Mathematical modelling of mass transfer during rehydration process of Aloe vera (Aloe barbadensis Miller)

Aloe vera (Aloe barbadensis Miller) slabs dried at 60 °C were rehydrated at three temperatures (20, 40 and 60 °C) in order to study the influence of temperature on the kinetics of mass transfer during rehydration phenomenon. Fick, Peleg and Weibull models were applied for rehydration modelling, as well as one new proposed model. All kinetic parameters of the models showed positive dependence on temperature, according to the Arrhenius-type equation. Weibull model and the new proposed model provided the best fit quality for each rehydration curve based on the statistical tests RMS, SSE and Chi-square. In accordance with the results, both models may be used to estimate the rehydration time of A. vera. Furthermore, two rehydration indices (RR and WHC) were analysed, which decreased as temperature increased. These indices confirm that drying process modifies the cell structure of A. vera, reducing the rehydration ability due to cellular and structural disruption that takes place during dehydration.     

Model predictive control springer,Berlin, 1999, ISBN 3540762418, 280 pages

This volume is a recent addition to the Camacho and Bordons' book ‘Model Predictive Control in the Process Industry’, edited by Springer Verlag. The book presents a complete review of the theory and applications of Model Predictive Control MPC, from the simple unconstrained SISO case to the more complex constrained MIMO situations. Special attention is given to the Generalized Predictive Controller that is one of the most known and cited MPC strategies. In all the chapters the results are illustrated with simulation examples and also with some experimental results that validated the controllers and tuning rules analyzed in the book. Copyright © 2003 John Wiley & Sons, Ltd.     

A new rigid‐viscoplastic model for simulating thermal strain effects in metal‐forming processes

A new rigid‐viscoplastic model that includes the effect of thermal strains when modelling steady‐state metal‐forming processes was developed. A symmetric approximation to the resulting non‐symmetric stiffness matrix was derived. The thermo‐mechanical flow formulation was implemented using the pseudo‐concentrations technique. The new formulation was numerically tested showing that it provides reliable results. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of nitrogen and sulfur fertilization on glucosinolates in the leaves and roots of broccoli sprouts (Brassica oleracea var. italica)

Broccoli (Brassica oleracea L. var. italica cv. Marathon) sprouts are a rich source of glucosinolates, particularly 4‐methylsulfinylbutyl glucosinolate (glucoraphanin), the precursor of the chemoprotective isothiocyanate, sulforaphane. Sulfur and nitrogen fertilization have been shown to influence the pattern and levels of glucosinolates in mature broccoli, but little information is available on the fertilization of sprouts, a transient stage of broccoli growth, which have been recommended for salads. Therefore, an experiment was set up to evaluate the effect of N and S fertilization on the glucosinolate content of the aerial part and roots of broccoli sprouts. Nitrogen was tested at 0, 45.5, 91.0 mg L^?1 and sulfur at 0, 14.6 and 29.2 mg L^?1. The results showed that total glucosinolates in the aerial part were significantly higher (P < 0.001) than in the roots. The major glucosinolates in the aerial part were 4‐methylsulfinylbutyl and 3‐methylsulfinylpropyl whereas in the roots they were 2‐phenylethyl and 4‐methylthiobutyl. Fertilization of broccoli sprouts had a significant (P < 0.001) detrimental effect on the levels of aliphatic glucosinolates whereas the opposite was noted for indole and aromatic glucosinolates, for some of the fertilization combinations tested. Overall, the results indicate that broccoli sprouts do not benefit from fertilization. Copyright © 2006 Society of Chemical Industry     

Speedup and scalability analysis of Master–Slave applications on large heterogeneous clusters

Although cluster environments have an enormous potential processing power, real applications that take advantage of this power remain an elusive goal. This is due, in part, to the lack of understanding about the characteristics of the applications best suited for these environments. This paper focuses on Master/Slave applications for large heterogeneous clusters. It defines application, cluster and execution models to derive an analytic expression for the execution time. It defines speedup and derives speedup bounds based on the inherent parallelism of the application and the aggregated computing power of the cluster. The paper derives an analytical expression for efficiency and uses it to define scalability of the algorithm–cluster combination based on the isoefficiency metric. Furthermore, the paper establishes necessary and sufficient conditions for an algorithm–cluster combination to be scalable which are easy to verify and use in practice. Finally, it covers the impact of network contention as the number of processors grow.     

Computational method for the design of ducts

This paper describes an inverse method that applies to two-dimensional, irrotational and incompressible flow, based on a transformation of variables from the physical plane defined by (x, y), to a computational plane defined by the stream function ψ, and the velocity potential, ?. In this new plane, the resulting differential equation describing the flow is relatively simple, and should be solved in a domain that presents always a rectangular shape, facilitating the generation of a numerical grid appropriate to the problem. The solution of this equation gives the distribution of the x coordinate throughout the flow field, while the values of the y coordinate are calculated by integration of the previous result. Some of the numerical details of the procedure will be discussed, with special emphasis on the numerical treatment of the boundary conditions. The application of the described method to the design of a curved duct with an overall deflection of around 90° will be presented, with the aim of showing the potentialities of the method, which is computationally quite simple.     

Hollow‐fiber dispersion‐free extraction and stripping of Pb(II) in the presence of Cd(II) using D2EHPA under recirculating operation mode

Lead(II) and cadmium(II) solvent extraction (SX) with D2EHPA dissolved in heptane and kerosene from aqueous chloride media was studied. Extraction reaction stoichiometries and extraction equilibrium constants were evaluated. Application of a dispersion‐free membrane‐based extraction and stripping technique with two hollow‐fiber contactors under recirculating operation mode allowed a quantitative (>97%) removal of lead from the aqueous solution in the extraction module with a separation factor of 19 and a 62% recovery in the back‐extraction module with a separation factor of 6.3 after 7 h under optimum conditions. Mass‐transfer coefficients for the system were evaluated. Optimal conditions for transport and separation are reported and compared using SX and the membrane‐based technique. Copyright © 2004 Society of Chemical Industry     

Controlled Thickness Deposition of Ultrathin Ceramic Films by Spin Coating

This work describes the combined use of nanocrystal water-based colloidal suspensions with spin-coating deposition in order to obtain ultrathin ceramic films. We have used tin oxide (SnO₂) nanoparticles, with particle diameter sizes ranging from 1–5.5 nm, to develop the deposition approach. Films obtained under several conditions were characterized by ellipsometry and atomic force microscopy, showing that the process has the ability to produce ultrathin ceramic films, with thickness ranging from 10–100 nm, with good particle packing. Additionally, electrical measurements in the films indicate good homogeneity and potential for various applications.     

High precision analysis of finlines on semiconductor substrate

In this study, the effect of the metallization thickness in finlines on semiconcuctor substrate is researched. The propagation parameters are computed to measure the inluence of the metallization. The theory and numerical results are presented to the propagation constant and characteristic impedance of the bilateral and unilateral finlines. The full wave analysis of the transverse transmission line — TTL method is used to determine the electromagnetic fields of the structure in Fourier transform domain — FTD. Applying the suitable boundary conditions, the moment method and expanding the fields in a set of suitable bases functions, a homogeneous matrix system is obtained and the propagation constant is computed. The characteristic impedance is obtained using the relation of the voltage in the slot and the transmitted power by the structure. Computational programs are developed to obtain numerical results to the propagation parameters composed by the propagation constant and characteristic impedance.