1,720,958 research outputs found
Sensitivity analysis in polymerization reactions using the divergence criterion
No full textA general runaway criterion based on the divergence of the system has recently been
developed. In this work we have applied the criterion to polymerization reactions. The
runaway limits (or parametric sensitive regions) have been found and compared with
previous criteria. The results show that the new criterion is able to distinguish between runaway
and non-runaway behaviour for these types of systems. A considerable advantage over existing
criteria is that it can be calculated on-line using only temperature measurements and, hence, it
constitutes the core of an early warning runaway detection system we are developing
On-line calibration and determination of the heat of reaction for laboratory scale heat transfer calorimeters
No full textAbstract A simple method for the on-line calibration, in which both the heat transfer coefficient and the heat capacity of the reactor contents are determined, is described for laboratory scale heat transfer calorimeters. The calorimeter is operated in the isoperibolic mode for the calibration and a constant power is supplied to a resistor placed inside the reactor. The reactor heat balance differential equation is used to produce a set of linear simultaneous equations with each data acquisition cycle giving one equation. The heat transfer coefficient and the heat capacity are obtained from this set of equations by linear least squares. The application of the calibration procedure is illustrated by experiments in which the heat of reaction is determined on-line fora simulated reaction with first order kinetics and for the hydrolysis of acetic anhydride.
Keywords
calibration, hydrolysis of acetic anhydride, reaction calorimetr
Fitting isoperibolic calorimeter data for reactions with pseudo-first order chemical kinetics
Full text linkThe non-linear least squares fitting of the chemical heat flow and the reactor temperature are compared for reactions with
pseudo-first order chemical kinetics carried out in an isoperibolic calorimeter operating quasi-isothermally. Both methods give very
similar results for the reaction rate constant and enthalpy of reaction but fitting the reactor temperature appears to have some advantages
especially when there is an enthalpy of mixing of the reagents
The integration of an ultraviolet-visible spectrometer and a reaction calorimeter
No full textA small ultraviolet-visible absorption spectrometer which uses fibre optic coupled immersion
probes has been incorporated into a laboratory scale reaction calorimeter. The combined instrument
has been tried out using the hydrolysis of acetic anhydride as a test reaction. With the calorimeter operating
in the isoperibolic mode good agreement is found for the pseudo-first order reaction rate constant
as determined from spectroscopic and calorimetric measurements. Experiments have been
made in order to follow the reaction indirectly using optical pH measurements with acid-base indicators.
The possibility of determining the temperature dependence of the rate constant in a single experiment
has also been investigated
THE USE OF MEMBRANE PROCESSES IN THE CLARIFICATION OF ORANGE AND LEMON JUICES
No full textThe ultrafiltration of orange and lemon juices has been investigated on a pilot-plant scale at constant concentration using tubular configuration polymeric and ceramic membranes. The permeate fluxes were found to be strongly dependent on the tangential feed velocity at the membrane but almost independent of the driving force at average pressures over the membrane greater than ≈0.2 MPa. These results are due to the formation of a pectin-pulp deposit on the membrane, which effectively controls the ultrafiltration. Because of their different surface structures and roughness this deposit has different properties for the ceramic and polymeric membranes. This causes the latter to behave as rough tubes. The ceramic membranes give higher permeate fluxes at a lower Reynolds number than the polymeric membranes. This and their smooth tube behaviour indicate the possibility of greater energy efficiency for the industrial application of the ceramic than of the polymeric membrane
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
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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