Comparison of computational performance of GA and PSO optimization techniques when designing similar systems – Typical PWR core case

This paper compares the performance of two optimization techniques, particle swarm optimization (PSO) and genetic algorithm (GA) applied to the design a typical reduced scale two loop Pressurized Water Reactor (PWR) core, at full power in single phase forced circulation flow. This comparison aims at analyzing the performance in reaching the global optimum, considering that both heuristics are based on population search methods, that is, methods whose population (candidate solution set) evolve from one generation to the next using a combination of deterministic and probabilistic rules. The simulated PWR, similar to ANGRA 1 power plant, was used as a case example to compare the performance of PSO and GA. Results from simulations indicated that PSO is more adequate to solve this kind of problem.     

Adaptive motion control law of a robotic wheelchair

In the present work, a dynamic model of a robotic wheelchair is developed considering a lateral deviation of the center of mass. The Lyapunov and input/output stability theories are used to design a novel tracking and positioning adaptive control for the robotic wheelchair. Properties of the dynamic model with respect to its matrices and parameters are shown. A filter is used to obtain a closed loop equation that allows designing the adaptive control law. Then, a projection algorithm is used to improve the adaptive control in the sense of avoiding parameter drift. Experimental results show good performance of the adaptive control.     

Effects of turbulent flow on the corrosion inhibition properties of 2‐mercaptobenzimidazole

The electrochemical techniques, that is, polarization resistance (R_p) and potentiodynamic polarization curves, were used in order to determine the effect of turbulent flow on the corrosion inhibiting effect of 2‐mercaptobenzimidazole (2‐MBI) on API 5L X52 grade steel samples immersed in a 3% NaCl aqueous solution saturated with CO₂ at 60 °C. Turbulent flow conditions were controlled using a rotating cylinder electrode (RCE). An inhibition efficiency of 98% was measured at a concentration of 10 ppm of 2‐MBI at a rotation rate of 5000 rpm. This efficiency value is similar to those efficiency values measured at 25 and 40 ppm 2‐MBI and at the same rotation rate. These observations suggest that as the turbulent flow conditions increase the corrosion inhibiting effect of 2‐MBI is enhanced. 2‐MBI follows a Langmuir adsorption isotherm. The calculated values of adsorption equilibrium constant (K_ads) and adsorption free energy ($\Delta G_{{\rm ads}}^{{\rm o}} $ ) suggest that the adsorption process taking place is chemical. The polarization curves indicate that the 2‐MBI does not modify the electrochemical mechanism of the anodic (Fe dissolution) and cathodic (hydrogen evolution) reactions. It is suggested that 2‐MBI decreases the rate at which these reactions occur, blocking the active sites on the steel surface.     

Imidazolium,Pyridinium and Dimethyl-Ethylbenzyl Ammonium Derived Compounds as Mixed Corrosion Inhibitors in Acidic Medium

Seven cationic surfactants: 1-methyl-3-tetradecyl imidazolium bromide, 1-methyl-3-hexadecyl imidazolium bromide, N,N-tetradecyl pyridinium bromide, N,N-hexadecyl pyridinium bromide, N,N-dimethyl-N-ethylbenzyl ammonium bromide, N,N-dimethyl-N-ethylbenzyl ammonium laurate and N,N-dimethyl-N-ethylbenzyl ammonium acetate, were investigated at different doses (10, 25, 50, 100, and 200 ppm) as corrosion inhibitors for steel grade API 5L X52 in hydrochloric acid 2 M using a weight loss technique, impedance and polarization resistance methods. The corrosion inhibition of steel grade API 5L X52 of the cationic surfactants was attributed to their molecular structure (heterocyclic ring, hydrophobic chain length and counterion) that enhances adsorption onto steel surface. The best protective efficiency of the film was higher than 90% (N,N-Dimethyl-N-ethylbenzyl ammonium acetate). It is important to know how organic inhibitor films grown on the metallic surface in order to achieve superior corrosion inhibition, hence experimental findings were described by Langmuir adsorption isotherm. The Electrochemical Impedance Spectroscopy spectrums were fitted by means of the Voigt model.     

Optimization of the transesterification reaction in biodiesel production

In this paper response surface methodology (RSM) was used to study the transesterification reaction of rapeseed oil for biodiesel production. The three main factors that drive the conversion of triglycerides into fatty acid methyl esters (FAME) were studied according to a full factorial design at two levels. These factors were catalyst concentration (KOH), temperature and reaction time. The range investigated for each factor was selected taking into account the process of Fox Petroli S.p.A. Analysis of variance (ANOVA) was used to determine the significance of the factors and their interactions which primarily affect the first of the two transesterification stages. This analysis evidenced the best operating conditions of the first transesterification reaction performed at Fox’s plant: KOH concentration 0.6% w/w, temperature 50 °C and reaction time 90 min with a CH₃OH to KOH ratio equal to 60. Three empirical models were derived to correlate the experimental results, suitable to predict the behavior of triglyceride, diglyceride and monoglyceride concentration. These models showed a good agreement with the experimental results, demonstrating that this methodology may be useful for industrial process optimization.     

Effect of Niobium Oxide on the Structure and Properties of Melt‐Derived Bioactive Glasses

The effects of adding Nb₂O₅ on the physical properties and glass structure of two glass series derived from the 45S5 Bioglass^® have been studied. The multinuclear ²⁹Si, ³¹P, and ²³Na solid‐state MAS NMR spectra of the glasses, Raman spectroscopy and the determination of some physical properties have generated insight into the structure of the glasses. The ²⁹Si MAS NMR spectra suggest that Nb⁵⁺ ions create cross‐links between several oxygen sites, breaking Si–O–Si bonds to form a range of polyhedra [Nb(OM)_6?y(OSi)_y], where 1 ≤ y ≤ 5 and M = Na, Ca, or P. The Raman spectra show that the Nb–O–P bonds would occur in the terminal sites. Adding Nb₂O₅ significantly increases the density and the stability against devitrification, as indicated by ΔT(T_x ? T_g). Bioglass particle dispersions prepared by incorporating up to 1.3 mol% Nb₂O₅ by replacing P₂O₅ or up to 1.0 mol% Nb₂O₅ by replacing SiO₂ in 45S5 Bioglass^® using deionized water or solutions buffered with HEPES showed a significant increase in the pH during the early steps of the reaction, compared using the rate and magnitude during the earliest stages of BG45S5 dissolution.     

Reburning and burnout simulations of natural gas for heavy oil combustion

Reburning and burnout simulations were carried out through PLUG code of CHEMKIN-III using a reduced mechanism, in order to determine preliminary experimental parameters for achieving maximum NO_x reduction to implement the reburning technology for heavy oil combustion in pilot scale equipments in Brazil. Gas compositions at the entrance of the reburning zone were estimated by the AComb program. Simulations were performed for eight conditions in the usual range of operational parameters for natural gas reburning. The maximum NO reduction (ca. 50%) was reached with 10 and 17.5% of power via natural gas and 1.5 and 3.0% O₂ excess, respectively, at 1273 K. The model predicts 250 ppm of NO, 50 ppm of CO and air mass flows in the range of about 50-130 kg/h for burnout.     

Alternative Distributed Algorithms for Network Utility Maximization: Framework and Applications

Network utility maximization (NUM) problem formulations provide an important approach to conduct network resource allocation and to view layering as optimization decomposition. In the existing literature, distributed implementations are typically achieved by means of the so-called dual decomposition technique. However, the span of decomposition possibilities includes many other elements that, thus far, have not been fully exploited, such as the use of the primal decomposition technique, the versatile introduction of auxiliary variables, and the potential of multilevel decompositions. This paper presents a systematic framework to exploit alternative decomposition structures as a way to obtain different distributed algorithms, each with a different tradeoff among convergence speed, message passing amount and asymmetry, and distributed computation architecture. Several specific applications are considered to illustrate the proposed framework, including resource-constrained and direct-control rate allocation, and rate allocation among QoS classes with multipath routing. For each of these applications, the associated generalized NUM formulation is first presented, followed by the development of novel alternative decompositions and numerical experiments on the resulting new distributed algorithms. A systematic enumeration and comparison of alternative vertical decompositions in the future will help complete a mathematical theory of network architectures.     

Improved representation and genetic operators for linear genetic programming for automated program repair

Genetic improvement for program repair can fix bugs or otherwise improve software via patch evolution. Consider GenProg, a prototypical technique of this type. GenProg’s crossover and mutation operators manipulate individuals represented as patches. A patch is composed of high-granularity edits that indivisibly comprise an edit operation, a faulty location, and a fix statement used in replacement or insertions. We observe that recombination and mutation of such high-level units limits the technique’s ability to effectively traverse and recombine the repair search spaces. We propose a reformulation of program repair representation, crossover, and mutation operators such that they explicitly traverse the three subspaces that underlie the search problem: the Operator, Fault and Fix Spaces. We provide experimental evidence validating our insight, showing that the operators provide considerable improvement over the baseline repair algorithm in terms of search success rate and efficiency. We also conduct a genotypic distance analysis over the various types of search, providing insight as to the influence of the operators on the program repair search problem.     

Probiotics in Goat Milk Products: Delivery Capacity and Ability to Improve Sensory Attributes

Dairy foods, particularly those of bovine origin, are the predominant vehicles for delivery of probiotic bacteria. Caprine (goat) milk also possesses potential for successful delivery of probiotics, and despite its less appealing flavor in some products, the use of goat milk as a probiotic carrier has rapidly increased over the last decade. This review reports on the diversity, applicability, and potential of using probiotics to enhance the sensory properties of goat milk and goat milk‐based products. A brief conceptual introduction to probiotic microorganisms is followed by an account of the unique physicochemical, nutritive, and beneficial aspects of goat milk, emphasizing its advantages as a probiotic carrier. The sensory properties of probiotic‐enriched goat milk products are also discussed. The maintenance of probiotic viability and desirable physicochemical characteristics in goat milk products over shelf life is possible. However, the unpleasant sensory features of some goat milk products remain a major disadvantage that hinder its wider utilization. Nevertheless, certain measures such as fortification with selected probiotic strains, inclusion of fruit pulps and popular flavor compounds, and production of commonly consumed tailor‐made goat milk‐based products have potential to overcome this limitation. In particular, certain probiotic bacteria release volatile compounds as a result of their metabolism, which are known to play a major role in the aroma profile and sensory aspects of the final products.