Optimisation of osmotic dehydration process of guavas by response surface methodology and desirability function

Response surface methodology was used to assess the effects of osmotic solution concentration (40–60°Brix), process temperature (20–40 °C) and vacuum pulse application time (0–20 min) at 100 mbar on water loss (WL), weight reduction (WR), solid gain (SG), water activity (a_w), colour parameters and mechanical properties of guava slices. Optimal process conditions were determined through the desirability function approach and quality characteristics of osmotically dehydrated guavas were analysed. Only models obtained for WL, WR and a_w were suitable to describe the experimental data. The desirability function showed that optimal conditions for osmotic dehydration of guavas were: osmotic solution concentration at 60°Brix, process temperature at 32 °C and 20 min of vacuum pulse application. Under optimal conditions, colour and mechanical properties of treated guavas were similar to fresh fruit, presenting WL of 29.01 g/100 g, WR of 25.91 g/100 g, SG of 3.10 g/100 g and a_w of 0.979.     

Improvement of photoelectrochemical and optical characteristics of MEH-PPV using titanium dioxide nanoparticles

The use of bulk heterojunctions can increase the efficiency of exciton dissociation in polymer-based photovoltaics. We prepared and characterized bulk heterojunctions of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and titanium dioxide nanoparticles deposited by spin coating on indium tin oxide substrates. The surface morphology of the MEH-PPV+TiO₂ composite films revealed that addition of TiO₂ nanoparticles increased the film roughness. The effect of TiO₂ nanoparticles on the photoelectrochemical and optical characteristics of MEH-PPV polymer heterojunctions was studied. Addition of TiO₂ nanoparticles improved the absorbance of MEH-PPV composite films. Moreover, the photocurrent of the composite devices increased with the TiO₂ nanoparticle concentration. These observations provide an insight into new approaches to improve the light collection efficiency in photoconductive polymers.     

Effect of the fiber content and plasticizer type on the rheological and mechanical properties of poly(vinyl chloride)/green coconut fiber composites

A series of poly(vinyl chloride) (PVC)/green coconut fiber (GCF) composites, with dioctyl phthalate (DOP) or thermoplastic polyurethane (TPU) as a plasticizer, were prepared by melt mixing. Their properties were studied in the molten state with an advanced nonlinear harmonic testing technique; in the solid state, the hardness and impact resistance were evaluated, and scanning electron microscopy was used for fractured surfaces. The effect of the fiber loading was investigated, as well as the role of the plasticizer. PVC–GCF composites are heterogeneous materials that, in the molten state, exhibit essentially a nonlinear viscoelastic character, in contrast to pure PVC, which has a linear viscoelastic region up to 50–60% strain. The complex modulus increases with the GCF content but in such a manner that the observed reinforcement is at best of hydrodynamic origin, without any specific chemical (i.e., permanent) interaction occurring between the polymer matrix and the fibers. As expected, PVC offers good wetting of GCFs, as reflected by the easy mixing and the rheological and mechanical properties. Fibers can be incorporated into PVC up to a 30% concentration without any problem, with the PVC/plasticizer ratio kept constant. Higher GCF levels could therefore be considered. Replacing DOP in part with TPU gives some benefit in terms of impact resistance, likely because of the viscoelastic nature of the latter and the associated energy absorption effects. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Investigation of NBR-cellulose II nanocomposites by rheometric and equilibrium swelling properties

Nanocomposites of butadiene-acrylonitrile copolymer (NBR) and cellulose II were obtained from mixtures of nitrile rubber latex and cellulose xanthate by using a co-coagulation system. The influences of low and medium acrylonitrile content in NBR and the cellulose II content, varying from 0 to 30 phr, were investigated by means of rheometric and equilibrium swelling experiments. The cure parameters obtained from the Oscillating Disk Rheometer data were utilized to characterize the structure of cellulose II present in the rubber vulcanizates through Wolff’s equation. The swelling experiments were analyzed by using Flory-Rehner theory and Kraus and Cunneen-Russel equations to evaluate the NBR-Cel II interaction. From the results it was possible to conclude that cellulose II promotes a positive influence on cure parameters and crosslinking formation. It was also observed that the high butadiene content in NBR facilitated the interaction rubber-cellulosic component. The dispersion and distribution of cellulose in NBR matrix gave rise to nanomaterials, as observed by transmission electron microscopy.     

Some properties of Rényi entropy and Rényi entropy rate

In this paper, we define the conditional Rényi entropy and show that the so-called chain rule holds for the Rényi entropy. Then, we introduce a relation for the rate of Rényi entropy and use it to derive the rate of the Rényi entropy for an irreducible-aperiodic Markov chain. We also show that the bound for the Rényi entropy rate is simply the Shannon entropy rate.     

Non-linear effects in moisture adsorption by chocolate

Summary We show that the moisture adsorption by a chocolate film is best described by a non-linear diffusion equation. We found an approximate analytical solution and determined the diffusion parameters by fitting this solution to experimental data. An adsorption experiment alone may be used to determine the moisture transmission properties of the material, significantly reducing the experimental effort.     

Effect of king palm (Archontophoenix alexandrae) flour incorporation on physicochemical and textural characteristics of gluten-free cookies

The replacement of the blend of rice flour (70%) and corn starch (30%) with king palm flour [ Archontophoenix alexandrae (F. Muell.) H. Wendl. and Drude] at levels of 0–30% was investigated for its effects on the chemical and physical characteristics of gluten-free dough and cookies. Cookies containing 10, 20 and 30% of king palm flour were analysed by twenty-one celiac consumers through preference-ranking test. Ash, minerals, and dietary fibre contents increased in cookies that were added with king palm flour. Compared with the control dough, the incorporation of king palm flour increased the firmness and decreased the adhesiveness of dough samples. The incorporation of king palm flour increased the hardness of cookies in relation to the control dough. None of the cookies differed significantly ( P  > 0.05) in the lightness (L*) parameter. All formulations produced cookies with hue angles around 60, which indicate a tendency to brown colour. The study reveals that the incorporation of king palm flour showed desirable results in nutritional characteristics, because of the increase of the dietary fibre and minerals contents. In this study, the cookies preferred by celiac consumers were those containing 10 and 20% of king palm flour ( P  > 0.05).     

Influence of morphology and surface charge on the suitability of palygorskite as drilling fluid

This study investigates the influence of physical chemistry properties of three palygorskites from Brazil on the suitability of the dispersions for use as a component of drilling fluid. Characterization and technological tests have been carried out.The analysis were done with X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Thermo Gravimetric Analysis (TGA), Scanning Electronic Microscopy (SEM), Laser Particle Sizer and Electro Kinetic Sonic Amplitude (ESA). The samples were prepared as recommended by Petrobras' Normalization Standard (N-1967, 1984).Both the morphology and surface charge of the particles have a major effect on the suitability as the drilling fluid. The dark São Pedro palygorskite sample showed the best suitability in both fresh and salt water. The dark and white São Pedro samples were classified as type 1 palygorskite and are of high yield. The Boa Vista sample was classified as medium yield.     

Lumped Approach to a Multi-Period–Multi-Reservoir Cyclic Storage System Optimization

Cyclic storage system (CSS) refers to the joint development and operation of surface impoundment and subsurface subsystems with natural and physical interaction and a prespecified operating rule which manages the inter-relation between different components of the system. This paper presents a lumped modeling approach to a generalized large scale cyclic storage system. The model is capable to optimally design and operate a cyclic system in an irrigable area. The excitation units with pronounced impact and a complexity of the semi-distributed model are replaced with approximated lumped functions, while maintaining a desirable level of accuracy in the system’s performance in a long-term planning horizon. The proposed model has a MINLP structure, which is solved using powerful well-known LINGO solver. Design capacities of different components of the system and the associated operating rules parameters are considered as decision variables that minimize total cost of operating costs over the planning horizon. Extensive simulation runs show that the derived operating rules perform quite satisfactory with non-significant deficits over the entire horizon.     

Effects of cross-linking and acetylation on oat starch properties

Starch samples separated from oat were modified with two different levels of POCl₃ (0.5 and 1.0 g kg⁻¹) as a cross-linking agent and two different levels of acetic anhydride (6% and 8% (w/w)) for acetylation. Swelling factor, thermal properties and retrogradation measurements were evaluated to characterise the influence of phosphorylation and acetylation on oat starch. Cross-linking decreased the swelling factor and did not improve gelatinization temperature while it increased synaeresis in comparison with native starch. Acetylation increased swelling factor but reduced gelatinization temperature and synaeresis of oat starch.