1,721,015 research outputs found
Thermal analysis (TG-DTA) and isotopic characterization (13C and 15N) of humic acids from different origins. Applied Geochemistry
No full textThermal analyses (TG-DTA), elemental composition and isotope analyses (13C and 15N) were performed on humic acids (HA) from peats (P), leonardites (Le) and lignites (L), 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 delta 13C and delta 15N 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 fro
Fate of N in soil amended with 15N-labelled residues of winter cereals combined with an organic N fertilizer
No full textIn organic farming winter cereals, as cover crops, provide nutrients, when they return to soil as crop residues. The fate of N deriving from two decomposing 15N-labelled winter cereals, with or without the supply of an organic N fertiliser, was studied in a field experiment. The stabilisation of residues N in soil aggregates and the portion lost from the system were also evaluated. Barley or triticale residues were incubated alone or with hydrolysed leather (L) in mesocosms over one year. The residues derived N was measured in soil and in soil aggregate size fractions >250m (macroaggregates, macro); 53-250m (microaggregates, micro); <53m (silt and clay, s+c) obtained by wet sieving. Barley degradation (77% of the initial amount) was faster than triticale degradation (55%). The L slowed down the barley degradation (72%) and speeded that of triticale (64%). Greater amount of residues N was in macro and micro than in s+c. The presence of L reduced the residues N stabilised in the finest fractions. The losses of barley N were reduced by the L addition, those from triticale were increased. The fate of residues N was affected by the L application that influenced the residues mineralisation, the stabilisation and the losses of their derived N
Litter quality changes during decomposition investigated by thermal analysis
No full textThe litter decomposition process depends on the litter chemical composition, especially the ratio between more labile compounds, cellulose, and the recalcitrant lignin and waxes. Their determination is crucial to predict the process, though lignin measurement presents some limitations due to drawbacks of the different methods. Thermal analysis has been successfully applied to several organic materials in order to obtain quali-quantitative information of the chemical structure of the sample. In this work TG-DTA was used in a short-term litter decomposition study of two broadleaf forest stands of contrasting ages, and the results were compared to those obtained with a chemical method (Klason’s method) commonly used to quantify cellulose and lignin. TG-DTA was applied to the litter and to the cell walls (CW) extracted from the litter, whose cellulose and lignin content was determined using the Klason’s method. When applied to litter, thermal analysis showed a weak correlation with the Klason’s method, though it allowed the detection of the dynamics of waxes, that increased during the decomposition and could influence the later stages of the process. Contrastingly, a good correlation between cellulose and lignin determined with the two methods was found when TG-DTA was applied to the CW. In this case TG-DTA, according to NMR data, also highlighted the changes in the CW chemical structure compared with that of the litters, in particular the loss of waxes and the decreased thermostability of aromatic components. Moreover, a new concept of quality of the decomposing litter, based on the balance between the energy stored in the litter and the energy needed to release it obtained by thermal analysis, was recently introduced. Samples of the old forest litter had an initial energetic balance more favorable than those collected in the young stand. At the end of the period, the decrease in litter quality was greater in the young than in the old forest samples, due to the combined effect of the higher degradation of thermolabile substances and the accumulation of more thermostable components. Thermal analysis seems to have a good potential in litter decomposition studies, as it can link structural and energetic changes during the process
Biodegradable plastics: Effects on functionality and fertility of two different soils
Full text linkIn agriculture, the use of soil biodegradable mulch films could represent an eco-friendly alternative to conventional
plastic films. However, soil biodegradable mulch films incorporated into the soil through tillage, being not
only a physical but also a biogeochemical input, is expected to influence the soil quality by affecting its functions.
Therefore, the eco-compatibility of these biodegradable plastics needs to be evaluated for their impact on
different soil functions. To understand the effect of biodegradable plastics on soil quality (i.e. microbial biomass,
nitrogen cycle, and activity of soil enzymes involved in the biochemical processes of carbon and nitrogen), we
added increasing quantities of biodegradable plastics in two different soils: a loamy (Cambisol) and sandy
(Arenosol) soil. The results highlight that the carbon added through the biodegradable plastics influenced the
processes linked to carbon and nitrogen cycles. Significant effects were observed mainly with the highest dose of
biodegradable plastics added (1%), resulting in a higher growth of microbial biomass, increased carbon mineralisation,
and increased immobilisation of available nitrogen. The results also underline the importance of
evaluating the impact of biodegradable plastics in different soils because all the processes considered are also
influenced also by soil physicochemical characteristics
Carbon sequestration and distribution in soil aggregate fractions under Miscanthus and giant reed in the Mediterranean area
No full textIn this study, we assessed the carbon (C) distribution within soil aggregates, macroaggregates (Macro),
microaggregates (micro), and silt and clay (s + c) through three soil depths (0– 0.15, 0.15–0.30, and 0.30–
0.60 m) and af ter 9 years of land conversion from two annual crops continuous wheat and maize/wheat
rotation to Miscanthus and giant reed, respectively. The 13 C natural abundance analysis wa s combined
with physical fractionation to trace the fate of the new C that wa s derived from Miscanthus and giant reed
in aggregate fractions. Macro always represented the highest proportion of the soil and the highest
amount of C. In Miscanthus, the amount of C decreased from the 0–0.15 to the 0.30–0.60 m soil layer,
whereas the C storage capacity of micro and s + c increased with depth. In giant reed, the distribution of
the soil fractions and the associated C were more uniform in all of the layers. The new C derived from the
perennial species wa s mainly concentrated in the upper layer in the Macro under Miscanthus , whereas it
wa s more evenly distributed in the three layers and the fractions under giant reed. Irrespective of the
fractions, in the Miscanthus plantation, the great C accumulation wa s derived from both the new C
directly entering the soil and the old C that wa s preserved from mineralization. Conversely, in the giant
reed plantation, C accumulation wa s only derived from the new C component. These patterns reflect the
different structure of the root apparatus of the two perennial species, which were mainly concentrated in
the upper layer of Miscanthus and were more evenly distributed in soil profile of the giant reed. It is likely
that this is responsible for the different mechanisms of C storage and turnover
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
Stabilization of mineral oil hydrocarbons in recycled paper pulp by organo-functionalized mesoporous silicas and evaluation of migration to food
No full textThe occurrence of mineral oil hydrocarbons (MOH) in cellulose-based packaging is mainly due to the offset printing process where MOH are used as a ink pigments' solvent. The MOH migration from paper/paperboard to food is matter of concern for EFSA, members state authorities, consumers, and food industry. In this study, the feasibility to stabilize MOH by adding a sorbent into recycled paper obtained through a common washing process was investigated and the migration to wheat flour/Tenax® assessed. Among several white/pale yellow porous materials, organo-modified powder silica MCM-41-Si(CH3)3 showed the best combination between affinity for MOH (184% dw) and stability to thermal regeneration. A freshly issued newspaper with >3000 mg MOH kg-1 was used to produce recycled paper at a laboratory-scale plant. MCM-41-Si(CH3)3 was added at the pulping step (1% dw) and the sorbent-enriched pulp handled according to a washing paper production process with no effect on the paper optical brightness. The MOH content of the wheat flour in contact with the sorbent-enriched paper under accelerated migration conditions (15 days at 40 °C) resulted 20% of that contacted with control paper (4.3 ± 1.1 and 20.4 ± 5.5 mg kg-1, respectively), despite its contamination was 24% higher than the control. On the contrary, Tenax® contamination resulted 56.0 ± 10.0 and 47 ± 14.0 mg kg-1 when exposed to sorbent-enriched and control paper, respectively
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
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