Subset simulation method including fitness-based seed selection for reliability analysis

Probability estimation of rare events is a challenging task in the reliability theory. Subset simulation (SS) is a robust simulation technique that transforms a rare event into a sequence of multiple intermediate failure events with large probabilities and efficiently approximates the mentioned probability. Proper handling of a reliability problem by this method requires employing a suitable sampling approach to transmit samples toward the failure set. Markov Chain Monte Carlo (MCMC) is a suitable sampling approach that solves the SS transition phase using the failed sample of each simulation level as the seed of next samples. This paper is aimed to study the seed selection effect on the SS accuracy through several seed selection approaches inspired by the genetic algorithm and particle filter and using the main PDF of the variables to assign a mass function probability to each subset sample in the failure domain. Roulette wheel (I, II), tournament and proportional probability techniques are then employed to choose the weighed samples as seeds to be placed in the MCMC to transmit the samples. To examine the capability of each approach, reliabilities of some engineering problems were investigated and results showed that the proposed approaches could find proper failure sets better than the original SS method, especially in problems with several failure domains.

     

Shape effect of cavity flameholder on mixing zone of hydrogen jet at supersonic flow

Cavity flameholder is known as an efficient technique for providing the ignition zone. In this research, computational fluid dynamic is applied to study the influence of the various shapes of cavity as flameholder on the mixing efficiency inside the scramjet. To evaluate different shapes of cavity flame holder, the Reynolds-averaged Navier–Stokes equations with (SST) turbulence model are solved to reveal the effect of significant parameters. The influence of trapezoidal, circle and rectangular cavity on fuel distribution is expansively analyzed. Moreover, the influence of various Mach numbers (M = 1.2, 2 and 3) on mixing rate and flow feature inside the cavity is examined. The comprehensive parametric studies are also done. Our findings show that the trapezoidal cavity is more efficient than other shapes in the preservation of the ignition zone within the cavity. In addition, the increase of free stream Mach number intensifies the main circulations within cavity and this induces a stable ignition zone within cavity.     

Effect of microbial transglutaminase and setting condition on gel properties of blend fish protein isolate recovered by alkaline solubilisation/isoelectric precipitation

The effect of microbial transglutaminase (M-TGase) (0–0.6 units g⁻¹ sample) and setting condition (25 °C/180 min, 30 °C/120 min, 35 °C/60 min and 40 °C/30 min) on gel properties of blend protein isolate of gutted kilka and silver carp was studied. The protein isolate provided a good substrate for M-TGase activity so that a low amount of M-TGase (0.2 unit g⁻¹ sample) substantially improved textural properties and water holding capacity (WHC) of the gels. Breaking force of the gels was positively affected by M-TGase up to 0.6 unit g⁻¹ sample, but it negatively affected their WHC. Prior setting at 25–35 °C increased the breaking force of proteins compared to directly heated gel, resulting in maximum breaking force at 35 °C/60 min. However, the setting at 40 °C/30 min caused proteolysis, which was reflected in higher amounts of TCA-soluble peptides and gel weakening. Denser microstructure and higher myosin heavy chain polymerisation observed in the gels which experienced the setting was well correlated with improvement in textural properties.     

Effects of type and dosages of organic depressants on pyrite floatability in microflotation system

Pyrite is considered as a disturbing sulfide mineral in the beneficiation of sulfide minerals and coal and in order to prevent floating of pyrite in the flotation, different inorganic, organic and biological depressants could be used. The most important organic pyrite depressants are starch, dextrin, guargum, carboxymethyl cellulose (CMC), ethylene diamine tetra acetic acid (EDTA), Diethylenetriamine (DETA). In this paper, flotation experiments were carried out by modified Halimond tube. At first, flotation experiments were performed to obtain optimal pyrite flotation condition (suitable collector and frother for maximum recovery). In optimal condition (collector: KAX?+?KIPX , 16?ppm; collector condition time: 4?min; frother: Poly Propylene Glycol (A65), 20?ppm; frother condition time: 30?s), pyrite recovery increased to 95.63%. Flotation kinetics experiments were performed and various kinetic models were evaluated on pyrite flotation. The results showed that flotation kinetics of pyrite is second-order. After obtaining optimal condition for flotation and kinetic studies, the effects of type and dosage of different organic depressants including starch, dextrin, guargum, carboxymethyl cellulose, EDTA and DETA at three concentrations (50, 100, 150?ppm) at neutral pH were comprehensively investigated. The results of the experiments showed that DETA can significantly reduce the recovery of pyrite at 150?ppm by 44%.     

Decentralized consensus protocol for a class of high‐order multiagent systems

This paper proposes a consensus protocol for a class of high‐order multiagent systems under directed networks. It is supposed that each agent is exposed to an external disturbance additive to its control input. Based on the optimization theory, the consensus protocol gains are designed in order to attenuate the effects of the external disturbances on the performance of the multiagent system. The main problem of existing high‐order consensus protocols in the literature is the dependency of the design on the information of coupling matrices associated with networks topologies. Despite existing high‐order consensus protocols in the literature, the proposed consensus protocol can be designed in a fully decentralized manner based on no global information. The main idea of the design is to propose an control formulation in which the coupling information of the agents is considered as exogenous signals, while the coupling effects of these signals lead to achieving consensus in the multiagent system. Numerical examples verify the effectiveness of the proposed consensus protocol. Copyright © 2016 John Wiley & Sons, Ltd.     

Microbial Dissolution of Zn-Pb Sulfide Minerals Using Mesophilic Iron and Sulfur-Oxidizing Acidophiles

The purpose of this study is to test the feasibility of using mixed culture of iron and sulfur-oxidizing bacteria for the dissolution of metals from high-grade zinc and lead sulfide ore. Considering that the roll crusher could reduce the ore size to less than 2 mm, this size fraction was selected in order to study the possibility of removing mill circuit. Effects of parameters such as pulp density, initial pH, Fe²⁺, oxidation–reduction potential (ORP), and pH fluctuations were investigated, as well. The maximum Zn dissolution was achieved under the conditions of initial pH 2, initial 75 g/L FeSO₄ · 7H₂O, and pulp density of 50 g/L. The results indicated that under the optimum conditions, about 68.8% of zinc was leached during 24 days of bacterial leaching treatment. The lead recoveries were low (about 1%), because of precipitation of Pb as lead arsenate chloride. Furthermore, the surface studies by using SEM images showed that during chemical leaching the ore dissolution starts from surface discontinuities, but in bacterial leaching all surface becomes involved. In addition, in another process the ore was leached separately with sulfuric acid and sodium hydroxide, and then final results were compared to the bacterial leaching tests in order to find the optimum hydrometallurgical method to extract zinc and lead from these ores.     

Prevalence and risk factors associated with campylobacter infections in broiler flocks in Shiraz, southern Iran

Campylobacter species are among the most common bacterial causes of human gastroenteritis in many countries, and poultry meat is considered as a major source of human campylobacteriosis. The present study was conducted to determine the prevalence of infection by Campylobacter jejuni and Campylobacter coli in broiler flocks in Shiraz and to investigate the possible risk factors for the campylobacter infections in this area. For detection of campylobacter, multiplex polymerase chain reaction (mPCR) was used. Between August and September 2009, a total of 100 broiler flocks from 100 commercial broiler farms were selected at slaughter and campylobacter status was determined by mPCR on caecal samples. Data about farms and flocks were collected by questionnaires. Approximately 76% (95% CI: 67-84%) of the flocks were positive for C. jejuni or C. coli. Twenty two percent were positive for C. jejuni, 32% for C. coli and 22% for both species. Results of the statistical analysis using multivariable logistic regression showed that the odds of flock infection decreased when level of owner's education (years) increased (OR = 0.86, P = 0.04), also odds of infection was nearly five times higher when age at slaughter was ≥ 45 days compared with < 45 days (OR = 5.3, P = 0.003) and use of antibiotic medications at early stage of production period was negatively associated with the infection status of the flock (OR = 0.33, OR = 0.059). We found no evidence of the effects of any other factors such as time interval between successive flocks, hygiene measures and number of broiler houses on the farm on the prevalence of campylobacter infection. Getting more attention to the health education issues and planning qualitative studies to reveal the behavioral aspects of the management policy, may be subjects of interest for future researches.     

Web Geometry of a System of First-Order Autonomous Ordinary Differential Equations

Journal of Dynamical and Control Systems - The goal of this paper is to propose Cartan equivalence problem for a system of n first-order autonomous ordinary differential equations (ODEs) under a...