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ADSORPTION OF TRICLOPYR ON SOIL AND SOME OF ITS COMPONENTS
No full textThe adsorption of triclopyr [[(3,5,6-trichloro-2-pyridynyl)oxy] acetic acid] by homoionic clays, soil organic matter (H- and Ca-saturated), and seven soils was studied. The extent of adsorption on clays decreased in the order of decreasing acidity of the saturating cations. The H-organic matter was more active in triclopyr adsorption than Ca-organic matter and Ca-clay, whereas studies on mixtures of clay and organic matter indicated that the interaction between these two soil components reduced the surfaces available for triclopyr adsorption. Adsorption isotherms conformed to the Freundlich equation. It was found that in soil the Freundlich adsorption constant decreased linearly with organic matter (r = 0.930) and adsorption decreased with increasing pH. Multiple-regression analysis indicated that k(f) values were better correlated if cation-exchange capacity and pH (r = 0.989) were simultaneously taken into account
HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF THE HERBICIDE IMAZAPYR RESIDUES IN WATER AND SOIL
No full textA rapid method for determining residues of the herbicide imazapyr in water and soil is described. The soil samples were extracted with aqueous methanol and, after concentrating, the residue was estimated by HPLC with UV detection at 250 nm. Imazapyr dissolved in water was quantified by injecting the samples without any previous treatments. Analyses were performed without clean-up of soil and water samples. The pre-concentration of samples was required only at very low herbicide amounts. The maximum recovery was achieved by methanol/water (3:2 v/v) with both soils after three extraction procedures. The detection limits were 0.01 mg/l and 0.05 mg/kg in water and soil, respectively
EFFECT OF METAL-BINDING ABILITY ON THE ADSORPTION OF ACIFLUORFEN ON SOIL
No full textThe adsorption of acifluorfen, the sodium salt of 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid, on six soils of various physical and chemical properties as well as its dependence on the exchangeable cation (Ca2+ and Na+) and on soil pH was studied. Adsorption isotherms conformed to the Freundlich equation. Soil saturation by Na+ ions produced a strong decrease in acifluorfen adsorption, whereas the opposite finding was observed for Ca-saturated soils. Adsorption was found to, be correlated with cation-exchange capacity (CEC) much better than with other soil properties and decreased with increasing pH. At comparable pH, variations of k(f) values after Ca saturation of soils indicated that complex formation reactions, leading to precipitation of insoluble complexes, contribute to simulate high adsorption
ADSORPTION AND DESORPTION OF DIMEPIPERATE BY SOILS
No full textThe adsorption and desorption of dimepiperate, S-(alpha,alpha-dimethylbenzyl)-1-piperidinecarbothioate, on three soils of various physical and chemical properties was studied. Adsorption isotherms conformed to Freundlich equation. The k(f) values increased with increasing organic carbon content of the soils. To confirm the effect of organic matter, the adsorption of the herbicide was studied after removal of organic matter by peroxidation. This soil treatment caused a sequential loss of adsorptive capacity. Desorption isotherms also conformed to Freundlich equation, but K(des) values were higher than those for adsorption and increased with increase in concentration of initially adsorbed dimepiperate. Hysteresis was indicated by the decrease in slope of desorption compared to adsorption isotherms. Hysteresis decreased with increasing methanol content in the extracting solution. The factors involved are discussed
Influence of organic matter and its clay complexes on metolachlor adsorption on soil
No full textThe absorption of metolachlor, 2-chloro-6'-ethyl-N-(2-methoxy-1-methylethyl) acet-o-toluidide was studied on three soils of various physical and chemical properties. Adsorption isotherms conformed to the Freundlich equation. The k(f) values increased with increasing organic carbon content of the soils. However, variations in k(oc) values by a factor of four were observed within three natural soils. For a given soil, the k(oc) values remained essentially unchanged after lowering the carbon content by hydrogen peroxide oxidation. These results suggest that the contribution of organic matter to total metolachlor adsorption process is influenced by association mechanisms between organic and inorganic soil constituents. Studies with mixtures of clay and organic matter indicate that the interaction between the two soil components reduces the surfaces available for metolachlor adsorption
Photolysis of dimepiperate in aqueous solution
No full textDimepiperate, S-(1-methyl-1-phenylethyl) piperidine-1-carbothioate (I) was degraded in aqueous solution by ultraviolet irradiation into piperidine (II), alpha-methylstyrene (III), acetophenone (IV), and formaldehyde (V). The reaction followed first-order kinetics. In sunlight the reaction occurred only in the presence of a sensitiser and afforded the same four photolytic degradation products. In the absence of oxygen the herbicide was converted much more rapidly, but yielded only (II) and (III) as products. A mechanism which accounts for the formation of the photoproducts is proposed
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
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