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Morphological, chemical and mineralogical characterization of some soils developed on hard carbonate rocks in Sardinia
Full text linkThis preliminary note considers 19 profiles of Sardinian soils developed on hard limestone,
dolomitic limestone and dolomite of different age and territorial condition, reporting on the
description of the profiles and their physical, chemical and mineralogical characteristics. The
results indicate that the soils examined belong to xeric subgroups of three orders: Entisols,
Inceptisols and Alfisols.
All the profiles show a clay texture and the clayey constituents are related to the degree of soil
evolution
Chemical and spectroscopic analysis of caffeic acid transformation following the interaction with Fe(III) trapped in a Ca-polygalacturonate network
No full textInfluenza dei metodi di estrazione e di purificazione sul dosaggio in HPLC degli idrossifenoli
No full textFour different extraction methods were compard, in oder to optimize the HPLC separation and quantitation
of hydroxyphenols in «Thymus capitatus». One method was not suitable for HPLC ansly,is, whereas
the others partially destroyed the hydroxyphenols extracted from the plant. The Charpentier-Cowles me
thod was, found the most effective allowing to analyse, in spite of the losses, most of the free phenolic
acids and of those bounded extractable in hot acidic medium but not in ethanol. For the phenolics in free
form a method whith recoverier greater than those obtained with Hagerman Nicholson and Horvat-Senter
methods was developed
Electrochemical properties of Fe and Al hydroxides as affected by different supporting electrolytes
No full textPotentiometric titration curves of Fe and Al hydroxides, carried out in presence of different electrolytes
(KCI, Kbr, KI, KNO3, KCIO4) were elaborated by the Stern theory through a computered program.
The zero points of charge (zpc), calculated from the intersection point of the titration curves at different
ionic strenght, varied from pH 7.10 to pH 7.65 for Fe hydroxides and from pH 9.10 pH 9.45 for Al hydroxi
des.
For Fe compounds, a good match was found between the experimental values and those calculated by
the Stern model. High deviations were observed only with KCIO4, in whose presence a lowering of the zpc
was registered.
Also in Al hydroxides the proposed model was not reliable below zpc, indicating that the surface interac
tions are somewhat involved in specific adsorption phenomena
Describing the adsorption of potential determining ions on variable charge mineral surfaces
No full textA computer program was developed to elaborate the titration curves of amphoteric surfaces according to
the double layer theory. The zpc, identified from the intersection point of the titration curves carried out
at different ionic strengths, fell at pH 3.15, 9.45 and 7.65 for Si, AI and Fe hydroxides, respectively. The
Stern model described quite satisfactorily the relation between σ0and ψ0. Some problem was presented
by Si surfaces which were then treated by a different calculation procedure.
The δ values, the Stern layer thickness, were very high for the SI surfaces and increased with decreasing
ionic strength. A different behaviour was showed by AI and Fe hydroxides; in these cases δ values were
very low and increased with increasing electrolyte concentration. These results were discussed in terms
of surface structures and activity of the supporting electrolyte
Role of the caffeic acid oxidation products on the iron mobilization at the soil-root interface
Full text linkPrevious results show that the reduction of Fe(III) by caffeiic acid (CAF) is strongly influenced by the pH
of the reaction medium (DEIANA et al., 1995). In particular, it has been found that al pH > 3.8 the
reducing activity of CAF towards the Fe(III) ions in solution is low, but it increases when Fe(III) is
complexed as Fe(III)-polygalacturonate. The mobilization of the Fe(II) ions, which form upon the Fe(III) reduction, has been shown to depend mainly on the nature of the Fe(III)-polygalacturonate complexes (DEIANA et al., 1994a). In particular, it bas been observed a high redox activity of CAF towards Fe(III) when the metal ion is coordinated by the carboxilic groups of the macromolecule. The Fe(III) reduction has been found to decrease when an oxydrilic group was inserted in the Fe(III) coordination sphere. The
Fe(II) produced partly diffuses into the external solution and partly is still strongly held by the polysaccharidic matrix. The oxidation of CAF by Fe(III) gives rise to the formation of products (OP) with different polymerization degree, some of which are similar to those found in natural systems (DEIANA et al., 1994b). In order to determine the role of these products in the Fe(III) reduction as well as
in the mobilization of the Fe(II) produced it was set up an electrochemical method to synthetize these products (DEIANA et al., 1994b). Here are reported some results about the interaction which establish between the CAF oxidation products and iron in both oxidized and reduced form
Effects of Al substitution on goethite formation
No full textGoethites containing up to 32.7 mole % Al were synthesized and characterized through diffractometry,
spectrometry, DSC and chemical techniques. Results indicate that crystal growth was favoured or hindered depending on the percentage of aluminum incorporated into the structure. Goethites to which 5-10 mole % Al were initially added crystallized best, as shown by the highest crystallite dimensions calculated from X-ray and Mössbauer analyses, and by the lowest surface areas values. Over such substitution degree goethite crystallization was hindered and for sample synthesized in presence of 40 mole % Al the
separation of a discrete amount of gibbsite and bayerite occurred.
Both crystallinity and Al-substitution degree influenced the goethite dehydroxylation endothermic peak
temperature playing a competitive action in the peak shift. In fact, the increase in the thermal stability induced by the presence of Al3+ions into the structure was counteracted by the decrease due to the particle size reduction.
The stabilizing effect of aluminum was confirmed by the oxalate treatment which removed from the Al-free
sample a Fe amount higher than that from the sample containing about 20 mole % Al, although both
had similar crystallinity
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
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