1,720,962 research outputs found
Structural similarity of humic substances from hydrochar obtained from vinasse and sugarcane bagasse with those of the Amazonian dark earth
No full textAs Terras Pretas de índio (TPI) são solos conhecidos pela fertilidade associada à matéria orgânica recalcitrante e reativa. Tem se tentado reproduzir experimentalmente a natureza química da matéria orgânica da TPI por meio do tratamento térmico da biomassa, sendo o processo de pirólise e o de carbonização hidrotérmica (CHT) os mais empregados. As substâncias húmicas (SH) constituem parte da matéria orgânica do solo e influenciam suas propriedades químicas, físicas e biológicas, e, portanto, sua fertilidade. O objetivo desse estudo foi o de extrair SH das TPI e substâncias do tipo húmicas (STH) de carvão hidrotérmico (CH) produzido com bagaço de cana-de-açúcar e vinhaça, visando sua caracterização e comparação da funcionalidade química. Foi realizada a CHT do bagaço de cana-de-açúcar, da vinhaça e da mistura de bagaço de cana-de-açúcar e vinhaça com e sem adição de ácido fosfórico. As STH foram extraídas dos CH e as SH da TPI e também de uma área adjacente (ADJ) em profundidade. As amostras foram caracterizadas por meio de ressonância magnética nuclear de 13C, reações de hidrólise e metilação térmicas acopladas à cromatografia gasosa e espectrometria de massas (Thermochemolysis GC-MS), termogravimetria, análise composicional, fluorescência molecular e foram submetidas a bioensaios com sementes de milho. A CHT gerou STH caracterizadas pela presença de grupos aromáticos e cadeias alifáticas, sendo que a adição de ácido no meio reacional deixou as STH mais hidrofóbicas, com maior rigidez estrutural causada principalmente pelo conteúdo aromático. As STH podem ser classificadas em 2 tipos: 1-STH composta por frações hidrofílicas (O-Arila e O-Alquila) e hidrofóbicas (C-Arila), na qual possuem um arranjo mais flexível liberando moléculas bioativas; 2-STH compostas por frações mais hidrofóbicas (C-Alquílico) que não apresentaram bioatividade. As SH das TPI apresentaram maior complexidade e hidrofobicidade estrutural quando comparadas com as ADJ. As SH apresentaram características diferentes em função da profundidade do solo, sendo as SH da TPI mais humificadas em superfície, enquanto as da área adjacente em profundidade. As STH do CH de bagaço de cana-de-açúcar foram as que apresentaram maior similaridade com as SH pela presença de compostos fenólicos, na qual influenciaram o crescimento inicial das sementes milho e se diferiram pela maior presença de estruturas polissacarídicas nas SH. As STH mostraram semelhança com a matéria orgânica natural e mostraram bioatividade em sementes de milho, dependendo da matéria-prima utilizada.Amazonian Dark Earth (ADE) is known for the higher fertility associated with the recalcitrant and reactive organic matter. It has been tried to mimic experimentally the chemical nature of the organic matter from ADE by the thermal treatment of biomass, employing the pyrolytic process and hydrothermal carbonization (HTC). Humic substances (HS) is part of soil organic matter and influences the chemical, physical and biological properties, playing an import role in the soil fertility. The main objective this study was to extract HS from ADE and humic-like substances (HLS) from hydrochar (HC), aiming to access the composition and to compare the chemical functionality. The HTC of sugarcane bagasse, vinasse and the mixture of sugarcane bagasse and vinasse were carried out with and without addition of phosphoric acid in the reaction medium. HLS were extracted from HC and HS from TPI and also from surrounding soil (SR) in depth. The samples were characterized by 13C nuclear magnetic resonance, thermal hydrolysis and methylation reactions coupled to gas chromatography and mass spectrometry (Thermochemolysis GC-MS), thermogravimetry, composition analysis, molecular fluorescence and were submitted to bioassays using maize seeds. The HTC process generated a HLS characterized by the presence of aromatic groups and aliphatic chains, and the addition of phosphoric acid in the medium reaction left the HLS more hydrophobic, with greater structural rigidity mainly by the aromatic content. HLS presented two supramolecular structures: 1-HLS composed by hydrophilic (O-Aryl and O-Alkyl) and hydrophobic (C-Aryl) moieties, which they have a flexible arrangement enabling the release of bioactive molecules; 2-HLS composed by more hydrophobic (Calkyl) moieties that did not showed bioactivity. The HS from ADE showed a greater structural complexity and hydrophobicity than SR. The HS presented different characteristics in depth; HS from ADE seems to be more humified on top layer, while the SR is in depth. The HLS of HC of sugarcane bagasse were the ones that presented the highest similarity to HS by the presence of phenolic compounds, which influenced the initial growth of the maize seeds and were different due to the greater presence of polysaccharide structures in the soil. The HLS generated employing the HTC process showed similarity with natural organic matter and bioactivity in maize seeds, depending on the raw material.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)17/05575-217/17991-
Sustainable intensification of Brazilian degraded pastures: a study on soil carbon sequestration, organic matter pools, and chemical transformations
Get PDFNo Brasil, estima-se que 95 milhões de hectares de pastagens estejam parcialmente degradadas, exigindo a adoção de práticas de manejo que promovam a recuperação e aumentem a produtividade. A intensificação de pastagens, por meio de práticas como adubação, controle da taxa de lotação e pastejo rotativo, melhora a produção de forragem, aumenta a produtividade animal e tem o potencial de aumentar os estoques de carbono orgânico no solo, melhorando as dinâmicas de matéria orgânica do solo (MOS). Este estudo avaliou o impacto da conversão de pastagem degradada (DP) em diferentes pastagens intensificadas: pastagem irrigada com alta taxa de lotação (IHS) e 600 kg N ha-1, e pastagens de sequeiro com alta (RHS) e moderada (RMS) taxa de lotação, aplicando 400 e 200 kg N ha-1, respectivamente. Uma floresta nativa adjacente (FO) serviu como área de referência. As amostras de solo foram coletadas até 1 metro de profundidade em 2011 e 2020. O teor de carbono foi medido utilizando um analisador elementar, e a origem do carbono foi rastreada por meio da abundância isotópica natural de carbono-13 (δ13C). A MOS foi analisada através de extrações químicas (ácido fúlvico [FA], ácido húmico [HA], humina [HUM]) e fracionamento físico (matéria orgânica particulada [POM] e matéria orgânica associada a minerais [MAOM]). A intensificação das pastagens resultou em aumentos significativos nos estoques de carbono, que passaram de 100 Mg C ha-1 em DP para 139 Mg C ha-1 nas RHS e 162 Mg C ha-1 nas RMS, níveis comparáveis aos da floresta nativa (148 Mg C ha-1). Entretanto, a alta intensificação em IHS não resultou em um aumento significativo do estoque de carbono em comparação com DP. O aumento na MOS concentrou-se principalmente nos primeiros 0-30 cm do solo, impulsionado pela incorporação de carbono derivado das forrageiras, conforme indicado pela análise de δ13C. A espectroscopia de fluorescência induzida por laser (índice HLIFS) e a razão atômica H/C indicaram um acúmulo de compostos alifáticos na MOS das pastagens RHS e RMS em comparação com FO, DP e IHS. A extração química favoreceu seletivamente certos compostos, conforme revelado pela análise de RMN de 13C. O AF foi predominantemente composto por grupos O-alquila, o AH apresentou uma mistura de grupos C-arila, O-alquila e C-alquila, enquanto a HUM era composta principalmente por estruturas C-alquila. Aproximadamente 90% da MOS nas pastagens estava armazenada na fração MAOM, associada a partículas do tamanho de argila. A POM exibiu características semelhantes a forragem, enquanto a MAOM estava mais degradada, contendo menos O-alquila, mais C-carbonila e C-alquila, e apresentando uma menor razão C/N. A análise de RMN das partículas do tamanho de argila revelou que a MAOM abrange uma variedade de funcionalidades químicas, indicando que todas elas podem ser estabilizadas na MAOM. NanoSIMS revelou uma distribuição heterogênea da MOS em partículas do tamanho de argila compostas por Si, Al e Fe, indicando que essas partículas não estavam saturadas com MOS e sugerindo diferentes arranjos espaciais da MOS em escala microscópica. O estudo demonstrou que o aumento do estoque de carbono em pastagens intensificadas, em comparação com pastagens degradadas, ocorreu principalmente na fração de MAOM, que apresentou uma composição química diversificada, incluindo compostos aromáticos e alifáticos. O sistema RMS promoveu o sequestro de carbono a uma taxa de 2 Mg C ha-1 ano-1, preservando a MOS da vegetação nativa enquanto incorporava carbono derivado da forragem. O provável mecanismo de estabilização foi a transformação dos resíduos de forragem, ricos em O-Alquila, em formas oxidadas de MAOM, indicadas pelo conteúdo de C-Carbonila e C-Alquila. A intensificação sustentável de pastagens, em níveis moderados, pode aumentar o sequestro de carbono em pastagens degradadas por meio de melhorias no manejo do solo e dos animais.In Brazil, over 95 million hectares of pastures are partially degraded, necessitating management practices that promote recovery and enhance productivity. Sustainable intensification, including fertilization, stocking rate control, and pasture rotation, can increase animal production and potentially boost soil carbon stocks by improving soil organic matter (SOM) dynamics. This study assessed the impact of transforming degraded pastures (DP) into various intensified pasture systems. These included irrigated pastures with high stocking rates (IHS), which received 600 kg N ha-1, as well as rainfed pastures with high (RHS) and moderate stocking rates, applying 400 kg N ha-1 and 200 kg N ha-1, respectively. An adjacent native forest (FO) served as a reference site. Soil samples were collected to a depth of 1 meter in both 2011 and 2020. Carbon content was measured using an elemental analyzer, and carbon origin was traced through natural carbon-13 isotopic abundance (δ13C). SOM was analyzed using chemical extractions (obtaining fulvic acid [FA], humic acid [HA], humin [HUM]) and physical fractionation (obtaining particulate organic matter [POM] and mineral-associated organic matter [MAOM]). Pasture intensification increased carbon stocks from 100 Mg C ha-1 in DP to 139 Mg C ha-1 in RHS and 162 Mg C ha-1 in RMS, comparable to the native forest (148 Mg C ha-1). However, high intensification in IHS did not result in significant additional carbon stock compared to DP. The increase in SOM was primarily concentrated in the top 0-30 cm of soil, driven by the incorporation of forage-derived carbon, as indicated by δ13C analysis. Laser-induced fluorescence spectroscopy (HLIFS index) and the H/C atomic ratio indicated an accumulation of aliphatic compounds in SOM from RHS and RMS pastures compared to FO, DP, and IHS. Chemical extraction selectively favored certain compounds, as revealed by 13C NMR analysis. FA predominantly comprised O-Alkyl moieties, HA contained a mixture of C-Aryl, O-Alkyl, and C-Alkyl groups, while HUM was mainly composed of C-Alkyl structures. Approximately 90% of the SOM in pastures was stored in the MAOM fraction, associated with clay-sized particles. POM exhibited characteristics similar to forage, while MAOM was more degraded, containing less O-Alkyl, more C-Carbonyl and C-Alkyl, and a lower C/N ratio. Occluded POM (oPOM) contained mainly hydrophobic compounds (C-Alkyl and C-Aryl). NMR analysis of clay-sized particles revealed that MAOM comprised a range of chemical functionalities, differing from extracts of FA, HA, and HUM. NanoSIMS analysis showed heterogeneous distribution of SOM within clay-sized particles composed of Si, Al, and Fe, indicating these particles were not saturated with SOM and suggesting different SOM spatial arrangements on the microscale. The study demonstrated that increased carbon storage in intensified pastures, compared to DP, occurred primarily in the MAOM fraction, which had a diverse chemical composition including aromatic and aliphatic compounds. RMS promoted carbon sequestration at a rate of 2.48 Mg C ha-1 year-1, preserving SOM from native vegetation while incorporating forage-derived carbon. The likely stabilization mechanism was the transformation of forage residues, rich in O-Alkyl, into oxidized MAOM forms indicated by O-Carbonyl and C-Alkyl content. Sustainable pasture intensification, at moderate levels, can enhance carbon sequestration in degraded pasture through improved soil and animal management
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
