1,720,962 research outputs found
Applicazione della reologia alla valutazione e interpretazione dell'invecchiamento del bitume
No full textThe application of rheology to the evaluation of bitumen ageing
No full textOver the past few years, rheology has been extensively used in order to classify and evaluate bituminous binders according to their performance properties. This has led to a better knowledge of bitumen behaviour that occurs when subjected to different thermal and mechanical conditions, as seen during road construction and service in the field. In the present work, rheology has been applied to evaluate the properties of three vacuum residues before and after ageing. The influence of ageing on the rheological properties and temperature susceptibility was studied on whole vacuum residues and on their respective maltene fractions. Ageing produces fundamental modifications in the colloidal structure of both the vacuum residues and their maltenes fractions. The role of maltenes is important as the role of asphaltenes in determining the residue viscoelastic response. (C) 2000 Elsevier Science Ltd. All rights reserved
Further Developments in Toxicity Cell Biosensors
No full textThis paper describes three new immobilized toxicity cell biosensors based on the perturbation of the respiratory activity of Saccharomyces cerevisiae yeast cells. The signal detected is in one case related to the carbon dioxide developed during cell respiration and in the other two cases to the subsequent pH variation, detected using, as transducer device, respectively a classical glass electrode, or a solid stare electrode (FET). A comparison was also carried out with the corresponding biosensor using the oxygen electrode as transducer
Macrostructure and rheological properties of chemically modified residues and bitumens
No full textRheological and X-ray scattering techniques were applied to investigate how the addition of phosphorus compounds to a refinery vacuum residue (Safaniya) modifies its macroscopic behavior. The modified vacuum residue has a colloidal structure different from the original product. Rheological data show the more “gellike” nature of the modified sample in the temperature range from 0 to 40 °C. Its higher polydispersity and lower fractal dimension Df also indicate that a shift toward a more gellike state occurs. The modified sample flow properties appear to be strongly dependent on the chemical and structural modifications of the single separated fractions. Compared to the strong modifications involving the asphaltene fraction, the changes which occur to the resin fraction properties are less important
Toxicity order of cholanic acids using an immobilised cell biosensor
No full textThere is considerable published evidence of the use of cells of various species to evaluate the toxicity of numerous compounds, many of pharmaceutical interest. The coupling of cell colonies with a suitable transduction device has led to the development in recent years of toxicity biosensors based on the alteration of a process or a cell metabolic function by the toxic substance under examination. A biosensor based on immobilised yeast cells (Saccharomyces cerevisiae) has been developed recently in this department for the purpose of performing a rapid toxicity test in aqueous environmental matrices. This biosensor has now been used in the toxicity screening of a number of sodium salts of conjugated and free cholanic acids. The ''toxicity degree'' scale, which was found by placing in decreasing order the values of the slopes of the straight lines obtained by quantifying changes in the behaviour of the respirometric curve, plotted before and after incubation, using known concentrations of cholanic acid sodium salts, was: deoxycholic acid > chenodeoxycholic acid > ursodeoxycholic acid > cholic acid, for free cholanic acids; and glycodeoxycholic acid > glycochenodeoxycholic acid > glycocholic acid, for glycocholanic acids. These values are in good agreement with published toxicity data obtained in vitro. This sensor can thus be considered to provide a valid instrument for the preliminary evaluation of the toxicity of organic compounds or drugs
Comparison Between an Inhibition Enzymatic Sensor and Toxicity Biosensors in the Determination of Polluting Metal Ions
No full textIn the present research two different types of biosensor were developed to heavy metal ion determination: a classical glucose oxidase inhibition biosensor and an immobilised cell toxicity biosensor using as transducer a CO2 gaseous diffusion electrode of the potentiometric type. A comparison was also made between the responses of these biosensors and those obtained in previous tests using a immobilised cell toxicity biosensor in which the transducer consisted of a O-2 gaseous diffusion electrode of the amperometric type
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
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