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Hydrodynamic and rheological properties of Irvingia gabonensis gum
Get PDFThe polysaccharide component of Irvingia gabonensis endosperm was isolated and its hydrodynamic and rheological properties investigated. The polysaccharide is an arabinogalactan and contains small amounts of rhamnose, galacturonic acid, glucose and glucuronic acid.
The polysaccharide displayed typical polyelectrolyte behaviour in solution. The intrinsic viscosity at infinite ionic strength, a measure of the hydrodynamic volume of the uncharged polysaccharide molecule, was obtained as 4.9 dl/g. The macromolecules have a semi flexible backbone with a Smidsrod stiffness parameter of 0.085. The polysaccharide exhibited non-Newtonian behaviour at all the concentrations (0.2% to 3.0% (w/v)) investigated. Cox-Merz plots showed that η( ) and η*(ω) were closely superimposable except at low shear rates and higher concentrations, where η* > η. The high Mw (1.56 x 106 g/mol) and its random coil conformation show Irvingia gabonensis polysaccharide has potential for application as thickener
Fresh expressions: reaching those psychological types conventional forms of church find it hard to reach?
Get PDFThe Fresh Expressions movement aims to extend the reach of church life among groups less well accessed by conventional church. This pilot study tests that claim within the framework of psychological type theory. A sample of 74 women and 49 men attending Fresh Expressions completed the Francis Psychological Type Scales to enable their profile to be set alongside the profile of 2,135 women and 1,169 men attending conventional Anglican congregations reported by Francis, Robbins, and Craig (2011). The data provided some support for the view that Fresh Expressions were reaching psychological types other forms of church find it harder to reach
Behavioral study of the surrogate model-aware evolutionary search framework
Get PDFThe surrogate model-aware evolutionary search (SMAS) framework is an emerging model management method for surrogate model assisted evolutionary algorithms (SAEAs). SAEAs based on SMAS outperform several state-of-the-art SAEAs using other model management methods and show promising results in real-world computationally expensive optimization problems. However, there is little behavioral study of the SMAS framework, and appropriate rules for its search strategy, training data selection and key parameter selection for different types of problems have not been provided yet. In this paper, with a newly proposed training data selection method, the SMAS framework's behaviour with different search strategies and training data selection methods is investigated. The empirical rules in terms of problem characteristics are obtained and the method to construct an SAEA based on the SMAS framework is updated. Experiments using 24 widely used benchmark test problems and the test problems in the CEC 2014 competition of computationally expensive optimization are carried out, which validate the proposed empirical rules
Extraction of chitin from prawn shells and conversion to low molecular mass chitosan
Get PDFExtraction and depolymerisation of chitin and chitosan from prawn shells was carried out using various chemical procedures. Sodium hydroxide and hydrochloric acid solutions were used for deproteination and demineralisation, respectively, while acetone was used for decolourisation. The amount of chitin and subsequently chitosan obtained was ∼35% and 25% respectively of the dry weight of the shells. The chitin was deacetylated using sodium hydroxide at 100 °C and the influence of the concentration of the reagent and duration of the reaction was investigated. The degree of deacetylation (DD) of the chitosan was evaluated by FTIR and NMR spectroscopy and the molecular mass distribution was determined by Gel Permeation Chromatography. It was found that the final DD was significantly higher using 50% sodium hydroxide solution (73% ± 9%) compared to 25% sodium hydroxide solution (40% ± 5%). It was noted also that the deacetylation reaction was more than 80% completed after 2 h but the chitosan produced had higher molecular mass while chitosan produced after 10 h had lower molecular mass and higher degree of deacetylation. The molecular mass distribution was bimodal for all the samples and consisted of a broad high molecular mass peak (peak 1) and a sharp low molecular mass peak (peak 2). The Mw of peak 1 decreased from ∼1.3 × 106 after 2 h reaction with sodium hydroxide to 3.1 × 105 after 10 h reaction indicating that depolymerisation and deacetylation occurred simultaneously. Peak 2 had a Mw of ∼2.4–9.9 × 103
An Efficient Evolutionary Algorithm for Chance-constrained Bi-objective Stochastic Optimization
Get PDFIn engineering design and manufacturing optimization, the trade-off between a quality performance metric and the probability of satisfying all performance specifications (yield) of a product naturally leads to a chance-constrained bi-objective stochastic optimization problem (CBSOP). A new method, called MOOLP (multi-objective uncertain optimization with ordinal optimization (OO)), Latin supercube sampling and parallel computation), is proposed in this paper for dealing with the CBSOP. This proposed method consists of a constraint satisfaction phase and an objective optimization phase. In its constraint satisfaction phase, by using the OO technique, an adequate number of samples are allocated to promising solutions, and the number of unnecessary MC simulations for noncritical solutions can be reduced. This can achieve more than five times speed enhancement compared to the application of using an equal number of samples for each candidate solution. In its MOEA/D-based objective optimization phase, by using LSS, more than five times speed enhancement can be achieved with the same estimation accuracy compared to primitive MC simulation. Parallel computation is also used for speedup. A real-world problem of the bi-objective variation-aware sizing for an analog integrated circuit is used in this paper as a practical application. The experiments clearly demonstrate the advantages of MOOLP
Synthesis, characterization and emulsification properties of dodecenyl succinic anhydride derivatives of gum arabic
Get PDFGum Arabic, GA, has been chemically modified using dodecenyl succinic anhydride (DDSA) in aqueous solution and the products have been characterized and their solution and emulsification properties evaluated. FTIR was used to confirm that derivatisation had occurred and the hydrophobe incorporation and reaction efficiency was determined by a simple titration method. The derivatives, DGA5 and DGA10 were found to contain 5 and 10 %w/w DDSA respectively. Surface tension and dye solubilisation measurements demonstrated that the modified GA samples aggregated in solution at a specific concentration, referred to as the critical aggregation concentration, CAC. The value of the CAC was found to be a function of the degree of substitution and values of 0.1% and 0.04% were obtained for DGA5 and DGA10 respectively. The emulsification properties of the polymers were assessed by determination of the droplet size as a function of polymer concentration and time using laser diffraction. The droplet size decreased for all samples as the polymer concentration increased but the minimum droplet size obtained increased in the order DGA10 < DGA5 < GA indicating enhanced emulsification efficiency with increasing hydrophobe content. The effect of ageing on emulsion stability was assessed and the droplet size of emulsions prepared with GA and DGA5 increased with time but remained constant for samples prepared with DGA10. Emulsion creaming was followed using the Turbiscan and it was noted that DGA5 and DGA10 were much more effective than GA at reducing creaming. The results have demonstrated that the modified gum Arabic samples have potential application for microencapsulation
Mechanical behaviour of aircraft relevant aluminium wrought alloys at low temperatures
Get PDFThe mechanical behaviour of the commercial aluminium alloys EN AW-5182, EN AW-6016 and EN AW-7021 is investigated at temperatures ranging from 298 to 77 K and strain rates from 1.7 × 10−3 to 6.6 × 10−2 s−1. A device that allows testing at cryogenic temperatures is developed and demonstrated, where the specimens are subject to uniaxial tensile loads. The influence of a solution heat treatment for precipitation hardenable alloys is shown. The strain-hardening coefficient is determined and mapped in terms of the experimentally investigated uniform elongation. The experimental data of tested aluminium alloys are compared with EN AW-1050A-H14, which is used as a reference. The effect of the Portevin–LeChatelier effect on ductility and strength is discussed. The Ludwik relationship is adapted to describe materials showing a Portevin–LeChatelier effect
An Efficient Method for Antenna Design Optimization Based on Evolutionary Computation and Machine Learning Techniques
Get PDFIn recent years, various methods from the evolutionary computation (EC) field have been applied to electromagnetic (EM) design problems and have shown promising results. However, due to the high computational cost of the EM simulations, the efficiency of directly using evolutionary algorithms is often very low (e.g., several weeks' optimization time), which limits the application of these methods for many industrial applications. To address this problem, a new method, called surrogate model assisted differential evolution for antenna synthesis (SADEA), is presented in this paper. The key ideas are: (1) A Gaussian Process (GP) surrogate model is constructed on-line to predict the performances of the candidate designs, saving a lot of computationally expensive EM simulations. (2) A novel surrogate model-aware evolutionary search mechanism is proposed, directing effective global search even when a traditional high-quality surrogate model is not available. Three complex antennas and two mathematical benchmark problems are selected as examples. Compared with the widely used differential evolution and particle swarm optimization, SADEA can obtain comparable results, but achieves a 3 to 7 times speed enhancement for antenna design optimization
Control of the properties of xanthan / glucomannan mixed gels by varying xanthan fine structure
Get PDFThe interaction of native xanthan gum, deacetylated xanthan gum and depyruvated xanthan gum with konjac glucomannan has been studied using DSC and controlled stress rheometry. In the absence of electrolyte the DSC cooling curves for native xanthan and deacetylated xanthan showed a single peak and there was a corresponding sharp increase in the storage modulus indicating gel formation. It is apparent that on cooling, association of the konjac glucomannan with the native xanthan molecules is triggered by the xanthan coil-helix transition. In the presence of electrolyte, there were two DSC peaks observed. The higher temperature DSC peak was attributed to the xanthan coil-helix transition while the lower temperature DSC peak was attributed to konjac glucomannan – xanthan association as noted by an increase in the storage modulus. The gels formed were much weaker than those in the absence of electrolyte. The DSC cooling curves for depyruvated xanthan in the absence of electrolyte showed two peaks. The higher temperature peak was attributed to the coil-helix transition while the lower temperature peak corresponded to gelation as noted by an increase in the storage modulus. The gels were very much weaker than for native xanthan gum and deacetylated xanthan gum
Competitive adsorption between sugar beet pectin (SBP) and hydroxypropyl methylcellulose (HPMC) at the oil/water interface
Get PDFThe emulsification performance, stability and competitive adsorption of two natural food emulsifiers, sugar beet pectin (SBP) and hydroxypropyl methylcellulose (HPMC) have been investigated. Both can reduce the surface tension and emulsify oil in water. However, due to their different structure and conformation they operate via different mechanisms. Using 15% middle chain triglycerides (MCTs) oil, the amounts of SBP and HPMC adsorbed in emulsions made with these individually and in mixtures were determined. The interfacial concentration (Γ) for SBP stabilized emulsion was ∼1.25 mg/m2 and for HPMC 3.5 mg/m2. The higher adsorption of HPMC was due to multilayer adsorption, whereas SBP adsorbed as a monolayer. Competitive adsorption between SBP and HPMC was also investigated. When the HPMC concentration approached that of adsorbed SBP, the effect of HPMC became dominant and at 1.5 wt.% controlled the behaviour of the mixed emulsions, which were then almost independent of SBP. The minor role of SBP was mainly to decrease the proportion of large droplets in the emulsion. A model to describe the competitive adsorption between SBP and HPMC is propose