1,721,004 research outputs found
Analysis of the molecular weight distribution in free radical polymerization: Modelling of the MWD from the analysis of experimental GPC curves
No full textIn this paper different techniques for the deconvolution of experimental gel permeation chromatography (GPC) curves of polymers obtained from batch reactors are examined with the aim of improving the modelling of the polymerization process. The deconvoution of the GPC curves gives insight into the effects of diffusive phenomena on the values of the average molecular weights (Mn and Mw) and the molecular weight distribution (MWD) of the polymer. Two methods, one based on a two-peak deconvolution and the other one based on a multi-peak deconvolution, are compared. The different characteristics and relative merits of the two methods are illustrated using several sets of experimental data. In conclusion, the first method is less accurate but allows a separation of the two contributions given by the chemical and diffusive control of the MWD; the second method has a sound theoretical background (confirms the prediction of the free volume theory) and is potentially much superior but the results prove to be more sensitive to the quality of the experimental part
Un disegno per Isola delle Femmine. Indagini digitali su Gianni Pirrone
No full textPer tentare un primo approccio alla lettura del pensiero architettonico del periodo è sembrato utile prendere spunto proprio dal primo ‘lavoro’ di Gianni Pirrone, la sua tesi di laurea del 1950 di cui sono stati relatori Edoardo Caracciolo e Luigi Epifanio. Il ridisegno critico non solo fa prendere corpo al pensiero del giovane Pirrone ma evidenzia, attraverso la schedatura dei disegni, l’approccio, a quel tempo, della Scuola di Architettura di Palermo ai temi della progettazione architettonica e urbana
OPTIMIZATION OF BATCH POLYMERIZATION REACTORS - MODELING AND EXPERIMENTAL RESULTS FOR SUSPENSION POLYMERIZATION OF METHYLMETHACRYLATE
No full textA model for the simulation of suspension polymerization of MMA has been developed, which allows to accounts for the effect of diffusive phenomena on reaction rate and to evaluate molecular weight distribution under non-isothermal conditions. The model has been validated by experimental runs carried out in a laboratory reactor. Obtained results show that an increase of the reaction temperature during the gel effect time can have a favourable influence on the polymer quality. The control of temperature profiles in the reactor is indicated as an interesting operating strategy to be adopted in industrial units
Optimal operation strategies to control the molecular weight distribution of polymer products
No full textA mathematical model for bulk and suspension polymerization of methylmethacrylate has been extended to solution polymerization and verified experimentally. On the basis of the model two operating strategies are analysed for suspension and concentrated solution polymerization.
For suspension polymerization, a batch operation under isothermal followed by adiabatic conditions can be adopted in industrial reactors. This gives a good approximation to the optimal temperature profile which makes it possible to eliminate the bimodality in the molecule weight distribution curves.
For concentrated solutions carried out in a tubular reactor, the solvent concentration can play a key role in limiting the increase in molecular weight during the gel effect and thus in controlling the molecular weight distributio
Enhancing MPC formulations by identification and estimation of valve stiction
Full text linkA common source of poor control performance in industrial processes is represented by stiction in control valves, which often induces offset, oscillating behavior, and even loss of stability. Recent studies have investigated the effectiveness of embedding stiction models into model predictive controller (MPC) schemes, moving from stiction unaware to different stiction aware formulations, which help to remove fluctuations and may guarantee higher set-point tracking ability. To this aim, along with the process model the controller needs to use a dynamic model of sticky valves. This paper proposes an efficient, computational approach to obtain both valve and process dynamics, under the framework of Hammerstein system identification, which is based on nonlinear, gradient-based, numerical optimization. In order to improve the computational behavior and effectiveness of the methodology, a recently proposed smoothed model of stiction is deployed. The proposed methodology is validated in several (single-input single-output, and multivariable) examples, where the effectiveness of the obtained stiction aware MPC regulator is also evaluated against a stiction unaware counterpart
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
- …
