1,720,976 research outputs found
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
On the measurement of local gas hold-up and interfacial area in gas–liquid contactors via light sheet and image analysis
No full textParticle image velocimetry techniques coupled with advanced image processing tools are receiving an increasing interest for measuring flow quantities and local bubble-size distributions in gas–liquid contactors.
Aim of this work is that of providing a numerical procedure able to reconstruct local gas hold-up and specific interfacial area from images obtained by laser sheet illumination. A correction for measured quantities accounting for laser sheet thickness is proposed and tested by means of Monte Carlo simulations. The algorithms proposed are robust and independent of any measured parameters of the actual bubble size distribution
Experimental assessment of reverse electrodialysis in closed loop configuration fed by NH4HCO3-water solutions
No full textClosed loop reverse electrodialysis is a novel technology for converting low-temperature waste heat into electric energy. This innovative heat engine consists of two units: (i) a reverse electrodialysis unit where power is produced exploiting the concentration difference between a diluted and a concentrated salt solution and (ii) a thermally driven regeneration unit where low-grade waste heat is used to re-establish the original salinity gradient between the two salt solutions.
Among all the possible salt solutions suitable as working fluid in such application, Thermolytic salts solutions, in particular Ammonium bicarbonate solutions, may be promising thanks to their characteristic thermally degradation properties. The thermolytic salt ions dissolved in water are converted into ammonia and carbon dioxide when heated up above a certain temperature (around 60°C). Then, dissolved thermolytic salt can be removed nearly completely from the dilute solution by means of a thermal desorption process and absorbed again in the concentrate solution, thus restoring the salinity gradient exploited by the reverse electrodialysis unit.
In this work, for the first time a lab scale prototype of a Closed-loop reverse electrodialysis fed by ammonium bicarbonate aqueous solutions was built and tested. The proposed prototype consists of a conventional reverse electrodialysis unit and a regeneration unit constituted by (i) a vapour stripping column and (ii) a barometric column. The process performances in terms of power output, thermal power consumption, thermal and exergy efficiency were experimentally assessed. Also the influence of operating conditions, e.g. solutions concentrations was investigated. First experimental results demonstrated the feasibility of the process
Mass transfer and hydrodynamic characteristics of unbaffled stirred bio-reactors: influence of impeller design
No full textUnbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of processes where the presence of baffles is undesirable for some reason. For instance, in the case of shear sensitive cell cultivation (e.g. human cells), unbaffled tanks have been recently found to be able to provide sufficient mass transfer through the free surface vortex. As a consequence the need for bubble formation and subsequent bursting, along with relevant cells damage, is conveniently avoided. In this work the influence of impeller geometry on mass transfer performance and power demand of an unbaffled stirred vessel operating both in sub-critical conditions (the free surface vortex has not yet reached the impeller) and in super-critical conditions (the free surface vortex has reached the impeller and a gas phase is ingested and dispersed inside the reactor) is presented.
Experimental results show that the mass transfer performance of unbaffled systems is mainly affected by specific power consumption. Among the stirrer geometries investigated a simple PBT was found to provide the most interesting oxygen transfer performance in the sub-critical regime, and can therefore be regarded as a particularly suitable stirrer for shear sensitive cultures. As regards the super-critical regime, unbaffled tanks are found to provide a performance comparable with that of the standard (baffled) bioreactors, hence resulting in a viable alternative also for fermentations involving robust cells
NH4HCO3–water solutions regeneration in RED closed loop applications
No full textReverse Electrodialysis (RED) in closed loop arrangement (Reverse Electrodialysis Heat Engine - REDHE) is a promising technology to convert low-grade waste heat into electricity. RED is a membrane process exploiting the salinity gradient between a concentrated and a diluted solution to generate electrical current. Due to the transfer phenomena occurring in the RED unit, the two exiting solutions are partially mixed. Thermal regeneration processes can be used to restore the initial conditions of the two solutions, thus closing the loop.
In this regard, ammonium hydrogen carbonate (NH4HCO3) salt solutions are suitable for such applications, being able to decompose at temperatures above 40-45 °C into a gaseous phase containing NH3 and CO2. Low temperature waste heat (T<80°C) can be used in a suitable thermal regeneration unit to recover these gases contained in the dilute solution. The decomposed gases, once stripped, can be finally reabsorbed in the concentrate one, thereby restoring the initial concentrations.
The present work investigates two kinds of regeneration units fed by NH4HCO3-water solutions. More precisely (i) an air stripping column and (ii) a distillation column were designed, built and analysed both via experiments and process modelling. The effect of several operative conditions on the removal efficiency of the two systems was investigated. In particular, for the case of the stripping column the influence of flowrate (air and inlet solution) and regeneration temperature was analysed, while, for the case of the distillation column, different pressures and reboiler duties were tested. Effect of feed solution concentrations was studied in both cases.
Finally, two models were developed on Aspen Plus® software, one for each kind of regeneration unit. Model results were compared with the experimental ones and a good agreement was found, thus validating the two models proposed
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
Free vortex shape in Uncovered Unbaffled Stirred Tanks (UUST) agitated by Rushton turbines
No full textThe main feature of unbaffled stirred tanks is the highly swirling liquid motion, which leads to the formation of a central vortex on the liquid free surface, when the vessel is operated without top-cover (Uncovered Unbaffled Stirred Tanks, UUST).
In this work, original data on fluid dynamics characteristics of (UUST) agitated by a Rushton turbine are presented. In particular, digital image analysis is employed to accurately assess vortex shape and validate an original model for its description. The model describes vortex shape in the case of sub-critical systems (when vortex bottom is placed above the impeller plane) as well as in the case of super-critical systems (when vortex bottom falls below the impeller plane). In the latter case, a sudden change of fluid-dynamic features is observed, since the vessel starts behaving as a self-ingesting system, with the generation of a gas-liquid dispersion. Data on the overall mass transfer both in the case of sub-critical and super-critical regimes are presented and compared with relevant data obtained in baffled vessel of similar size. Finally, original data about periodic oscillations of the liquid free surface, a phenomenon not investigated so far, are presented and preliminarily discusse
Optimisation of 5-hydroxy methyfurfural (5-HMF) production from biomass through heterogeneous catalysis
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