non methanogenic anaerobic environments can be particularly challenging owing to the variability of the metabolic products. In particular, both hydrogen production and consumption take place at the same time due to the simultaneous occurrence of Dark Fermentation (DF) and homoacetogenis. The goal of this study is to investigate the kinetic and thermodynamic aspects of the biochemical pathways involved in the fermentation of ultrafiltered cheese whey; to this aim, a continuous digester was operated under three different Hydraulic Retention Times (6, 9 and 12 h) and fixed pH (5.5). A mathematical model, based on a variable stoichiometry approach, was implemented and calibrated; the proposed model allowed the determination of the parameters governing the most relevant pathways, namely homoacetogenesis and butyric and ethanol-type DF. A special focus was given to the quantification of the hydrogen turnover rate; the model proved to be an effective tool, in addition to widely adopted techniques such as microbial and isotopic analysis, for obtaining a deeper comprehension of the crucial aspects governing the non-methanogenic process
Thermal analysis (TG-DTA) and isotopic characterization ( 13C-15N) of humic acids from different origins
No full textThermal analyses (TG-DTA), elemental composition and isotope analyses (13C and 15N) were performed on humic acids (HA) from peats, leonardites and lignites, in order to investigate their structure and the changes taking place during the humification process. Thermal analyses showed structural differences between HA samples in relation to their coalification rank. In particular the lignite HA were characterized by a more stable chemical composition at high temperatures. The δ13C and δ15N values can provide information on the biogeochemical processes involved in HA formation. In particular, peat HA were linked to anoxic environments that enable plant residues to persist in their structure. In contrast, leonardite and lignite HA formation seems to be governed by different biogeochemical processes from those responsible for peat diagenesis. However, the isotopic analyses did not provide any distinction between leonardite and lignite HA. On the basis of the data presented in this study, it may be concluded that TG-DTA and isotope ratio measurements are powerful tools for investigating the formation pathway of humic substances from coals. © 2004 Elsevier Ltd. All rights reserved
How Perennial Grass has Modified Distribution of Organic Carbon in a Peach Orchard in Emilia-Romagna Region (Italy)
Full text linkIn this study, the distribution of the total and humified organic carbon in a peach orchard tilled-irrigated on the row and perennial grassed on the inter-row space after 16 years of cultivation were evaluated. The TOC has shown differences not statistically significant in the 0-20 cm horizon, whereas the difference in the row vs. inter-row 20-40 cm horizon was significant. The highest content of humic substances was found in the 0-20 cm of the inter-row with perennial grass vs. row tilled soil: the absence of tillage increases the accumulation of humified compounds. DRIFT and TG-DTA analysis pointed out only some small structural variation in the humic fraction of the samples taken from the layer at depth 20-40 cm
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
Quantitative estimation of peat, brown coal and lignite humic acids using chemical parameters, 1H-NMR and DTA analyses
No full textHumic acids extracted from peats (P), brown coals (BC) and lignites (L), were characterized using different (chemical, 1H-nuclear magnetic resonance spectroscopy and differential thermal analysis) techniques. Fourteen variables were obtained from these analyses and only five were selected because uncorrelated in multiple partial correlation. The chosen variables were C concentration, aliphatic and aromatic components and the heat of reaction of the second exothermic peak. The multivariate discriminant analysis was performed on these variables and a discriminant function was obtained which was able to efficiently separate the P, BC and L. This function enables simple predictions on samples of unknown origin. The straightforward method proposed and the results obtained are discussed. © 2003 Elsevier Science Ltd. All rights reserved
Effect of long-term compost fertilization on the distribution of organic carbon and nitrogen in soil aggregates
Full text linkSoil fertility is mainly related to soil total organic carbon (C) that should be preserved in order to optimize soil quality and functionality. Consequently, the use of organic amendments could be a possible strategy to increase soil C and nitrogen (N) storage particularly in orchard systems where the disturbance of soil is reduced thus making favorable conditions for C and N stabilization. The aim of this study was to evaluate the distribution and stabilization of organic C and total N in aggregate fractions after a 14-years-period of compost application to a peach orchard. The trial was conducted in the southeastern Po valley, on a commercial nectarine orchard and the following treatments were compared in a complete randomized block design with four replicates: 1. unfertilized control; 2. mineral fertilization; 3. compost at a rate of 10 Mg dry weight ha−1 yr−1. At the end of orchard lifetime, soil was sampled from the row at four depths (0–0.15, 0.16–0.25, 0.26–0.45, and 0.46–0.65 m) and physically fractionated to separate macroaggregates (> 250 μm), microaggregates (250–50 μm) and silt and clay (< 50 μm) that were analyzed for organic C, total N, δ13C, and δ15N. Compost addition induced a significant increase of macroaggregates (66%), no changes in microaggregates and a decrease of silt and clay (22%) compared to control and mineral fertilization. With compost the accumulation of organic C and total N content in the macroaggregates was four-five times higher than the other two treatments in all the depths, therefore almost 50% of the soil organic C was in this fraction, compared to 20–24% in the control and mineral. In the micro-aggregates more C and N accumulated only in the two top layers, while no effect was observed in the silt and clay fraction. From macro-to microaggregates to the silt and clay fraction, the C/N ratio shifted from 9 to 7.5 to 6 on average indicating that the C and N stabilized in the finer fractions is mainly of microbial origin. The enrichment in C and N isotopic composition from macro-to micro to silt and clay is also indicative of the isotopic fractionation due to microbial metabolism and the consequent stabilization of microbial residues in the finer fractions. In the control and mineral, only receiving orchard litter, this change was observed in all the layers, on the contrary, with compost similar δ13C and δ15N values characterized the fractions in the top soil layer suggesting the occlusion of compost in all the fraction. With depth the macroaggregates maintained the same δ13C and δ15N values indicating consistent redistribution of compost in deep soil layers, while the finest fractions showed a progressive enrichment of δ13C due to the presence of C fractionated during
microbial metabolism and progressively stabilized. In conclusion, compost supply leads to
positive effects on C and N accumulation and stabilization also in the deeper layers favoring the increase of long-term soil fertility and C storage
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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